mknod(2) -- Linux man page



mknod - create a special or ordinary file  


#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);


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 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 must be one of S_IFREG, S_IFCHR, S_IFBLK, S_IFIFO or S_IFSOCK to specify a normal 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; 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 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 returns zero on success, or -1 if an error occurred (in which case, errno is set appropriately).  


mode requested creation of something other than a regular file, FIFO (named pipe), or Unix domain socket, and the caller is not the superuser; also returned if the filesystem containing pathname does not support the type of node requested.
mode requested creation of something other than a normal file, device special file, FIFO or socket.
pathname already exists.
pathname points outside your accessible address space.
The parent directory does not allow write permission to the process, or one of the directories in pathname did not allow search (execute) permission.
pathname was too long.
A directory component in pathname does not exist or is a dangling symbolic link.
A component used as a directory in pathname is not, in fact, a directory.
Insufficient kernel memory was available.
pathname refers to a file on a read-only filesystem.
Too many symbolic links were encountered in resolving pathname.
The device containing pathname has no room for the new node.


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. One should make directories with mkdir, and FIFOs with mkfifo.

There are many infelicities in the protocol underlying NFS. Some of these affect mknod.  


fcntl(2), mkdir(2), mount(2), socket(2), stat(2), umask(2), unlink(2), mkfifo(3)