The chown command can change the ownership and group ownership of a files/directories. The files, directories and processes (which are again files) in Linux are owned by users.
The owner and group ownership is important as the security of files through permissions (the DAC) is set as 'owner', 'group owner' and 'others'.
1) Change Ownership
To change the ownership of a file, chown is provided with two arguments, the new owner and the file whose owner is to be changed.
# ls -l corpora/stopwords/english
-rw-r--r-- 1 root root 623 Dec 10 2012 corpora/stopwords/english# chown raghu corpora/stopwords/english
# ls -l corpora/stopwords/english
-rw-r--r-- 1 raghu root 623 Dec 10 2012 corpora/stopwords/english
The root user is the owner of the file, chown commands makes raghu user the new owner.
2) Changing owner and group
If the owner is followed by a colon and a group name (without spaces), the group name is changed as well.
# ls -l corpora/stopwords/danish
-rw-r--r-- 1 root root 424 Dec 10 2012 corpora/stopwords/danish# chown raghu:altair corpora/stopwords/danish
# ls -l corpora/stopwords/danish
-rw-r--r-- 1 raghu altair 424 Dec 10 2012 corpora/stopwords/danish
Now the new owner of the file is raghu and the new group owner is altair group.
Now, in this syntax involving colon, if a colon but no group name follows the user name, the given user is made the owner of the file and that user's login group is made as the group owner of the file.
# ls -l corpora/stopwords/dutch
-rw-r--r-- 1 root root 453 Dec 10 2012 corpora/stopwords/dutch# chown raghu: corpora/stopwords/dutch
# ls -l corpora/stopwords/dutch
-rw-r--r-- 1 raghu raghu 453 Dec 10 2012 corpora/stopwords/dutch
If the colon and group are mentioned, only the group of the file is changed. In this case, the command works like chgrp command.
# ls -l corpora/stopwords/finnish
-rw-r--r-- 1 root root 1579 Dec 10 2012 corpora/stopwords/finnish# chown :altair corpora/stopwords/finnish
# ls -l corpora/stopwords/finnish
-rw-r--r-- 1 root altair 1579 Dec 10 2012 corpora/stopwords/finnish
3) Changing permissions for directories recursively
The ownership of the directories and files contained in them can be changed recursively with -R option.
# ls -l /home/jones/
total 12
-rw-rw-r-- 1 jones javaproject 0 Aug 19 2012 file1
drwxrwxr-x 2 jones jones 4096 Aug 19 2012 hello# chown -R raghu /home/jones/
# ls -l /home/jones/
total 12
-rw-rw-r-- 1 raghu javaproject 0 Aug 19 2012 file1
drwxrwxr-x 2 raghu jones 4096 Aug 19 2012 hello
4) Verbose output
The --verbose option shows all the ownership changing. It outputs the diagnostics for each file processed
# chown -R --verbose jones /home/jones/
changed ownership of `/home/jones/hello' to jones
changed ownership of `/home/jones/.emacs' to jones
changed ownership of `/home/jones/.bash_history' to jones
changed ownership of `/home/jones/.bash_logout' to jones
changed ownership of `/home/jones/.bashrc' to jones
changed ownership of `/home/jones/file1' to jones
changed ownership of `/home/jones/.mozilla/plugins' to jones
changed ownership of `/home/jones/.mozilla/extensions' to jones
changed ownership of `/home/jones/.mozilla' to jones
changed ownership of `/home/jones/.bash_profile' to jones
changed ownership of `/home/jones/' to jones
The verbose option outputs processing of each file even when the changes are not made. But with -c or --changes option, the output is reported only when changes are made. For example,
# chown -R --verbose jones /home/jones/
ownership of `/home/jones/hello' retained as jones
ownership of `/home/jones/.emacs' retained as jones
ownership of `/home/jones/.bash_history' retained as jones
ownership of `/home/jones/.bash_logout' retained as jones
ownership of `/home/jones/.bashrc' retained as jones
ownership of `/home/jones/file1' retained as jones
ownership of `/home/jones/.mozilla/plugins' retained as jones
ownership of `/home/jones/.mozilla/extensions' retained as jones
ownership of `/home/jones/.mozilla' retained as jones
ownership of `/home/jones/.bash_profile' retained as jones
ownership of `/home/jones/' retained as jones
# chown -R -c jones /home/jones/
5) Silent operation
The normal users cannot change the ownership of files owned by others. So an error is displayed when a normal user tries to change the ownership.
[[email protected] ~]$ chown raghu /etc/
chown: changing ownership of `/etc/': Operation not permitted
But if we use -f or --silent or --quiet option, the error is not displayed.
[[email protected] ~]$ chown -f raghu /etc/
[[email protected] ~]$
6) Preserve root
To prevent changing the ownership of / directory recursively, --preserve-root is used.
[[email protected] ~]# chown -R --preserve-root raghu /
chown: changing ownership of `/proc/1/task/1/fd/10': Permission denied
chown: changing ownership of `/proc/1/task/1/fd': Permission denied
chown: changing ownership of `/proc/1/task/1/fdinfo/10': Permission denied
chown: changing ownership of `/proc/1/task/1/fdinfo': Permission denied
chown: changing ownership of `/proc/1/task/1/environ': Permission denied
chown: changing ownership of `/proc/1/task/1/auxv': Permission denied
chown: changing ownership of `/proc/1/task/1/status': Permission denied
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