After upgrading Docker on my Ubuntu 24.04 Servers to version 29.0.0, Swarm services suddenly inherit:
Max open files: soft=1024, hard=524288
MongoDB, Redis, etc. suddenly throw file descriptor errors like too many open files on Mongo
Adding ulimits to stack YAML fixes it. Downgrading Docker does not fix it.
Why is this the case and how to fix it?
The containerd.io package for ubuntu 24.04 was upgraded on 2025-11-10 from 1.7.29 to 2.1.5.
This version’s /usr/lib/systemd/system/containerd.service removed:
LimitNOFILE=infinity
As a consequence it seems that containerd now starts with systemd’s default soft limit of 1024 and Docker Swarm inherits these limits. The old behavior (soft=hard=infinity) disappeared.
One can detect this inside a container checking the applied limits on the processes doing e.g.
cat /proc/1/limits
In my case i saw Max open files 1024 524288 .
Checking the containerd version using
$ containerd --version
containerd containerd.io v2.1.5 fcd43222d6b07379a4be9786bda52438f0dd16a1
I could see the containerd version increased to 2.1.5 .
We can change this specific behavior while keeping the current containerd version if we reintroduce the LimitNOFILE field into the container.service by doing this:
sudo systemctl edit containerd.service
Then we add the field with a higher number
[Service]
LimitNOFILE=64000
and reload
sudo systemctl daemon-reload
sudo systemctl restart containerd
sudo systemctl restart docker
Just add the limits in the yaml file you want to deploy
ulimits:
nofile:
soft: 64000
hard: 64000
I did not try this, but a clean uninstall and reinstall of container.io should resolve the issue too.
Note: The issue persists even if you downgrade Docker because containerd.io stays upgraded unless you downgrade manually.