mknod, mknodat - 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);
#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
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.
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).)
The user's quota of disk blocks or inodes on the filesystem has been exhausted.
pathname
already exists. This includes the case where
pathname
is a symbolic link, dangling or not.
pathname
points outside your accessible address space.
mode
requested creation of something other than a regular
file, device special file, FIFO or socket.
Too many symbolic links were encountered in resolving
pathname
.
pathname
was too long.
A directory component in pathname
does not exist or is a
dangling symbolic link.
Insufficient kernel memory was available.
The device containing pathname
has no room for the new
node.
A component used as a directory in pathname
is not, in fact,
a directory.
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.
pathname
refers to a file on a read-only filesystem.
The following additional errors can occur for mknodat():
dirfd
is not a valid file descriptor.
pathname
is relative and dirfd
is a file descriptor
referring to a file other than a directory.
mknodat() was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4.
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().
This page is part of release 5.10 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
https://www.kernel.org/doc/man-pages/.