Recently my phone keeps on restarting randomly through the day, and I would like to trace what is the cause for that.

I tried this app https://play.google.com/store/apps/details?id=org.jtb.alogrec but it doesn't seem to work in Android 6 (It creates the file but it doesn't write anything)

Any ideas on how can I get the logcat or how can I identify the problem?