Essential Linux Monitoring Tools Every Sysadmin Should Know

System Monitoring Tools

nmon

nmon outputs data to the screen or to a CSV file, allowing you to view CPU, memory, network, filesystem, and top processes. Data can also be added to an RRD database for further analysis.

Conky

Conky monitors a wide range of operating‑system data, supports IMAP/POP3 and many popular music players, and can be extended with Lua scripts or custom programs.

Glances

Glances presents the maximum amount of information using minimal resources, works in client/server mode, supports remote monitoring and provides a web interface.

Saidar

Saidar is a tiny tool that shows basic system‑resource information in full‑screen mode, focusing on simplicity.

RRDtool

RRDtool processes RRD databases, handling time‑series data such as CPU load or temperature, and can generate graphical reports.

monit

monit sends alerts and can restart services on failure, checks various data sources, and offers a web UI for easier monitoring.

Linux Process Explorer

Linux Process Explorer resembles the OSX/Windows Activity Monitor, providing a broader view than top/ps and showing per‑process memory and CPU usage.

df

df (disk free) is a standard UNIX utility that displays available disk space for mounted filesystems.

discus

discus improves upon df by adding colors, graphics and numeric highlights.

xosview

xosview is a classic system monitor that provides a simple overview of various components, including IRQ.

Dstat

Dstat replaces vmstat, iostat, netstat and ifstat, showing real‑time system resources, exporting CSV, and supporting plugins for extended functionality.

Net‑SNMP

Net‑SNMP is a suite that uses the Simple Network Management Protocol to collect accurate server information.

incron

incron watches a directory tree and can trigger actions on changes, e.g., copying new files from directory a to directory b.

monitorix

monitorix is a lightweight system monitor that tracks a single machine, provides many metrics, and includes a built‑in HTTP server for charts and reports.

vmstat

vmstat (virtual memory statistics) is a small built‑in tool that displays memory usage and other system stats.

uptime

uptime quickly shows how long the system has been running, the number of logged‑in users, and the 1‑, 5‑, and 15‑minute load averages.

mpstat

mpstat monitors CPU usage. Example: mpstat -P ALL reports per‑CPU statistics and can be run periodically.

pmap

pmap reports a process's memory map, helping identify memory bottlenecks.

ps

ps provides an overview of all current processes; use ps -A to list every process.

sar

sar, part of the sysstat package, collects, reports and stores various system metrics such as CPU, memory and I/O usage.

collectl

collectl, similar to sar, gathers performance metrics with sub‑second resolution and can feed graphing tools; it offers broader monitoring than sar.

iostat

iostat (also part of sysstat) monitors I/O performance, providing data useful for system tuning.

free

free displays total and used memory, as well as kernel buffers, for the current system.

/proc filesystem

The /proc filesystem exposes kernel statistics, allowing detailed inspection of hardware and system state.

GKrellm

GKrellm is a graphical application that monitors hardware status (CPU, memory, disks, network) and can also watch selected mail readers.

Gnome System Monitor

The Gnome System Monitor shows process dependencies in a tree, lets you kill or renice processes, and displays metrics in chart form.

Log Monitoring Tools

GoAccess

GoAccess is a real‑time web‑log analyzer for Apache, Nginx and CloudFront, outputting HTML, JSON or CSV with basic statistics, request counts, 404 pages, visitor locations, etc.

Logwatch

Logwatch parses system logs and generates daily reports for selected sections, reducing the time needed for log analysis.

Swatch

Swatch monitors logs, matches user‑defined regular expressions, and sends notifications via email or console, useful for intrusion detection.

MultiTail

MultiTail lets you view multiple log files in a single window, merging them and applying color highlighting through regular expressions.

Infrastructure Monitoring Tools

Server Density

Server Density offers a web UI for alerts, charting of network metrics, website monitoring, user permissions, and supports Nagios plugins.

OpenNMS

OpenNMS provides event management, discovery, service monitoring and data collection, customizable for various network environments.

SysUsage

SysUsage continuously monitors the system using sar and other commands, provides alerts on thresholds, stores statistics, and offers a web UI for viewing data.

brainypdm

brainypdm is a cross‑platform data‑management and monitoring tool that collects data from Nagios and other sources, displaying it in customizable web charts.

PCP

PCP efficiently gathers metrics from many hosts, offers a plugin framework, and provides web or GUI access to graphs, suitable for large‑scale monitoring.

KDE System Guard

KDE System Guard combines system monitoring and task management, allowing you to view services across machines, kill or start processes from a unified interface.

Munin

Munin monitors networks and systems, alerts on threshold breaches, uses RRDtool for graphs, and provides a web UI with many plugins.

Nagios

Nagios is a system and network monitor that tracks multiple servers, offers alerting and a rich plugin ecosystem.

Zenoss

Zenoss provides a web UI for monitoring all system and network metrics, auto‑discovers resources, modifies configurations, and supports Nagios plugins.

Cacti

Cacti is a network‑graphing solution that uses RRDtool for data storage, polls services at intervals, and can be extended with shell scripts.

Zabbix

Zabbix is an open‑source infrastructure monitoring solution that stores statistics in databases, has a C core, PHP front‑end, and optional agents; it is a strong alternative when you prefer not to install agents.

PS: If you have additional suggestions, feel free to leave a comment.