chrony Sync Check Shell Script

Clock skew breaks TLS, Kerberos, and distributed logs — a chrony sync check shell script is an easy cron job that alerts when offset exceeds a few hundred milliseconds.

What this script does

Uses timedatectl show -p NTPSynchronized
Parses chronyc tracking offset when chrony installed
Threshold on absolute offset milliseconds
Fallback message when chrony missing
Exit 1 for monitoring hooks

Prerequisites

systemd or chrony
chronyc in PATH if using offset parse
Root optional for chronyc

Step 1: Save the script

sudo nano /usr/local/bin/chrony-check.sh
sudo chmod +x /usr/local/bin/chrony-check.sh

Step 2: Full script (scroll to read)

chrony-check.sh

#!/usr/bin/env bash
set -euo pipefail

MAX_OFFSET_MS="${MAX_OFFSET_MS:-500}"
LOG="/var/log/chrony-check.log"

log(){ echo "[$(date '+%F %T')] $*" | tee -a "$LOG"; }

synced=$(timedatectl show -p NTPSynchronized --value 2>/dev/null || echo "unknown")
log "NTPSynchronized=$synced"

if [[ "$synced" != "yes" ]]; then
  log "FAIL not synchronized"
  exit 1
fi

if command -v chronyc >/dev/null 2>&1; then
  off=$(chronyc tracking 2>/dev/null | awk -F: '/RMS offset|Last offset/ {gsub(/[^0-9.-]/,"",$2); print $2; exit}' || true)
  if [[ -n "$off" ]]; then
    # rough: treat field as seconds if small decimal
    ms=$(awk -v o="$off" 'BEGIN{printf "%.0f", (o<10?o*1000:o)}')
    log "offset approx ${ms}ms (threshold $MAX_OFFSET_MS)"
    if (( ms > MAX_OFFSET_MS )); then
      log "FAIL offset too high"
      exit 1
    fi
  fi
fi

log "OK"
exit 0

Scroll inside the box to read the full script.

Step 3: Configure settings

Guide: timedatectl
Logs and time: journalctl
VMs: sync after snapshot restore or vMotion

Shell script checking chrony time synchronization

Step 4: Test manually

./chrony-check.sh

MAX_OFFSET_MS=50 ./chrony-check.sh

Schedule with cron

sudo crontab -e

Add:

*/30 * * * * /usr/local/bin/chrony-check.sh >> /var/log/chrony-check.log 2>&1

chrony Time Sync Check Shell Script Linux (timedatectl, Alert)