# pax

## PROLOG



           This manual page is part of the POSIX Programmer's Manual.  The
           Linux implementation of this interface may differ (consult the
           corresponding Linux manual page for details of Linux behavior), or
           the interface may not be implemented on Linux.
    


## NAME



           pax — portable archive interchange
    


## SYNOPSIS



           pax **[** -dv**] [** -c|-n**] [** -H|-L**] [** -o _options_**] [** -f _archive_**] [** -s _replstr_**]**...
               **[**_pattern_...**]**
    
           pax -r**[** -c|-n**] [** -dikuv**] [** -H|-L**] [** -f _archive_**] [** -o _options_**]**... **[** -p _string_**]**...
               **[** -s _replstr_**]**... **[**_pattern_...**]**
    
           pax -w **[** -dituvX**] [** -H|-L**] [** -b _blocksize_**] [[** -a**] [** -f _archive_**]] [** -o _options_**]**...
               **[** -s _replstr_**]**... **[** -x _format_**] [**_file_...**]**
    
           pax -r -w **[** -diklntuvX**] [** -H|-L**] [** -o _options_**]**... **[** -p _string_**]**...
               **[** -s _replstr_**]**... **[**_file_...**]**_directory_
    


## DESCRIPTION



           The _pax_ utility shall read, write, and write lists of the members
           of archive files and copy directory hierarchies. A variety of
           archive formats shall be supported; see the **-x** _format_ option.
    
           The action to be taken depends on the presence of the **-r** and **-w**
           options. The four combinations of **-r** and **-w** are referred to as the
           four modes of operation: **list** , **read** , **write** , and **copy** modes,
           corresponding respectively to the four forms shown in the SYNOPSIS
           section.
    
           **list** In **list** mode (when neither **-r** nor **-w** are specified), _pax_
                     shall write the names of the members of the archive file
                     read from the standard input, with pathnames matching
                     the specified patterns, to standard output. If a named
                     file is of type directory, the file hierarchy rooted at
                     that file shall be listed as well.
    
           **read** In **read** mode (when **-r** is specified, but **-w** is not), _pax_
                     shall extract the members of the archive file read from
                     the standard input, with pathnames matching the
                     specified patterns. If an extracted file is of type
                     directory, the file hierarchy rooted at that file shall
                     be extracted as well. The extracted files shall be
                     created performing pathname resolution with the
                     directory in which _pax_ was invoked as the current
                     working directory.
    
                     If an attempt is made to extract a directory when the
                     directory already exists, this shall not be considered
                     an error. If an attempt is made to extract a FIFO when
                     the FIFO already exists, this shall not be considered an
                     error.
    
                     The ownership, access, and modification times, and file
                     mode of the restored files are discussed under the **-p**
                     option.
    
           **write** In **write** mode (when **-w** is specified, but **-r** is not), _pax_
                     shall write the contents of the _file_ operands to the
                     standard output in an archive format. If no _file_
                     operands are specified, a list of files to copy, one per
                     line, shall be read from the standard input and each
                     entry in this list shall be processed as if it had been
                     a _file_ operand on the command line. A file of type
                     directory shall include all of the files in the file
                     hierarchy rooted at the file.
    
           **copy** In **copy** mode (when both **-r** and **-w** are specified), _pax_
                     shall copy the _file_ operands to the destination
                     directory.
    
                     If no _file_ operands are specified, a list of files to
                     copy, one per line, shall be read from the standard
                     input. A file of type directory shall include all of the
                     files in the file hierarchy rooted at the file.
    
                     The effect of the **copy** shall be as if the copied files
                     were written to a _pax_ format archive file and then
                     subsequently extracted, except that copying of sockets
                     may be supported even if archiving them in write mode is
                     not supported, and that there may be hard links between
                     the original and the copied files. If the destination
                     directory is a subdirectory of one of the files to be
                     copied, the results are unspecified. If the destination
                     directory is a file of a type not defined by the System
                     Interfaces volume of POSIX.1‐2017, the results are
                     implementation-defined; otherwise, it shall be an error
                     for the file named by the _directory_ operand not to
                     exist, not be writable by the user, or not be a file of
                     type directory.
    
           In **read** or **copy** modes, if intermediate directories are necessary
           to extract an archive member, _pax_ shall perform actions equivalent
           to the _mkdir_() function defined in the System Interfaces volume of
           POSIX.1‐2017, called with the following arguments:
    
            *  The intermediate directory used as the _path_ argument
    
            *  The value of the bitwise-inclusive OR of S_IRWXU, S_IRWXG, and
               S_IRWXO as the _mode_ argument
    
           If any specified _pattern_ or _file_ operands are not matched by at
           least one file or archive member, _pax_ shall write a diagnostic
           message to standard error for each one that did not match and exit
           with a non-zero exit status.
    
           The archive formats described in the EXTENDED DESCRIPTION section
           shall be automatically detected on input. The default output
           archive format shall be implementation-defined.
    
           A single archive can span multiple files. The _pax_ utility shall
           determine, in an implementation-defined manner, what file to read
           or write as the next file.
    
           If the selected archive format supports the specification of
           linked files, it shall be an error if these files cannot be linked
           when the archive is extracted. For archive formats that do not
           store file contents with each name that causes a hard link, if the
           file that contains the data is not extracted during this _pax_
           session, either the data shall be restored from the original file,
           or a diagnostic message shall be displayed with the name of a file
           that can be used to extract the data. In traversing directories,
           _pax_ shall detect infinite loops; that is, entering a previously
           visited directory that is an ancestor of the last file visited.
           When it detects an infinite loop, _pax_ shall write a diagnostic
           message to standard error and shall terminate.
    


## OPTIONS



           The _pax_ utility shall conform to the Base Definitions volume of
           POSIX.1‐2017, _Section 12.2_ , _Utility Syntax Guidelines_ , except that
           the order of presentation of the **-o** , **-p** , and **-s** options is
           significant.
    
           The following options shall be supported:
    
           **-r** Read an archive file from standard input.
    
           **-w** Write files to the standard output in the specified
                     archive format.
    
           **-a** Append files to the end of the archive. It is
                     implementation-defined which devices on the system
                     support appending. Additional file formats unspecified
                     by this volume of POSIX.1‐2017 may impose restrictions
                     on appending.
    
           **-b** _blocksize_
                     Block the output at a positive decimal integer number of
                     bytes per write to the archive file. Devices and archive
                     formats may impose restrictions on blocking. Blocking
                     shall be automatically determined on input. Conforming
                     applications shall not specify a _blocksize_ value larger
                     than 32256. Default blocking when creating archives
                     depends on the archive format. (See the **-x** option
                     below.)
    
           **-c** Match all file or archive members except those specified
                     by the _pattern_ or _file_ operands.
    
           **-d** Cause files of type directory being copied or archived
                     or archive members of type directory being extracted or
                     listed to match only the file or archive member itself
                     and not the file hierarchy rooted at the file.
    
           **-f** _archive_
                     Specify the pathname of the input or output archive,
                     overriding the default standard input (in **list** or **read**
                     modes) or standard output (**write** mode).
    
           **-H** If a symbolic link referencing a file of type directory
                     is specified on the command line, _pax_ shall archive the
                     file hierarchy rooted in the file referenced by the
                     link, using the name of the link as the root of the file
                     hierarchy.  Otherwise, if a symbolic link referencing a
                     file of any other file type which _pax_ can normally
                     archive is specified on the command line, then _pax_ shall
                     archive the file referenced by the link, using the name
                     of the link. The default behavior, when neither **-H** or **-L**
                     are specified, shall be to archive the symbolic link
                     itself.
    
           **-i** Interactively rename files or archive members. For each
                     archive member matching a _pattern_ operand or file
                     matching a _file_ operand, a prompt shall be written to
                     the file **/dev/tty**.  The prompt shall contain the name of
                     the file or archive member, but the format is otherwise
                     unspecified. A line shall then be read from **/dev/tty**.
                     If this line is blank, the file or archive member shall
                     be skipped. If this line consists of a single period,
                     the file or archive member shall be processed with no
                     modification to its name. Otherwise, its name shall be
                     replaced with the contents of the line. The _pax_ utility
                     shall immediately exit with a non-zero exit status if
                     end-of-file is encountered when reading a response or if
                     **/dev/tty** cannot be opened for reading and writing.
    
                     The results of extracting a hard link to a file that has
                     been renamed during extraction are unspecified.
    
           **-k** Prevent the overwriting of existing files.
    
           **-l**(The letter ell.) In **copy** mode, hard links shall be made
                     between the source and destination file hierarchies
                     whenever possible. If specified in conjunction with **-H**
                     or **-L** , when a symbolic link is encountered, the hard
                     link created in the destination file hierarchy shall be
                     to the file referenced by the symbolic link. If
                     specified when neither **-H** nor **-L** is specified, when a
                     symbolic link is encountered, the implementation shall
                     create a hard link to the symbolic link in the source
                     file hierarchy or copy the symbolic link to the
                     destination.
    
           **-L** If a symbolic link referencing a file of type directory
                     is specified on the command line or encountered during
                     the traversal of a file hierarchy, _pax_ shall archive the
                     file hierarchy rooted in the file referenced by the
                     link, using the name of the link as the root of the file
                     hierarchy.  Otherwise, if a symbolic link referencing a
                     file of any other file type which _pax_ can normally
                     archive is specified on the command line or encountered
                     during the traversal of a file hierarchy, _pax_ shall
                     archive the file referenced by the link, using the name
                     of the link. The default behavior, when neither **-H** or **-L**
                     are specified, shall be to archive the symbolic link
                     itself.
    
           **-n** Select the first archive member that matches each
                     _pattern_ operand. No more than one archive member shall
                     be matched for each pattern (although members of type
                     directory shall still match the file hierarchy rooted at
                     that file).
    
           **-o** _options_
                     Provide information to the implementation to modify the
                     algorithm for extracting or writing files. The value of
                     _options_ shall consist of one or more <comma>-separated
                     keywords of the form:
    
                         _keyword_**[[** :**]** =_value_**][** ,_keyword_**[[** :**]** =_value_**]** , ...**]**
    
                     Some keywords apply only to certain file formats, as
                     indicated with each description. Use of keywords that
                     are inapplicable to the file format being processed
                     produces undefined results.
    
                     Keywords in the _options_ argument shall be a string that
                     would be a valid portable filename as described in the
                     Base Definitions volume of POSIX.1‐2017, _Section 3.282_ ,
                     _Portable Filename Character Set_.
    
                     **Note:** Keywords are not expected to be filenames, merely
                            to follow the same character composition rules as
                            portable filenames.
    
                     Keywords can be preceded with white space. The _value_
                     field shall consist of zero or more characters; within
                     _value_ , the application shall precede any literal <comma>
                     with a <backslash>, which shall be ignored, but
                     preserves the <comma> as part of _value_.  A <comma> as
                     the final character, or a <comma> followed solely by
                     white space as the final characters, in _options_ shall be
                     ignored. Multiple **-o** options can be specified; if
                     keywords given to these multiple **-o** options conflict,
                     the keywords and values appearing later in command line
                     sequence shall take precedence and the earlier shall be
                     silently ignored. The following keyword values of
                     _options_ shall be supported for the file formats as
                     indicated:
    
                     **delete** =_pattern_
                           (Applicable only to the **-x pax** format.) When used
                           in **write** or **copy** mode, _pax_ shall omit from
                           extended header records that it produces any
                           keywords matching the string pattern. When used in
                           **read** or **list** mode, _pax_ shall ignore any keywords
                           matching the string pattern in the extended header
                           records. In both cases, matching shall be
                           performed using the pattern matching notation
                           described in _Section 2.13.1_ , _Patterns Matching a_
                           _Single Character_ and _Section 2.13.2_ , _Patterns_
                           _Matching Multiple Characters_.  For example:
    
                               -o **delete** =_security_.*
    
                           would suppress security-related information. See
                           _pax Extended Header_ for extended header record
                           keyword usage.
    
                           When multiple **-odelete=pattern** options are
                           specified, the patterns shall be additive; all
                           keywords matching the specified string patterns
                           shall be omitted from extended header records that
                           _pax_ produces.
    
                     **exthdr.name** =_string_
                           (Applicable only to the **-x pax** format.) This
                           keyword allows user control over the name that is
                           written into the **ustar** header blocks for the
                           extended header produced under the circumstances
                           described in _pax Header Block_.  The name shall be
                           the contents of _string_ , after the following
                           character substitutions have been made:
                         ┌───────────┬────────────────────────────────────────┐
                         │  _string_   │                                        │
                         │ **Includes:** │              **Replaced by:** │
                         ├───────────┼────────────────────────────────────────┤
                         │ %d        │ The directory name of the file,        │
                         │           │ equivalent to the result of the        │
                         │           │ _dirname_ utility on the translated      │
                         │           │ pathname.                              │
                         │ %f        │ The filename of the file, equivalent   │
                         │           │ to the result of the _basename_ utility  │
                         │           │ on the translated pathname.            │
                         │ %p        │ The process ID of the _pax_ process.     │
                         │ %%        │ A **'%'** character.                       │
                         └───────────┴────────────────────────────────────────┘
    
                           Any other **'%'** characters in _string_ produce
                           undefined results.
    
