# id

## 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



           id — return user identity
    


## SYNOPSIS



           id **[**_user_**]**
    
           id -G **[** -n**] [**_user_**]**
    
           id -g **[** -nr**] [**_user_**]**
    
           id -u **[** -nr**] [**_user_**]**
    


## DESCRIPTION



           If no _user_ operand is provided, the _id_ utility shall write the
           user and group IDs and the corresponding user and group names of
           the invoking process to standard output. If the effective and real
           IDs do not match, both shall be written. If multiple groups are
           supported by the underlying system (see the description of
           {NGROUPS_MAX} in the System Interfaces volume of POSIX.1‐2017),
           the supplementary group affiliations of the invoking process shall
           also be written.
    
           If a _user_ operand is provided and the process has appropriate
           privileges, the user and group IDs of the selected user shall be
           written. In this case, effective IDs shall be assumed to be
           identical to real IDs. If the selected user has more than one
           allowable group membership listed in the group database, these
           shall be written in the same manner as the supplementary groups
           described in the preceding paragraph.
    


## OPTIONS



           The _id_ utility shall conform to the Base Definitions volume of
           POSIX.1‐2017, _Section 12.2_ , _Utility Syntax Guidelines_.
    
           The following options shall be supported:
    
           **-G** Output all different group IDs (effective, real, and
                     supplementary) only, using the format **"%u\n"**.  If there
                     is more than one distinct group affiliation, output each
                     such affiliation, using the format **" %u"** , before the
                     <newline> is output.
    
           **-g** Output only the effective group ID, using the format
                     **"%u\n"**.
    
           **-n** Output the name in the format **"%s"** instead of the
                     numeric ID using the format **"%u"**.
    
           **-r** Output the real ID instead of the effective ID.
    
           **-u** Output only the effective user ID, using the format
                     **"%u\n"**.
    


## OPERANDS



           The following operand shall be supported:
    
           _user_      The login name for which information is to be written.
    


## STDIN



           Not used.
    


## INPUT FILES



           None.
    


## ENVIRONMENT VARIABLES



           The following environment variables shall affect the execution of
           _id_ :
    
           _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_ for 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_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).
    
           _LC_MESSAGES_
                     Determine the locale that should be used to affect the
                     format and contents of diagnostic messages written to
                     standard error and informative messages written to
                     standard output.
    
           _NLSPATH_   Determine the location of message catalogs for the
                     processing of _LC_MESSAGES_.
    


## ASYNCHRONOUS EVENTS



           Default.
    


## STDOUT



           The following formats shall be used when the _LC_MESSAGES_ locale
           category specifies the POSIX locale. In other locales, the strings
           _uid_ , _gid_ , _euid_ , _egid_ , and _groups_ may be replaced with more
           appropriate strings corresponding to the locale.
    
               "uid=%u(%s) gid=%u(%s)\n", <_real user ID_ >, <_user-name_ >,
                   <_real group ID_ >, <_group-name_ >
    
           If the effective and real user IDs do not match, the following
           shall be inserted immediately before the **'\n'** character in the
           previous format:
    
               " euid=%u(%s)"
    
           with the following arguments added at the end of the argument
           list:
    
               <_effective user ID_ >, <_effective user-name_ >
    
           If the effective and real group IDs do not match, the following
           shall be inserted directly before the **'\n'** character in the format
           string (and after any addition resulting from the effective and
           real user IDs not matching):
    
               " egid=%u(%s)"
    
           with the following arguments added at the end of the argument
           list:
    
               <_effective group-ID_ >, <_effective group name_ >
    
           If the process has supplementary group affiliations or the
           selected user is allowed to belong to multiple groups, the first
           shall be added directly before the <newline> in the format string:
    
               " groups=%u(%s)"
    
           with the following arguments added at the end of the argument
           list:
    
               <_supplementary group ID_ >, <_supplementary group name_ >
    
           and the necessary number of the following added after that for any
           remaining supplementary group IDs:
    
               ",%u(%s)"
    
           and the necessary number of the following arguments added at the
           end of the argument list:
    
               <_supplementary group ID_ >, <_supplementary group name_ >
    
           If any of the user ID, group ID, effective user ID, effective
           group ID, or supplementary/multiple group IDs cannot be mapped by
           the system into printable user or group names, the corresponding
           **"(%s)"** and _name_ argument shall be omitted from the corresponding
           format string.
    
           When any of the options are specified, the output format shall be
           as described in the OPTIONS section.
    


## STDERR



           The standard error shall be used only for diagnostic messages.
    


## OUTPUT FILES



           None.
    


## EXTENDED DESCRIPTION



           None.
    


## EXIT STATUS



           The following exit values shall be returned:
    
            0    Successful completion.
    
           >0    An error occurred.
    


## CONSEQUENCES OF ERRORS



           Default.
    
           _The following sections are informative._
    


## APPLICATION USAGE



           Output produced by the **-G** option and by the default case could
           potentially produce very long lines on systems that support large
           numbers of supplementary groups.  (On systems with user and group
           IDs that are 32-bit integers and with group names with a maximum
           of 8 bytes per name, 93 supplementary groups plus distinct
           effective and real group and user IDs could theoretically overflow
           the 2048-byte {LINE_MAX} text file line limit on the default
           output case. It would take about 186 supplementary groups to
           overflow the 2048-byte barrier using _id_ **-G**).  This is not expected
           to be a problem in practice, but in cases where it is a concern,
           applications should consider using _fold_ **-s** before post-processing
           the output of _id_.
    


## EXAMPLES



           None.
    


## RATIONALE



           The functionality provided by the 4 BSD _groups_ utility can be
           simulated using:
    
               id -Gn [ user ]
    
           The 4 BSD command _groups_ was considered, but it was not included
           because it did not provide the functionality of the _id_ utility of
           the SVID. Also, it was thought that it would be easier to modify
           _id_ to provide the additional functionality necessary to systems
           with multiple groups than to invent another command.
    
           The options **-u** , **-g** , **-n** , and **-r** were added to ease the use of _id_
           with shell commands substitution. Without these options it is
           necessary to use some preprocessor such as _sed_ to select the
           desired piece of information. Since output such as that produced
           by:
    
               id -u -n
    
           is frequently wanted, it seemed desirable to add the options.
    


## FUTURE DIRECTIONS



           None.
    


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