# Messed up permissions. Fired.

· streambinder

Assume you’re a systems administrator. And you made a mistake. A terrible mistake. The kind of mistake that make you think you’re a horrible and incompetent sysadmin. Ok, it’s me.

I was at the head of the systems from a year and was working on a bash migration script for a web-server. I just needed something to move websites and SQL instances from a server to another. Oh, useless details: I was testing that script on the same machine which I would have moved everything from. The production machine.

You know, a faulty instruction in a for or while cycle and the magic begins. As probably everyone knows, mailbox folders - as everything else in a filesystem - tend to require their own specific permissions and owners in order to work properly, and that was expected by my script: it entered every mailbox folder, in every mail domain, and fixed its permissions. Assume we are on /var/vmail/domain.net; it contains a boxes.txt file, which describes many details about mail domain, its mailboxes and many other things. Now, consider this simple snippet:

cat boxes.txt | while read mailbox; do
mailbox_user=$(echo${mailbox} | first_manipulation)
mailbox_full="${mailbox_user}@domain.net" mailbox_folder=$(echo ${mailbox} | latter_manipulation) cd${mailbox_folder}
chown -R ${mailbox_user} . cd .. done  Ok, nothing evidently bad, if first_manipulation and latter_manipulation do their job. They currently didn’t. Actually, I wrote a latter_manipulation that brought my mailbox_folder to be non-valued, or - even worse - valued with .. I wasn’t expected to handle a non-valued variable, though. The result? Assume that domain.net contained three mailboxes: streambinder, d33pcode, bamless and randomguy. My while cycle would do three iterations: # instructions 1 cd . chown -R streambinder cd .. 2 cd . chown -R d33pcode cd .. 3 cd . chown -R bamless cd .. 4 cd . chown -R randomguy cd .. So, starting from /var/vmail/domain.net, translated: # instructions 1 chown -R streambinder /var/vmail/domain.net/ 2 chown -R d33pcode /var/vmail/ 3 chown -R bamless /var/ 4 chown -R randomguy / Effective result? randomguy is the new systems administrator of that machine. He ownes everything on the machine. What about me? I’m fired. Fortunately, it hasn’t gone that way. But as you may understand, that was a very critical situation, in which every machine service died, as no more able to read/write any of its files, sshd, too. While both shouting against myself and searching on Google for something that could save me from getting fired, found something really useful using rpm, RedHat’s package manager. In fact, 90% of the filesystem could be repaired by resetting perms and ugids referring to packages default specifications: for package in$(rpm -qa); do
rpm --setperms ${package} rpm --setugids${package}
done


Obviously it probably won’t fix anything, but most of it.

NB: this applies only on RPM-based linux distributions.

Finally, a really, really important hint about one of most useful utilies I found: use scheduled getfacl, it will save you from situations like the one above. Its man docet: «for each file, getfacl displays the file name, owner, the group, and the Access Control List (ACL)». It’s actually really useful to backup file/path permissions status, and - in case you burst again the filesystem - to restore them using setfacl (from the same package). Schedule a daily backup of filesystem permissions status, leaning to the crontab utility: crontab -e. The crontab instruction 0 0 * * * getfacl -R / > /root/backup.acl will execute the backup daily at 00:00.

This way you’ll have a daily backup of filesystem permissions and if you have to restore the situation due to a catastrophic mistake as the one I made, just run setfacl --restore=/root/backup.acl and you’re good to go and forgot about how stupid you are.