                           If no **-o exthdr.name=string** is specified, _pax_
                           shall use the following default value:
    
                               %d/PaxHeaders.%p/%f
    
                     **globexthdr.name** =_string_
                           (Applicable only to the **-x pax** format.) When used
                           in **write** or **copy** mode with the appropriate
                           options, _pax_ shall create global extended header
                           records with **ustar** header blocks that will be
                           treated as regular files by previous versions of
                           _pax_.  This keyword allows user control over the
                           name that is written into the **ustar** header blocks
                           for global extended header records. The name shall
                           be the contents of string, after the following
                           character substitutions have been made:
                         ┌───────────┬────────────────────────────────────────┐
                         │  _string_   │                                        │
                         │ **Includes:** │              **Replaced by:** │
                         ├───────────┼────────────────────────────────────────┤
                         │ %n        │ An integer that represents the         │
                         │           │ sequence number of the global extended │
                         │           │ header record in the archive, starting │
                         │           │ at 1.                                  │
                         │ %p        │ The process ID of the _pax_ process.     │
                         │ %%        │ A **'%'** character.                       │
                         └───────────┴────────────────────────────────────────┘
    
                           Any other **'%'** characters in _string_ produce
                           undefined results.
    
                           If no **-o globexthdr.name=string** is specified, _pax_
                           shall use the following default value:
    
                               $TMPDIR/GlobalHead.%p.%n
    
                           where $_TMPDIR_ represents the value of the _TMPDIR_
                           environment variable. If _TMPDIR_ is not set, _pax_
                           shall use **/tmp**.
    
                     **invalid** =_action_
                           (Applicable only to the **-x pax** format.) This
                           keyword allows user control over the action _pax_
                           takes upon encountering values in an extended
                           header record that, in **read** or **copy** mode, are
                           invalid in the destination hierarchy or, in **list**
                           mode, cannot be written in the codeset and current
                           locale of the implementation. The following are
                           invalid values that shall be recognized by _pax_ :
    
                           --  In **read** or **copy** mode, a filename or link name
                               that contains character encodings invalid in
                               the destination hierarchy. (For example, the
                               name may contain embedded NULs.)
    
                           --  In **read** or **copy** mode, a filename or link name
                               that is longer than the maximum allowed in the
                               destination hierarchy (for either a pathname
                               component or the entire pathname).
    
                           --  In **list** mode, any character string value
                               (filename, link name, user name, and so on)
                               that cannot be written in the codeset and
                               current locale of the implementation.
    
                           The following mutually-exclusive values of the
                           _action_ argument are supported:
    
                           **binary** In **write** mode, _pax_ shall generate a
                                     **hdrcharset** =**BINARY** extended header record
                                     for each file with a filename, link
                                     name, group name, owner name, or any
                                     other field in an extended header record
                                     that cannot be translated to the UTF‐8
                                     codeset, allowing the archive to contain
                                     the files with unencoded extended header
                                     record values. In **read** or **copy** mode, _pax_
                                     shall use the values specified in the
                                     header without translation, regardless
                                     of whether this may overwrite an
                                     existing file with a valid name. In **list**
                                     mode, _pax_ shall behave identically to
                                     the **bypass** action.
    
                           **bypass** In **read** or **copy** mode, _pax_ shall bypass
                                     the file, causing no change to the
                                     destination hierarchy.  In **list** mode,
                                     _pax_ shall write all requested valid
                                     values for the file, but its method for
                                     writing invalid values is unspecified.
    
                           **rename** In **read** or **copy** mode, _pax_ shall act as
                                     if the **-i** option were in effect for each
                                     file with invalid filename or link name
                                     values, allowing the user to provide a
                                     replacement name interactively.  In **list**
                                     mode, _pax_ shall behave identically to
                                     the **bypass** action.
    
                           **UTF‐8** When used in **read** , **copy** , or **list** mode
                                     and a filename, link name, owner name,
                                     or any other field in an extended header
                                     record cannot be translated from the **pax**
                                     UTF‐8 codeset format to the codeset and
                                     current locale of the implementation,
                                     _pax_ shall use the actual UTF‐8 encoding
                                     for the name. If a **hdrcharset** extended
                                     header record is in effect for this
                                     file, the character set specified by
                                     that record shall be used instead of
                                     UTF‐8. If a **hdrcharset** =**BINARY** extended
                                     header record is in effect for this
                                     file, no translation shall be performed.
    
                           **write** In **read** or **copy** mode, _pax_ shall write
                                     the file, translating the name,
                                     regardless of whether this may overwrite
                                     an existing file with a valid name. In
                                     **list** mode, _pax_ shall behave identically
                                     to the **bypass** action.
    
                           If no **-o invalid=option** is specified, _pax_ shall
                           act as if **-oinvalid=bypass** were specified. Any
                           overwriting of existing files that may be allowed
                           by the **-oinvalid=** actions shall be subject to
                           permission (**-p**) and modification time (**-u**)
                           restrictions, and shall be suppressed if the **-k**
                           option is also specified.
    
                     **linkdata**
                           (Applicable only to the **-x pax** format.) In **write**
                           mode, _pax_ shall write the contents of a file to
                           the archive even when that file is merely a hard
                           link to a file whose contents have already been
                           written to the archive.
    
                     **listopt** =_format_
                           This keyword specifies the output format of the
                           table of contents produced when the **-v** option is
                           specified in **list** mode. See _List Mode Format_
                           _Specifications_.  To avoid ambiguity, the
                           **listopt=format** shall be the only or final
                           **keyword=value** pair in a **-o** option-argument; all
                           characters in the remainder of the option-argument
                           shall be considered part of the format string.
                           When multiple **-olistopt=format** options are
                           specified, the format strings shall be considered
                           a single, concatenated string, evaluated in
                           command line order.
    
                     **times**
                           (Applicable only to the **-x** _pax_ format.) When used
                           in **write** or **copy** mode, _pax_ shall include **atime** and
                           **mtime** extended header records for each file. See
                           _pax Extended Header File Times_.
    
                     In addition to these keywords, if the **-x** _pax_ format is
                     specified, any of the keywords and values defined in _pax_
                     _Extended Header_ , including implementation extensions,
                     can be used in **-o** option-arguments, in either of two
                     modes:
    
                     **keyword** =_value_
                           When used in **write** or **copy** mode, these
                           keyword/value pairs shall be included at the
                           beginning of the archive as **typeflag g** global
                           extended header records. When used in **read** or **list**
                           mode, these keyword/value pairs shall act as if
                           they had been at the beginning of the archive as
                           **typeflag g** global extended header records.
    
                     **keyword** :=_value_
                           When used in **write** or **copy** mode, these
                           keyword/value pairs shall be included as records
                           at the beginning of a **typeflag x** extended header
                           for each file. (This shall be equivalent to the
                           <equals-sign> form except that it creates no
                           **typeflag g** global extended header records.) When
                           used in **read** or **list** mode, these keyword/value
                           pairs shall act as if they were included as
                           records at the end of each extended header; thus,
                           they shall override any global or file-specific
                           extended header record keywords of the same names.
                           For example, in the command:
    
                               pax -r -o "
                               gname:=mygroup,
                               " <archive
    
                           the group name will be forced to a new value for
                           all files read from the archive.
    
                     The precedence of **-o** keywords over various fields in the
                     archive is described in _pax Extended Header Keyword_
                     _Precedence_.  If the **-o delete** =_pattern_ , **-o keyword** =_value_ ,
                     or **-o keyword** :=_value_ options are used to override or
                     remove any extended header data needed to find files in
                     an archive (e.g., **-o delete=size** for a file whose size
                     cannot be represented in a **ustar** header or **-o size=100**
                     for a file whose size is not 100 bytes), the behavior is
                     undefined.
    
           **-p** _string_ Specify one or more file characteristic options
                     (privileges). The _string_ option-argument shall be a
                     string specifying file characteristics to be retained or
                     discarded on extraction. The string shall consist of the
                     specification characters **a** , **e** , **m** , **o** , and **p**.  Other
                     implementation-defined characters can be included.
                     Multiple characteristics can be concatenated within the
                     same string and multiple **-p** options can be specified.
                     The meaning of the specification characters are as
                     follows:
    
                     a     Do not preserve file access times.
    
                     e     Preserve the user ID, group ID, file mode bits
                           (see the Base Definitions volume of POSIX.1‐2017,
                           _Section 3.169_ , _File Mode Bits_), access time,
                           modification time, and any other implementation-
                           defined file characteristics.
    
                     m     Do not preserve file modification times.
    
                     o     Preserve the user ID and group ID.
    
                     p     Preserve the file mode bits. Other implementation-
                           defined file mode attributes may be preserved.
    
                     In the preceding list, ``preserve'' indicates that an
                     attribute stored in the archive shall be given to the
                     extracted file, subject to the permissions of the
                     invoking process. The access and modification times of
                     the file shall be preserved unless otherwise specified
                     with the **-p** option or not stored in the archive. All
                     attributes that are not preserved shall be determined as
                     part of the normal file creation action (see _Section_
                     _1.1.1.4_ , _File Read_ , _Write_ , _and Creation_).
    
                     If neither the **e** nor the **o** specification character is
                     specified, or the user ID and group ID are not preserved
                     for any reason, _pax_ shall not set the S_ISUID and
                     S_ISGID bits of the file mode.
    
                     If the preservation of any of these items fails for any
                     reason, _pax_ shall write a diagnostic message to standard
                     error. Failure to preserve these items shall affect the
                     final exit status, but shall not cause the extracted
                     file to be deleted.
    
                     If file characteristic letters in any of the _string_
                     option-arguments are duplicated or conflict with each
                     other, the ones given last shall take precedence. For
                     example, if **-p eme** is specified, file modification times
                     are preserved.
    
           **-s** _replstr_
                     Modify file or archive member names named by _pattern_ or
                     _file_ operands according to the substitution expression
                     _replstr_ , using the syntax of the _ed_ utility. The
                     concepts of ``address'' and ``line'' are meaningless in
                     the context of the _pax_ utility, and shall not be
                     supplied. The format shall be:
    
                         -s /_old_ /_new_ /**[** gp**]**
    
                     where as in _ed_ , _old_ is a basic regular expression and
                     _new_ can contain an <ampersand>, **'\n'**(where _n_ is a
                     digit) back-references, or subexpression matching. The
                     _old_ string shall also be permitted to contain <newline>
                     characters.
    
                     Any non-null character can be used as a delimiter (**'/'**
                     shown here). Multiple **-s** expressions can be specified;
                     the expressions shall be applied in the order specified,
                     terminating with the first successful substitution.  The
                     optional trailing **'g'** is as defined in the _ed_ utility.
                     The optional trailing **'p'** shall cause successful
                     substitutions to be written to standard error.  File or
                     archive member names that substitute to the empty string
                     shall be ignored when reading and writing archives.
    
           **-t** When reading files from the file system, and if the user
                     has the permissions required by _utime_() to do so, set
                     the access time of each file read to the access time
                     that it had before being read by _pax_.
    
           **-u** Ignore files that are older (having a less recent file
                     modification time) than a pre-existing file or archive
                     member with the same name.  In **read** mode, an archive
                     member with the same name as a file in the file system
                     shall be extracted if the archive member is newer than
                     the file. In **write** mode, an archive file member with the
                     same name as a file in the file system shall be
                     superseded if the file is newer than the archive member.
                     If **-a** is also specified, this is accomplished by
                     appending to the archive; otherwise, it is unspecified
                     whether this is accomplished by actual replacement in
                     the archive or by appending to the archive. In **copy**
                     mode, the file in the destination hierarchy shall be
                     replaced by the file in the source hierarchy or by a
                     link to the file in the source hierarchy if the file in
                     the source hierarchy is newer.
    
           **-v** In **list** mode, produce a verbose table of contents (see
                     the STDOUT section).  Otherwise, write archive member
                     pathnames to standard error (see the STDERR section).
    
           **-x** _format_ Specify the output archive format. The _pax_ utility shall
                     support the following formats:
    
                     **cpio** The **cpio** interchange format; see the EXTENDED
                               DESCRIPTION section. The default _blocksize_ for
                               this format for character special archive
                               files shall be 5120.  Implementations shall
                               support all _blocksize_ values less than or
                               equal to 32256 that are multiples of 512.
    
                     **pax** The **pax** interchange format; see the EXTENDED
                               DESCRIPTION section. The default _blocksize_ for
                               this format for character special archive
                               files shall be 5120.  Implementations shall
                               support all _blocksize_ values less than or
                               equal to 32256 that are multiples of 512.
    
                     **ustar** The **tar** interchange format; see the EXTENDED
                               DESCRIPTION section. The default _blocksize_ for
                               this format for character special archive
                               files shall be 10240.  Implementations shall
                               support all _blocksize_ values less than or
                               equal to 32256 that are multiples of 512.
    
                     Implementation-defined formats shall specify a default
                     block size as well as any other block sizes supported
                     for character special archive files.
    
                     Any attempt to append to an archive file in a format
                     different from the existing archive format shall cause
                     _pax_ to exit immediately with a non-zero exit status.
    
           **-X** When traversing the file hierarchy specified by a
                     pathname, _pax_ shall not descend into directories that
                     have a different device ID (_st_dev_ ; see the System
                     Interfaces volume of POSIX.1‐2017, _stat_()).
    
           Specifying more than one of the mutually-exclusive options **-H** and
           **-L** shall not be considered an error and the last option specified
           shall determine the behavior of the utility.
    
           The options that operate on the names of files or archive members
           (**-c** , **-i** , **-n** , **-s** , **-u** , and **-v**) shall interact as follows. In **read**
           mode, the archive members shall be selected based on the user-
           specified _pattern_ operands as modified by the **-c** , **-n** , and **-u**
           options. Then, any **-s** and **-i** options shall modify, in that order,
           the names of the selected files.  The **-v** option shall write names
           resulting from these modifications.
    
           In **write** mode, the files shall be selected based on the user-
           specified pathnames as modified by the **-n** and **-u** options. Then,
           any **-s** and **-i** options shall modify, in that order, the names of
           these selected files.  The **-v** option shall write names resulting
           from these modifications.
    
           If both the **-u** and **-n** options are specified, _pax_ shall not
           consider a file selected unless it is newer than the file to which
           it is compared.
    
