MKNOD(2) manual page
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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 modedev_t " dev );
Feature Test Macro Requirements for glibc (see feature_test_macros(7)
):
mknod():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
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
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(2)
, 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(2)
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(2)
).
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(2)
.
chmod(2)
, chown(2)
, fcntl(2)
, mkdir(2)
, mount(2)
, socket(2)
, stat(2)
,
umask(2)
, unlink(2)
, makedev(3)
, mkfifo(3)
, path_resolution(7)
This
page is part of release 3.78 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 http://www.kernel.org/doc/man-pages/.
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