Ever since I have "upgraded" to systemd on Arch Linux, I keep losing logs when an unexpected lockup happens. I hit the same log-losing issue one month ago and just hit the issue again. There are also independent other confirmations.
- While doing some stuff in Java and with network-related utilities, I saw that KDE (the clock) was frozen. The CPU fan became noisy and the heat was rising. The mouse pointer could still be moved though.
- I tried to ssh from another machine (failed due to "no route to host")
- I waited a few minutes, perhaps the NMI watchdog could kill the offending task. No dice.
- Ctrl + Alt + F1 did not work either, even after SysRq + R
- Since the above steps did not work, I decided to issue the SysRq sequence R-E-I. After E, the screen became black, but no console either. Not even after SysRq + K
- So, this session appears to be lost, the only thing that can be done is gathering debugging information. Looking at Wikipedia, I decided to press SysRq + d (display held locks) among some others.
- After pressing SysRq + S I waited a second and then rebooted with SysRq + B.
- After rebooting and logging into a console, I saw no traces of any crash. The most recently logged entry was from using Wireshark, but there was still a gap of 45 minutes.
(I was running Linux v3.8-rc5-218-ga56e160 btw)
So, how can I make sure that my logs are retained when abnormally rebooting due to a lockup?