Ubuntu Manpage: mknod, mknodat - create a special or ordinary file

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 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(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
       interpreted 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
       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).

COLOPHON

       This  page  is  part of release 4.04 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/.