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Check dns

Overview

Performs a DNS lookup and resolves a hostname to one or more IP addresses. Queries the name servers configured on the local machine (e.g. those listed in /etc/resolv.conf). Measures and alerts on the lookup response time. Works with both IPv4 and IPv6.

Data Collection:

  • Uses Python's socket.getaddrinfo() to perform DNS resolution
  • Only the name servers configured on the machine running this check are queried - you cannot query other DNS servers
  • When no arguments are given, the check tries to resolve localhost on port 53, and the full range of results for any available protocol is returned
  • The connection type can be narrowed down using --type (udp, udp6, tcp, tcp6)

Fact Sheet

Fact Value
Check Plugin Download https://github.com/Linuxfabrik/monitoring-plugins/tree/main/check-plugins/dns
Nagios/Icinga Check Name check_dns
Check Interval Recommendation Every 15 minutes
Can be called without parameters Yes
Runs on Cross-platform
Compiled for Windows Yes

Help

usage: dns [-h] [-V] [--always-ok] [-c CRIT] [-H HOSTNAME] [-p PORT]
           [--type {udp,udp6,tcp,tcp6}] [-w WARN]

Performs a DNS lookup and resolves a hostname to one or more IP addresses.
Queries the name servers configured on the local machine (e.g. those listed in
/etc/resolv.conf). Measures and alerts on the lookup response time. Works with
both IPv4 and IPv6.

options:
  -h, --help            show this help message and exit
  -V, --version         show program's version number and exit
  --always-ok           Always returns OK.
  -c, --critical CRIT   CRIT threshold for DNS lookup time in milliseconds.
                        Default: None
  -H, --hostname HOSTNAME
                        Hostname or IP address to resolve. Default: localhost
  -p, --port PORT       Port number to query. Default: 53
  --type {udp,udp6,tcp,tcp6}
                        Connection type to narrow the list of returned
                        addresses.
  -w, --warning WARN    WARN threshold for DNS lookup time in milliseconds.
                        Default: None

Usage Examples

./dns --hostname $(hostname)
./dns --hostname www.example.org --type udp --port 53 --warning 1000 --critical 5000

Output:

Lookup for webserver.linuxfabrik.ch returns 192.168.26.43 (tcp4:53), 192.168.26.43 (udp4:53), 192.168.26.43 (ip4:53)

States

  • OK if the hostname resolves successfully and the lookup time is below the thresholds.
  • WARN on socket errors, address-related errors, or network timeouts.
  • WARN if the DNS lookup time is >= --warning.
  • CRIT if the DNS lookup time is >= --critical.
  • --always-ok suppresses all alerts and always returns OK.

Perfdata / Metrics

Name Type Description
time Seconds DNS lookup time in milliseconds.

Credits, License