# mknod

## 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



           mknod, mknodat — make directory, special file, or regular file
    


## SYNOPSIS



           #include <sys/stat.h>
    
           int mknod(const char *_path_ , mode_t _mode_ , dev_t _dev_);
    
           #include <fcntl.h>
    
           int mknodat(int _fd_ , const char *_path_ , mode_t _mode_ , dev_t _dev_);
    


## DESCRIPTION



           The _mknod_() function shall create a new file named by the pathname
           to which the argument _path_ points.
    
           The file type for _path_ is OR'ed into the _mode_ argument, and the
           application shall select one of the following symbolic constants:
                   ┌────────────┬──────────────────────────────────┐
                   │    **Name** │           **Description** │
                   ├────────────┼──────────────────────────────────┤
                   │ S_IFIFO    │ FIFO-special                     │
                   │ S_IFCHR    │ Character-special (non-portable) │
                   │ S_IFDIR    │ Directory (non-portable)         │
                   │ S_IFBLK    │ Block-special (non-portable)     │
                   │ S_IFREG    │ Regular (non-portable)           │
                   └────────────┴──────────────────────────────────┘
    
           The only portable use of _mknod_() is to create a FIFO-special file.
           If _mode_ is not S_IFIFO or _dev_ is not 0, the behavior of _mknod_() is
           unspecified.
    
           The permissions for the new file are OR'ed into the _mode_ argument,
           and may be selected from any combination of the following symbolic
           constants:
             ┌────────────┬─────────────────────────────────────────────┐
             │    **Name** │                 **Description** │
             ├────────────┼─────────────────────────────────────────────┤
             │ S_ISUID    │ Set user ID on execution.                   │
             │ S_ISGID    │ Set group ID on execution.                  │
             │ S_IRWXU    │ Read, write, or execute (search) by owner.  │
             │ S_IRUSR    │ Read by owner.                              │
             │ S_IWUSR    │ Write by owner.                             │
             │ S_IXUSR    │ Execute (search) by owner.                  │
             │ S_IRWXG    │ Read, write, or execute (search) by group.  │
             │ S_IRGRP    │ Read by group.                              │
             │ S_IWGRP    │ Write by group.                             │
             │ S_IXGRP    │ Execute (search) by group.                  │
             │ S_IRWXO    │ Read, write, or execute (search) by others. │
             │ S_IROTH    │ Read by others.                             │
             │ S_IWOTH    │ Write by others.                            │
             │ S_IXOTH    │ Execute (search) by others.                 │
             │ S_ISVTX    │ On directories, restricted deletion flag.   │
             └────────────┴─────────────────────────────────────────────┘
    
           The user ID of the file shall be initialized to the effective user
           ID of the process. The group ID of the file shall be initialized
           to either the effective group ID of the process or the group ID of
           the parent directory. Implementations shall provide a way to
           initialize the file's group ID to the group ID of the parent
           directory. Implementations may, but need not, provide an
           implementation-defined way to initialize the file's group ID to
           the effective group ID of the calling process. The owner, group,
           and other permission bits of _mode_ shall be modified by the file
           mode creation mask of the process. The _mknod_() function shall
           clear each bit whose corresponding bit in the file mode creation
           mask of the process is set.
    
           If _path_ names a symbolic link, _mknod_() shall fail and set _errno_ to
           **[EEXIST]**.
    
           Upon successful completion, _mknod_() shall mark for update the last
           data access, last data modification, and last file status change
           timestamps of the file. Also, the last data modification and last
           file status change timestamps of the directory that contains the
           new entry shall be marked for update.
    
           Only a process with appropriate privileges may invoke _mknod_() for
           file types other than FIFO-special.
    
           The _mknodat_() function shall be equivalent to the _mknod_() function
           except in the case where _path_ specifies a relative path. In this
           case the newly created directory, special file, or regular file is
           located relative to the directory associated with the file
           descriptor _fd_ instead of the current working directory. If the
           access mode of the open file description associated with the file
           descriptor is not O_SEARCH, the function shall check whether
           directory searches are permitted using the current permissions of
           the directory underlying the file descriptor. If the access mode
           is O_SEARCH, the function shall not perform the check.
    
