my ubuntu 16.04 server occassionaly reboots itself and i dont have a clue why? below is the syslog file content which have keyword named Shutdown
Nov 21 13:51:42 AB-active-server systemd[1]: Created slice User Slice of support.
Nov 21 13:51:42 AB-active-server systemd[1]: Starting User Manager for UID 1000...
Nov 21 13:51:42 AB-active-server systemd[1]: Started Session 1196 of user support.
Nov 21 13:51:42 AB-active-server systemd[18340]: Reached target Sockets.
Nov 21 13:51:42 AB-active-server systemd[18340]: Reached target Paths.
Nov 21 13:51:42 AB-active-server systemd[18340]: Reached target Timers.
Nov 21 13:51:42 AB-active-server systemd[18340]: Reached target Basic System.
Nov 21 13:51:42 AB-active-server systemd[18340]: Reached target Default.
Nov 21 13:51:42 AB-active-server systemd[18340]: Startup finished in 15ms.
Nov 21 13:51:42 AB-active-server systemd[1]: Started User Manager for UID 1000.
Nov 21 13:51:42 AB-active-server console-kit-daemon[21735]: (process:18348): GLib-CRITICAL **: g_slice_set_config: assertion 'sys_page_size == 0' failed
Nov 21 13:51:42 AB-active-server console-kit-daemon[21735]: missing action
Nov 21 13:51:44 AB-active-server systemd[1]: Stopping User Manager for UID 1000...
Nov 21 13:51:44 AB-active-server systemd[18340]: Stopped target Default.
Nov 21 13:51:44 AB-active-server systemd[18340]: Reached target Shutdown.
Nov 21 13:51:44 AB-active-server console-kit-daemon[21735]: (process:18386): GLib-CRITICAL **: g_slice_set_config: assertion 'sys_page_size == 0' failed
Nov 21 13:51:44 AB-active-server console-kit-daemon[21735]: missing action
Nov 21 13:51:44 AB-active-server console-kit-daemon[21735]: console-kit-daemon[21735]: GLib-CRITICAL: Source ID 739 was not found when attempting to remove it
Nov 21 13:51:44 AB-active-server systemd[18340]: Starting Exit the Session...
Nov 21 13:51:44 AB-active-server console-kit-daemon[21735]: GLib-CRITICAL: Source ID 739 was not found when attempting to remove it
Nov 21 13:51:44 AB-active-server systemd[18340]: Stopped target Basic System.
Nov 21 13:51:44 AB-active-server systemd[18340]: Stopped target Timers.
Nov 21 13:51:44 AB-active-server systemd[18340]: Stopped target Sockets.
Nov 21 13:51:44 AB-active-server systemd[18340]: Stopped target Paths.
Nov 21 13:51:44 AB-active-server systemd[18340]: Received SIGRTMIN+24 from PID 18387 (kill).
Nov 21 13:51:44 AB-active-server systemd[1]: Stopped User Manager for UID 1000.
Nov 21 13:51:44 AB-active-server systemd[1]: Removed slice User Slice of support.
the server's disk partitions have 60%+ storage free and inodes are used 1% only
Memory is 60G and intel Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz