How to Monitor System Resources on Linux

Monitoring Resources on Linux

Knowing how to check what your system is doing is a fundamental Linux skill. Whether your machine is running slow, a process is eating RAM, or your disk is filling up, these tools give you the answers in seconds.

top — Real-Time Process Monitor

top is available on every Linux system and shows a live list of running processes sorted by CPU usage:

top

Key columns: %CPU (processor usage), %MEM (memory), RES (actual RAM used). Press q to quit, k to kill a process by PID, M to sort by memory.

htop — The User-Friendly Alternative

htop is a more visual, color-coded version of top with mouse support. Install it first:

sudo apt install htop   # Ubuntu/Debian
sudo dnf install htop   # Fedora

Then run htop. You get per-CPU bars, a memory bar, tree view of processes, and function key shortcuts at the bottom. Press F9 to kill a selected process.

free — Check Memory Usage

See total, used, and available RAM at a glance:

free -h

Sample output:

              total        used        free      shared  buff/cache   available
Mem:           15Gi        4.2Gi       8.1Gi       512Mi       3.1Gi       10.8Gi
Swap:         2.0Gi          0B       2.0Gi

The available column is the most important — it shows how much RAM new processes can actually use.

df — Check Disk Space

df -h

Shows how full each mounted filesystem is. Watch for any partition above 85% usage — that is your warning sign.

iostat and vmstat — Deeper Diagnostics

For disk I/O and CPU/memory stats over time:

# Install sysstat first
sudo apt install sysstat

# Disk read/write rates, 1-second intervals
iostat -x 1

# CPU, memory, swap activity
vmstat 1

Checking Network Usage

# Bandwidth per interface
ip -s link

# Live network monitor (install nethogs)
sudo apt install nethogs
sudo nethogs

Quick Reference

• top / htop — CPU and process overview
• free -h — RAM and swap usage
• df -h — disk space by filesystem
• iostat -x 1 — disk I/O rates
• sudo nethogs — network usage per process

Start with htop for a quick health check — it is the most informative single command for everyday Linux monitoring.