I found a very good site on magic key sequences – “Debian Administration – The magic sysreq options introduced”. So, it would seem that a safer way of rebooting a locked system would be to include the “u” sequence, which unmounts and then remounts all of your partitions, but as read-only. Especially interesting is the ability to trigger actions at the command line, using “echo h > /proc/sysrq-trigger”. I found that using this option actually sent everything to dmesg, and that the “t” option greatly increased CPU usage by causing klogd and syslogd to each consume over 40% CPU utilization (shown by running “top”). Running “dmesg | less” will display pages of dump information. I ran “dmesg | tail -n 700 | less”, and still had nothing but stack trace entries.
Thank God for magic keys.
Filed under: Kernel