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MKDIR(2) System Calls Manual MKDIR(2)

mkdir, mkdirat — make a directory file

#include <sys/stat.h>

int
mkdir(const char *path, mode_t mode);

#include <sys/stat.h>
#include <fcntl.h>

int
mkdirat(int fd, const char *path, mode_t mode);

The directory path is created with the access permissions specified by mode and restricted by the umask(2) of the calling process.

The directory's owner ID is set to the process's effective user ID. The directory's group ID is set to that of the parent directory in which it is created.

The () function is equivalent to () except that where path specifies a relative path, the newly created directory is created relative to the directory associated with file descriptor fd instead of the current working directory.

If () is passed the special value AT_FDCWD (defined in <fcntl.h>) in the fd parameter, the current working directory is used and the behavior is identical to a call to ().

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

mkdir() and mkdirat() will fail and no directory will be created if:

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A component of the path prefix is not a directory.
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A component of a pathname exceeded NAME_MAX characters, or an entire pathname (including the terminating NUL) exceeded PATH_MAX bytes.
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A component of the path prefix does not exist.
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Search permission is denied for a component of the path prefix, or write permission is denied on the parent directory of the directory to be created.
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Too many symbolic links were encountered in translating the pathname.
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The named file resides on a read-only file system.
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The named file exists.
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The new directory cannot be created because there is no space left on the file system that will contain the directory.
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There are no free inodes on the file system on which the directory is being created.
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The new directory cannot be created because the user's quota of disk blocks on the file system that will contain the directory has been exhausted.
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The user's quota of inodes on the file system on which the directory is being created has been exhausted.
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An I/O error occurred while making the directory entry or allocating the inode.
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An I/O error occurred while reading from or writing to the file system.
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path points outside the process's allocated address space.

Additionally, mkdirat() will fail if:

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The path argument specifies a relative path and the fd argument is neither AT_FDCWD nor a valid file descriptor.
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The path argument specifies a relative path and the fd argument is a valid file descriptor but it does not reference a directory.
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The path argument specifies a relative path but search permission is denied for the directory which the fd file descriptor references.

chmod(2), stat(2), umask(2)

The mkdir() and mkdirat() functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).

A mkdir() system call first appeared in Version 1 AT&T UNIX. It was renamed to makdir() in Version 2 AT&T UNIX. However, it did not exist from Version 4 AT&T UNIX to 4.1BSD; in those releases, mknod(2) had to be used. Since mkdir() reappeared in 4.1cBSD, it no longer requires superuser privileges and it automatically creates the ‘.’ and ‘..’ directory entries.

The mkdirat() system call has been available since OpenBSD 5.0.

March 23, 2017 OpenBSD-6.5