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():
       _XOPEN_SOURCE >= 500
           || /* Since glibc 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

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 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 stat(2).

   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.

   mknodat()
   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

   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 version 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
   function 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

   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

   This page is part of release 4.09 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
   https://www.kernel.org/doc/man-pages/.

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