       **List Mode Format Specifications**
           In **list** mode with the **-o listopt=format** option, the _format_
           argument shall be applied for each selected file. The _pax_ utility
           shall append a <newline> to the **listopt** output for each selected
           file. The _format_ argument shall be used as the _format_ string
           described in the Base Definitions volume of POSIX.1‐2017, _Chapter_
           _5_ , _File Format Notation_ , with the exceptions 1. through 6. defined
           in the EXTENDED DESCRIPTION section of _printf_ , plus the following
           exceptions:
    
           7.    The sequence (_keyword_) can occur before a format conversion
                 specifier. The conversion argument is defined by the value
                 of _keyword_.  The implementation shall support the following
                 keywords:
    
                 --  Any of the Field Name entries in _Table 4-14, ustar_
                     _Header Block_ and _Table 4-16, Octet-Oriented cpio Archive_
                     _Entry_.  The implementation may support the _cpio_ keywords
                     without the leading **c_** in addition to the form required
                     by _Table 4-16, Octet-Oriented cpio Archive Entry_.
    
                 --  Any keyword defined for the extended header in _pax_
                     _Extended Header_.
    
                 --  Any keyword provided as an implementation-defined
                     extension within the extended header defined in _pax_
                     _Extended Header_.
    
                 For example, the sequence **"%(charset)s"** is the string value
                 of the name of the character set in the extended header.
    
                 The result of the keyword conversion argument shall be the
                 value from the applicable header field or extended header,
                 without any trailing NULs.
    
                 All keyword values used as conversion arguments shall be
                 translated from the UTF‐8 encoding (or alternative encoding
                 specified by any **hdrcharset** extended header record) to the
                 character set appropriate for the local file system, user
                 database, and so on, as applicable.
    
           8.    An additional conversion specifier character, **T** , shall be
                 used to specify time formats. The **T** conversion specifier
                 character can be preceded by the sequence
                 (_keyword=subformat_), where _subformat_ is a date format as
                 defined by _date_ operands. The default _keyword_ shall be **mtime**
                 and the default subformat shall be:
    
                     %b %e %H:%M %Y
    
           9.    An additional conversion specifier character, **M** , shall be
                 used to specify the file mode string as defined in _ls_
                 Standard Output. If (_keyword_) is omitted, the **mode** keyword
                 shall be used. For example, **%.1M** writes the single character
                 corresponding to the <_entry type_ > field of the _ls_ **-l**
                 command.
    
           10.   An additional conversion specifier character, **D** , shall be
                 used to specify the device for block or special files, if
                 applicable, in an implementation-defined format. If not
                 applicable, and (_keyword_) is specified, then this conversion
                 shall be equivalent to %(_keyword_)u. If not applicable, and
                 (_keyword_) is omitted, then this conversion shall be
                 equivalent to <space>.
    
           11.   An additional conversion specifier character, **F** , shall be
                 used to specify a pathname. The **F** conversion character can
                 be preceded by a sequence of <comma>-separated keywords:
    
                     (_keyword_**[** ,_keyword_**]**... )
    
                 The values for all the keywords that are non-null shall be
                 concatenated together, each separated by a **'/'**.  The default
                 shall be (**path**) if the keyword **path** is defined; otherwise,
                 the default shall be (**prefix** ,**name**).
    
           12.   An additional conversion specifier character, **L** , shall be
                 used to specify a symbolic link expansion. If the current
                 file is a symbolic link, then **%L** shall expand to:
    
                     "%s -> %s", <_value of keyword_ >, <_contents of link_ >
    
                 Otherwise, the **%L** conversion specification shall be the
                 equivalent of **%F**.
    


## OPERANDS



           The following operands shall be supported:
    
           _directory_ The destination directory pathname for **copy** mode.
    
           _file_      A pathname of a file to be copied or archived.
    
           _pattern_   A pattern matching one or more pathnames of archive
                     members. A pattern must be given in the name-generating
                     notation of the pattern matching notation in _Section_
                     _2.13_ , _Pattern Matching Notation_ , including the filename
                     expansion rules in _Section 2.13.3_ , _Patterns Used for_
                     _Filename Expansion_.  The default, if no _pattern_ is
                     specified, is to select all members in the archive.
    


## STDIN



           In **write** mode, the standard input shall be used only if no _file_
           operands are specified. It shall be a file containing a list of
           pathnames, each terminated by a <newline> character.
    
           In **list** and **read** modes, if **-f** is not specified, the standard input
           shall be an archive file.
    
           Otherwise, the standard input shall not be used.
    


## INPUT FILES



           The input file named by the _archive_ option-argument, or standard
           input when the archive is read from there, shall be a file
           formatted according to one of the specifications in the EXTENDED
           DESCRIPTION section or some other implementation-defined format.
    
           The file **/dev/tty** shall be used to write prompts and read
           responses.
    


## ENVIRONMENT VARIABLES



           The following environment variables shall affect the execution of
           _pax_ :
    
           _LANG_      Provide a default value for the internationalization
                     variables that are unset or null. (See the Base
                     Definitions volume of POSIX.1‐2017, _Section 8.2_ ,
                     _Internationalization Variables_ the precedence of
                     internationalization variables used to determine the
                     values of locale categories.)
    
           _LC_ALL_    If set to a non-empty string value, override the values
                     of all the other internationalization variables.
    
           _LC_COLLATE_
                     Determine the locale for the behavior of ranges,
                     equivalence classes, and multi-character collating
                     elements used in the pattern matching expressions for
                     the _pattern_ operand, the basic regular expression for
                     the **-s** option, and the extended regular expression
                     defined for the **yesexpr** locale keyword in the
                     _LC_MESSAGES_ category.
    
           _LC_CTYPE_  Determine the locale for the interpretation of sequences
                     of bytes of text data as characters (for example,
                     single-byte as opposed to multi-byte characters in
                     arguments and input files), the behavior of character
                     classes used in the extended regular expression defined
                     for the **yesexpr** locale keyword in the _LC_MESSAGES_
                     category, and pattern matching.
    
           _LC_MESSAGES_
                     Determine the locale used to process affirmative
                     responses, and the locale used to affect the format and
                     contents of diagnostic messages and prompts written to
                     standard error.
    
           _LC_TIME_   Determine the format and contents of date and time
                     strings when the **-v** option is specified.
    
           _NLSPATH_   Determine the location of message catalogs for the
                     processing of _LC_MESSAGES_.
    
           _TMPDIR_    Determine the pathname that provides part of the default
                     global extended header record file, as described for the
                     **-o globexthdr=** keyword in the OPTIONS section.
    
           _TZ_        Determine the timezone used to calculate date and time
                     strings when the **-v** option is specified. If _TZ_ is unset
                     or null, an unspecified default timezone shall be used.
    


## ASYNCHRONOUS EVENTS



           Default.
    


## STDOUT



           In **write** mode, if **-f** is not specified, the standard output shall
           be the archive formatted according to one of the specifications in
           the EXTENDED DESCRIPTION section, or some other implementation-
           defined format (see **-x** _format_).
    
           In **list** mode, when the **-olistopt** =_format_ has been specified, the
           selected archive members shall be written to standard output using
           the format described under _List Mode Format Specifications_.  In
           **list** mode without the **-olistopt** =_format_ option, the table of
           contents of the selected archive members shall be written to
           standard output using the following format:
    
               "%s\n", <_pathname_ >
    
           If the **-v** option is specified in **list** mode, the table of contents
           of the selected archive members shall be written to standard
           output using the following formats.
    
           For pathnames representing hard links to previous members of the
           archive:
    
               "%s == %s\n", <_ls_ -l _listing_ >, <_linkname_ >
    
           For all other pathnames:
    
               "%s\n", <_ls_ -l _listing_ >
    
           where <_ls_ -l _listing_ > shall be the format specified by the _ls_
           utility with the **-l** option. When writing pathnames in this format,
           it is unspecified what is written for fields for which the
           underlying archive format does not have the correct information,
           although the correct number of <blank>-separated fields shall be
           written.
    
           In **list** mode, standard output shall not be buffered more than a
           pathname (plus any associated information and a <newline>
           terminator) at a time.
    


## STDERR



           If **-v** is specified in **read** , **write** , or **copy** modes, _pax_ shall write
           the pathnames it processes to the standard error output using the
           following format:
    
               "%s\n", <_pathname_ >
    
           These pathnames shall be written as soon as processing is begun on
           the file or archive member, and shall be flushed to standard
           error. The trailing <newline>, which shall not be buffered, is
           written when the file has been read or written.
    
           If the **-s** option is specified, and the replacement string has a
           trailing **'p'** , substitutions shall be written to standard error in
           the following format:
    
               "%s >> %s\n", <_original pathname_ >, <_new pathname_ >
    
           In all operating modes of _pax_ , optional messages of unspecified
           format concerning the input archive format and volume number, the
           number of files, blocks, volumes, and media parts as well as other
           diagnostic messages may be written to standard error.
    
           In all formats, for both standard output and standard error, it is
           unspecified how non-printable characters in pathnames or link
           names are written.
    
           When using the **-xpax** archive format, if a filename, link name,
           group name, owner name, or any other field in an extended header
           record cannot be translated between the codeset in use for that
           extended header record and the character set of the current
           locale, _pax_ shall write a diagnostic message to standard error,
           shall process the file as described for the **-o invalid=** option,
           and then shall continue processing with the next file.
    


## OUTPUT FILES



           In **read** mode, the extracted output files shall be of the archived
           file type.  In **copy** mode, the copied output files shall be the
           type of the file being copied. In either mode, existing files in
           the destination hierarchy shall be overwritten only when all
           permission (**-p**), modification time (**-u**), and invalid-value
           (**-oinvalid=**) tests allow it.
    
           In **write** mode, the output file named by the **-f** option-argument
           shall be a file formatted according to one of the specifications
           in the EXTENDED DESCRIPTION section, or some other implementation-
           defined format.
    


## EXTENDED DESCRIPTION



       **pax Interchange Format**
           A _pax_ archive tape or file produced in the **-xpax** format shall
           contain a series of blocks. The physical layout of the archive
           shall be identical to the **ustar** format described in _ustar_
           _Interchange Format_.  Each file archived shall be represented by
           the following sequence:
    
            *  An optional header block with extended header records. This
               header block is of the form described in _pax Header Block_ ,
               with a _typeflag_ value of **x** or **g**.  The extended header records,
               described in _pax Extended Header_ , shall be included as the
               data for this header block.
    
            *  A header block that describes the file. Any fields in the
               preceding optional extended header shall override the
               associated fields in this header block for this file.
    
            *  Zero or more blocks that contain the contents of the file.
    
           At the end of the archive file there shall be two 512-byte blocks
           filled with binary zeros, interpreted as an end-of-archive
           indicator.
    
           A schematic of an example archive with global extended header
           records and two actual files is shown in _Figure 4-1, pax Format_
           _Archive Example_.  In the example, the second file in the archive
           has no extended header preceding it, presumably because it has no
           need for extended attributes.
    
                         **Figure 4-1: pax Format Archive Example**
    
       **pax Header Block**
           The **pax** header block shall be identical to the **ustar** header block
           described in _ustar Interchange Format_ , except that two additional
           _typeflag_ values are defined:
    
           x     Represents extended header records for the following file in
                 the archive (which shall have its own **ustar** header block).
                 The format of these extended header records shall be as
                 described in _pax Extended Header_.
    
           g     Represents global extended header records for the following
                 files in the archive. The format of these extended header
                 records shall be as described in _pax Extended Header_.  Each
                 value shall affect all subsequent files that do not override
                 that value in their own extended header record and until
                 another global extended header record is reached that
                 provides another value for the same field. The _typeflag_ **g**
                 global headers should not be used with interchange media
                 that could suffer partial data loss in transporting the
                 archive.
    
           For both of these types, the _size_ field shall be the size of the
           extended header records in octets. The other fields in the header
           block are not meaningful to this version of the _pax_ utility.
           However, if this archive is read by a _pax_ utility conforming to
           the ISO POSIX‐2:1993 standard, the header block fields are used to
           create a regular file that contains the extended header records as
           data. Therefore, header block field values should be selected to
           provide reasonable file access to this regular file.
    
           A further difference from the **ustar** header block is that data
           blocks for files of _typeflag_ 1 (the digit one) (hard link) may be
           included, which means that the size field may be greater than
           zero. Archives created by _pax_ **-o linkdata** shall include these data
           blocks with the hard links.
    
       **pax Extended Header**
           A **pax** extended header contains values that are inappropriate for
           the **ustar** header block because of limitations in that format:
           fields requiring a character encoding other than that described in
           the ISO/IEC 646:1991 standard, fields representing file attributes
           not described in the **ustar** header, and fields whose format or
           length do not fit the requirements of the **ustar** header. The values
           in an extended header add attributes to the following file (or
           files; see the description of the _typeflag_ **g** header block) or
           override values in the following header block(s), as indicated in
           the following list of keywords.
    
           An extended header shall consist of one or more records, each
           constructed as follows:
    
               "%d %s=%s\n", <_length_ >, <_keyword_ >, <_value_ >
    
           The extended header records shall be encoded according to the
           ISO/IEC 10646‐1:2000 standard UTF‐8 encoding. The <_length_ > field,
           <blank>, <equals-sign>, and <newline> shown shall be limited to
           the portable character set, as encoded in UTF‐8. The <_keyword_ >
           fields can be any UTF‐8 characters.  The <_length_ > field shall be
           the decimal length of the extended header record in octets,
           including the trailing <newline>.  If there is a **hdrcharset**
           extended header in effect for a file, the _value_ field for any
           **gname** , **linkpath** , **path** , and **uname** extended header records shall be
           encoded using the character set specified by the **hdrcharset**
           extended header record; otherwise, the _value_ field shall be
           encoded using UTF‐8. The _value_ field for all other keywords
           specified by POSIX.1‐2008 shall be encoded using UTF‐8.
    
