How do I get dmesg to store a log file? My phone keeps rebooting. I want to know what dmesg says at the moment it reboots, so I can diagnose. Unfortunately, the reboots don't happen predictably, and only when I'm using it. I can't keep my phone connected to my laptop for days on end. I have it connected via adb right now, and of course the little varlet isn't rebooting. There is no last_kmsg, either. The version is LineageOS 14. I'm posting here because the answer to this question would presumably apply to all unix-based systems. If you don't like, I suppose punt it over to Android. What I'm envisioning is it writing to the log constantly until it reboots. I realise that if the phone doesn't reboot itself, the log will eventually fill up the SD card. So I'm picturing a script like: dmesg to log.1 if log.1 >1mb, delete it dmesg log.2 if log.2 >1mb, delete it dmesg to log.1 I don't have the skills to write it though. Can anyone help?

If you have the wherewithall to run a `bash` script this will maintain a file counter and use it to create an circular sequence of `dmesg` log files.


#!/bin/bash
dir=/path/to/storage # Location of persistent storage

[[ -z "$dir/count" ]] && echo 0 >"$dir/count" # Seed the counter if missing

while sleep 0.25
do
count=$(( $(cat "$dir/count") +1 )) # Read the counter and increment
[[ $count -gt 600 ]] && count=1 # Reset so we can reuse diskspace

echo $count >"$dir/count" # Save the new value
dmesg >"$dir/dmesg.$count" # Write the data
done


You will need to review the resulting set of up to 600 log files in date-modified order (`ls -t`) because they will be written and rewritten like a circular buffer.