chown: Change file owner and groupchown changes the user and/or group ownership of each given file
to new-owner or to the user and group of an existing reference file.
Synopsis:
chown [option]… {new-owner | --reference=ref_file} file…
If used, new-owner specifies the new owner and/or group as follows (with no embedded white space):
[owner] [ : [group] ]
Specifically:
If only an owner (a user name or numeric user ID) is given, that user is made the owner of each given file, and the files’ group is not changed.
If the owner is followed by a colon and a group (a group name or numeric group ID), with no spaces between them, the group ownership of the files is changed as well (to group).
If a colon but no group name follows owner, that user is made the owner of the files and the group of the files is changed to owner’s login group.
If the colon and following group are given, but the owner
is omitted, only the group of the files is changed; in this case,
chown performs the same function as chgrp.
If only a colon is given, or if new-owner is empty, neither the owner nor the group is changed.
If owner or group is intended to represent a numeric user or group ID, then you may specify it with a leading ‘+’. See chown, chgrp, chroot, id: Disambiguating user names and IDs.
Some older scripts may still use ‘.’ in place of the ‘:’ separator.
POSIX 1003.1-2001 (see Standards conformance) does not
require support for that, but for backward compatibility GNU
chown supports ‘.’ so long as no ambiguity results,
although it issues a warning and support may be removed in future versions.
New scripts should avoid the use of ‘.’ because it is not
portable, and because it has undesirable results if the entire
owner‘.’group happens to identify a user whose name
contains ‘.’.
It is system dependent whether a user can change the group to an arbitrary one, or the more portable behavior of being restricted to setting a group of which the user is a member.
The chown command sometimes clears the set-user-ID or
set-group-ID permission bits. This behavior depends on the policy and
functionality of the underlying chown system call, which may
make system-dependent file mode modifications outside the control of
the chown command. For example, the chown command
might not affect those bits when invoked by a user with appropriate
privileges, or when the
bits signify some function other than executable permission (e.g.,
mandatory locking).
When in doubt, check the underlying system behavior.
The program accepts the following options. Also see Common options.
Verbosely describe the action for each file whose ownership actually changes.
Do not print error messages about files whose ownership cannot be changed.
Change a file’s ownership only if it has current attributes specified
by old-owner. old-owner has the same form as new-owner
described above.
This option is useful primarily from a security standpoint in that
it narrows considerably the window of potential abuse.
For example, to reflect a user ID numbering change for one user’s files
without an option like this, root might run
find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
But that is dangerous because the interval between when the find
tests the existing file’s owner and when the chown is actually run
may be quite large.
One way to narrow the gap would be to invoke chown for each file
as it is found:
find / -owner OLDUSER -exec chown -h NEWUSER {} \;
But that is very slow if there are many affected files. With this option, it is safer (the gap is narrower still) though still not perfect:
chown -h -R --from=OLDUSER NEWUSER /
Do not act on symbolic links themselves but rather on what they point to. This is the default when not operating recursively.
Combining this dereferencing option with the --recursive option may create a security risk: During the traversal of the directory tree, an attacker may be able to introduce a symlink to an arbitrary target; when the tool reaches that, the operation will be performed on the target of that symlink, possibly allowing the attacker to escalate privileges.
Act on symbolic links themselves instead of what they point to.
This mode relies on the lchown system call.
On systems that do not provide the lchown system call,
no diagnostic is issued, but see --verbose.
Fail upon any attempt to recursively change the root directory, /. Without --recursive, this option has no effect. See Treating / specially.
Cancel the effect of any preceding --preserve-root option. See Treating / specially.
Change the user and group of each file to be the same as those of ref_file. If ref_file is a symbolic link, do not use the user and group of the symbolic link, but rather those of the file it refers to.
Output a diagnostic for every file processed.
If a symbolic link is encountered during a recursive traversal
on a system without the lchown system call, and --no-dereference
is in effect, then issue a diagnostic saying neither the symbolic link nor
its referent is being changed.
Recursively change ownership of directories and their contents.
If --recursive (-R) is specified and a command line argument is a symbolic link to a directory, traverse it. See Traversing symlinks.
In a recursive traversal, traverse every symbolic link to a directory that is encountered.
Combining this dereferencing option with the --recursive option may create a security risk: During the traversal of the directory tree, an attacker may be able to introduce a symlink to an arbitrary target; when the tool reaches that, the operation will be performed on the target of that symlink, possibly allowing the attacker to escalate privileges.
See Traversing symlinks.
Do not traverse any symbolic links. This is the default if none of -H, -L, or -P is specified. See Traversing symlinks.
An exit status of zero indicates success, and a nonzero value indicates failure.
Examples:
# Change the owner of /u to "root". chown root /u # Likewise, but also change its group to "staff". chown root:staff /u # Change the owner of /u and subfiles to "root". chown -hR root /u