On 11/19/18 10:48 AM, Theodore Y. Ts'o wrote: > On Mon, Nov 19, 2018 at 08:51:17PM +0530, AIAMUZZ wrote: >> Hi, >> >> I have this nagging and frustrating boot freeze i often face on my >> Deepin OS boot ... Deepin OS i think uses 'journalctl' to record logs >> on its system. >> >> 'journalctl' however seems to record boot logs ONLY for successful >> boots ... boot logs for instances of boot freezes/hangs that are >> issued with a ... 'Ctrl+Alt+Del' ... key combination or the ... Magic >> Sysrq 'b' ... key combination to get out of the frozen/hung machine >> state are just not aved in the 'journalctl' log ... >> >> Is there any option using Magic Sysrq that will enable me to record >> the failed/frozen/hung boot information to a file for troubleshooting >> before i reboot the system using the option 'b' ? >> >> If not ... Isn't it a good idea to have such an option added to Magic >> Sysrq options, that can save/record the boot/system logs upto that >> point, until just before we restart the machines ? > > This is a hard problem to solve, because there's no place to store the > information, at least not in the general case. The problem is on an > unsuccessful boot, the root file system may not have been mounted yet. > Heck, the storage devices might not have been probed at all! > > If your hardware has a place to store dmesg output across reboots (via > one of the CONFIG_PSTORE_* kernel configuration options) then this > would be an easy problem --- in fact, it would be the default even > with out needing a magic sysrq to request it. The problem is that > most x86 devices do not have hardware capable of supporting > CONFIG_PSTORE. If you have a custom BIOS which doesn't clear memory > across a warm reset, that would make things easy. Unless, unless you > are a big cloud company using custom hardware and/or a custom BIOS, > life is much more difficult. :-( > > One alternative solution you can use is to simply use a serial > console, and have a another computer monitoring the output from the > serial console. This will allow you to see all of the kernel messages > during early bootup and afterwards. So this is also useful for when > your X server dies and your system mysteriously reboot; either > CONFIG_PSTORE_* hardware or using a serial console might allow you to > see the kernel oops message which took out your desktop machine. (Or > in the case of servers, you can cross connect your servers' serial > ports so that one server is monitoring another server's serial > consoles.) > > Cheers,
Yes, all of that. Having some kind of pstore on x86 would be wonderful. kexec/kdump used to be an option also. I haven't tried it lately. -- ~Randy