check_ntp_sync

check_ntp_sync

Monitoring plugin to verify local NTP synchronization on any server.

Compatible with Nagios/NRPE/MRPE and CheckMK local check.

What it checks

• NTP offset from the reference clock
• Stratum level
• Leap status (chrony)
• Synchronization state

Detection chain

The script tries multiple NTP clients in order, using the first one that works:

1. chronyc tracking — offset, stratum, leap status, source
2. ntpq -c peers — offset and stratum from the active peer (*)
3. timedatectl show — systemd-timesyncd synchronization state
4. ntpdate -q — query-only (does not modify the clock), last resort

If none are available → UNKNOWN.

Requirements

• Bash (no external dependencies beyond standard coreutils + awk)
• At least one NTP client: chrony, ntpd, systemd-timesyncd, or ntpdate

Quick install (one-liner)

CheckMK local check (900s cache)

sudo mkdir -p /usr/lib/check_mk_agent/local/900 && sudo curl -fsSL https://raw.githubusercontent.com/rdemsystems/prod-tools/main/monitoring/check_ntp_sync/check_ntp_sync -o /usr/lib/check_mk_agent/local/900/check_ntp_sync && sudo chmod +x /usr/lib/check_mk_agent/local/900/check_ntp_sync

Nagios / NRPE

sudo curl -fsSL https://raw.githubusercontent.com/rdemsystems/prod-tools/main/monitoring/check_ntp_sync/check_ntp_sync -o /usr/lib/nagios/plugins/check_ntp_sync && sudo chmod +x /usr/lib/nagios/plugins/check_ntp_sync

Installation (from clone)

git clone https://github.com/rdemsystems/prod-tools.git
sudo prod-tools/monitoring/check_ntp_sync/install.sh

The install script auto-detects CheckMK or Nagios and copies to the right location.

MRPE

Add to /etc/check_mk/mrpe.cfg:

NTP_Sync /path/to/check_ntp_sync -w 50 -c 200

Usage

check_ntp_sync [OPTIONS]

Options:
  -w, --warning <ms>     Offset warning threshold in ms (default: 50)
  -c, --critical <ms>    Offset critical threshold in ms (default: 200)
  -s, --ntp-server <srv> NTP server for fallback query (default: pool.ntp.org)
  --checkmk              Force CheckMK output
  --nagios               Force Nagios output
  -v, --verbose          Show details
  -h, --help             Show help

Output examples

Nagios (default)

OK - NTP offset 2.3ms (source: pool.ntp.org, stratum 2) | ntp_offset=0.002300s;0.050000;0.200000 stratum=2

CheckMK

P "NTP Sync" ntp_offset=0.002300;0.050000;0.200000 stratum=2 OK - NTP offset 2.3ms (source: pool.ntp.org, stratum 2)

Alert conditions

Condition	WARNING	CRITICAL
NTP offset	> 50ms (default)	> 200ms (default)
Chrony leap status != Normal	WARNING	—
Stratum > 10	WARNING	> 15
No NTP client detected	—	UNKNOWN

License

MIT