mknod(2) — Linux manual page


mknod(2)                   System Calls Manual                  mknod(2)

NAME         top

       mknod, mknodat - create a special or ordinary file

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <sys/stat.h>

       int mknod(const char *pathname, mode_t mode, dev_t dev);

       #include <fcntl.h>           /* Definition of AT_* constants */
       #include <sys/stat.h>

       int mknodat(int dirfd, const char *pathname, mode_t mode, dev_t dev);

   Feature Test Macro Requirements for glibc (see

           _XOPEN_SOURCE >= 500
               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION         top

       The system call mknod() creates a filesystem node (file, device
       special file, or named pipe) named pathname, with attributes
       specified by mode and dev.

       The mode argument specifies both the file mode to use and the
       type of node to be created.  It should be a combination (using
       bitwise OR) of one of the file types listed below and zero or
       more of the file mode bits listed in inode(7).

       The file mode is modified by the process's umask in the usual
       way: in the absence of a default ACL, the permissions of the
       created node are (mode & ~umask).

       The file type must be one of S_IFREG, S_IFCHR, S_IFBLK, S_IFIFO,
       or S_IFSOCK to specify a regular file (which will be created
       empty), character special file, block special file, FIFO (named
       pipe), or UNIX domain socket, respectively.  (Zero file type is
       equivalent to type S_IFREG.)

       If the file type is S_IFCHR or S_IFBLK, then dev specifies the
       major and minor numbers of the newly created device special file
       (makedev(3) may be useful to build the value for dev); otherwise
       it is ignored.

       If pathname already exists, or is a symbolic link, this call
       fails with an EEXIST error.

       The newly created node will be owned by the effective user ID of
       the process.  If the directory containing the node has the set-
       group-ID bit set, or if the filesystem is mounted with BSD group
       semantics, the new node will inherit the group ownership from its
       parent directory; otherwise it will be owned by the effective
       group ID of the process.

       The mknodat() system call operates in exactly the same way as
       mknod(), except for the differences described here.

       If the pathname given in pathname is relative, then it is
       interpreted relative to the directory referred to by the file
       descriptor dirfd (rather than relative to the current working
       directory of the calling process, as is done by mknod() for a
       relative pathname).

       If pathname is relative and dirfd is the special value AT_FDCWD,
       then pathname is interpreted relative to the current working
       directory of the calling process (like mknod()).

       If pathname is absolute, then dirfd is ignored.

       See openat(2) for an explanation of the need for mknodat().

RETURN VALUE         top

       mknod() and mknodat() return zero on success.  On error, -1 is
       returned and errno is set to indicate the error.

ERRORS         top

       EACCES The parent directory does not allow write permission to
              the process, or one of the directories in the path prefix
              of pathname did not allow search permission.  (See also

       EBADF  (mknodat()) pathname is relative but dirfd is neither
              AT_FDCWD nor a valid file descriptor.

       EDQUOT The user's quota of disk blocks or inodes on the
              filesystem has been exhausted.

       EEXIST pathname already exists.  This includes the case where
              pathname is a symbolic link, dangling or not.

       EFAULT pathname points outside your accessible address space.

       EINVAL mode requested creation of something other than a regular
              file, device special file, FIFO or socket.

       ELOOP  Too many symbolic links were encountered in resolving

              pathname was too long.

       ENOENT A directory component in pathname does not exist or is a
              dangling symbolic link.

       ENOMEM Insufficient kernel memory was available.

       ENOSPC The device containing pathname has no room for the new

              A component used as a directory in pathname is not, in
              fact, a directory.

              (mknodat()) pathname is relative and dirfd is a file
              descriptor referring to a file other than a directory.

       EPERM  mode requested creation of something other than a regular
              file, FIFO (named pipe), or UNIX domain socket, and the
              caller is not privileged (Linux: does not have the
              CAP_MKNOD capability); also returned if the filesystem
              containing pathname does not support the type of node

       EROFS  pathname refers to a file on a read-only filesystem.

VERSIONS         top

       POSIX.1-2001 says: "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."  However, nowadays one
       should never use mknod() for this purpose; one should use
       mkfifo(3), a function especially defined for this purpose.

       Under Linux, mknod() cannot be used to create directories.  One
       should make directories with mkdir(2).

STANDARDS         top


HISTORY         top

              SVr4, 4.4BSD, POSIX.1-2001 (but see VERSIONS).

              Linux 2.6.16, glibc 2.4.  POSIX.1-2008.

NOTES         top

       There are many infelicities in the protocol underlying NFS.  Some
       of these affect mknod() and mknodat().

SEE ALSO         top

       mknod(1), chmod(2), chown(2), fcntl(2), mkdir(2), mount(2),
       socket(2), stat(2), umask(2), unlink(2), makedev(3), mkfifo(3),
       acl(5), path_resolution(7)

COLOPHON         top

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Linux man-pages 6.9.1          2024-05-02                       mknod(2)

Pages that refer to this page: mknod(1)fcntl(2)mkdir(2)open(2)syscalls(2)unlink(2)dev_t(3type)makedev(3)mkfifo(3)remove(3)intro(4)fstab(5)proc_pid_attr(5)capabilities(7)inode(7)signal-safety(7)mount(8)xfs_db(8)