           The <_keyword_ > field shall be one of the entries from the following
           list or a keyword provided as an implementation extension.
           Keywords consisting entirely of lowercase letters, digits, and
           periods are reserved for future standardization. A keyword shall
           not include an <equals-sign>.  (In the following list, the
           notations ``file(s)'' or ``block(s)'' is used to acknowledge that
           a keyword affects the following single file after a _typeflag_ **x**
           extended header, but possibly multiple files after _typeflag_ **g**.
           Any requirements in the list for _pax_ to include a record when in
           **write** or **copy** mode shall apply only when such a record has not
           already been provided through the use of the **-o** option. When used
           in **copy** mode, _pax_ shall behave as if an archive had been created
           with applicable extended header records and then extracted.)
    
           **atime** The file access time for the following file(s),
                     equivalent to the value of the _st_atime_ member of the
                     **stat** structure for a file, as described by the _stat_()
                     function. The access time shall be restored if the
                     process has appropriate privileges required to do so.
                     The format of the <_value_ > shall be as described in _pax_
                     _Extended Header File Times_.
    
           **charset** The name of the character set used to encode the data in
                     the following file(s). The entries in the following
                     table are defined to refer to known standards;
                     additional names may be agreed on between the originator
                     and recipient.
                   ┌─────────────────────────┬───────────────────────────────┐
                   │         **< value>         **│        **Formal Standard** │
                   ├─────────────────────────┼───────────────────────────────┤
                   │ ISO-IR 646 1990         │ ISO/IEC 646:1990              │
                   │ ISO-IR 8859 1 1998      │ ISO/IEC 8859‐1:1998           │
                   │ ISO-IR 8859 2 1999      │ ISO/IEC 8859‐2:1999           │
                   │ ISO-IR 8859 3 1999      │ ISO/IEC 8859‐3:1999           │
                   │ ISO-IR 8859 4 1998      │ ISO/IEC 8859‐4:1998           │
                   │ ISO-IR 8859 5 1999      │ ISO/IEC 8859‐5:1999           │
                   │ ISO-IR 8859 6 1999      │ ISO/IEC 8859‐6:1999           │
                   │ ISO-IR 8859 7 1987      │ ISO/IEC 8859‐7:1987           │
                   │ ISO-IR 8859 8 1999      │ ISO/IEC 8859‐8:1999           │
                   │ ISO-IR 8859 9 1999      │ ISO/IEC 8859‐9:1999           │
                   │ ISO-IR 8859 10 1998     │ ISO/IEC 8859‐10:1998          │
                   │ ISO-IR 8859 13 1998     │ ISO/IEC 8859‐13:1998          │
                   │ ISO-IR 8859 14 1998     │ ISO/IEC 8859‐14:1998          │
                   │ ISO-IR 8859 15 1999     │ ISO/IEC 8859‐15:1999          │
                   │ ISO-IR 10646 2000       │ ISO/IEC 10646:2000            │
                   │ ISO-IR 10646 2000 UTF-8 │ ISO/IEC 10646, UTF-8 encoding │
                   │ BINARY                  │ None.                         │
                   └─────────────────────────┴───────────────────────────────┘
    
                     The encoding is included in an extended header for
                     information only; when _pax_ is used as described in
                     POSIX.1‐2008, it shall not translate the file data into
                     any other encoding. The **BINARY** entry indicates unencoded
                     binary data.
    
                     When used in **write** or **copy** mode, it is implementation-
                     defined whether _pax_ includes a **charset** extended header
                     record for a file.
    
           **comment** A series of characters used as a comment. All characters
                     in the <_value_ > field shall be ignored by _pax_.
    
           **gid** The group ID of the group that owns the file, expressed
                     as a decimal number using digits from the
                     ISO/IEC 646:1991 standard. This record shall override
                     the _gid_ field in the following header block(s). When
                     used in **write** or **copy** mode, _pax_ shall include a _gid_
                     extended header record for each file whose group ID is
                     greater than 2097151 (octal 7777777).
    
           **gname** The group of the file(s), formatted as a group name in
                     the group database. This record shall override the _gid_
                     and _gname_ fields in the following header block(s), and
                     any _gid_ extended header record. When used in **read** , **copy** ,
                     or **list** mode, _pax_ shall translate the name from the
                     encoding in the header record to the character set
                     appropriate for the group database on the receiving
                     system. If any of the characters cannot be translated,
                     and if neither the **-oinvalid=UTF‐8** option nor the
                     **-oinvalid=binary** option is specified, the results are
                     implementation-defined.  When used in **write** or **copy**
                     mode, _pax_ shall include a **gname** extended header record
                     for each file whose group name cannot be represented
                     entirely with the letters and digits of the portable
                     character set.
    
           **hdrcharset**
                     The name of the character set used to encode the value
                     field of the **gname** , **linkpath** , **path** , and **uname** _pax_
                     extended header records. The entries in the following
                     table are defined to refer to known standards;
                     additional names may be agreed between the originator
                     and the recipient.
                   ┌─────────────────────────┬───────────────────────────────┐
                   │         **< value>         **│        **Formal Standard** │
                   ├─────────────────────────┼───────────────────────────────┤
                   │ ISO-IR 10646 2000 UTF-8 │ ISO/IEC 10646, UTF-8 encoding │
                   │ BINARY                  │ None.                         │
                   └─────────────────────────┴───────────────────────────────┘
    
                     If no **hdrcharset** extended header record is specified,
                     the default character set used to encode all values in
                     extended header records shall be the
                     ISO/IEC 10646‐1:2000 standard UTF‐8 encoding.
    
                     The **BINARY** entry indicates that all values recorded in
                     extended headers for affected files are unencoded binary
                     data from the underlying system.
    
           **linkpath** The pathname of a link being created to another file, of
                     any type, previously archived. This record shall
                     override the _linkname_ field in the following **ustar**
                     header block(s). The following **ustar** header block shall
                     determine the type of link created. If _typeflag_ of the
                     following header block is 1, it shall be a hard link. If
                     _typeflag_ is 2, it shall be a symbolic link and the
                     **linkpath** value shall be the contents of the symbolic
                     link. The _pax_ utility shall translate the name of the
                     link (contents of the symbolic link) from the encoding
                     in the header to the character set appropriate for the
                     local file system. When used in **write** or **copy** mode, _pax_
                     shall include a **linkpath** extended header record for each
                     link whose pathname cannot be represented entirely with
                     the members of the portable character set other than
                     NUL.
    
           **mtime** The file modification time of the following file(s),
                     equivalent to the value of the _st_mtime_ member of the
                     **stat** structure for a file, as described in the _stat_()
                     function. This record shall override the _mtime_ field in
                     the following header block(s). The modification time
                     shall be restored if the process has appropriate
                     privileges required to do so. The format of the <_value_ >
                     shall be as described in _pax Extended Header File Times_.
    
           **path** The pathname of the following file(s). This record shall
                     override the _name_ and _prefix_ fields in the following
                     header block(s). The _pax_ utility shall translate the
                     pathname of the file from the encoding in the header to
                     the character set appropriate for the local file system.
    
                     When used in **write** or **copy** mode, _pax_ shall include a
                     _path_ extended header record for each file whose pathname
                     cannot be represented entirely with the members of the
                     portable character set other than NUL.
    
           **realtime.**_any_
                     The keywords prefixed by ``realtime.'' are reserved for
                     future standardization.
    
           **security.**_any_
                     The keywords prefixed by ``security.'' are reserved for
                     future standardization.
    
           **size** The size of the file in octets, expressed as a decimal
                     number using digits from the ISO/IEC 646:1991 standard.
                     This record shall override the _size_ field in the
                     following header block(s). When used in **write** or **copy**
                     mode, _pax_ shall include a _size_ extended header record
                     for each file with a size value greater than 8589934591
                     (octal 77777777777).
    
           **uid** The user ID of the file owner, expressed as a decimal
                     number using digits from the ISO/IEC 646:1991 standard.
                     This record shall override the _uid_ field in the
                     following header block(s). When used in **write** or **copy**
                     mode, _pax_ shall include a _uid_ extended header record for
                     each file whose owner ID is greater than 2097151 (octal
                     7777777).
    
           **uname** The owner of the following file(s), formatted as a user
                     name in the user database. This record shall override
                     the _uid_ and _uname_ fields in the following header
                     block(s), and any _uid_ extended header record. When used
                     in **read** , **copy** , or **list** mode, _pax_ shall translate the
                     name from the encoding in the header record to the
                     character set appropriate for the user database on the
                     receiving system. If any of the characters cannot be
                     translated, and if neither the **-oinvalid=UTF‐8** option
                     nor the **-oinvalid=binary** option is specified, the
                     results are implementation-defined.  When used in **write**
                     or **copy** mode, _pax_ shall include a **uname** extended header
                     record for each file whose user name cannot be
                     represented entirely with the letters and digits of the
                     portable character set.
    
           If the <_value_ > field is zero length, it shall delete any header
           block field, previously entered extended header value, or global
           extended header value of the same name.
    
           If a keyword in an extended header record (or in a **-o** option-
           argument) overrides or deletes a corresponding field in the **ustar**
           header block, _pax_ shall ignore the contents of that header block
           field.
    
           Unlike the **ustar** header block fields, NULs shall not delimit
           <_value_ >s; all characters within the <_value_ > field shall be
           considered data for the field. None of the length limitations of
           the **ustar** header block fields in _Table 4-14, ustar Header Block_
           shall apply to the extended header records.
    
       **pax Extended Header Keyword Precedence**
           This section describes the precedence in which the various header
           records and fields and command line options are selected to apply
           to a file in the archive. When _pax_ is used in **read** or **list** modes,
           it shall determine a file attribute in the following sequence:
    
            1. If **-odelete=keyword-prefix** is used, the affected attributes
               shall be determined from step 7., if applicable, or ignored
               otherwise.
    
            2. If **-o** _keyword_ := is used, the affected attributes shall be
               ignored.
    
            3. If **-okeyword:=value** is used, the affected attribute shall be
               assigned the value.
    
            4. If there is a _typeflag_ **x** extended header record, the affected
               attribute shall be assigned the <_value_ >. When extended header
               records conflict, the last one given in the header shall take
               precedence.
    
            5. If **-okeyword=value** is used, the affected attribute shall be
               assigned the value.
    
            6. If there is a _typeflag_ **g** global extended header record, the
               affected attribute shall be assigned the <_value_ >. When global
               extended header records conflict, the last one given in the
               global header shall take precedence.
    
            7. Otherwise, the attribute shall be determined from the **ustar**
               header block.
    
       **pax Extended Header File Times**
           The _pax_ utility shall write an **mtime** record for each file in **write**
           or **copy** modes if the file's modification time cannot be
           represented exactly in the **ustar** header logical record described
           in _ustar Interchange Format_.  This can occur if the time is out of
           **ustar** range, or if the file system of the underlying
           implementation supports non-integer time granularities and the
           time is not an integer. All of these time records shall be
           formatted as a decimal representation of the time in seconds since
           the Epoch. If a <period> (**'.'**)  decimal point character is
           present, the digits to the right of the point shall represent the
           units of a subsecond timing granularity, where the first digit is
           tenths of a second and each subsequent digit is a tenth of the
           previous digit. In **read** or **copy** mode, the _pax_ utility shall
           truncate the time of a file to the greatest value that is not
           greater than the input header file time. In **write** or **copy** mode,
           the _pax_ utility shall output a time exactly if it can be
           represented exactly as a decimal number, and otherwise shall
           generate only enough digits so that the same time shall be
           recovered if the file is extracted on a system whose underlying
           implementation supports the same time granularity.
    
       **ustar Interchange Format**
           A **ustar** archive tape or file shall contain a series of logical
           records. Each logical record shall be a fixed-size logical record
           of 512 octets (see below). Although this format may be thought of
           as being stored on 9-track industry-standard 12.7 mm (0.5 in)
           magnetic tape, other types of transportable media are not
           excluded. Each file archived shall be represented by a header
           logical record that describes the file, followed by zero or more
           logical records that give the contents of the file. At the end of
           the archive file there shall be two 512-octet logical records
           filled with binary zeros, interpreted as an end-of-archive
           indicator.
    
           The logical records may be grouped for physical I/O operations, as
           described under the **-b** _blocksize_ and **-x ustar** options. Each group
           of logical records may be written with a single operation
           equivalent to the _write_() function. On magnetic tape, the result
           of this write shall be a single tape physical block. The last
           physical block shall always be the full size, so logical records
           after the two zero logical records may contain undefined data.
    
           The header logical record shall be structured as shown in the
           following table. All lengths and offsets are in decimal.
    
                             **Table 4-14: ustar Header Block**
                  ┌────────────┬──────────────┬────────────────────┐
                  │ **Field Name** │ **Octet Offset** │ **Length (in Octets)** │
                  ├────────────┼──────────────┼────────────────────┤
                  │ _name_       │       0      │        100         │
                  │ _mode_       │     100      │          8         │
                  │ _uid_        │     108      │          8         │
                  │ _gid_        │     116      │          8         │
                  │ _size_       │     124      │         12         │
                  │ _mtime_      │     136      │         12         │
                  │ _chksum_     │     148      │          8         │
                  │ _typeflag_   │     156      │          1         │
                  │ _linkname_   │     157      │        100         │
                  │ _magic_      │     257      │          6         │
                  │ _version_    │     263      │          2         │
                  │ _uname_      │     265      │         32         │
                  │ _gname_      │     297      │         32         │
                  │ _devmajor_   │     329      │          8         │
                  │ _devminor_   │     337      │          8         │
                  │ _prefix_     │     345      │        155         │
                  └────────────┴──────────────┴────────────────────┘
    
           All characters in the header logical record shall be represented
           in the coded character set of the ISO/IEC 646:1991 standard. For
           maximum portability between implementations, names should be
           selected from characters represented by the portable filename
           character set as octets with the most significant bit zero. If an
           implementation supports the use of characters outside of <slash>
           and the portable filename character set in names for files, users,
           and groups, one or more implementation-defined encodings of these
           characters shall be provided for interchange purposes.
    
