Tag Archives: ROOter

Remote Logging from OpenWRT to Rsyslog

This one is brief and simple. I have six routers going right now (and a ridiculously long article still in draft explaining why), all running OpenWRT. I had them set to save logs to local thumb drives, which, frankly, was a pain in the butt. I concluded that I wanted them all logging to a single remote system for simplicity – the old EEE PC netbook that I use as a network terminal for basic maintenance. It has a good old fashioned spinning disk hard drive, and won’t suffer from a ton of log writes like the thumb drives (or heavens forbid the internal storage) on the routers would.

After going through several tutorials that were either a bit complicated or a bit incomplete for my specific use, it turned out to be obnoxiously simple to implement. I could’ve gotten it all done in under half an hour if I’d already known exactly what I was doing, and most of that time was repetitively ssh-ing into six different routers.

That said, here it is: quick, dirty, with no missing or extra steps!

Set up your log server first

My logserver is running Debian Buster, which already came with rsyslog configured with very sensible basic settings (logging to file in /var/log/, and rotation already set up). All I had to do was enable listening on TCP or UDP 514 (I’ve opened both but am using TCP), then set up some very basic filtering to sort the remote messages the way I wanted.

All changes can be accomplished quickly in /etc/rsyslog.conf. Starting at the top, we uncomment the lines that start the server listening:

# provides UDP syslog reception
module(load="imudp")
input(type="imudp" port="514")

# provides TCP syslog reception
module(load="imtcp")
input(type="imtcp" port="514")

# List of sub networks authorized to connect :
$AllowedSender UDP, 127.0.0.1, 192.168.0.0/16
$AllowedSender TCP, 127.0.0.1, 192.168.0.0/16

The last group there was added based on the recommendations of a tutorial, and restricts senders to localhost and my local network (I have hosts on five subnets, most people could be using 192.168.1.0/24 or whichever single subnet they’ve configured).

Next, near the bottom of the file, you need to decide how you want your messages stored. If you don’t change anything, they’ll be mixed into your other logs from your localhost. You can do a lot of more complicated things, but I wanted one subdirectory per remote host, with all messages in a single syslog.log. Here’s how you get that, in the rules section and above your rules for normal localhost messages:

###############
#### RULES ####
###############

#
# ADDED BY CHUCK
# Redirect all messages received from the network to subfolders first
# From example on stackexchange saved in notes.
#

$template uzzellnet,"/var/log/%HOSTNAME%/syslog.log"

if $fromhost-ip startswith "192.168." then -?uzzellnet
& stop

The template can be named anything. This test checks all log messages to see if they are from remote hosts in my local net – if so, it sends them all to a single file based on the remote hostname. The template statement must be before the test, and “& stop” tells it that any logs meeting this test should not be further processed below with localhost messages.

Obviously your log server will need a static IP to do this job. If you haven’t set one already, you can either set it manually from the server, or (my recommendation) just configure your DHCP router to automatically provision that machine with a static IP.

That’s it for configuring the server! It really is that simple. Just restart rsyslog on your server:

chuck@raul:/etc$ sudo systemctl restart rsyslog

Now, set up each remote OpenWRT host

All settings for logging are stored in /etc/config/system. By default, everything is logged to a ring buffer in memory, and lost on reboot. Not useful if something happens that causes a lockup, etc., but it is awfully handy to read from the command line when you’re already logged in via ssh, so we want to keep that functionality – messages should both be stored in the ring buffer and sent to the remote server.

In /etc/config/system, add or change the following three lines (using the static IP address you’ve provisioned for your log server):

        option log_ip '192.168.1.209'
        option log_port '514'
        option log_proto 'tcp'

You can leave it the default UDP if you prefer – there’s less network overhead, but most of us aren’t really hurting for network capacity. TCP is generally worth it for logging unless you really don’t care if you miss the occasional message.

Now, just restart your logs so the new settings are picked up:

/etc/init.d/log restart
/etc/init.d/system restart

Next, log a test message. It can say anything. This was the one from the last of my six routers to configure, a test machine I’m still setting up to replace one of my production routers soon:

root@FASTer2:~# logger "First test message from Faster2!"

That should produce a log line both locally and remotely. Check the ring buffer:

root@FASTer2:~# logread
Thu Dec 17 20:22:07 2020 daemon.info logread[424]: Logread connected to 192.168.1.209:514
Thu Dec 17 20:22:21 2020 user.notice root: First test message from Faster2!

Now, on your log server, you should see a new directory for your host created in your log folder (probably /var/log/ if you’re using Debian defaults). We said in rsyslog.conf earlier that the file should be in that subfolder and named syslog.log, so let’s test receipt:

chuck@raul:~$ sudo cat /var/log/FASTer2/syslog.log
[sudo] password for chuck:
Dec 17 20:22:07 FASTer2 logread[424]: Logread connected to 192.168.1.209:514
Dec 17 20:22:21 FASTer2 root: First test message from Faster2!

That’s it! We’re all set to go. You can obviously get way more elaborate than this, but a simple 1:1 replacement of OpenWRT’s default ring buffer with a neatly sorted single log file will probably cover most users’ needs.

Enjoy!