mknod(2)



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():
           _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 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), char-
       acter 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; other-
       wise 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 path-
              name did not allow search permission.   (See  also  path_resolu-
              tion(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  dan-
              gling 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 behav-
       ior of mknod() is unspecified."  However, nowadays one should never use
       mknod()  for  this  purpose; one should use mkfifo(3), a function espe-
       cially 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().

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_reso-
       lution(7)

COLOPHON
       This page is part of release 4.16 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/.

Linux                             2017-09-15                          MKNOD(2)

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