MKNOD(2)                            Linux Programmer's Manual                            MKNOD(2)



NAME
       mknod, mknodat - create a special or ordinary file

SYNOPSIS
       #include <sys/types.h>
       #include <sys/stat.h>
       #include <fcntl.h>
       #include <unistd.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 feature_test_macros(7)):

       mknod():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION
       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 permissions to use and the type of node to be cre‐
       ated.  It should be a combination (using bitwise OR) of one of the file types listed below
       and the permissions for the new node.

       The  permissions  are modified by the process's umask in the usual way: 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.

   mknodat()
       The mknodat() system call operates in exactly the same way as  mknod(2),  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(2) for a relative pathname).

       If  pathname  is relative and dirfd is the special value AT_FDCWD, then pathname is inter‐
       preted relative to the current working directory of the calling process (like mknod(2)).

       If pathname is absolute, then dirfd is ignored.

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

RETURN VALUE
       mknod() and mknodat() return zero on success, or -1 if an error occurred (in  which  case,
       errno is set appropriately).

ERRORS
       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 path_resolution(7).)

       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.

       ENAMETOOLONG
              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 node.

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

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

       The following additional errors can occur for mknodat():

       EBADF  dirfd is not a valid file descriptor.

       ENOTDIR
              pathname is relative and dirfd is a file descriptor referring to a file other  than
              a directory.

VERSIONS
       mknodat()  was added to Linux in kernel 2.6.16; library support was added to glibc in ver‐
       sion 2.4.

CONFORMING TO
       mknod(): SVr4, 4.4BSD, POSIX.1-2001 (but see below), POSIX.1-2008.

       mknodat(): POSIX.1-2008.

NOTES
       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  func‐
       tion especially defined for this purpose.

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

       There are many infelicities in the protocol underlying NFS.  Some of these affect  mknod()
       and mknodat(2).

SEE ALSO
       chmod(2), chown(2), fcntl(2), mkdir(2), mount(2), socket(2), stat(2), umask(2), unlink(2),
       makedev(3), mkfifo(3), path_resolution(7)

COLOPHON
       This page is part of release 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2014-02-21                                   MKNOD(2)