Failed to allocate directory watch

While running apt-get upgrade, I was getting a Failed to allocate directory watch: Too many open files error.

It’s similar to this warning from Visual Studio Code, but this warning seems to be caused by having a large number of containers running.

You can see the current limits with sysctl fs.inotify. On Ubuntu, with the defaults, these are as follows:

fs.inotify.max_queued_events = 16384
fs.inotify.max_user_instances = 128
fs.inotify.max_user_watches = 65536

To fix the problem, I added /etc/sysctl.d/60-fs-inotify.conf, with the following contents:

fs.inotify.max_queued_events = 32768
fs.inotify.max_user_instances = 512
fs.inotify.max_user_watches = 524288

To reload the new settings, you need to run sudo sysctl --system.