On my MythTV Backend, I find there are a number of error conditions that I want to monitor and be alerted about if they should happen. For example, as of late, I’ve been having issues with the one of the drives in my RAID configuration (under load I’m getting errors that I think are a result of an old SATA controller), which causes the RAID to drop into degraded mode, and error messages to be logged by the kernel. In a situation like this, I wanted a tool that could monitor my log files and email me if “interesting” things happen.
Now, the first thing I did was search the web for something that would do the job. swatch popped up immediately as one alternative. It’s a nice, simple Perl script which takes a configuration file that defines a log file to monitor, and a series of rules which define what to look for. Unfortunately, it can only monitor one log file at a time (you need to run multiple instances and have multiple configuration files if you want to monitor multiple files), and it has to run continuously in the background. And, quite frankly, the configuration file is a tad byzantine for my taste.
Another common option is logwatch. This application is definitely a lot more flexible, but the configuration is, again, rather complicated. And, at least as far as I can tell, it’s really meant to be run once a day for a given date range, as opposed to operating as a regular, polling application.
And thus ended my search, with the conclusion that it’d really be a lot simpler just to write my own tool. And this pwatch was born. pwatch is a simple Perl script that takes an Apache-style configuration file and processes your log files. Each matching event triggers an action, and then the event is recorded in an SQLite database. Run pwatch again and it’ll skip any events it’s seen before and only report new ones. The result is that you can just fire off pwatch in a cronjob on a regular basis (I run it every five minutes), and it can alert you if something interesting has happened.
Now, pwatch is pretty basic at this point, and I probably won’t add much more to it unless people ask for it (or unless I need it). For example, at this point, the only action it knows how to take on an event is to send out an email. But adding new features should be trivial enough, so if anyone has any ideas, let me know. And if you find pwatch useful, send me an email!
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