Suppose you happen to accidentally do sudo chown -R www-data:www-data * whilst the current directory is /var. Now that’s a fairly daft thing to do! but we all make mistakes. There doesn’t seem to be an easy way to correct this other than restore a backup or look at another machine with a similar setup. Rather than having to restore a backup I looked at a machine with a similar setup, the machine has lighttpd, mysql, and sendmail installed on it so I built the following script based on the permissions with those packages installed on a fresh install of Debian Squeeze
#!/bin/bash echo "Setting Directory ownership" && chown -R root:root /var && chown -R man:root /var/cache/man && chown -R www-data:www-data /var/cache/lighttpd && chown -R libuuid:libuuid /var/lib/libuuid && chown -R smmta:smmsp /var/lib/sendmail && chown -R mysql:mysql /var/lib/mysql && chown -R www-data:www-data /var/log/lighttpd && chown -R mysql:adm /var/log/mysql && chown -R www-data:www-data /var/run/lighttpd && chown -R mysql:root /var/run/mysqld && chown -R smmsp:smmsp /var/run/sendmail/msp && chown -R smmta:smmsp /var/run/sendmail/mta && chown -R smmta:smmsp /var/spool/mqueue && chown -R smmsp:smmsp /var/spool/mqueue-client && chown -R root:staff /var/local && chown -R root:mail /var/mail && chown -R root:smmta /var/run/sendmail && chown -R root:smmsp /var/run/sendmail/stampdir && chown -R root:crontab /var/spool/cron/crontabs && chown -R www-data:www-data /var/www && echo "Setting File ownership" && chown root:smmsp /var/lib/sendmail/dead.letter && chown root:adm /var/log/auth.log /var/log/boot /var/log/daemon.log /var/log/debug /var/log/dmesg* /var/log/fsck/checkfs /var/log/fsck/checkroot /var/log/kern.log /var/log/lpr.log /var/log/mail.err /var/log/mail.info /var/log/mail.log /var/log/mail.warn /var/log/messages /var/log/news/news.crit /var/log/news/news.err /var/log/news/news.notice /var/log/syslog /var/log/user.log && chown root:utmp /var/log/lastlog /var/log/btmp /var/log/wtmp /var/run/utmp && chown root:smmsp /var/run/sendmail/mta/smsocket /var/run/sendmail/stampdir/reload && chown -f root:smmsp /var/run/sendmail/mta/sendmail.pid && chown mysql:adm /var/log/mysql.err /var/log/musql.log && chown -f mysql:adm /var/run/mysqld.pid && echo "Done."
In addition you will need to set the ownership permissions of /var/spool/cron/crontabs/<user> and /var/mail/<user> depending on the users on the system.
Giles Bathgate 
I wish I could say “what a stupid thing to do” but I’ve done almost the same myself once so I won’t.
I’ve exactly done the same command on /var/www putting on ssh “chown -R www-data.www-data .*” … You saved my life today!!!
Glad that this worked for you. Perhaps I should find out what the default permissions would be on other Distros, and versions.
I did the same thing with /usr. I wanted to change /usr/eclipse and did not realize I was one directory back and now I changed ownership of all files in /usr. I am on the road and not able to look at another distro. Any ideas on where I can get the default ownership of Debian files in the /usr directory (including mysql). Thanks!
/usr is a fairly large directory structure. Fortunately I can tell you it is almost exclusively owned by root:root
giles@tandoori:~$ find /usr -! -user root
/usr/bin/at
/usr/bin/at on my system is owned by daemon:daemon
I modified it to remove the && as I wasn’t concerned about every command succeeding. And I removed some of the ones that were not present on my system. Anyway, you’re a time saver! Thank you:)
#!/bin/bash
echo “Setting Directory ownership”
chown -R root:root /var
chown -R man:root /var/cache/man
chown -R libuuid:libuuid /var/lib/libuuid
chown -R mysql:mysql /var/lib/mysql
chown -R www-data:www-data /var/log/lighttpd
chown -R mysql:adm /var/log/mysql
chown -R www-data:www-data /var/run/lighttpd
chown -R mysql:root /var/run/mysqld
chown -R smmsp:smmsp /var/run/sendmail/msp
chown -R smmta:smmsp /var/run/sendmail/mta
chown -R smmta:smmsp /var/spool/mqueue
chown -R smmsp:smmsp /var/spool/mqueue-client
chown -R root:staff /var/local
chown -R root:mail /var/mail
chown -R root:smmta /var/run/sendmail
chown -R root:smmsp /var/run/sendmail/stampdir
chown -R root:crontab /var/spool/cron/crontabs
chown -R www-data:www-data /var/www
echo “Setting File ownership”
chown root:smmsp /var/lib/sendmail/dead.letter
chown root:adm
Thanks dude!