CheckMK

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tags:

• monitoring
• sysadmin

• linux

  Checkmk Server Sysadmin Cheatsheet

Checkmk is a comprehensive IT monitoring solution originally developed by Mathias Kettner in 2008 as an extension to Nagios. It has since evolved into a standalone monitoring platform available in two editions: Raw (open-source, Nagios core) and Enterprise/Cloud (commercial, proprietary CMC core). Checkmk provides auto-discovery, agent-based and agentless monitoring, alerting, graphing, and dashboards.

Common use cases / Типичные сценарии: Infrastructure monitoring (servers, network, cloud), application monitoring, SNMP-based device monitoring, log monitoring, service-level monitoring (SLA), auto-discovery of services.

Status / Статус: Actively developed and widely used in enterprise environments. Checkmk is a modern evolution of the Nagios ecosystem. Alternatives include Zabbix (full-featured open-source), Prometheus + Grafana (cloud-native, metrics-focused), Datadog (SaaS), VictoriaMetrics (TSDB), Icinga (Nagios fork).

Default ports / Порты по умолчанию: 80/443 (Web UI), 6556/tcp (Agent), 5000/tcp (Site Apache), 8000/tcp (Agent Controller registration)

📚 Table of Contents

• 1. Installation & Configuration
• 2. OMD Site Management
• 3. Core Management
• 4. Sysadmin Operations
• 5. Security
• 6. Backup & Restore
• 7. Troubleshooting & Tools
• 8. Logrotate Configuration
• Documentation Links

1. Installation & Configuration

Install Checkmk Server

[!TIP] Download the correct edition and OS version from the official site: https://checkmk.com/download / Скачайте нужную редакцию и версию ОС с официального сайта.

# RHEL/AlmaLinux 9 (Raw Edition)
wget "https://download.checkmk.com/checkmk/2.3.0/check-mk-raw-2.3.0-el9-38.x86_64.rpm"
dnf install check-mk-raw-*.rpm

# Debian/Ubuntu (Raw Edition)
wget "https://download.checkmk.com/checkmk/2.3.0/check-mk-raw-2.3.0_0.bookworm_amd64.deb"
dpkg -i check-mk-raw-*.deb
apt -f install  # Fix dependencies / Установить зависимости

Install Checkmk Agent

Download from your Checkmk site URL: http://<HOST>/<SITE>/check_mk/agents/

# RPM (RHEL/AlmaLinux)
rpm -Uvh check-mk-agent-*.noarch.rpm

# DEB (Debian/Ubuntu)
dpkg -i check-mk-agent_*.deb

Editions Comparison

2. OMD Site Management

Checkmk uses OMD (Open Monitoring Distribution) to manage monitoring "sites" (instances). Each site is an isolated environment with its own configuration, users, and data. / Checkmk использует OMD для управления «сайтами» (инстансами) мониторинга.

Create & Manage Sites

# List all sites
omd sites

# Create new site
omd create <SITE_NAME>

# Start/Stop site
omd start <SITE_NAME>
omd stop <SITE_NAME>

# Restart site
omd restart <SITE_NAME>

# Site status
omd status <SITE_NAME>

# Configure site interactively
omd config <SITE_NAME>

# Update site to new version
omd update <SITE_NAME>

Switch to Site User

All cmk commands must be run as the site user. / Все команды cmk запускаются от пользователя сайта.

su - <SITE_NAME>

Important OMD Paths

3. Core Management

Checkmk CLI (cmk) / CLI Checkmk

All commands below are run as site user (su - <SITE_NAME>). / Все команды ниже запускаются от пользователя сайта.

# Service discovery (inventory)
cmk -I <HOST>              # Discover new services / Обнаружить новые сервисы
cmk -II <HOST>             # Full re-discovery / Полное переобнаружение
cmk --detect-plugins <HOST>  # Detect available plugins / Определить доступные плагины

# Activate changes
cmk -R                    # Reload configuration / Перезагрузить конфигурацию
cmk -O                    # Restart core / Перезапустить ядро
cmk -G                    # Generate config only (no reload) / Только сгенерировать конфиг

# Debugging
cmk -v <HOST>             # Verbose check / Подробная проверка
cmk --debug -vvn <HOST>   # Detailed debug check / Детальная отладка
cmk -D <HOST>             # Show host info / Показать информацию о хосте

# Agent output
cmk -d <HOST>             # Fetch raw agent output / Получить сырой вывод агента

Web UI Access

# Default URL / URL
http://<HOST>/<SITE>/check_mk/
# Default credentials: cmkadmin / <PASSWORD_SET_AT_CREATION>

Local Checks

Place executable scripts in /usr/lib/check_mk_agent/local/ on monitored hosts. / Поместите исполняемые скрипты в эту папку на контролируемых хостах.

