The Danger of fuzzy matching over one's PATH

Awhile back I noticed my personal mnt/ directory, my (empty) personal tmp/ directory, and a few symbolic links disappeared from my home directory. I only noticed because I use unison¹ to synchronize my desktop and laptop homedirs. The actual amount of removed directories and symbolic links were staggering, and it costed me five minutes of extra effort to search through the unison UI to ignore files I don’t want to synchronize. Repeat this a few times a day, with the problem occurring at seemingly random intervals, and you’ve wasted minutes out of every day, which adds up to hours every month.

For months I had not figured out what the problem was. By chance I had noticed while using my application launcher, I had accidentally not ran links -g ² but instead had ran cleanlinks. I wonder to myself what was I running by accident, as I had done this before, but had not thought anything of it, assuming it was a program that would print usage or perform a no-operation by default.

I was wrong.

Turns out cleanlinks searches the current working directory for empty directories and broken symbolic links. Both are useful. For example I keep empty directories in ~/mnt/ to mount sshfs stuff, and I prefer to use ~/tmp/ as a work directory because no system scripts will touch it.³ I had a few broken symbolic links scattered about, from weird git repositories working trees to some stale user-level systemd unit links from my archlinux install.

Making things more interesting, if you run cleanlinks --help, or with any flags, it operates as usual. So it’s a mistake to also do cleanlinks /some/directory/i/want/to/clean. As a part of imake,⁴ the old X11 ecosystem build tools, cleanlinks will be installed on many systems and it’s not safe to run it lest you enjoy random stuff being messed about with in your current directory.

How did I manage to run cleanlinks so many times? I did not have links installed on the affected machine. And even after I did install it, I forgot to remove cleanlinks from my rofi runcache. So it had a higher precedence to match than links in certain cases. Hence I ran it a few times on accident even after installing links.

Therefore, I strongly recommend one doesn’t fuzzy match over their PATH. Who knows what other nasty tools ship on your system that will lay waste your productivity, or worse, damage your personal files.

Regardless, I have yet to heed my own warning. Maybe I should just use .desktop files, but then again, maybe there exists a cleanlinks.desktop… Ideally, I’ll create a directory of symlinks to programs I want to launch from rofi. Someday :)

§About Unison

I should mention unison is a superb tool for synchronizing your data. It shows the user a list of changes to each directory being synchronized, waits for the user to decide which way each file should be synchronized:

1. Send file from host A to B
2. Send file from host B to A
3. Ignore the file this time
4. Ignore the file permanently
5. Merge the files

Because unison doesn’t try to be fancy or automatic, it is easy to understand what is happening.