           However, the _pax_ utility shall never create filenames on the local
           system that cannot be accessed via the procedures described in
           POSIX.1‐2008. If a filename is found on the medium that would
           create an invalid filename, it is implementation-defined whether
           the data from the file is stored on the file hierarchy and under
           what name it is stored. The _pax_ utility may choose to ignore these
           files as long as it produces an error indicating that the file is
           being ignored.
    
           Each field within the header logical record is contiguous; that
           is, there is no padding used. Each character on the archive medium
           shall be stored contiguously.
    
           The fields _magic_ , _uname_ , and _gname_ are character strings each
           terminated by a NUL character. The fields _name_ , _linkname_ , and
           _prefix_ are NUL-terminated character strings except when all
           characters in the array contain non-NUL characters including the
           last character. The _version_ field is two octets containing the
           characters **"00"**(zero-zero). The _typeflag_ contains a single
           character. All other fields are leading zero-filled octal numbers
           using digits from the ISO/IEC 646:1991 standard IRV. Each numeric
           field is terminated by one or more <space> or NUL characters.
    
           The _name_ and the _prefix_ fields shall produce the pathname of the
           file. A new pathname shall be formed, if _prefix_ is not an empty
           string (its first character is not NUL), by concatenating _prefix_
           (up to the first NUL character), a <slash> character, and _name_ ;
           otherwise, _name_ is used alone. In either case, _name_ is terminated
           at the first NUL character. If _prefix_ begins with a NUL character,
           it shall be ignored. In this manner, pathnames of at most 256
           characters can be supported. If a pathname does not fit in the
           space provided, _pax_ shall notify the user of the error, and shall
           not store any part of the file—header or data—on the medium.
    
           The _linkname_ field, described below, shall not use the _prefix_ to
           produce a pathname. As such, a _linkname_ is limited to 100
           characters. If the name does not fit in the space provided, _pax_
           shall notify the user of the error, and shall not attempt to store
           the link on the medium.
    
           The _mode_ field provides 12 bits encoded in the ISO/IEC 646:1991
           standard octal digit representation.  The encoded bits shall
           represent the following values:
    
                                **Table: ustar** _mode_ **Field**
    ┌───────────┬──────────────────┬─────────────────────────────────────────────────┐
    │ **Bit Value** │ **POSIX.1‐2008 Bit** │                   **Description** │
    ├───────────┼──────────────────┼─────────────────────────────────────────────────┤
    │   04000   │ S_ISUID          │ Set UID on execution.                           │
    │   02000   │ S_ISGID          │ Set GID on execution.                           │
    │   01000   │ <reserved>       │ Reserved for future standardization.            │
    │   00400   │ S_IRUSR          │ Read permission for file owner class.           │
    │   00200   │ S_IWUSR          │ Write permission for file owner class.          │
    │   00100   │ S_IXUSR          │ Execute/search permission for file owner class. │
    │   00040   │ S_IRGRP          │ Read permission for file group class.           │
    │   00020   │ S_IWGRP          │ Write permission for file group class.          │
    │   00010   │ S_IXGRP          │ Execute/search permission for file group class. │
    │   00004   │ S_IROTH          │ Read permission for file other class.           │
    │   00002   │ S_IWOTH          │ Write permission for file other class.          │
    │   00001   │ S_IXOTH          │ Execute/search permission for file other class. │
    └───────────┴──────────────────┴─────────────────────────────────────────────────┘
    
           When appropriate privileges are required to set one of these mode
           bits, and the user restoring the files from the archive does not
           have appropriate privileges, the mode bits for which the user does
           not have appropriate privileges shall be ignored. Some of the mode
           bits in the archive format are not mentioned elsewhere in this
           volume of POSIX.1‐2017. If the implementation does not support
           those bits, they may be ignored.
    
           The _uid_ and _gid_ fields are the user and group ID of the owner and
           group of the file, respectively.
    
           The _size_ field is the size of the file in octets. If the _typeflag_
           field is set to specify a file to be of type 1 (a link) or 2 (a
           symbolic link), the _size_ field shall be specified as zero. If the
           _typeflag_ field is set to specify a file of type 5 (directory), the
           _size_ field shall be interpreted as described under the definition
           of that record type. No data logical records are stored for types
           1, 2, or 5.  If the _typeflag_ field is set to 3 (character special
           file), 4 (block special file), or 6 (FIFO), the meaning of the
           _size_ field is unspecified by this volume of POSIX.1‐2017, and no
           data logical records shall be stored on the medium. Additionally,
           for type 6, the _size_ field shall be ignored when reading. If the
           _typeflag_ field is set to any other value, the number of logical
           records written following the header shall be (_size_ +511)/512,
           ignoring any fraction in the result of the division.
    
           The _mtime_ field shall be the modification time of the file at the
           time it was archived. It is the ISO/IEC 646:1991 standard
           representation of the octal value of the modification time
           obtained from the _stat_() function.
    
           The _chksum_ field shall be the ISO/IEC 646:1991 standard IRV
           representation of the octal value of the simple sum of all octets
           in the header logical record. Each octet in the header shall be
           treated as an unsigned value. These values shall be added to an
           unsigned integer, initialized to zero, the precision of which is
           not less than 17 bits. When calculating the checksum, the _chksum_
           field is treated as if it were all <space> characters.
    
           The _typeflag_ field specifies the type of file archived. If a
           particular implementation does not recognize the type, or the user
           does not have appropriate privileges to create that type, the file
           shall be extracted as if it were a regular file if the file type
           is defined to have a meaning for the _size_ field that could cause
           data logical records to be written on the medium (see the previous
           description for _size_).  If conversion to a regular file occurs,
           the _pax_ utility shall produce an error indicating that the
           conversion took place. All of the _typeflag_ fields shall be coded
           in the ISO/IEC 646:1991 standard IRV:
    
           0       Represents a regular file. For backwards-compatibility, a
                   _typeflag_ value of binary zero (**'\0'**) should be recognized
                   as meaning a regular file when extracting files from the
                   archive. Archives written with this version of the archive
                   file format create regular files with a _typeflag_ value of
                   the ISO/IEC 646:1991 standard IRV **'0'**.
    
           1       Represents a file linked to another file, of any type,
                   previously archived. Such files are identified by having
                   the same device and file serial numbers, and pathnames
                   that refer to different directory entries. All such files
                   shall be archived as linked files.  The linked-to name is
                   specified in the _linkname_ field with a NUL-character
                   terminator if it is less than 100 octets in length.
    
           2       Represents a symbolic link. The contents of the symbolic
                   link shall be stored in the _linkname_ field.
    
           3,4     Represent character special files and block special files
                   respectively.  In this case the _devmajor_ and _devminor_
                   fields shall contain information defining the device, the
                   format of which is unspecified by this volume of
                   POSIX.1‐2017. Implementations may map the device
                   specifications to their own local specification or may
                   ignore the entry.
    
           5       Specifies a directory or subdirectory. On systems where
                   disk allocation is performed on a directory basis, the
                   _size_ field shall contain the maximum number of octets
                   (which may be rounded to the nearest disk block allocation
                   unit) that the directory may hold.  A _size_ field of zero
                   indicates no such limiting. Systems that do not support
                   limiting in this manner should ignore the _size_ field.
    
           6       Specifies a FIFO special file. Note that the archiving of
                   a FIFO file archives the existence of this file and not
                   its contents.
    
           7       Reserved to represent a file to which an implementation
                   has associated some high-performance attribute.
                   Implementations without such extensions should treat this
                   file as a regular file (type 0).
    
           A‐Z     The letters **'A'** to **'Z'** , inclusive, are reserved for custom
                   implementations. All other values are reserved for future
                   versions of this standard.
    
           It is unspecified whether files with pathnames that refer to the
           same directory entry are archived as linked files or as separate
           files. If they are archived as linked files, this means that
           attempting to extract both pathnames from the resulting archive
           will always cause an error (unless the **-u** option is used) because
           the link cannot be created.
    
           It is unspecified whether files with the same device and file
           serial numbers being appended to an archive are treated as linked
           files to members that were in the archive before the append.
    
           Attempts to archive a socket shall produce a diagnostic message
           when **ustar** interchange format is used, but may be allowed when **pax**
           interchange format is used. Handling of other file types is
           implementation-defined.
    
           The _magic_ field is the specification that this archive was output
           in this archive format. If this field contains **ustar**(the five
           characters from the ISO/IEC 646:1991 standard IRV shown followed
           by NUL), the _uname_ and _gname_ fields shall contain the
           ISO/IEC 646:1991 standard IRV representation of the owner and
           group of the file, respectively (truncated to fit, if necessary).
           When the file is restored by a privileged, protection-preserving
           version of the utility, the user and group databases shall be
           scanned for these names. If found, the user and group IDs
           contained within these files shall be used rather than the values
           contained within the _uid_ and _gid_ fields.
    
       **cpio Interchange Format**
           The octet-oriented **cpio** archive format shall be a series of
           entries, each comprising a header that describes the file, the
           name of the file, and then the contents of the file.
    
           An archive may be recorded as a series of fixed-size blocks of
           octets.  This blocking shall be used only to make physical I/O
           more efficient.  The last group of blocks shall always be at the
           full size.
    
           For the octet-oriented **cpio** archive format, the individual entry
           information shall be in the order indicated and described by the
           following table; see also the _< cpio.h>_ header.
    
                     **Table 4-16: Octet-Oriented cpio Archive Entry**
            ┌──────────────────────┬────────────────────┬─────────────────┐
            │  **Header Field Name** │ **Length (in Octets)** │ **Interpreted as** │
            ├──────────────────────┼────────────────────┼─────────────────┤
            │ _c_magic_              │          6         │ Octal number    │
            │ _c_dev_                │          6         │ Octal number    │
            │ _c_ino_                │          6         │ Octal number    │
            │ _c_mode_               │          6         │ Octal number    │
            │ _c_uid_                │          6         │ Octal number    │
            │ _c_gid_                │          6         │ Octal number    │
            │ _c_nlink_              │          6         │ Octal number    │
            │ _c_rdev_               │          6         │ Octal number    │
            │ _c_mtime_              │         11         │ Octal number    │
            │ _c_namesize_           │          6         │ Octal number    │
            │ _c_filesize_           │         11         │ Octal number    │
            ├──────────────────────┼────────────────────┼─────────────────┤
            │ **Filename Field Name** │       **Length** │ **Interpreted as** │
            ├──────────────────────┴────────────────────┴─────────────────┤
            │ _c_name_                 _c_namesize_           Pathname string │
            ├──────────────────────┬────────────────────┬─────────────────┤
            │ **File Data Field Name** │       **Length** │ **Interpreted as** │
            ├──────────────────────┴────────────────────┴─────────────────┤
            │ _c_filedata_             _c_filesize_           Data            │
            └─────────────────────────────────────────────────────────────┘
    
       **cpio Header**
           For each file in the archive, a header as defined previously shall
           be written. The information in the header fields is written as
           streams of the ISO/IEC 646:1991 standard characters interpreted as
           octal numbers. The octal numbers shall be extended to the
           necessary length by appending the ISO/IEC 646:1991 standard IRV
           zeros at the most-significant-digit end of the number; the result
           is written to the most-significant digit of the stream of octets
           first.  The fields shall be interpreted as follows:
    
           _c_magic_   Identify the archive as being a transportable archive by
                     containing the identifying value **"070707"**.
    
           _c_dev_ , _c_ino_
                     Contains values that uniquely identify the file within
                     the archive (that is, no files contain the same pair of
                     _c_dev_ and _c_ino_ values unless they are links to the same
                     file). The values shall be determined in an unspecified
                     manner.
    
           _c_mode_    Contains the file type and access permissions as defined
                     in the following table.
    
                             **Table 4-17: Values for cpio c_mode Field**
                   ──┬───────────────────────┬─────────┬─────────────────────── │
                     │**File Permissions Name** │**Value** │     **Indicates** │
                   ──┼───────────────────────┼─────────┼─────────────────────── │
                     │C_IRUSR                 │000400   │Read by owner            │
                     │C_IWUSR                 │000200   │Write by owner           │
                     │C_IXUSR                 │000100   │Execute by owner         │
                     │C_IRGRP                 │000040   │Read by group            │
                     │C_IWGRP                 │000020   │Write by group           │
                     │C_IXGRP                 │000010   │Execute by group         │
                     │C_IROTH                 │000004   │Read by others           │
                     │C_IWOTH                 │000002   │Write by others          │
                     │C_IXOTH                 │000001   │Execute by others        │
                     │C_ISUID                 │004000   │Set _uid_                  │
                     │C_ISGID                 │002000   │Set _gid_                  │
                     │C_ISVTX                 │001000   │Reserved                 │
                   ──┼───────────────────────┼─────────┼─────────────────────── │
                     │  **File Type Name** │**Value** │     **Indicates** │
                   ──┼───────────────────────┼─────────┼─────────────────────── │
                     │C_ISDIR                 │040000   │Directory                │
                     │C_ISFIFO                │010000   │FIFO                     │
                     │C_ISREG                 │0100000   │Regular file             │
                     │C_ISLNK                 │0120000   │Symbolic link            │
                     │                       │         │                        │
                     │ C_ISBLK               │  060000 │ Block special file     │
                     │ C_ISCHR               │  020000 │ Character special file │
                     │ C_ISSOCK              │ 0140000 │ Socket                 │
                     │                       │         │                        │
                     │ C_ISCTG               │ 0110000 │ Reserved               │
                     └───────────────────────┴─────────┴────────────────────────┘
    
                     Directories, FIFOs, symbolic links, and regular files
                     shall be supported on a system conforming to this volume
                     of POSIX.1‐2017; additional values defined previously
                     are reserved for compatibility with existing systems.
                     Additional file types may be supported; however, such
                     files should not be written to archives intended to be
                     transported to other systems.
    
