Before we leave the topic of system-logger configuration and use, we should cover a tool that can be used to test your new configurations regardless of which log dæmon you use. logger is a command-line application that sends messages to the system logger. Besides its relevance as a diagnostic tool, logger especially is useful for adding logging functionality to shell scripts.
The usage we're interested in here is diagnostics. (Although, come to think of it, you really should use this tool in any important scripts you routinely run, especially ones that run unattended via cron or at.) The easiest way to explain how to use logger in this regard is with an example.
Suppose you've reconfigured syslog to send all dæmon messages with priority “warn” to /var/log/warnings. To test the new syslog.conf file, you'd first restart syslogd and klogd, then you'd enter a command like this:
mylinuxbox:~# logger -p daemon.warn "This is only a test."
As you can see, logger's syntax is simple. The -p parameter allows you to specify a facility/priority selector. Everything after this selector, and any other parameters or flags, is taken to be the message.
Because I'm a fast typist, I often use while-do loops in interactive bash sessions to run impromptu scripts (actually complex command lines). The following sequence of bash commands works either interactively or in a script:
mylinuxbox:~# for i in > do > logger -p daemon.$i "Test daemon message, level $i" > done
This sends test messages to the dæmon facility for each of all eight priorities. Listing 2, presented in the form of an actual script, generates messages for all facilities at each priority level.
Hopefully that's enough to get you started in building, testing and using custom syslog configurations. May your logs be detailed, plentiful, closely watched and uninteresting!
Mick Bauer (firstname.lastname@example.org) is a network security consultant in the Twin Cities area. He's been a Linux devotee since 1995 and an OpenBSD zealot since 1997, and enjoys getting these cutting-edge OSes to run on obsolete junk.
- Let's Go to Mars with Martian Lander
- VMware's Clarity Design System
- Applied Expert Systems, Inc.'s CleverView for TCP/IP on Linux
- Papa's Got a Brand New NAS
- My Childhood in a Cigar Box
- Jetico's BestCrypt Container Encryption for Linux
- Rogue Wave Software's TotalView for HPC and CodeDynamics
- Smith Charts for All
- Debugging Democracy
- Linux Journal January 2017
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