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PROLOG
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.
NAME
mkdir, mkdirat — make a directory
SYNOPSIS
#include <sys/stat.h>
int mkdir(const char *path, mode_t mode);
#include <fcntl.h>
int mkdirat(int fd, const char *path, mode_t mode);
DESCRIPTION
The mkdir() function shall create a new directory with name path. The file permission
bits of the new directory shall be initialized from mode. These file permission bits of
the mode argument shall be modified by the process' file creation mask.
When bits in mode other than the file permission bits are set, the meaning of these
additional bits is implementation-defined.
The directory's user ID shall be set to the process' effective user ID. The directory's
group ID shall be set to the group ID of the parent directory or to the effective group ID
of the process. Implementations shall provide a way to initialize the directory's group ID
to the group ID of the parent directory. Implementations may, but need not, provide an
implementation-defined way to initialize the directory's group ID to the effective group
ID of the calling process.
The newly created directory shall be an empty directory.
If path names a symbolic link, mkdir() shall fail and set errno to [EEXIST].
Upon successful completion, mkdir() shall mark for update the last data access, last data
modification, and last file status change timestamps of the directory. Also, the last data
modification and last file status change timestamps of the directory that contains the new
entry shall be marked for update.
The mkdirat() function shall be equivalent to the mkdir() function except in the case
where path specifies a relative path. In this case the newly created directory is created
relative to the directory associated with the file descriptor fd instead of the current
working directory. If the access mode of the open file description associated with the
file descriptor is not O_SEARCH, the function shall check whether directory searches are
permitted using the current permissions of the directory underlying the file descriptor.
If the access mode is O_SEARCH, the function shall not perform the check.
If mkdirat() is passed the special value AT_FDCWD in the fd parameter, the current working
directory shall be used and the behavior shall be identical to a call to mkdir().
RETURN VALUE
Upon successful completion, these functions shall return 0. Otherwise, these functions
shall return -1 and set errno to indicate the error. If -1 is returned, no directory shall
be created.
ERRORS
These functions shall fail if:
EACCES Search permission is denied on a component of the path prefix, or write permission
is denied on the parent directory of the directory to be created.
EEXIST The named file exists.
ELOOP A loop exists in symbolic links encountered during resolution of the path argument.
EMLINK The link count of the parent directory would exceed {LINK_MAX}.
ENAMETOOLONG
The length of a component of a pathname is longer than {NAME_MAX}.
ENOENT A component of the path prefix specified by path does not name an existing
directory or path is an empty string.
ENOSPC The file system does not contain enough space to hold the contents of the new
directory or to extend the parent directory of the new directory.
ENOTDIR
A component of the path prefix names an existing file that is neither a directory
nor a symbolic link to a directory.
EROFS The parent directory resides on a read-only file system.
In addition, the mkdirat() function shall fail if:
EACCES The access mode of the open file description associated with fd is not O_SEARCH and
the permissions of the directory underlying fd do not permit directory searches.
EBADF The path argument does not specify an absolute path and the fd argument is neither
AT_FDCWD nor a valid file descriptor open for reading or searching.
ENOTDIR
The path argument is not an absolute path and fd is a file descriptor associated
with a non-directory file.
These functions may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the
path argument.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic
link produced an intermediate result with a length that exceeds {PATH_MAX}.
The following sections are informative.
EXAMPLES
Creating a Directory
The following example shows how to create a directory named /home/cnd/mod1, with
read/write/search permissions for owner and group, and with read/search permissions for
others.
#include <sys/types.h>
#include <sys/stat.h>
int status;
...
status = mkdir("/home/cnd/mod1", S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
APPLICATION USAGE
None.
RATIONALE
The mkdir() function originated in 4.2 BSD and was added to System V in Release 3.0.
4.3 BSD detects [ENAMETOOLONG].
The POSIX.1‐1990 standard required that the group ID of a newly created directory 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 chown() to set the group ID after the directory is created, or
determine under what conditions the implementation will set the desired group ID.
The purpose of the mkdirat() function is to create a directory 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 the call to mkdir(), resulting in unspecified
behavior. By opening a file descriptor for the target directory and using the mkdirat()
function it can be guaranteed that the newly created directory is located relative to the
desired directory.
FUTURE DIRECTIONS
None.
SEE ALSO
chmod(), mkdtemp(), mknod(), umask()
The Base Definitions volume of POSIX.1‐2017, <fcntl.h>, <sys_stat.h>, <sys_types.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1-2017, Standard for Information Technology -- Portable Operating System Interface
(POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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 http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have
been introduced during the conversion of the source files to man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .