System Log

bgm's trick for enabling system log
-bsd_out 1 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
 * 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 /usr/sbin/syslogd
 * 1) "reboot & enjoy your kernel and other messages" (bgm)

Note
The syslog will grow very big quite quickly if you use WinterBoard's debug setting, but the folder /private/var/log 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, enter Terminal.app and run: rm /var/log/syslog; mknod /var/log/syslog c 3 2 This will delete (rm) the file and create a /dev/null. (mknod *** c 3 2)

To reenable, enter Terminal.app and run: rm /var/log/syslog touch /var/log/syslog

This will delete (rm) the file and and make a blank regular file. (touch)

SBSettings Toggle
An SBSettings toggle for enabling/disabling syslog is available at BigBoss' Cydia repository. The syslog &gt; /var/log/syslog package from saurik's repo is not a dependency and you must manually install it also.

Terminal.app
As iOS is Unix based, it comes as no surprise that its syslog can be read using the same tools desktop Unix and Linux power users use; provided the tools are compiled for ARM. The most common tool is []. If you don't have it yet, just run an  on the package. In order to use it, just connect to the syslog socket with the following command: socat - UNIX-CONNECT:/var/run/lockdown/syslog.sock This gives an interactive shell with the syslog daemon (no need to enable file output). If you execute the  command, the shell will print out new messages as they arrive.

With a Mac through lockdownd
A binary (and its source code) to view ASL messages from Mac using the MobileDevice.framework has been made available on http://newosxbook.com/index.php?page=downloads.

Reference

 * Google Code
 * Full History