           _c_uid_     Contains the user ID of the owner.
    
           _c_gid_     Contains the group ID of the group.
    
           _c_nlink_   Contains a number greater than or equal to the number of
                     links in the archive referencing the file. If the **-a**
                     option is used to append to a _cpio_ archive, then the _pax_
                     utility need not account for the files in the existing
                     part of the archive when calculating the _c_nlink_ values
                     for the appended part of the archive, and need not alter
                     the _c_nlink_ values in the existing part of the archive
                     if additional files with the same _c_dev_ and _c_ino_ values
                     are appended to the archive.
    
           _c_rdev_    Contains implementation-defined information for
                     character or block special files.
    
           _c_mtime_   Contains the latest time of modification of the file at
                     the time the archive was created.
    
           _c_namesize_
                     Contains the length of the pathname, including the
                     terminating NUL character.
    
           _c_filesize_
                     Contains the length in octets of the data section
                     following the header structure.
    
       **cpio Filename**
           The _c_name_ field shall contain the pathname of the file. The
           length of this field in octets is the value of _c_namesize_.
    
           If a filename is found on the medium that would create an invalid
           pathname, it is implementation-defined whether the data from the
           file is stored on the file hierarchy and under what name it is
           stored.
    
           All characters shall be represented in the ISO/IEC 646:1991
           standard IRV. For maximum portability between implementations,
           names should be selected from characters represented by the
           portable filename character set as octets with the most
           significant bit zero. If an implementation supports the use of
           characters outside the portable filename character set in names
           for files, users, and groups, one or more implementation-defined
           encodings of these characters shall be provided for interchange
           purposes. However, the _pax_ utility shall never create filenames on
           the local system that cannot be accessed via the procedures
           described previously in this volume of POSIX.1‐2017. If a filename
           is found on the medium that would create an invalid filename, it
           is implementation-defined whether the data from the file is stored
           on the local file system and under what name it is stored. The _pax_
           utility may choose to ignore these files as long as it produces an
           error indicating that the file is being ignored.
    
       **cpio File Data**
           Following _c_name_ , there shall be _c_filesize_ octets of data.
           Interpretation of such data occurs in a manner dependent on the
           file. For regular files, the data shall consist of the contents of
           the file. For symbolic links, the data shall consist of the
           contents of the symbolic link. If _c_filesize_ is zero, no data
           shall be contained in _c_filedata_.
    
           When restoring from an archive:
    
            *  If the user does not have appropriate privileges to create a
               file of the specified type, _pax_ shall ignore the entry and
               write an error message to standard error.
    
            *  Only regular files and symbolic links have data to be
               restored. Presuming a regular file meets any selection
               criteria that might be imposed on the format-reading utility
               by the user, such data shall be restored.
    
            *  If a user does not have appropriate privileges to set a
               particular mode flag, the flag shall be ignored. Some of the
               mode flags in the archive format are not mentioned elsewhere
               in this volume of POSIX.1‐2017. If the implementation does not
               support those flags, they may be ignored.
    
       **cpio Special Entries**
           FIFO special files, directories, and the trailer shall be recorded
           with _c_filesize_ equal to zero. Symbolic links shall be recorded
           with _c_filesize_ equal to the length of the contents of the
           symbolic link.  For other special files, _c_filesize_ is unspecified
           by this volume of POSIX.1‐2017. The header for the next file entry
           in the archive shall be written directly after the last octet of
           the file entry preceding it. A header denoting the filename
           **TRAILER!!!** shall indicate the end of the archive; the contents of
           octets in the last block of the archive following such a header
           are undefined.
    


## EXIT STATUS



           The following exit values shall be returned:
    
            0    All files were processed successfully.
    
           >0    An error occurred.
    


## CONSEQUENCES OF ERRORS



           If _pax_ cannot create a file or a link when reading an archive or
           cannot find a file when writing an archive, or cannot preserve the
           user ID, group ID, or file mode when the **-p** option is specified, a
           diagnostic message shall be written to standard error and a non-
           zero exit status shall be returned, but processing shall continue.
           In the case where _pax_ cannot create a link to a file, _pax_ shall
           not, by default, create a second copy of the file.
    
           If the extraction of a file from an archive is prematurely
           terminated by a signal or error, _pax_ may have only partially
           extracted the file or (if the **-n** option was not specified) may
           have extracted a file of the same name as that specified by the
           user, but which is not the file the user wanted.  Additionally,
           the file modes of extracted directories may have additional bits
           from the S_IRWXU mask set as well as incorrect modification and
           access times.
    
           _The following sections are informative._
    


## APPLICATION USAGE



           Caution is advised when using the **-a** option to append to a _cpio_
           format archive. If any of the files being appended happen to be
           given the same _c_dev_ and _c_ino_ values as a file in the existing
           part of the archive, then they may be treated as links to that
           file on extraction. Thus, it is risky to use **-a** with _cpio_ format
           except when it is done on the same system that the original
           archive was created on, and with the same _pax_ utility, and in the
           knowledge that there has been little or no file system activity
           since the original archive was created that could lead to any of
           the files appended being given the same _c_dev_ and _c_ino_ values as
           an unrelated file in the existing part of the archive. Also, when
           (intentionally) appending additional links to a file in the
           existing part of the archive, the _c_nlink_ values in the modified
           archive can be smaller than the number of links to the file in the
           archive, which may mean that the links are not preserved on
           extraction.
    
           The **-p**(privileges) option was invented to reconcile differences
           between historical _tar_ and _cpio_ implementations. In particular,
           the two utilities use **-m** in diametrically opposed ways. The **-p**
           option also provides a consistent means of extending the ways in
           which future file attributes can be addressed, such as for
           enhanced security systems or high-performance files. Although it
           may seem complex, there are really two modes that are most
           commonly used:
    
           **-p e** ``Preserve everything''. This would be used by the
                   historical superuser, someone with all appropriate
                   privileges, to preserve all aspects of the files as they
                   are recorded in the archive. The **e** flag is the sum of **o**
                   and **p** , and other implementation-defined attributes.
    
           **-p p** ``Preserve'' the file mode bits. This would be used by the
                   user with regular privileges who wished to preserve
                   aspects of the file other than the ownership. The file
                   times are preserved by default, but two other flags are
                   offered to disable these and use the time of extraction.
    
           The one pathname per line format of standard input precludes
           pathnames containing <newline> characters. Although such pathnames
           violate the portable filename guidelines, they may exist and their
           presence may inhibit usage of _pax_ within shell scripts. This
           problem is inherited from historical archive programs. The problem
           can be avoided by listing filename arguments on the command line
           instead of on standard input.
    
           It is almost certain that appropriate privileges are required for
           _pax_ to accomplish parts of this volume of POSIX.1‐2017.
           Specifically, creating files of type block special or character
           special, restoring file access times unless the files are owned by
           the user (the **-t** option), or preserving file owner, group, and
           mode (the **-p** option) all probably require appropriate privileges.
    
           In **read** mode, implementations are permitted to overwrite files
           when the archive has multiple members with the same name. This may
           fail if permissions on the first version of the file do not permit
           it to be overwritten.
    
           The **cpio** and **ustar** formats can only support files up to 8589934592
           bytes (8 ∗ 2^30) in size.
    
           When archives containing binary header information are listed ,
           the filenames printed may cause strange behavior on some
           terminals.
    
           When all of the following are true:
    
            1. A file of type directory is being placed into an archive.
    
            2. The **ustar** archive format is being used.
    
            3. The pathname of the directory is less than or equal to 155
               bytes long (it will fit in the _prefix_ field in the **ustar**
               header block).
    
            4. The last component of the pathname of the directory is longer
               than 100 bytes long (it will not fit in the _name_ field in the
               **ustar** header block).
    
           some implementations of the _pax_ utility will place the entire
           directory pathname in the _prefix_ field, set the _name_ field to an
           empty string, and place the directory in the archive.  Other
           implementations of the _pax_ utility will give an error under these
           conditions because the _name_ field is not large enough to hold the
           last component of the directory name.  This standard allows either
           behavior. However, when extracting a directory from a **ustar** format
           archive, this standard requires that all implementations be able
           to extract a directory even if the _name_ field contains an empty
           string as long as the _prefix_ field does not also contain an empty
           string.
    


## EXAMPLES



           The following command:
    
               pax -w -f /dev/rmt/1m .
    
           copies the contents of the current directory to tape drive 1,
           medium density (assuming historical System V device naming
           procedures—the historical BSD device name would be **/dev/rmt9**).
    
           The following commands:
    
               mkdir _newdir_
               pax -rw _olddir newdir_
    
           copy the _olddir_ directory hierarchy to _newdir_.
    
               pax -r -s ',^//*usr//*,,' -f a.pax
    
           reads the archive **a.pax** , with all files rooted in **/usr** in the
           archive extracted relative to the current directory.
    
           Using the option:
    
               -o listopt="%M %(atime)T %(size)D %(name)s"
    
           overrides the default output description in Standard Output and
           instead writes:
    
               -rw-rw--- Jan 12 15:53 2003 1492 /usr/foo/bar
    
           Using the options:
    
               -o listopt='%L\t%(size)D\n%.7' \
               -o listopt='(name)s\n%(atime)T\n%T'
    
           overrides the default output description in Standard Output and
           instead writes:
    
               /usr/foo/bar -> /tmp   1492
               /usr/fo
               Jan 12 15:53 1991
               Jan 31 15:53 2003
    


## RATIONALE



           The _pax_ utility was new for the ISO POSIX‐2:1993 standard. It
           represents a peaceful compromise between advocates of the
           historical _tar_ and _cpio_ utilities.
    
           A fundamental difference between _cpio_ and _tar_ was in the way
           directories were treated. The _cpio_ utility did not treat
           directories differently from other files, and to select a
           directory and its contents required that each file in the
           hierarchy be explicitly specified. For _tar_ , a directory matched
           every file in the file hierarchy it rooted.
    
           The _pax_ utility offers both interfaces; by default, directories
           map into the file hierarchy they root. The **-d** option causes _pax_ to
           skip any file not explicitly referenced, as _cpio_ historically did.
           The _tar_ **-**_style_ behavior was chosen as the default because it was
           believed that this was the more common usage and because _tar_ is
           the more commonly available interface, as it was historically
           provided on both System V and BSD implementations.
    
           The data interchange format specification in this volume of
           POSIX.1‐2017 requires that processes with ``appropriate
           privileges'' shall always restore the ownership and permissions of
           extracted files exactly as archived. If viewed from the historic
           equivalence between superuser and ``appropriate privileges'',
           there are two problems with this requirement. First, users running
           as superusers may unknowingly set dangerous permissions on
           extracted files. Second, it is needlessly limiting, in that
           superusers cannot extract files and own them as superuser unless
           the archive was created by the superuser. (It should be noted that
           restoration of ownerships and permissions for the superuser, by
           default, is historical practice in _cpio_ , but not in _tar_.)  In
           order to avoid these two problems, the _pax_ specification has an
           additional ``privilege'' mechanism, the **-p** option. Only a _pax_
           invocation with the privileges needed, and which has the **-p** option
           set using the **e** specification character, has appropriate
           privileges to restore full ownership and permission information.
    
           Note also that this volume of POSIX.1‐2017 requires that the file
           ownership and access permissions shall be set, on extraction, in
           the same fashion as the _creat_() function when provided with the
           mode stored in the archive. This means that the file creation mask
           of the user is applied to the file permissions.
    
           Users should note that directories may be created by _pax_ while
           extracting files with permissions that are different from those
           that existed at the time the archive was created. When extracting
           sensitive information into a directory hierarchy that no longer
           exists, users are encouraged to set their file creation mask
           appropriately to protect these files during extraction.
    
           The table of contents output is written to standard output to
           facilitate pipeline processing.
    
           An early proposal had hard links displaying for all pathnames.
           This was removed because it complicates the output of the case
           where **-v** is not specified and does not match historical _cpio_
           usage. The hard-link information is available in the **-v** display.
    
           The description of the **-l** option allows implementations to make
           hard links to symbolic links.  Earlier versions of this standard
           did not specify any way to create a hard link to a symbolic link,
           but many implementations provided this capability as an extension.
           If there are hard links to symbolic links when an archive is
           created, the implementation is required to archive the hard link
           in the archive (unless **-H** or **-L** is specified). When in **read** mode
           and in **copy** mode, implementations supporting hard links to
           symbolic links should use them when appropriate.
    
           The archive formats inherited from the POSIX.1‐1990 standard have
           certain restrictions that have been brought along from historical
           usage. For example, there are restrictions on the length of
           pathnames stored in the archive.  When _pax_ is used in **copy**(**-rw**)
           mode (copying directory hierarchies), the ability to use
           extensions from the **-xpax** format overcomes these restrictions.
    