           If _mknodat_() is passed the special value AT_FDCWD in the _fd_
           parameter, the current working directory shall be used and the
           behavior shall be identical to a call to _mknod_().
    


## RETURN VALUE



           Upon successful completion, these functions shall return 0.
           Otherwise, these functions shall return -1 and set _errno_ to
           indicate the error. If -1 is returned, the new file shall not be
           created.
    


## ERRORS



           These functions shall fail if:
    
           **EACCES** A component of the path prefix denies search permission, or
                  write permission is denied on the parent directory.
    
           **EEXIST** The named file exists.
    
           **EINVAL** An invalid argument exists.
    
           **EIO** An I/O error occurred while accessing the file system.
    
           **ELOOP** A loop exists in symbolic links encountered during
                  resolution of the _path_ argument.
    
           **ENAMETOOLONG**
                  The length of a component of a pathname is longer than
                  {NAME_MAX}.
    
           **ENOENT** A component of the path prefix of _path_ does not name an
                  existing file or _path_ is an empty string.
    
           **ENOENT** or **ENOTDIR**
                  The _path_ argument contains at least one non-<slash>
                  character and ends with one or more trailing <slash>
                  characters. If _path_ without the trailing <slash> characters
                  would name an existing file, an **[ENOENT]** error shall not
                  occur.
    
           **ENOSPC** The directory that would contain the new file cannot be
                  extended or the file system is out of file allocation
                  resources.
    
           **ENOTDIR**
                  A component of the path prefix names an existing file that
                  is neither a directory nor a symbolic link to a directory.
    
           **EPERM** The invoking process does not have appropriate privileges
                  and the file type is not FIFO-special.
    
           **EROFS** The directory in which the file is to be created is located
                  on a read-only file system.
    
           The _mknodat_() function shall fail if:
    
           **EACCES** The access mode of the open file description associated
                  with _fd_ is not O_SEARCH and the permissions of the
                  directory underlying _fd_ do not permit directory searches.
    
           **EBADF** The _path_ argument does not specify an absolute path and the
                  _fd_ argument is neither AT_FDCWD nor a valid file descriptor
                  open for reading or searching.
    
           **ENOTDIR**
                  The _path_ argument is not an absolute path and _fd_ is a file
                  descriptor associated with a non-directory file.
    
           These functions may fail if:
    
           **ELOOP** More than {SYMLOOP_MAX} symbolic links were encountered
                  during resolution of the _path_ argument.
    
           **ENAMETOOLONG**
                  The length of a pathname exceeds {PATH_MAX}, or pathname
                  resolution of a symbolic link produced an intermediate
                  result with a length that exceeds {PATH_MAX}.
    
           _The following sections are informative._
    


## EXAMPLES



       **Creating a FIFO Special File**
           The following example shows how to create a FIFO special file
           named **/home/cnd/mod_done** , with read/write permissions for owner,
           and with read permissions for group and others.
    
               #include <sys/types.h>
               #include <sys/stat.h>
    
               dev_t dev;
               int   status;
               ...
               status  = mknod("/home/cnd/mod_done", S_IFIFO | S_IWUSR |
                   S_IRUSR | S_IRGRP | S_IROTH, dev);
    


## APPLICATION USAGE



           The _mkfifo_() function is preferred over this function for making
           FIFO special files.
    


## RATIONALE



           The POSIX.1‐1990 standard required that the group ID of a newly
           created file be set to the group ID of its parent directory or to
           the effective group ID of the creating process. FIPS 151‐2
           required that implementations provide a way to have the group ID
           be set to the group ID of the containing directory, but did not
           prohibit implementations also supporting a way to set the group ID
           to the effective group ID of the creating process.  Conforming
           applications should not assume which group ID will be used. If it
           matters, an application can use _chown_() to set the group ID after
           the file is created, or determine under what conditions the
           implementation will set the desired group ID.
    
           The purpose of the _mknodat_() function is to create directories,
           special files, or regular files in directories other than the
           current working directory without exposure to race conditions. Any
           part of the path of a file could be changed in parallel to a call
           to _mknod_(), resulting in unspecified behavior. By opening a file
           descriptor for the target directory and using the _mknodat_()
           function it can be guaranteed that the newly created directory,
           special file, or regular file is located relative to the desired
           directory.
    


## FUTURE DIRECTIONS



           None.
    


* * *