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Incremental Backups

Strategies​

StrategyFlagHow It Works
Incremental--link-destHard-links unchanged files, copies changed ones
Differential--compare-destCopies only files that differ from reference
Full(none)Copies everything every time

Commands​

# Incremental snapshot (most common)
rsync -av --link-dest=/backup/latest \
 /var/www/html/ /backup/$(date +%F)/
ln -sfn /backup/$(date +%F) /backup/latest

# Differential from last full backup
rsync -av --compare-dest=/backup/full-baseline/ \
 /var/www/html/ /backup/diff-$(date +%F)/

# Full backup
rsync -av /var/www/html/ /backup/full-$(date +%F)/

# Verify backup matches source
rsync -avnc /var/www/html/ /backup/latest/

# Restore from snapshot
rsync -av /backup/2024-01-15/ /var/www/html/

# Cleanup old backups (keep 14 days)
find /backup/ -maxdepth 1 -type d -name "20*" -mtime +14 -exec rm -rf {} \;

Complete Backup Script​

#!/bin/bash
set -euo pipefail
SRC="/var/www/html/"
BASE="/backup"
TODAY="$BASE/$(date +%F)"

rsync -av --link-dest="$BASE/latest" "$SRC" "$TODAY/"
ln -sfn "$TODAY" "$BASE/latest"
find "$BASE" -maxdepth 1 -type d -name "20*" -mtime +14 -exec rm -rf {} \;
tip

With --link-dest, every snapshot looks like a full backup but only uses extra space for changed files.