Network Security Hacks

Steer Syslog

Make syslog work harder, and spend less time looking through huge log files.

The default syslog installation on many distributions doesn’t do a very good job of filtering classes of information into separate files. If you see a jumble of messages from Sendmail, sudo, BIND, and other system services in /var/log/messages, then you should probably review your /etc/syslog.conf.

There are a number of facilities and priorities that syslog can filter on. These facilities include auth, auth-priv, cron, daemon, kern, lpr, mail, news, syslog, user, uucp, and local0 through local7. In addition, each facility can have one of eight priorities: debug, info, notice, warning, err, crit, alert, and emerg.

Note that applications decide for themselves at what facility and priority to log (and the best apps let you choose), so they may not be logged as you expect. Here’s a sample /etc/syslog.conf that attempts to shuffle around what gets logged where:

auth.warning                            /var/log/auth
mail.err                                /var/log/maillog
kern.*                                  /var/log/kernel
cron.crit                               /var/log/cron
*.err;mail.none                         /var/log/syslog
*.info;auth.none;mail.none              /var/log/messages

#*.=debug                               /var/log/debug

local0.info                             /var/log/cluster
local1.err                              /var/log/spamerica

All of the lines in this example will log the specified priority (or higher) to the respective file. The special priority none tells syslog not to bother logging the specified facility at all. The local0 through local7 facilities are supplied for use with your own programs, however you ...