A friendly word of advice for anyone running Steam on Linux: Do not—do NOT—manually move your Steam directory from its default location. Users have reported that doing so has resulted in the deletion of everything in their directory trees, including, in at least one case, backups on an external drive.
The problem first came to light last week by way of GitHub user Keyvin, who moved his Steam folder to a new location but was then unable to launch it, even after browsing and pointing to the new location. After a crash and restart, it reinstalled itself and all appeared well, he wrote, "until I looked and saw that Steam had apparently deleted everything owned by my user recursively from the root directory. Including my 3TB external drive I back everything up to that was mounted under /media."
Another user lost his entire Home directory while debugging Steam, according to Readwrite, which said that the problem appears to be "a script bug in which an incorrect empty setting gets passed into an rm -rf command that erases files in a given directory, plus all the subdirectories in the home directory (and all their subdirectories, and so on, and so on)."
Valve told Gamesbeat that it has received "only a handful" of reports from Linux users who have been impacted by the bug, which is fortunate, but it has not yet been able to reproduce the problem internally. It is continuing to investigate, however, and in the meantime has added some "additional checks" to keep it from happening again.
Linux users who have run into this problem can email firstname.lastname@example.org for more information. Everyone else would probably do well to avoid messing with anything under the hood until Valve sounds the all-clear.