mknodat(2) — Linux manual page


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

NAME         top

       mknod, mknodat - create a special or ordinary file

SYNOPSIS         top

       #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)):

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

DESCRIPTION         top

       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.

       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         top

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

ERRORS         top

       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

       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 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.

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

       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.

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

VERSIONS         top

       mknodat() was added to Linux in kernel 2.6.16; library support was
       added to glibc in version 2.4.

CONFORMING TO         top

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

       mknodat(): POSIX.1-2008.

NOTES         top

       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().

SEE ALSO         top

       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         top

       This page is part of release 5.09 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

Linux                            2020-08-13                         MKNOD(2)

Pages that refer to this page: creat(2)open(2)openat(2)syscalls(2)mkfifo(3)mkfifoat(3)signal-safety(7)