mknod(2) attempts to create a filesystem node (file, device special file or named pipe) named pathname, specified by mode and dev.
mode specifies both the permissions 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 the permissions for the new node.
The permissions are modified by the process's umask in the usual way: the permissions of the created node are (mode & umask).
The file type should be one of S_IFREG, S_IFCHR, S_IFBLK and S_IFIFO to specify a normal file (which will be created empty), character special file, block special file or FIFO (named pipe), respectively, or zero, which will create a normal file.
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; otherwise it is ignored.
If pathname already exists, or is a symlink, this call fails with an EEXIST error.
The newly created node will be owned by the effective uid 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 gid of the process.
mknod(2) returns zero on success, or -1 if an error occurred (in which case, errno is set appropriately).
SVr4 (but the call requires privilege and is thus not in POSIX), 4.4BSD. The Linux version differs from the SVr4 version in that it does not require root permission to create pipes, also in that no EMULTIHOP, ENOLINK, or EINTR error is documented.
POSIX 1003.1‐2001 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."
Under Linux, this call cannot be used to create directories or socket files, and cannot be used to create normal files by users other than the superuser. One should make directories with mkdir(2), and FIFOs with mkfifo(2).
There are many infelicities in the protocol underlying NFS. Some of these affect mknod(2).