Как узнать, почему сервер Ubuntu перезагрузился?

Я получил предупреждение с моего VPS-хоста, что мой VPS перезагрузился.

В /var/logs/auth.log я вижу следующую запись:

    Mar 17 19:09:34 master sshd[3558]: Server listening on 0.0.0.0 port 9922.
Mar 17 19:09:34 master sshd[3558]: Server listening on :: port 9922.
Mar 17 19:09:34 master systemd-logind[3539]: Watching system buttons on /dev/input/event0 (Power Button)
Mar 17 19:09:34 master systemd-logind[3539]: New seat seat0.

Если я открою файл с мой текстовый редактор, пробелы перед первой строкой - все NUL s.

В /var/log/syslog я вижу:

Mar 17 19:09:34 master rsyslogd: [origin software="rsyslogd" swVersion="7.4.4" x-pid="3518" x-info="http://www.rsyslog.com"] start
Mar 17 19:09:34 master rsyslogd: rsyslogd's groupid changed to 109
Mar 17 19:09:34 master rsyslogd: rsyslogd's userid changed to 104
Mar 17 19:09:34 master systemd-udevd[3079]: starting version 219
Mar 17 19:09:34 master ufw-init[2040]: modprobe: ERROR: ../libkmod/libkmod.c:557 kmod_search_moddep() could not open moddep file '/lib/modules/4.9.7-x86_64-linode80/modules.dep.bin'
Mar 17 19:09:34 master networking[3095]: * Configuring network interfaces...
Mar 17 19:09:34 master systemd[1]: Started udev Kernel Device Manager.
Mar 17 19:09:34 master systemd[1]: Started Show Plymouth Boot Screen.
Mar 17 19:09:34 master systemd[1]: Started Dispatch Password Requests to Console Directory Watch.
Mar 17 19:09:34 master systemd[1]: Starting Dispatch Password Requests to Console Directory Watch.
Mar 17 19:09:34 master systemd[1]: Reached target Paths.
Mar 17 19:09:34 master systemd[1]: Starting Paths.
Mar 17 19:09:34 master systemd[1]: Started Forward Password Requests to Plymouth Directory Watch.
Mar 17 19:09:34 master systemd[1]: Starting Copy rules generated while the root was ro...
Mar 17 19:09:34 master systemd[1]: Starting Flush Journal to Persistent Storage...
Mar 17 19:09:34 master systemd[1]: Found device /dev/ttyS0.
Mar 17 19:09:34 master systemd[1]: Started Copy rules generated while the root was ro.
Mar 17 19:09:34 master systemd[1]: Started Flush Journal to Persistent Storage.
Mar 17 19:09:34 master systemd[1]: Starting Create Volatile Files and Directories...
Mar 17 19:09:34 master loadkeys[3082]: Loading /etc/console-setup/cached.kmap.gz
Mar 17 19:09:34 master systemd-tmpfiles[3159]: [/usr/lib/tmpfiles.d/var.conf:14] Duplicate line for path "/var/log", ignoring.
Mar 17 19:09:34 master systemd[1]: Started Set console keymap.
Mar 17 19:09:34 master systemd-udevd[3123]: could not open moddep file '/lib/modules/4.9.7-x86_64-linode80/modules.dep.bin'
Mar 17 19:09:34 master systemd-udevd[3122]: could not open moddep file '/lib/modules/4.9.7-x86_64-linode80/modules.dep.bin'
Mar 17 19:09:34 master systemd-udevd[3121]: could not open moddep file '/lib/modules/4.9.7-x86_64-linode80/modules.dep.bin'
Mar 17 19:09:34 master systemd[1]: Started Create Volatile Files and Directories.
Mar 17 19:09:34 master systemd[1]: Started Network Time Synchronization.
Mar 17 19:09:34 master systemd[1]: Reached target System Time Synchronized.
Mar 17 19:09:34 master systemd[1]: Starting System Time Synchronized.
Mar 17 19:09:34 master systemd[1]: Starting Update UTMP about System Boot/Shutdown...
Mar 17 19:09:34 master systemd-udevd[3127]: Could not generate persistent MAC address for dummy0: No such file or directory
Mar 17 19:09:34 master systemd-udevd[3124]: Could not generate persistent MAC address for ip6tnl0: No such file or directory
Mar 17 19:09:34 master systemd[1]: Started Update UTMP about System Boot/Shutdown.
Mar 17 19:09:34 master systemd[1]: Found device QEMU_HARDDISK.
Mar 17 19:09:34 master systemd[1]: Started Uncomplicated firewall.
Mar 17 19:09:34 master systemd[1]: Activating swap /dev/sdb...
Mar 17 19:09:34 master systemd[1]: Created slice system-ifup.slice.
...

Что может быть причиной перезагрузки ?