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CHOWN(2) FreeBSD System Calls Manual CHOWN(2)

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

Standard C Library (libc, -lc)

#include <unistd.h>

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

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

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

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

The owner ID and group ID of the file named by path or referenced by fd is changed as specified by the arguments owner and group. The owner of a file may change the group to a group of which he or she is a member, but the change owner capability is restricted to the super-user.

The chown() system call 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 if not executed by the super-user. The chown() system call follows symbolic links to operate on the target of the link rather than the link itself.

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

The lchown() system call is similar to chown() but does not follow symbolic links.

The fchownat() system call is equivalent to the chown() and lchown() except in the case where path specifies a relative path. In this case the file to be changed is determined relative to the directory associated with the file descriptor fd instead of the current working directory.

Values for flag are constructed by a bitwise-inclusive OR of flags from the following list, defined in <fcntl.h>:

If path names a symbolic link, ownership of the symbolic link is changed.
Only walk paths below the directory specified by the fd descriptor. See the description of the O_RESOLVE_BENEATH flag in the open(2) manual page.
If the path argument is an empty string, operate on the file or directory referenced by the descriptor fd. If fd is equal to AT_FDCWD, operate on the current working directory.

If fchownat() is passed the special value AT_FDCWD in the fd parameter, the current working directory is used and the behavior is identical to a call to chown() or lchown() respectively, depending on whether or not the AT_SYMLINK_NOFOLLOW bit is set in the flag argument.

One of the owner or group id's 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.

The chown() and lchown() will fail and the file will be unchanged if:
A component of the path prefix is not a directory.
A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
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 operation would change the ownership, but the effective user ID is not the super-user.
The named file has its immutable or append-only flag set, see the chflags(2) manual page for more information.
The named file resides on a read-only file system.
The path argument points outside the process's allocated address space.
An I/O error occurred while reading from or writing to the file system.
Corrupted data was detected while reading from the file system.

The fchown() system call will fail if:

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

In addition to the errors specified for chown() and lchown(), the fchownat() system call may fail if:

The path argument does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid file descriptor open for searching.
The value of the flag argument is not valid.
The path argument is not an absolute path and fd is neither AT_FDCWD nor a file descriptor associated with a directory.
path is an absolute path, or contained a ".." component leading to a directory outside of the directory hierarchy specified by fd, and the process is in capability mode or the AT_RESOLVE_BENEATH flag was specified.

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

The chown() system call is expected to conform to IEEE Std 1003.1-1990 (“POSIX.1”). The fchownat() system call follows The Open Group Extended API Set 2 specification.

The chown() function appeared in Version 1 AT&T UNIX. The fchown() system call appeared in 4.2BSD.

The chown() system call was changed to follow symbolic links in 4.4BSD. The lchown() system call was added in FreeBSD 3.0 to compensate for the loss of functionality.

The fchownat() system call appeared in FreeBSD 8.0.

March 30, 2021 FreeBSD 13.1-RELEASE

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