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CHOWN(2) System Calls Manual CHOWN(2)

chown, lchown, fchownat, fchown — change owner and group of a file or link

#include <unistd.h>

int
chown(const char *path, uid_t owner, gid_t group);

int
lchown(const char *path, uid_t owner, gid_t group);

int
fchown(int fd, uid_t owner, gid_t group);

#include <fcntl.h>
#include <unistd.h>

int
fchownat(int fd, const char *path, uid_t owner, gid_t group, int flag);

The owner ID and group ID of the file (or link) named by path or referenced by fd is changed as specified by the arguments owner and group. The owner of a file may change its group to one the owner is a member of. The change owner capability is restricted to the superuser.

By default, () clears the set-user-ID and set-group-ID bits on the file to prevent accidental or mischievous creation of set-user-ID and set-group-ID programs. This behaviour can be overridden by setting the sysctl(8) variable fs.posix.setuid to zero.

() operates similarly to how chown() operated on older systems, and does not follow symbolic links. It allows the owner and group of a symbolic link to be set.

The () function is equivalent to either the chown() or lchown() function depending on the value of flag (see below), except that where path specifies a relative path, the file whose ownership is changed is determined 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 chown() or lchown(), depending on whether or not the AT_SYMLINK_NOFOLLOW bit is set in flag.

The flag argument is the bitwise OR of zero or more of the following values:

If path names a symbolic link, then the ownership of the symbolic link is changed.

() is particularly useful when used in conjunction with the file locking primitives (see flock(2)).

One of the owner or group IDs may be left unchanged by specifying it as -1.

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.

chown(), lchown(), and fchownat() will fail and the file or link will be unchanged if:

[]
A component of the path prefix is not a directory.
[]
A component of a pathname exceeded NAME_MAX characters, or an entire pathname (including the terminating NUL) exceeded PATH_MAX bytes.
[]
The named file does not exist.
[]
Search permission is denied for a component of the path prefix.
[]
Too many symbolic links were encountered in translating the pathname.
[]
The effective user ID is not the superuser.
[]
The named file resides on a read-only file system.
[]
path points outside the process's allocated address space.
[]
An I/O error occurred while reading from or writing to the file system.

Additionally, fchownat() will fail if:

[]
The value of the flag argument was neither zero nor AT_SYMLINK_NOFOLLOW.
[]
The path argument specifies a relative path and the fd argument is neither AT_FDCWD nor a valid file descriptor.
[]
The path argument specifies a relative path and the fd argument is a valid file descriptor but it does not reference a directory.
[]
The path argument specifies a relative path but search permission is denied for the directory which the fd file descriptor references.

fchown() will fail if:

[]
fd does not refer to a valid descriptor.
[]
fd refers to a socket, not a file.
[]
The effective user ID is not the superuser.
[]
The named file resides on a read-only file system.
[]
An I/O error occurred while reading from or writing to the file system.

chgrp(1), chmod(2), flock(2), chown(8)

The chown(), fchown(), fchownat(), and lchown() functions are expected to conform to IEEE Std 1003.1-2008 (“POSIX.1”).

The chown() system call first appeared in Version 1 AT&T UNIX. Since Version 6 AT&T UNIX it supports changing the group as well, and in Version 7 AT&T UNIX group was made a separate argument.

The fchown() system call first appeared in 4.1cBSD.

The chown() and fchown() system calls were changed to follow symbolic links in 4.4BSD; therefore, and for compatibility with AT&T System V Release 4 UNIX, the lchown() system call was added to OpenBSD 2.1.

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

February 18, 2022 OpenBSD-7.4