.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: GPL-1.0-or-later
.\"
.TH mkdir 2 2025-05-17 "Linux man-pages (unreleased)"
.SH NAME
mkdir, mkdirat \- create a directory
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <sys/stat.h>
.\" .B #include <unistd.h>
.P
.BI "int mkdir(const char *" path ", mode_t " mode );
.P
.BR "#include <fcntl.h>           " "/* Definition of AT_* constants */"
.B #include <sys/stat.h>
.P
.BI "int mkdirat(int " dirfd ", const char *" path ", mode_t " mode );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR mkdirat ():
.nf
    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _ATFILE_SOURCE
.fi
.SH DESCRIPTION
.BR mkdir ()
attempts to create a directory named
.IR path .
.P
The argument
.I mode
specifies the mode for the new directory (see
.BR inode (7)).
It is modified by the process's
.I umask
in the usual way: in the absence of a default ACL, the mode of the
created directory is
.RI ( mode " & \[ti]" umask " & 0777)."
Whether other
.I mode
bits are honored for the created directory depends on the operating system.
For Linux, see VERSIONS below.
.P
The newly created directory will be owned by the effective user ID of the
process.
If the directory containing the file has the set-group-ID
bit set, or if the filesystem is mounted with BSD group semantics
.RI ( "mount \-o bsdgroups"
or, synonymously
.IR "mount \-o grpid" ),
the new directory will inherit the group ownership from its parent;
otherwise it will be owned by the effective group ID of the process.
.P
If the parent directory has the set-group-ID bit set, then so will the
newly created directory.
.\"
.\"
.SS mkdirat()
The
.BR mkdirat ()
system call operates in exactly the same way as
.BR mkdir (),
except for the differences described here.
.P
If
.I path
is relative, then it is interpreted relative to the directory
referred to by the file descriptor
.I dirfd
(rather than relative to the current working directory of
the calling process, as is done by
.BR mkdir ()
for a relative pathname).
.P
If
.I path
is relative and
.I dirfd
is the special value
.BR AT_FDCWD ,
then
.I path
is interpreted relative to the current working
directory of the calling process (like
.BR mkdir ()).
.P
If
.I path
is absolute, then
.I dirfd
is ignored.
.P
See
.BR openat (2)
for an explanation of the need for
.BR mkdirat ().
.SH RETURN VALUE
.BR mkdir ()
and
.BR mkdirat ()
return zero on success.
On error, \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EACCES
The parent directory does not allow write permission to the process,
or one of the directories in
.I path
did not allow search permission.
(See also
.BR path_resolution (7).)
.TP
.B EBADF
.RB ( mkdirat ())
.I path
is relative but
.I dirfd
is neither
.B AT_FDCWD
nor a valid file descriptor.
.TP
.B EDQUOT
The user's quota of disk blocks or inodes on the filesystem has been
exhausted.
.TP
.B EEXIST
.I path
already exists (not necessarily as a directory).
This includes the case where
.I path
is a symbolic link, dangling or not.
.TP
.B EFAULT
.I path
points outside your accessible address space.
.TP
.B EINVAL
The final component ("basename") of the new directory's
.I path
is invalid
(e.g., it contains characters not permitted by the underlying filesystem).
.TP
.B ELOOP
Too many symbolic links were encountered in resolving
.IR path .
.TP
.B EMLINK
The number of links to the parent directory would exceed
.BR LINK_MAX .
.TP
.B ENAMETOOLONG
.I path
was too long.
.TP
.B ENOENT
A directory component in
.I path
does not exist or is a dangling symbolic link.
.TP
.B ENOMEM
Insufficient kernel memory was available.
.TP
.B ENOSPC
The device containing
.I path
has no room for the new directory.
.TP
.B ENOSPC
The new directory cannot be created because the user's disk quota is
exhausted.
.TP
.B ENOTDIR
A component used as a directory in
.I path
is not, in fact, a directory.
.TP
.B ENOTDIR
.RB ( mkdirat ())
.I path
is relative and
.I dirfd
is a file descriptor referring to a file other than a directory.
.TP
.B EPERM
The filesystem containing
.I path
does not support the creation of directories.
.TP
.B EROFS
.I path
refers to a file on a read-only filesystem.
.TP
.B EOVERFLOW
UID or GID mappings (see
.BR user_namespaces (7))
have not been configured.
.SH VERSIONS
Under Linux, apart from the permission bits, the
.B S_ISVTX
.I mode
bit is also honored.
.SS glibc notes
On older kernels where
.BR mkdirat ()
is unavailable, the glibc wrapper function falls back to the use of
.BR mkdir ().
When
.I path
is relative,
glibc constructs a pathname based on the symbolic link in
.I /proc/self/fd
that corresponds to the
.I dirfd
argument.
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
.TP
.BR mkdir ()
SVr4, BSD, POSIX.1-2001.
.\" SVr4 documents additional EIO, EMULTIHOP
.TP
.BR mkdirat ()
Linux 2.6.16,
glibc 2.4.
.SH NOTES
There are many infelicities in the protocol underlying NFS.
Some of these affect
.BR mkdir ().
.SH SEE ALSO
.BR mkdir (1),
.BR chmod (2),
.BR chown (2),
.BR mknod (2),
.BR mount (2),
.BR rmdir (2),
.BR stat (2),
.BR umask (2),
.BR unlink (2),
.BR acl (5),
.BR path_resolution (7)