Fix Server Randomly Reboots

Check System Logs First

Find why the server rebooted:

# Last boot reason
sudo last reboot
sudo last -x | grep shutdown

# Kernel message before reboot
sudo dmesg | tail -50
sudo journalctl --list-boots
sudo journalctl -b -1 -n 100

Common Causes

1. Out of Memory (OOM Killer)

Kernel kills processes and may cause instability:

sudo dmesg | grep -i "out of memory"
sudo dmesg | grep -i "oom"
sudo grep -i "killed process" /var/log/kern.log

Fix: Add RAM or optimize memory usage.

2. Hardware Issues (Dedicated/Cloud)

sudo dmesg | grep -i "error"
sudo smartctl -a /dev/sda
sudo mcelog

For VPS: contact support for host node issues.

3. Kernel Panic

sudo journalctl -k | grep -i "panic"
sudo dmesg | grep -i "panic"

Fix: update kernel or rollback changes.

4. Cron Jobs Running Reboot Commands

grep -r "reboot" /etc/cron*
grep -r "shutdown" /etc/cron*
sudo crontab -l

5. Overheating (Physical Servers)

sudo apt install lm-sensors -y
sudo sensors

6. Power Issues

VPS usually does not face power issues; contact provider support.

Prevent Random Reboots

sudo apt install linux-crashdump -y
sudo apt install monit -y

echo "#!/bin/bash
echo "$(date): System reboot detected" >> /var/log/reboot.log" | sudo tee /etc/profile.d/reboot-logger.sh