---
title: 'Linux Commands Every IT Professional Should Know Cold'
url: 'http://itlad.uk/blog/linux-commands-every-it-pro-needs'
markdown: 'http://itlad.uk/blog/linux-commands-every-it-pro-needs.md'
date: '2026-05-31'
description: 'Essential Linux commands every IT professional should know — networking, process management, disk analysis, log reading and the one-liners that save time.'
taxonomy:
  category:
    - tools
  tag:
    - linux
    - sysadmin
    - commands
    - terminal
    - shell
---

[ Home ](http://itlad.uk/)     [ Blog ](http://itlad.uk/blog)      Linux Commands Every IT Professional Should Know Cold    

# [Linux Commands Every IT Professional Should Know Cold](http://itlad.uk/blog/linux-commands-every-it-pro-needs)

 By [IT Lad](http://itlad.uk/about) 31 May 2026 

  [linux](http://itlad.uk/blog/tag:linux#body-wrapper) [sysadmin](http://itlad.uk/blog/tag:sysadmin#body-wrapper) [commands](http://itlad.uk/blog/tag:commands#body-wrapper) [terminal](http://itlad.uk/blog/tag:terminal#body-wrapper) [shell](http://itlad.uk/blog/tag:shell#body-wrapper)  

Not a beginner list. These are the commands that come up in real incidents, slow system diagnosis and network troubleshooting.

## Networking

```bash
ss -tulpn
```

Shows all listening TCP/UDP sockets with the process name and PID. Faster than `netstat`, same output. Run this first when you're looking for what's actually bound to a port.

```bash
ip route show
```

Prints the routing table. Add `ip route get 8.8.8.8` to see which interface and gateway handle a specific destination.

```bash
tcpdump -i eth0 port 443 -n
```

Capture HTTPS traffic on eth0. Add `-w /tmp/capture.pcap` to write to a file for Wireshark analysis. Replace `eth0` with `any` to capture across all interfaces.

## Process and Resource Management

```bash
ps aux --sort=-%cpu | head -10
```

Top 10 processes by CPU usage, with full command lines. More useful than `top` for scripting.

```bash
lsof -p PID
```

Lists every file, socket and device a specific process has open. Useful for finding what a runaway process is doing.

```bash
systemd-cgls
```

Shows the full cgroup tree — which systemd units are running and what processes they contain.

## Disk and Filesystem

```bash
du -sh /var/log/* | sort -rh | head -20
```

Top 20 largest items in `/var/log` by human-readable size. Swap the path to find what's eating space anywhere.

```bash
df -hT
```

Disk usage with filesystem type. The `-T` flag catches when something is mounted as tmpfs that shouldn't be.

```bash
lsblk -o NAME,SIZE,TYPE,MOUNTPOINT,FSTYPE
```

Block device tree with size, type and where each partition is mounted. Cleaner than `fdisk -l` for a quick overview.

## Log Analysis

```bash
journalctl -u nginx.service --since "1 hour ago" -f
```

Follow logs for a specific systemd service. Replace `nginx` with any unit name. Add `--no-pager` to pipe into grep.

```bash
grep -i "error\|fail\|crit" /var/log/syslog | tail -50
```

Pull the last 50 lines containing error-level keywords. Add `| sort | uniq -c | sort -rn` to count and rank recurring errors.

## One-Liners Worth Memorising

```bash
# Find files modified in the last 24 hours
find /etc -mtime -1 -type f

# Check which process is using a port
fuser 8080/tcp

# Watch a command output refresh every 2 seconds
watch -n2 'ss -tulpn | grep LISTEN'

# Count open file descriptors per process
lsof | awk '{print $1}' | sort | uniq -c | sort -rn | head -10
```

## The Terminal Setup That Makes All This Faster

A good terminal emulator and shell config saves more time than memorising commands. I use [tmux](https://www.amazon.com/s?k=tmux%2Blinux%2Bterminal%2Bmultiplexer%2Bbook&tag=itlad-21) for persistent sessions, `zsh` with Oh My Zsh, and `fzf` for history search. If you're still pressing the up arrow to find commands, `fzf` will change your workflow.

---

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