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.
See
openat(2) for an explanation of the need for
mknodat().
mknod() and
mknodat() return zero on success, or -1 if an error
occurred (in which case,
errno is set appropriately).
- 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 path_resolution(7).)
- 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.
- 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.
- ENOTDIR
- 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.
mknod(): SVr4, 4.4BSD, POSIX.1-2001 (but see below), POSIX.1-2008.
mknodat(): POSIX.1-2008.
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().
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)