Output format: <STATUS> <SERVICE_NAME> <PERF_DATA> <TEXT_OUTPUT> Status codes: 0 (OK), 1 (WARN), 2 (CRIT), 3 (UNKNOWN)

#!/bin/bash
# Example local check
echo "0 MyService count=42 OK - Service is running fine"

# Set executable permission
chmod +x /usr/lib/check_mk_agent/local/myscript

4. Sysadmin Operations

Service Management

# Manage via OMD (preferred)
omd start <SITE_NAME>       # Start all site services / Запустить все сервисы сайта
omd stop <SITE_NAME>        # Stop all site services / Остановить все сервисы
omd restart <SITE_NAME>     # Restart all site services / Перезапустить все сервисы
omd status <SITE_NAME>      # Check status / Проверить статус

# Or via systemd (starts all sites)
systemctl start apache2     # Start web server / Запустить веб-сервер
systemctl status apache2    # Check web server status / Статус веб-сервера

Log Locations

Logs are stored in the site's ~/var/log/ directory. / Логи хранятся в каталоге ~/var/log/ сайта.

# View logs as site user
su - <SITE_NAME>
tail -f var/log/cmc.log       # Enterprise core log / Лог ядра Enterprise
tail -f var/log/nagios.log    # Raw core log / Лог ядра Raw
tail -f var/log/web.log       # Web UI log / Лог веб-интерфейса

Firewall Configuration

# Allow web UI
firewall-cmd --permanent --add-service=http
firewall-cmd --permanent --add-service=https

# Allow agent port
firewall-cmd --permanent --add-port=6556/tcp

# Distributed monitoring (Livestatus)
firewall-cmd --permanent --add-port=6557/tcp
firewall-cmd --reload

5. Security

User Management

# Reset cmkadmin password
su - <SITE_NAME>
cmk-passwd cmkadmin

# Or via htpasswd (for Nagios core)
htpasswd ~/etc/htpasswd cmkadmin

LDAP Integration

Configure via Web UI: Setup → Users → LDAP & Active Directory

Agent Encryption

[!TIP] In Checkmk 2.2+, use the built-in Agent Controller with TLS for encrypted agent communication. This is the preferred method over legacy symmetric encryption. / В Checkmk 2.2+ используйте Agent Controller с TLS.

6. Backup & Restore

OMD Backup

# Backup site to file
omd backup <SITE_NAME> /backup/checkmk_<SITE_NAME>_$(date +%F).tar.gz

# Restore site from backup
omd restore <SITE_NAME> /backup/checkmk_<SITE_NAME>.tar.gz

[!WARNING] omd backup stops the site during backup. Schedule during maintenance windows. / omd backup останавливает сайт на время бэкапа. Планируйте на время обслуживания.

Manual Config Backup

# Backup configuration only
su - <SITE_NAME>
tar -czf /backup/checkmk_config_$(date +%F).tar.gz etc/check_mk/ etc/nagios/ etc/htpasswd

7. Troubleshooting & Tools

Common Issues

1. "Checkmk server is not running" in Web UI / "Checkmk

# Check site status
omd status <SITE_NAME>

# Check SELinux (RHEL)
getenforce
setsebool -P httpd_can_network_connect 1  # Allow Apache to connect / Разрешить Apache подключения

2. Agent Not Reachable

# Test agent from server
su - <SITE_NAME>
cmk -d <HOST>               # Fetch agent output / Получить вывод агента
cmk --debug -vvn <HOST>     # Detailed debug / Подробная отладка

# Test from network
nc -w 5 <HOST> 6556 | head -20

3. Performance Issues

# Check helper usage (Enterprise)
su - <SITE_NAME>
cmk --check-helper-usage

# Increase checkers in global settings
# Setup → General → Global Settings → Monitoring Core → Number of checker helpers

Debugging

# Enable debug logging temporarily
su - <SITE_NAME>

# Verbose check of specific host
cmk --debug -vvn <HOST>

# Check core status
omd status

8. Logrotate Configuration

[!NOTE] Checkmk/OMD manages log rotation internally via the site framework. Logs are rotated automatically in the OMD site's ~/var/log/ directory. Checkmk/OMD управляет ротацией логов внутренне через фреймворк сайта. Логи ротируются автоматически.

No external logrotate configuration is typically needed for Checkmk. / Внешняя конфигурация logrotate для Checkmk обычно не требуется.

Documentation Links

• Official Documentation: https://docs.checkmk.com/
• Checkmk Downloads: https://checkmk.com/download
• Checkmk User Guide: https://docs.checkmk.com/latest/en/
• Agent Installation: https://docs.checkmk.com/latest/en/agent_linux.html
• Checkmk REST API: https://docs.checkmk.com/latest/en/rest_api.html
• Community Forum: https://forum.checkmk.com/
• GitHub (Raw Edition): https://github.com/Checkmk/checkmk