PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

MKNOD(3P)                 POSIX Programmer's Manual                MKNOD(3P)

PROLOG         top

       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         top

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

SYNOPSIS         top

       #include <sys/stat.h>

       int mknod(const char *path, mode_t mode, dev_t dev);
       int mknodat(int fd, const char *path, mode_t mode, dev_t dev);

DESCRIPTION         top

       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 file descriptor was
       opened without O_SEARCH, the function shall check whether directory
       searches are permitted using the current permissions of the directory
       underlying the file descriptor. If the file descriptor was opened
       with 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         top

       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         top

       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
              names 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 fd was not opened with 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         top

   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         top

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

RATIONALE         top

       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         top

       None.

SEE ALSO         top

       chmod(3p), creat(3p), exec(1p), fstatat(3p), mkdir(3p), mkfifo(3p),
       open(3p), umask(3p)

       The Base Definitions volume of POSIX.1‐2008, sys_stat.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                           MKNOD(3P)

Pages that refer to this page: sys_stat.h(0p)chmod(3p)creat(3p)exec(3p)fchmod(3p)fstatat(3p)fstatvfs(3p)mkdir(3p)mkfifo(3p)open(3p)umask(3p)