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():
           _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), 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().

COLOPHON

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       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at https://www.kernel.org/doc/man-pages/.