           The default _blocksize_ value of 5120 bytes for _cpio_ was selected
           because it is one of the standard block-size values for _cpio_ , set
           when the **-B** option is specified. (The other default block-size
           value for _cpio_ is 512 bytes, and this was considered to be too
           small.) The default block value of 10240 bytes for _tar_ was
           selected because that is the standard block-size value for BSD
           _tar_.  The maximum block size of 32256 bytes (215-512 bytes) is the
           largest multiple of 512 bytes that fits into a signed 16-bit tape
           controller transfer register. There are known limitations in some
           historical systems that would prevent larger blocks from being
           accepted. Historical values were chosen to improve compatibility
           with historical scripts using _dd_ or similar utilities to
           manipulate archives. Also, default block sizes for any file type
           other than character special file has been deleted from this
           volume of POSIX.1‐2017 as unimportant and not likely to affect the
           structure of the resulting archive.
    
           Implementations are permitted to modify the block-size value based
           on the archive format or the device to which the archive is being
           written. This is to provide implementations with the opportunity
           to take advantage of special types of devices, and it should not
           be used without a great deal of consideration as it almost
           certainly decreases archive portability.
    
           The intended use of the **-n** option was to permit extraction of one
           or more files from the archive without processing the entire
           archive. This was viewed by the standard developers as offering
           significant performance advantages over historical
           implementations. The **-n** option in early proposals had three
           effects; the first was to cause special characters in patterns to
           not be treated specially. The second was to cause only the first
           file that matched a pattern to be extracted. The third was to
           cause _pax_ to write a diagnostic message to standard error when no
           file was found matching a specified pattern. Only the second
           behavior is retained by this volume of POSIX.1‐2017, for many
           reasons. First, it is in general not acceptable for a single
           option to have multiple effects. Second, the ability to make
           pattern matching characters act as normal characters is useful for
           parts of _pax_ other than file extraction. Third, a finer degree of
           control over the special characters is useful because users may
           wish to normalize only a single special character in a single
           filename. Fourth, given a more general escape mechanism, the
           previous behavior of the **-n** option can be easily obtained using
           the **-s** option or a _sed_ script. Finally, writing a diagnostic
           message when a pattern specified by the user is unmatched by any
           file is useful behavior in all cases.
    
           In this version, the **-n** was removed from the **copy** mode synopsis of
           _pax_ ; it is inapplicable because there are no pattern operands
           specified in this mode.
    
           There is another method than _pax_ for copying subtrees in
           POSIX.1‐2008 described as part of the _cp_ utility. Both methods are
           historical practice: _cp_ provides a simpler, more intuitive
           interface, while _pax_ offers a finer granularity of control. Each
           provides additional functionality to the other; in particular, _pax_
           maintains the hard-link structure of the hierarchy while _cp_ does
           not. It is the intention of the standard developers that the
           results be similar (using appropriate option combinations in both
           utilities). The results are not required to be identical; there
           seemed insufficient gain to applications to balance the difficulty
           of implementations having to guarantee that the results would be
           exactly identical.
    
           A single archive may span more than one file. It is suggested that
           implementations provide informative messages to the user on
           standard error whenever the archive file is changed.
    
           The **-d** option (do not create intermediate directories not listed
           in the archive) found in early proposals was originally provided
           as a complement to the historic **-d** option of _cpio_.  It has been
           deleted.
    
           The **-s** option in early proposals specified a subset of the
           substitution command from the _ed_ utility. As there was no reason
           for only a subset to be supported, the **-s** option is now compatible
           with the current _ed_ specification. Since the delimiter can be any
           non-null character, the following usage with single <space>
           characters is valid:
    
               pax -s " foo bar " ...
    
           The **-t** description is worded so as to note that this may cause the
           access time update caused by some other activity (which occurs
           while the file is being read) to be overwritten.
    
           The default behavior of _pax_ with regard to file modification times
           is the same as historical implementations of _tar_.  It is not the
           historical behavior of _cpio_.
    
           Because the **-i** option uses **/dev/tty** , utilities without a
           controlling terminal are not able to use this option.
    
           The **-y** option, found in early proposals, has been deleted because
           a line containing a single <period> for the **-i** option has
           equivalent functionality. The special lines for the **-i** option (a
           single <period> and the empty line) are historical practice in
           _cpio_.
    
           In early drafts, a **-e** _charmap_ option was included to increase
           portability of files between systems using different coded
           character sets. This option was omitted because it was apparent
           that consensus could not be formed for it. In this version, the
           use of UTF‐8 should be an adequate substitute.
    
           The ISO POSIX‐2:1993 standard and ISO POSIX‐1 standard
           requirements for _pax_ , however, made it very difficult to create a
           single archive containing files created using extended characters
           provided by different locales.  This version adds the **hdrcharset**
           keyword to make it possible to archive files in these cases
           without dropping files due to translation errors.
    
           Translating filenames and other attributes from a locale's
           encoding to UTF‐8 and then back again can lose information, as the
           resulting filename might not be byte-for-byte equivalent to the
           original. To avoid this problem, users can specify the **-o**
           **hdrcharset=binary** option, which will cause the resulting archive
           to use binary format for all names and attributes. Such archives
           are not portable among hosts that use different native encodings
           (e.g., EBCDIC _versus_ ASCII-based encodings), but they will allow
           interchange among the vast majority of POSIX file systems in
           practical use. Also, the **-o hdrcharset=binary** option will cause
           _pax_ in **copy** mode to behave more like other standard utilities such
           as _cp_.
    
           If the values specified by the **-o exthdr.name=value** , **-o**
           **globexthdr.name=value** , or by **$TMPDIR**(if **-o globexthdr.name** is not
           specified) require a character encoding other than that described
           in the ISO/IEC 646:1991 standard, a **path** extended header record
           will have to be created for the file. If a **hdrcharset** extended
           header record is active for such headers, it will determine the
           codeset used for the value field in these extended **path** header
           records. These **path** extended header records always need to be
           created when writing an archive even if **hdrcharset=binary** has been
           specified and would contain the same (binary) data that appears in
           the **ustar** header record prefix and _name_ fields. (In other words,
           an extended header **path** record is always required to be generated
           if the _prefix_ or _name_ fields contain non-ASCII characters even
           when **hdrcharset=binary** is also in effect for that file.)
    
           The **-k** option was added to address international concerns about
           the dangers involved in the character set transformations of **-e**
           (if the target character set were different from the source, the
           filenames might be transformed into names matching existing files)
           and also was made more general to protect files transferred
           between file systems with different {NAME_MAX} values (truncating
           a filename on a smaller system might also inadvertently overwrite
           existing files). As stated, it prevents any overwriting, even if
           the target file is older than the source. This version adds more
           granularity of options to solve this problem by introducing the
           **-oinvalid=option** —specifically the **UTF‐8** and **binary** actions. (Note
           that an existing file is still subject to overwriting in this
           case. The **-k** option closes that loophole.)
    
           Some of the file characteristics referenced in this volume of
           POSIX.1‐2017 might not be supported by some archive formats. For
           example, neither the **tar** nor **cpio** formats contain the file access
           time. For this reason, the **e** specification character has been
           provided, intended to cause all file characteristics specified in
           the archive to be retained.
    
           It is required that extracted directories, by default, have their
           access and modification times and permissions set to the values
           specified in the archive. This has obvious problems in that the
           directories are almost certainly modified after being extracted
           and that directory permissions may not permit file creation. One
           possible solution is to create directories with the mode specified
           in the archive, as modified by the _umask_ of the user, with
           sufficient permissions to allow file creation. After all files
           have been extracted, _pax_ would then reset the access and
           modification times and permissions as necessary.
    
           The list-mode formatting description borrows heavily from the one
           defined by the _printf_ utility. However, since there is no separate
           operand list to get conversion arguments, the format was extended
           to allow specifying the name of the conversion argument as part of
           the conversion specification.
    
           The **T** conversion specifier allows time fields to be displayed in
           any of the date formats. Unlike the _ls_ utility, _pax_ does not
           adjust the format when the date is less than six months in the
           past. This makes parsing the output more predictable.
    
           The **D** conversion specifier handles the ability to display the
           major/minor or file size, as with _ls_ , by using %-8(_size_)D.
    
           The **L** conversion specifier handles the _ls_ display for symbolic
           links.
    
           Conversion specifiers were added to generate existing known types
           used for _ls_.
    
       **pax Interchange Format**
           The new POSIX data interchange format was developed primarily to
           satisfy international concerns that the **ustar** and **cpio** formats did
           not provide for file, user, and group names encoded in characters
           outside a subset of the ISO/IEC 646:1991 standard. The standard
           developers realized that this new POSIX data interchange format
           should be very extensible because there were other requirements
           they foresaw in the near future:
    
            *  Support international character encodings and locale
               information
    
            *  Support security information (ACLs, and so on)
    
            *  Support future file types, such as realtime or contiguous
               files
    
            *  Include data areas for implementation use
    
            *  Support systems with words larger than 32 bits and timers with
               subsecond granularity
    
           The following were not goals for this format because these are
           better handled by separate utilities or are inappropriate for a
           portable format:
    
            *  Encryption
    
            *  Compression
    
            *  Data translation between locales and codesets
    
            *  _inode_ storage
    
           The format chosen to support the goals is an extension of the
           **ustar** format. Of the two formats previously available, only the
           **ustar** format was selected for extensions because:
    
            *  It was easier to extend in an upwards-compatible way. It
               offered version flags and header block type fields with room
               for future standardization. The **cpio** format, while possessing
               a more flexible file naming methodology, could not be extended
               without breaking some theoretical implementation or using a
               dummy filename that could be a legitimate filename.
    
            *  Industry experience since the original ``_tar_ wars'' fought in
               developing the ISO POSIX‐1 standard has clearly been in favor
               of the **ustar** format, which is generally the default output
               format selected for _pax_ implementations on new systems.
    
           The new format was designed with one additional goal in mind:
           reasonable behavior when an older _tar_ or _pax_ utility happened to
           read an archive. Since the POSIX.1‐1990 standard mandated that a
           ``format-reading utility'' had to treat unrecognized _typeflag_
           values as regular files, this allowed the format to include all
           the extended information in a pseudo-regular file that preceded
           each real file. An option is given that allows the archive creator
           to set up reasonable names for these files on the older systems.
           Also, the normative text suggests that reasonable file access
           values be used for this **ustar** header block. Making these header
           files inaccessible for convenient reading and deleting would not
           be reasonable. File permissions of 600 or 700 are suggested.
    
           The **ustar** _typeflag_ field was used to accommodate the additional
           functionality of the new format rather than magic or version
           because the POSIX.1‐1990 standard (and, by reference, the previous
           version of _pax_), mandated the behavior of the format-reading
           utility when it encountered an unknown _typeflag_ , but was silent
           about the other two fields.
    
           Early proposals for the first version of this standard contained a
           proposed archive format that was based on compatibility with the
           standard for tape files (ISO 1001, similar to the format used
           historically on many mainframes and minicomputers). This format
           was overly complex and required considerable overhead in volume
           and header records. Furthermore, the standard developers felt that
           it would not be acceptable to the community of POSIX developers,
           so it was later changed to be a format more closely related to
           historical practice on POSIX systems.
    
           The prefix and name split of pathnames in **ustar** was replaced by
           the single path extended header record for simplicity.
    
           The concept of a global extended header (_typeflag_**g**) was
           controversial. If this were applied to an archive being recorded
           on magnetic tape, a few unreadable blocks at the beginning of the
           tape could be a serious problem; a utility attempting to extract
           as many files as possible from a damaged archive could lose a
           large percentage of file header information in this case. However,
           if the archive were on a reliable medium, such as a CD‐ROM, the
           global extended header offers considerable potential size
           reductions by eliminating redundant information. Thus, the text
           warns against using the global method for unreliable media and
           provides a method for implanting global information in the
           extended header for each file, rather than in the _typeflag_ **g**
           records.
    
           No facility for data translation or filtering on a per-file basis
           is included because the standard developers could not invent an
           interface that would allow this in an efficient manner. If a
           filter, such as encryption or compression, is to be applied to all
           the files, it is more efficient to apply the filter to the entire
           archive as a single file. The standard developers considered
           interfaces that would invoke a shell script for each file going
           into or out of the archive, but the system overhead in this
           approach was considered to be too high.
    
           One such approach would be to have **filter=** records that give a
           pathname for an executable. When the program is invoked, the file
           and archive would be open for standard input/output and all the
           header fields would be available as environment variables or
           command-line arguments. The standard developers did discuss such
           schemes, but they were omitted from POSIX.1‐2008 due to concerns
           about excessive overhead. Also, the program itself would need to
           be in the archive if it were to be used portably.
    
           There is currently no portable means of identifying the character
           set(s) used for a file in the file system. Therefore, _pax_ has not
           been given a mechanism to generate charset records automatically.
           The only portable means of doing this is for the user to write the
           archive using the **-ocharset=string** command line option. This
           assumes that all of the files in the archive use the same
           encoding. The ``implementation-defined'' text is included to allow
           for a system that can identify the encodings used for each of its
           files.
    
           The table of standards that accompanies the charset record
           description is acknowledged to be very limited. Only a limited
           number of character set standards is reasonable for maximal
           interchange. Any character set is, of course, possible by prior
           agreement. It was suggested that EBCDIC be listed, but it was
           omitted because it is not defined by a formal standard. Formal
           standards, and then only those with reasonably large followings,
           can be included here, simply as a matter of practicality. The
           <_value_ >s represent names of officially registered character sets
           in the format required by the ISO 2375:1985 standard.
    
           The normal <comma> or <blank>-separated list rules are not
           followed in the case of keyword options to allow ease of argument
           parsing for _getopts_.
    
           Further information on character encodings is in _pax Archive_
           _Character Set Encoding/Decoding_.
    
           The standard developers have reserved keyword name space for
           vendor extensions. It is suggested that the format to be used is:
    
               _VENDOR.keyword_
    
           where _VENDOR_ is the name of the vendor or organization in all
           uppercase letters. It is further suggested that the keyword
           following the <period> be named differently than any of the
           standard keywords so that it could be used for future
           standardization, if appropriate, by omitting the _VENDOR_ prefix.
    
