Following are the some contents of my /etc/syslog-ng/syslog-ng.confrelated to logging in to the file debug.log

source s_sys { file ("/proc/kmsg" log_prefix("kernel: ")); unix-stream ("/dev/log"); internal(); # udp(ip( port(514)); };

destination d_mesg { file("/tmp/log/debug.log"); };

filter f_filter2 { level(info..emerg) and not facility(mail,authpriv,cron); };

log { source(s_sys); filter(f_filter2); destination(d_mesg); };

I would like to take your attention towards the line containing "filter". There you can see that i am filtering out the logs from mail, authpriv and cron. As far as my knowledge goes, mail, authpriv and cron are pre-defined facilities of syslog.

My query is :

I have a written a daemon named "pm" which also uses the syslog APIs for logging. Now whatever my daemon logs, goes into the file /tmp/log/debug.log as you can see above. I would like to filter out the logs of "pm" from going into /tmp/log/debug.log. To make it more clear i would like to have the filter like

filter f_filter2 { level(info..emerg) and not facility(mail,authpriv,cron,pm); };

Please Note : the difference in f_filter2 compared to above.

Is it possible to do this ? How can i prevent pm logs from going into /tmp/log/debug.log?


I got the answer.

We can create filters using the filter keyword:

filter <filtername> { expression; };

Where expression is a simple boolean expression. You can use "and", "or" and "not" to connect builtin functions. Functions can be one of:

  • facility(list of comma seperated facility names)

  • level(list of comma seperated priority nammes OR a range separated by "..")

  • program(regexp to match program name)

  • host(regexp to match program name)

  • match(regexp to match program name)

So, if we want to add our own program, for example "pm", to the filter use it like this:

filter f_filter2 { level(info..emerg) and not facility(mail,authpriv,cron) and program(pm); };

And if we want to filter out the log messages of "pm", use the filter like this :

filter f_filter2 { level(info..emerg) and not facility(mail,authpriv,cron) and not program(pm); };

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