SysLogHandler not writing to syslog with Python logging

Logging to syslog in Python

I was trying to use the standard Python logging module to write messages to syslog. The logging module has a SysLogHandler class which can log to a local or remote syslog daemon.

With no host specified, SysLogHandler uses localhost which is what I wanted. I tried to use SysLogHandler, but it just wouldn’t work. There was no error when I called the logging methods, but my messages didn’t show up in /var/log/syslog.

syslog module works

Python also has a standard syslog module. I tried it and it worked fine; my messages were written to the syslog file.

For example:

import syslog
syslog.syslog('test')

syslogd isn’t listening

After running Wireshark I found the SysLogHandler was correctly sending a UDP packet to localhost on port 514. I could also see there was an ICMP response indicating the UDP packet was not received on that port. syslog wasn’t listening!

Use /dev/log

Instead of sending to localhost, I wanted SysLogHandler to pass the message to syslog on the local machine in the same way the syslog Python module was doing.

The solution is to pass /dev/log as the address parameter to SysLogHandler. It’s not well documented, but it works.

For example:

import logging
from logging.handlers import SysLogHandler
logger = logging.getLogger()
logger.setLevel(logging.INFO)
syslog = SysLogHandler(address='/dev/log')
formatter = logging.Formatter('%(name)s: %(levelname)s %(message)s')
syslog.setFormatter(formatter)
logger.addHandler(syslog)

Easy when you know how.