I did not know the reasons but I remembered that one should try Alt + SysRq + R E I S U B upon a kernel panic. I tried this combination and the system rebooted immediately. Then I searched for relevant error messages in /var/log, but there was nothing there. In fact, the last logged message was from an hour before the reboot. I did find the following messages regarding the SysRq operations:
Code: Select all
Apr 28 18:30:58 debian kernel: [97145.977280] SysRq : Keyboard mode set to system default
Apr 28 18:30:59 debian kernel: [97146.531345] SysRq : This sysrq operation is disabled.
Apr 28 18:30:59 debian kernel: [97147.068320] SysRq : This sysrq operation is disabled.
Apr 28 18:31:00 debian kernel: [97147.522839] SysRq : Emergency Sync
Apr 28 18:31:00 debian kernel: [97147.523079] Emergency Sync complete
Apr 28 18:31:00 debian kernel: [97148.167408] SysRq : Emergency Remount R/O
This laptop only suspends to disk or to RAM, but it is never shut down. Its last reboot was on Tuesday, when the kernel was updated (from Backports).
Two questions:
1. Should I worry about those two SysRq operations (E I) being disabled?
2. Is the combination Alt+SysRq+R E I S U B the most effective one to recover a system? I already searched for information about it on the Internet and learnt what every operation does, but there are different combinations of them.