Section: POSIX Programmer's Manual (3P)
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
--- make directory, special file, or regular file
int mknod(const char *path, mode_t mode, dev_t dev);
int mknodat(int fd, const char *path, mode_t mode, dev_t dev);
function shall create a new file named by the pathname to which the
The file type for
is OR'ed into the
argument, and the application shall select one of the following
The only portable use of
is to create a FIFO-special file. If
is not S_IFIFO or
is not 0, the behavior of
The permissions for the new file are OR'ed into the
argument, and may be selected from any combination of the following
|S_ISUID||Set user ID on execution.|
|S_ISGID||Set group ID on execution.|
|S_IRWXU||Read, write, or execute (search) by owner.|
|S_IRUSR||Read by owner.|
|S_IWUSR||Write by owner.|
|S_IXUSR||Execute (search) by owner.|
|S_IRWXG||Read, write, or execute (search) by group.|
|S_IRGRP||Read by group.|
|S_IWGRP||Write by group.|
|S_IXGRP||Execute (search) by group.|
|S_IRWXO||Read, write, or execute (search) by others.|
|S_IROTH||Read by others.|
|S_IWOTH||Write by others.|
|S_IXOTH||Execute (search) by others.|
|S_ISVTX||On directories, restricted deletion flag.|
The user ID of the file shall be initialized to the effective user ID
of the process. The group ID of the file shall be initialized to either
the effective group ID of the process or the group ID of the parent
directory. Implementations shall provide a way to initialize the file's
group ID to the group ID of the parent directory. Implementations may,
but need not, provide an implementation-defined way to initialize the
file's group ID to the effective group ID of the calling process. The
owner, group, and other permission bits of
shall be modified by the file mode creation mask of the process. The
function shall clear each bit whose corresponding bit in the file mode
creation mask of the process is set.
names a symbolic link,
shall fail and set
Upon successful completion,
shall mark for update the last data access, last data modification,
and last file status change timestamps of the file. Also, the last
data modification and last file status change timestamps of the directory
that contains the new entry shall be marked for update.
Only a process with appropriate privileges may invoke
for file types other than FIFO-special.
function shall be equivalent to the
function except in the case where
specifies a relative path. In this case the newly created
directory, special file, or regular file is located relative to the
directory associated with the file descriptor
instead of the current working directory. If the file descriptor was
opened without O_SEARCH, the function shall check whether directory
searches are permitted using the current permissions of the directory
underlying the file descriptor. If the file descriptor was opened with
O_SEARCH, the function shall not perform the check.
is passed the special value AT_FDCWD in the
parameter, the current working directory shall be used and the behavior
shall be identical to a call to
Upon successful completion, these functions shall return 0.
Otherwise, these functions shall return -1 and set
to indicate the error. If -1 is returned, the new file shall
not be created.
These functions shall fail if:
A component of the path prefix denies search permission, or write
permission is denied on the parent directory.
The named file exists.
An invalid argument exists.
An I/O error occurred while accessing the file system.
A loop exists in symbolic links encountered during resolution of the
The length of a component of a pathname is longer than
A component of the path prefix of
does not name an existing file or
is an empty string.
- ENOENT or ENOTDIR
argument contains at least one non-<slash>
character and ends with one or more trailing
names an existing file, an
error shall not occur.
The directory that would contain the new file cannot be extended or the
file system is out of file allocation resources.
A component of the path prefix names an existing file that is neither
a directory nor a symbolic link to a directory.
The invoking process does not have appropriate privileges and the
file type is not FIFO-special.
The directory in which the file is to be created is located on a
read-only file system.
function shall fail if:
was not opened with O_SEARCH and the permissions of the directory
do not permit directory searches.
argument does not specify an absolute path and the
argument is neither AT_FDCWD nor a valid file descriptor open
for reading or searching.
argument is not an absolute path and
is a file descriptor associated with a non-directory file.
These functions may fail if:
symbolic links were encountered during resolution of the
The length of a pathname exceeds
or pathname resolution of a symbolic link produced an intermediate
result with a length that exceeds
The following sections are informative.
Creating a FIFO Special File
The following example shows how to create a FIFO special file named
with read/write permissions for owner, and with read permissions for
group and others.
status = mknod("/home/cnd/mod_done", S_IFIFO | S_IWUSR |
S_IRUSR | S_IRGRP | S_IROTH, dev);
function is preferred over this function for making FIFO special files.
The POSIX.1-1990 standard required that the group ID of a newly created file be
set to the group ID of its parent directory or to the effective group
ID of the creating process. FIPS 151-2 required that implementations provide
a way to have the group ID be set to the group ID of the containing
directory, but did not prohibit implementations also supporting a way
to set the group ID to the effective group ID of the creating process.
Conforming applications should not assume which group ID will be used. If
it matters, an application can use
to set the group ID after the file is created, or determine under
what conditions the implementation will set the desired group ID.
The purpose of the
function is to create directories, special files, or regular files in
directories other than the current working directory without exposure
to race conditions. Any part of the path of a file could be changed in
parallel to a call to
resulting in unspecified behavior. By opening a file descriptor for
the target directory and using the
function it can be guaranteed that the newly created directory, special
file, or regular file is located relative to the desired directory.
The Base Definitions volume of POSIX.1-2008,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
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