4.6 Objective 6: Manage File Ownership

Modification of ownership parameters may become necessary when moving files, setting up workgroups, or working in a user's directory as root. This is accomplished using the chown command, which can change user and group ownership, and the chgrp command for modifying group ownership.

The chown command supersedes chgrp because all of the chgrp command's functions are available in chown. However, many system administrators still habitually use chgrp, and it is often found in scripts and makefiles.

Syntax

chown [options] user-owner files
chown [options] user-owner. files
chown [options] user-owner.group-owner files
chown [options] .group-owner files
chown [options] --reference=rfile files

Description

Used to change the owner and/or group of files to user-owner and/or group-owner. In the first form, user-owner is made the owner of files and the group is not affected. In the second form (note the trailing dot on user-owner), the user-owner is made the owner of files and the group of the files is changed to user-owner's default group. In the third form, both user-owner and group-owner are assigned to files. In the fourth form, only the group-owner is assigned to files, and the user is not affected. In the fifth form, the owner and group of rfile is used as a template and applied to files. Since this program can handle all types of changes to groups, it replaces the chgrp command. Only the superuser may change file ownership, but group ownership may be set by anyone belonging to the target group-owner.

Frequently used options

-c

Like verbose mode, but report only changes.

-R

Use recursive mode, descending through directory hierarchies under files and making modifications throughout.

-v

Use verbose behavior, reporting actions for all files.

Example 1

As root, set the user of a file:

# chown -v jdoe afile
owner of afile changed to jdoe

Example 2

As root, set the user and group of a file:

# chown -v jdoe.sales afile
owner of afile changed to jdoe.sales

Example 3

Recursively change the group of the entire sls directory:

# chown -Rv .sales sls
owner of sls changed to .sales
owner of sls/file1 changed to .sales
owner of sls/file2 changed to .sales
...

Syntax

chgrp [options] group-owner files
chgrp [options] --reference=rfile files

Description

Change the group parameter of files to group-owner. In the first form, set the group-owner of files. In the second form, the group of rfile is used as a template and applied to files. Options and usage are the same as that of chown.

On the Exam Remember that only root can change file ownership. Also remember that chown can change not only the user but also the group ownership.