fstrim has default cron.weekly entry on docker containers (partner-images)

Workaround for now is to add `RUN rm /etc/cron.weekly/fstrim` to my Dockerfile

Interestingly enough I have a very similar issue with this but I'm running LXD containers so it seems the problem is not isolated to docker:

Email from cron:
/etc/cron.weekly/fstrim:
fstrim: cannot open /dev/.lxd-mounts: Permission denied
fstrim: /dev/lxd: FITRIM ioctl failed: Operation not permitted
fstrim: /: FITRIM ioctl failed: Operation not permitted

Like you I have 'rm /etc/cron.weekly/fstrim' in each container to resolve it.

I think a generic fix for this in the systemd world would be to add ConditionVirtualization=no to the fstrim.service unit.

fstrim.service in Xenial is in examples/

What we could do is modify the fstrim script in cron.weekly to something along those lines:

#!/bin/sh
# trim all mounted file systems which support it
+if ! /usr/bin/systemd-detect-virt -q -c; then
/sbin/fstrim --all || true
+ fi

at least the cron.weekly won't try to start fstrim inside a container automatically every sunday-ish IIRC.

or even better I think:

#!/bin/sh
# trim all mounted file systems which support it
+if /usr/bin/systemd-detect-virt -q -c; then
+exit 0
+fi
/sbin/fstrim --all || true

See #1589289 for recent details.