Android: How to get kernel logs after kernel panic?

Question

I am using an Android Custom ROM on my device, also with a custom boot.img (custom kernel + cmdline + ramdisk). I now want to be able to view the kernel logs immediately after a kernel panic, but unfortunately I can not use a serial console.

The good news: There seem to be some sources/modules in the Linux kernel of Android that are written exactly for this purpose. For example, the following lines are activated in my .config file for the kernel:

CONFIG_ANDROID_RAM_CONSOLE=y CONFIG_ANDROID_RAM_CONSOLE_ENABLE_VERBOSE=y CONFIG_APANIC=y CONFIG_APANIC_PLABEL="oem_log" 

My problem is: After I forced a kernel panic in order to test this, i.e. by loading a simple panic kernel module with insmod panic.ko, it seems that no log was written to the MTD named oem_log (which exists on my device). Secondly, the RAM also does not contain logs after reboot because it seems to be cleared - or the logs are not written either.

So how can I get the kernel logs after a panic? Also it would be helpful if there is a way I could test the APANIC on the running system. Maybe by using the kernel debug system? As of now I am pretty new to this.

Thanks in advance for any help!

Answer 1

As for me,

cat /proc/last_kmsg  

after reboot (caused by the kernel panic during insmod) does list messages relevant to the crash, like

[  424.909515] Kernel panic - not syncing: Fatal exception [  424.909606] Backtrace:  [  424.909790] [<c005a5ec>] (dump_backtrace+0x0/0x10c) from [<c05f38dc>] (dump_stack+0x18/0x1c) [  424.909973]  r6:c5cccf00 r5:00000000 r4:c08505a0 r3:00000000 

So you can at least try. I am working with Linux 3.0.31-g4f6d371 on Galaxy Nexus.

Answer 2

It seems at Android-7.0 or above, the last_kmesg log is moved to: /sys/fs/pstore/console-ramoops, so try:

cat /sys/fs/pstore/console-ramoops 

it works well for me on nexus-5x