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Memory and Swap Management — free, vmstat, Swap Configuration

A practical guide to checking server memory status, analyzing OOM causes, creating swap files, and tuning swappiness.

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Contents
  1. Checking Memory Status
  2. Detailed Memory Analysis
  3. Checking OOM (Out of Memory) Events
  4. Creating a Swap File
  5. Tuning swappiness

Checking Memory Status

Bash
#
free -h

# example:
#               total  used   free   shared  buff/cache  available
# Mem:           7.6G  2.1G   3.2G     45M        2.3G      5.1G
# Swap:          2.0G  100M   1.9G

# "available" (buff/cache )

Detailed Memory Analysis

Bash
# /proc/meminfo
cat /proc/meminfo | grep -E "MemTotal|MemFree|MemAvailable|SwapTotal|SwapFree"

#
ps aux --sort=-%mem | head -10

# vmstat + + CPU (1 )
vmstat 1 10

Checking OOM (Out of Memory) Events

Bash
# OOM killer
journalctl -k | grep -i "oom\|killed process\|memory"

# OOM score check
cat /proc/$(pgrep myapp)/oom_score

# OOM (-1000: )
echo -1000 > /proc/$(pgrep sshd)/oom_score_adj

Creating a Swap File

Cloud servers (AWS t2, t3) have no swap by default.

Bash
# 4GB file
fallocate -l 4G /swapfile
chmod 600 /swapfile
mkswap /swapfile
swapon /swapfile

# boot when
echo '/swapfile none swap sw 0 0' >> /etc/fstab

# check
swapon --show
free -h

Tuning swappiness

swappiness controls how aggressively the kernel uses swap instead of RAM (0–100, default 60).

Bash
# check
cat /proc/sys/vm/swappiness

# when
sysctl vm.swappiness=10

# settings
echo 'vm.swappiness=10' >> /etc/sysctl.conf
sysctl -p
  • Database servers: vm.swappiness=10 (prefer RAM)
  • General-purpose servers: vm.swappiness=10–30
  • The default of 60 is designed for desktops
#OOM#vmstat#free#linux
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