           The <_length_ > field in the extended header record was included to
           make it simpler to step through the records, even if a record
           contains an unknown format (to a particular _pax_) with complex
           interactions of special characters. It also provides a minor
           integrity checkpoint within the records to aid a program
           attempting to recover files from a damaged archive.
    
           There are no extended header versions of the _devmajor_ and _devminor_
           fields because the unspecified format **ustar** header field should be
           sufficient. If they are not, vendor-specific extended keywords
           (such as _VENDOR.devmajor_) should be used.
    
           Device and _i_ -number labeling of files was not adopted from _cpio_ ;
           files are interchanged strictly on a symbolic name basis, as in
           **ustar**.
    
           Just as with the **ustar** format descriptions, the new format makes
           no special arrangements for multi-volume archives. Each of the _pax_
           archive types is assumed to be inside a single POSIX file and
           splitting that file over multiple volumes (diskettes, tape
           cartridges, and so on), processing their labels, and mounting each
           in the proper sequence are considered to be implementation details
           that cannot be described portably.
    
           The **pax** format is intended for interchange, not only for backup on
           a single (family of) systems. It is not as densely packed as might
           be possible for backup:
    
            *  It contains information as coded characters that could be
               coded in binary.
    
            *  It identifies extended records with name fields that could be
               omitted in favor of a fixed-field layout.
    
            *  It translates names into a portable character set and
               identifies locale-related information, both of which are
               probably unnecessary for backup.
    
           The requirements on restoring from an archive are slightly
           different from the historical wording, allowing for non-monolithic
           privilege to bring forward as much as possible. In particular,
           attributes such as ``high performance file'' might be broadly but
           not universally granted while set-user-ID or _chown_() might be much
           more restricted. There is no implication in POSIX.1‐2008 that the
           security information be honored after it is restored to the file
           hierarchy, in spite of what might be improperly inferred by the
           silence on that topic. That is a topic for another standard.
    
           Links are recorded in the fashion described here because a link
           can be to any file type. It is desirable in general to be able to
           restore part of an archive selectively and restore all of those
           files completely. If the data is not associated with each link, it
           is not possible to do this. However, the data associated with a
           file can be large, and when selective restoration is not needed,
           this can be a significant burden.  The archive is structured so
           that files that have no associated data can always be restored by
           the name of any link name of any link, and the user may choose
           whether data is recorded with each instance of a file that
           contains data. The format permits mixing of both types of links in
           a single archive; this can be done for special needs, and _pax_ is
           expected to interpret such archives on input properly, despite the
           fact that there is no _pax_ option that would force this mixed case
           on output. (When **-o linkdata** is used, the output must contain the
           duplicate data, but the implementation is free to include it or
           omit it when **-o linkdata** is not used.)
    
           The time values are included as extended header records for those
           implementations needing more than the eleven octal digits allowed
           by the **ustar** format. Portable file timestamps cannot be negative.
           If _pax_ encounters a file with a negative timestamp in **copy** or
           **write** mode, it can reject the file, substitute a non-negative
           timestamp, or generate a non-portable timestamp with a leading
           **'-'**.  Even though some implementations can support finer file-time
           granularities than seconds, the normative text requires support
           only for seconds since the Epoch because the ISO POSIX‐1 standard
           states them that way. The **ustar** format includes only _mtime_ ; the
           new format adds _atime_ and _ctime_ for symmetry. The _atime_ access
           time restored to the file system will be affected by the **-p a** and
           **-p e** options. The _ctime_ creation time (actually _inode_ modification
           time) is described with appropriate privileges so that it can be
           ignored when writing to the file system. POSIX does not provide a
           portable means to change file creation time. Nothing is intended
           to prevent a non-portable implementation of _pax_ from restoring the
           value.
    
           The _gid_ , _size_ , and _uid_ extended header records were included to
           allow expansion beyond the sizes specified in the regular _tar_
           header. New file system architectures are emerging that will
           exhaust the 12-digit size field. There are probably not many
           systems requiring more than 8 digits for user and group IDs, but
           the extended header values were included for completeness,
           allowing overrides for all of the decimal values in the _tar_
           header.
    
           The standard developers intended to describe the effective results
           of _pax_ with regard to file ownerships and permissions;
           implementations are not restricted in timing or sequencing the
           restoration of such, provided the results are as specified.
    
           Much of the text describing the extended headers refers to use in
           ``**write** or **copy** modes''. The **copy** mode references are due to the
           normative text: ``The effect of the copy shall be as if the copied
           files were written to an archive file and then subsequently
           extracted ...''. There is certainly no way to test whether _pax_ is
           actually generating the extended headers in **copy** mode, but the
           effects must be as if it had.
    
       **pax Archive Character Set Encoding/Decoding**
           There is a need to exchange archives of files between systems of
           different native codesets. Filenames, group names, and user names
           must be preserved to the fullest extent possible when an archive
           is read on the receiving platform. Translation of the contents of
           files is not within the scope of the _pax_ utility.
    
           There will also be the need to represent characters that are not
           available on the receiving platform. These unsupported characters
           cannot be automatically folded to the local set of characters due
           to the chance of collisions. This could result in overwriting
           previous extracted files from the archive or pre-existing files on
           the system.
    
           For these reasons, the codeset used to represent characters within
           the extended header records of the _pax_ archive must be
           sufficiently rich to handle all commonly used character sets. The
           fields requiring translation include, at a minimum, filenames,
           user names, group names, and link pathnames. Implementations may
           wish to have localized extended keywords that use non-portable
           characters.
    
           The standard developers considered the following options:
    
            *  The archive creator specifies the well-defined name of the
               source codeset. The receiver must then recognize the codeset
               name and perform the appropriate translations to the
               destination codeset.
    
            *  The archive creator includes within the archive the character
               mapping table for the source codeset used to encode extended
               header records.  The receiver must then read the character
               mapping table and perform the appropriate translations to the
               destination codeset.
    
            *  The archive creator translates the extended header records in
               the source codeset into a canonical form. The receiver must
               then perform the appropriate translations to the destination
               codeset.
    
           The approach that incorporates the name of the source codeset
           poses the problem of codeset name registration, and makes the
           archive useless to _pax_ archive decoders that do not recognize that
           codeset.
    
           Because parts of an archive may be corrupted, the standard
           developers felt that including the character map of the source
           codeset was too fragile. The loss of this one key component could
           result in making the entire archive useless. (The difference
           between this and the global extended header decision was that the
           latter has a workaround—duplicating extended header records on
           unreliable media—but this would be too burdensome for large
           character set maps.)
    
           Both of the above approaches also put an undue burden on the _pax_
           archive receiver to handle the cross-product of all source and
           destination codesets.
    
           To simplify the translation from the source codeset to the
           canonical form and from the canonical form to the destination
           codeset, the standard developers decided that the internal
           representation should be a stateless encoding. A stateless
           encoding is one where each codepoint has the same meaning, without
           regard to the decoder being in a specific state. An example of a
           stateful encoding would be the Japanese Shift-JIS; an example of a
           stateless encoding would be the ISO/IEC 646:1991 standard
           (equivalent to 7-bit ASCII).
    
           For these reasons, the standard developers decided to adopt a
           canonical format for the representation of file information
           strings. The obvious, well-endorsed candidate is the
           ISO/IEC 10646‐1:2000 standard (based in part on Unicode), which
           can be used to represent the characters of virtually all
           standardized character sets. The standard developers initially
           agreed upon using UCS2 (16-bit Unicode) as the internal
           representation. This repertoire of characters provides a
           sufficiently rich set to represent all commonly-used codesets.
    
           However, the standard developers found that the 16-bit Unicode
           representation had some problems. It forced the issue of
           standardizing byte ordering. The 2-byte length of each character
           made the extended header records twice as long for the case of
           strings coded entirely from historical 7-bit ASCII. For these
           reasons, the standard developers chose the UTF‐8 defined in the
           ISO/IEC 10646‐1:2000 standard. This multi-byte representation
           encodes UCS2 or UCS4 characters reliably and deterministically,
           eliminating the need for a canonical byte ordering. In addition,
           NUL octets and other characters possibly confusing to POSIX file
           systems do not appear, except to represent themselves. It was
           realized that certain national codesets take up more space after
           the encoding, due to their placement within the UCS range; it was
           felt that the usefulness of the encoding of the names outweighs
           the disadvantage of size increase for file, user, and group names.
    
           The encoding of UTF‐8 is as follows:
    
               UCS4 Hex Encoding  UTF-8 Binary Encoding
    
               00000000-0000007F  0xxxxxxx
               00000080-000007FF  110xxxxx 10xxxxxx
               00000800-0000FFFF  1110xxxx 10xxxxxx 10xxxxxx
               00010000-001FFFFF  11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
               00200000-03FFFFFF  111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
               04000000-7FFFFFFF  1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
    
           where each **'x'** represents a bit value from the character being
           translated.
    
       **ustar Interchange Format**
           The description of the **ustar** format reflects numerous enhancements
           over pre-1988 versions of the historical _tar_ utility. The goal of
           these changes was not only to provide the functional enhancements
           desired, but also to retain compatibility between new and old
           versions. This compatibility has been retained.  Archives written
           using the old archive format are compatible with the new format.
    
           Implementors should be aware that the previous file format did not
           include a mechanism to archive directory type files. For this
           reason, the convention of using a filename ending with <slash> was
           adopted to specify a directory on the archive.
    
           The total size of the _name_ and _prefix_ fields have been set to meet
           the minimum requirements for {PATH_MAX}.  If a pathname will fit
           within the _name_ field, it is recommended that the pathname be
           stored there without the use of the _prefix_ field. Although the
           name field is known to be too small to contain {PATH_MAX}
           characters, the value was not changed in this version of the
           archive file format to retain backwards-compatibility, and instead
           the prefix was introduced. Also, because of the earlier version of
           the format, there is no way to remove the restriction on the
           _linkname_ field being limited in size to just that of the _name_
           field.
    
           The _size_ field is required to be meaningful in all implementation
           extensions, although it could be zero. This is required so that
           the data blocks can always be properly counted.
    
           It is suggested that if device special files need to be
           represented that cannot be represented in the standard format,
           that one of the extension types (**A** ‐**Z**) be used, and that the
           additional information for the special file be represented as data
           and be reflected in the _size_ field.
    
           Attempting to restore a special file type, where it is converted
           to ordinary data and conflicts with an existing filename, need not
           be specially detected by the utility. If run as an ordinary user,
           _pax_ should not be able to overwrite the entries in, for example,
           **/dev** in any case (whether the file is converted to another type or
           not). If run as a privileged user, it should be able to do so, and
           it would be considered a bug if it did not. The same is true of
           ordinary data files and similarly named special files; it is
           impossible to anticipate the needs of the user (who could really
           intend to overwrite the file), so the behavior should be
           predictable (and thus regular) and rely on the protection system
           as required.
    
           The value 7 in the _typeflag_ field is intended to define how
           contiguous files can be stored in a **ustar** archive. POSIX.1‐2008
           does not require the contiguous file extension, but does define a
           standard way of archiving such files so that all conforming
           systems can interpret these file types in a meaningful and
           consistent manner. On a system that does not support extended file
           types, the _pax_ utility should do the best it can with the file and
           go on to the next.
    
           The file protection modes are those conventionally used by the _ls_
           utility. This is extended beyond the usage in the ISO POSIX‐2
           standard to support the ``shared text'' or ``sticky'' bit. It is
           intended that the conformance document should not document
           anything beyond the existence of and support of such a mode.
           Further extensions are expected to these bits, particularly with
           overloading the set-user-ID and set-group-ID flags.
    
       **cpio Interchange Format**
           The reference to appropriate privileges in the **cpio** format refers
           to an error on standard output; the **ustar** format does not make
           comparable statements.
    
           The model for this format was the historical System V _cpio_**-c** data
           interchange format. This model documents the portable version of
           the **cpio** format and not the binary version. It has the flexibility
           to transfer data of any type described within POSIX.1‐2008, yet is
           extensible to transfer data types specific to extensions beyond
           POSIX.1‐2008 (for example, contiguous files). Because it describes
           existing practice, there is no question of maintaining upwards-
           compatibility.
    
       **cpio Header**
           There has been some concern that the size of the _c_ino_ field of
           the header is too small to handle those systems that have very
           large _inode_ numbers. However, the _c_ino_ field in the header is
           used strictly as a hard-link resolution mechanism for archives. It
           is not necessarily the same value as the _inode_ number of the file
           in the location from which that file is extracted.
    
           The name _c_magic_ is based on historical usage.
    
       **cpio Filename**
           For most historical implementations of the _cpio_ utility,
           {PATH_MAX} octets can be used to describe the pathname without the
           addition of any other header fields (the NUL character would be
           included in this count).  {PATH_MAX} is the minimum value for
           pathname size, documented as 256 bytes.  However, an
           implementation may use _c_namesize_ to determine the exact length of
           the pathname. With the current description of the _< cpio.h>_ header,
           this pathname size can be as large as a number that is described
           in six octal digits.
    
           Two values are documented under the _c_mode_ field values to provide
           for extensibility for known file types:
    
           **0110 000** Reserved for contiguous files. The implementation may
                     treat the rest of the information for this archive like
                     a regular file. If this file type is undefined, the
                     implementation may create the file as a regular file.
    
           This provides for extensibility of the **cpio** format while allowing
           for the ability to read old archives. Files of an unknown type may
           be read as ``regular files'' on some implementations.  On a system
           that does not support extended file types, the _pax_ utility should
           do the best it can with the file and go on to the next.
    


## FUTURE DIRECTIONS



           None.
    


* * *