Fix "Out of Memory" Error

Understanding OOM

When Linux runs out of memory, the OOM Killer terminates processes. Logs show:

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

Check Current Memory Status

free -h
cat /proc/meminfo
vmstat -s

Find Memory Hogs

ps aux --sort=-%mem | head -15
smem -r -k | head -20

Emergency Fixes

1. Add Swap Space

sudo fallocate -l 2G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

echo "/swapfile none swap sw 0 0" | sudo tee -a /etc/fstab

2. Kill Memory-Hungry Process

ps aux --sort=-%mem | head -2 | tail -1 | awk '{print $2}'
sudo kill -9 PID

3. Clear Caches

sudo sync && echo 3 > /proc/sys/vm/drop_caches

Preventive Configuration

Systemd Memory Limits

sudo systemctl set-property service-name MemoryMax=512M
sudo systemctl daemon-reload

OOM Behavior

sysctl -w vm.overcommit_memory=1
sysctl -w vm.overcommit_ratio=90

echo "vm.overcommit_memory=1" >> /etc/sysctl.conf
echo "vm.overcommit_ratio=90" >> /etc/sysctl.conf

Application Limits

• PHP: reduce memory_limit in php.ini
• MySQL: reduce innodb_buffer_pool_size
• Apache: reduce MaxRequestWorkers
• Node.js: use --max-old-space-size