13.2 chgrp: Change group ownership

chgrp changes the group ownership of each given file to group (which can be either a group name or a numeric group ID) or to the group of an existing reference file. See chown: Change file owner and group. Synopsis:

chgrp [option]… {group | --reference=ref_file} file…

If group is intended to represent a numeric group ID, then you may specify it with a leading ‘+’. See chown, chgrp, chroot, id: Disambiguating user names and IDs.

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 program accepts the following options. Also see Common options.

‘-c’ ¶

‘--changes’

Verbosely describe the action for each file whose group actually changes.

‘-f’ ¶

‘--silent’

‘--quiet’

Do not print error messages about files whose group cannot be changed.

‘--from=old-owner’ ¶

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 chgrp -h NEWUSER

But that is dangerous because the interval between when the find tests the existing file’s owner and when the chgrp is actually run may be quite large. One way to narrow the gap would be to invoke chgrp for each file as it is found:

find / -owner OLDUSER -exec chgrp -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:

chgrp -h -R --from=OLDUSER NEWUSER /

‘--dereference’ ¶

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.

‘-h’ ¶

‘--no-dereference’

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.

‘--preserve-root’ ¶

Fail upon any attempt to recursively change the root directory, /. Without --recursive, this option has no effect. See Treating / specially.

‘--no-preserve-root’ ¶

Cancel the effect of any preceding --preserve-root option. See Treating / specially.

‘--reference=ref_file’ ¶

Change the group of each file to be the same as that of ref_file. If ref_file is a symbolic link, do not use the group of the symbolic link, but rather that of the file it refers to.

‘-v’ ¶

‘--verbose’

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.

‘-R’ ¶

‘--recursive’

Recursively change the group ownership of directories and their contents.

‘-H’ ¶

If --recursive (-R) is specified and a command line argument is a symbolic link to a directory, traverse it. See Traversing symlinks.

‘-L’ ¶

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.

‘-P’ ¶

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 group of /u to "staff".
chgrp staff /u

# Change the group of /u and subfiles to "staff".
chgrp -hR staff /u