SyslogCore

Simple way to write to syslog aka /dev/log aka /var/log/syslog in .NET Core on Linux. Consists of one short C# file (70 lines!) that you can throw into your project. Tested in ASP.NET Core 5.

Usage

Syslog.Write(Syslog.Level.Warning, "MyAwesomeApp", "something went wrong");

The problem

.NET Core (aka .NET 5 and later) does not have a built-in logging provider for linux. The official recommendation is to use a 3rd party logger, like Serilog, NLog, Log4Net etc.

All heavyweight large libraries.

There's an ongoing discussion if a default logger should be a part of .NET runtime, but it's stall.

File logging is tricky

Where do you place the logs? How do you grant permissions to that location? How should the files be formatted? When do the files rotate/roll over? Microsoft couldn't decide and... simply ignored the problem.

Enter syslog

Why reinvent the wheel?!

Almost every linux distro comes with a built-in feature called syslog. It takes care of everything: queues messages, writes to log files, rotates files (via "logrotate"), and exists on literally every Linux machine. It has lots of ways to send messages to it: UDP-listener, TCP-listener, a "Unix socket" at /dev/log, a logger CLI command or a syslog() system function etc.

For Windows folks: think of it as an EventLog.Write, but for Linux

Works with docker too!

If you're running an app inside a container, docker logs will show these logs, zero configuration.

How do we use it in C#?

Just use the good old DllImport to reference the external libc library, and call the original syslog function. That's it. No Nugets, no dependency-injection.

Happy coding.

FAQ

1. What if (for some weird reason) syslog is not installed on my Linux?

Run sudo apt-get install rsyslog

2. Syslog is present on my machine but there's no logs

rsyslog might be present but it's not running (known issue with WSL2 for example). Check that its running, if not - start it:

$ service rsyslog status
 * rsyslogd is not running
$ sudo service rsyslog start

Then test that logging actually works:

$ logger testtesttest
$ tail -1 /var/log/syslog
Oct 11 13:51:18 DESKTOP-CDBR5NK jazz: testtesttest

3. What if I copy paste this into a cross-platform app that runs on both Windows and Linux?

No worries, the code checks if it runs on Windows or Linux before proceeding.