Docker container working as a mail server runs out of space
I will try to describe the issue with as many details as possible.
I have a Digital Ocean server 1GB RAM, 25GB SSD with Ubuntu 16.04. I have a docker container (docker version is: Docker version 18.03.0-ce, build 0520e24).
The docker container contains postfix, dovecot, mysql, roundcube and a few other services.
Everything works fine but when start to receive or send emails the free space diminishes and I end up with no free space.
Before that happens if I run “df -h” I get:
root@mail:~# df -h Filesystem Size Used Avail Use% Mounted on udev 488M 0 488M 0% /dev tmpfs 100M 9.3M 90M 10% /run /dev/vda1 25G 11G 14G 46% / tmpfs 497M 0 497M 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 497M 0 497M 0% /sys/fs/cgroup /dev/vda15 105M 3.4M 102M 4% /boot/efi overlay 25G 11G 14G 46% /var/lib/docker/overlay2/17795ba052726099d7ca962eb9756c8e5354483e388c3e326781249954172746/merged shm 64M 0 64M 0% /var/lib/docker/containers/559088336f8c6948d6940714b7e97aea765bc98ee6f237afe39406b2f3638e67/mounts/shm
When I run out of space “/dev/vda1” says “Used space 25GB” and also “overlay” says “Used 25GB”.
When I access the docker container:
docker attach SOME_ID
and I try to find directories and files of significant size or directories and files generated recently…supposing that in this way I will find the source of the issue…I can’t find anything.
This is quite confusing because according to “df -h” there is no free space and the issue is in the docker container but when I try to find suspicious files I can’t find any.
And also, if I reboot the whole machine (Turn off -> Turn on) the used space is emptied and the mail server gets back to normal. In a few days the issue happens again. The server runs out of space and I have to reboot it again.
May I please ask you for advice how to trace the source of the issue?