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Question

I'm running Lubuntu 16.04. After running the system for a while the wireless internet will stop working.

Dutifully, I run:

sudo service network-manager restart

But this returns the message:

Failed to add /run/systemd/ask-password to directory watch: No space left on device

But I have lots of space available on the hard disk, in RAM, and via swap. What's going on?

Answer

As discussed here, it turns out that the Crashplan back-up service is the most likely culprit. It uses many inotify watches and, eventually, eats them all up.

The immediate fix is to run:

sudo -i
echo 1048576 > /proc/sys/fs/inotify/max_user_watches
exit

To make more watches available.

The long-term fix is to edit the file /etc/sysctl.conf to include the line:

fs.inotify.max_user_watches=1048576

Edit: It's been a few days now, and the problem hasn't arisen since I performed the above.