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

NAME
       mknod, mknodat - create a special or ordinary file

SYNOPSIS
       #include <sys/stat.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 <= 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 effec‐
       tive 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.  On error, -1 is returned and errno is set to indicate the error.

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 permis‐
              sion.  (See also path_resolution(7).)

       EBADF  (mknodat()) pathname is relative but dirfd is neither AT_FDCWD nor a valid file descriptor.

       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.

       ENOTDIR
              (mknodat()) pathname is relative and dirfd is a file descriptor referring to a file other than 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.

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  un‐
       specified."  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
       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)

Linux                                                                          2021-08-27                                                                       MKNOD(2)