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



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

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 aa 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.

SEE ALSO
       chmod(), creat(), exec, fstatat(), mkdir(), mkfifo(), open(), umask()

       The Base Definitions volume of POSIX.1-2017, <fcntl.h>, <sys_stat.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  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.opengroup.org/unix/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                  2017                             MKNOD(3)
