System Log

bgm's trick for enabling system log

1. In the shell, do: echo "*.* /var/log/syslog" > /etc/syslog.conf

2. Add the following tags to /System/Library/LaunchDaemons/com.apple.syslogd.plist after the tag <string>/usr/sbin/syslogd</string>

<string>-bsd_out</string>
<string>1</string>

This will tell the Daemon Launcher to call /usr/sbin/syslogd -bsd_out 1, and we have configured it to write all messages to /var/log/syslog

3. "reboot & enjoy your kernel and other messages" (bgm)

Note

The syslog will grow very big quite quickly, but the folder /var/log/syslog is on the data partition (music, etc).
If you keep your device full of music, be careful you don't fill the partition. Unix systems tend to break when they cant write to the syslog. Keep an eye on it or employ some log rotation.

To disable: In a shell, do:

rm /var/log/syslog; mknod /var/log/syslog c 3 2

This will turn /var/log/syslog into a /dev/null

To reenable: In a shell, do:

rm /var/log/syslog; touch /var/log/syslog

This will remove the /dev/null and make a blank regular file

SBSettings Toggle

An SBSettings toggle for enabling/disabling syslog is available at BigBoss' Cydia repository.

Reference

http://code.google.com/p/iphone-elite/wiki/IphoneSyslogd
(full history: http://code.google.com/p/iphone-elite/source/list?path=/wiki/IphoneSyslogd.wiki&start=398)