TIL: the sticky bit

Retroactively published on 8 Mar 2019. A while ago I started keeping a journal of TILs, and I’ve decided to share some of them.

Today I learned about the sticky bit.

I set up a Samba share on a Raspberry Pi for our household scanner. The scanner dumps files into a shared directory, and we can triage them from our computers or phones. It seemed to be working fine, but then I realized that I wasn’t able to delete files. I could create and read files, but delete just didn’t work.

Here’s how the directory looked:

$ ls -lah / | grep scanner
drwxrwxrwt   2 scanner scanner 4.0K Oct  7 18:52 scanner

At first I figured there was some sort of group permissions problem. But adding my user to the scanner group didn’t solve it.

Turns out it was the t - the sticky bit. This was preventing any user who wasn’t scanner from deleting files in that directory.

Removing the sticky bit fixed the problem.

$ sudo chmod -t /scanner