How to Configure the maximal Number of Open File Handles¶

Introduction¶

The maximum number of open file/socket handles is by default limited to 1024. This is not enough for some apps (e.g. connectivity apps or databases).

The actual settings can be shown with:

ulimit -a

Maximum file handles:

cat /proc/sys/fs/file-max

Allocated, allocated but unused, maximum number of file handles:

cat /proc/sys/fs/file-nr

For a lot of apps the number of 1024 maximal opened file handles is sufficient.

If a larger number of opened file handles is required this can be done with the command ulimit, for example:

ulimit -n 16384

Your app should run this command in the startup phase of your app.

Therefor we recommend to:

Create a script in a sub folder e.g. ulimit-snap/ of your project.
And to add into your snapcraft.yaml file a daemon entry to call this script at startup.

Script

increase-ulimit.sh

#!/bin/sh
ulimit -n 16384

Daemon

snapcraft.yaml

parts:
ulimit-script:
    plugin: dump
    source: ./ulimit-snap

apps:
ulimit:
    daemon: simple
    command: increase-ulimit.sh

In this SDK an complete example project creating a demo snap is stored under samples-sh/ulimit-snap.

The sample project folder also contains a README.md file with further informations.