Symptom

When try to delete container, it failed to remove and reportd below error:

Solution

1. Find out which process has mounted this busy mountpoint:

/var/lib/docker/overlay/81dfae6c47d7919e91acb3947d2c2093d2e3549e16099279852796c7251d3026/merged

$ sudo find /proc -maxdepth 2 -type f -name "mountinfo" -exec grep -nl 81dfae6c47d {} \;
/proc/23512/mountinfo
/proc/23513/mountinfo
/proc/23610/mountinfo
/proc/23612/mountinfo

2. Check what’s the process according to above PID

$ ps axf | grep 23512 | grep -v grep 23512 ? Ss 0:00 php-fpm: master process (/etc/php-fpm.conf)

3. Restart the corresponding service,in my case, it is php-fpm processes mounted the busy mountpoint, so we need restart it

$ sudo systemctl restart php-fpm