Linux is at the heart of modern software development, powering everything from servers and cloud infrastructure to local development environments. Whether you’re a DevOps engineer, system administrator, or software developer, mastering Linux commands can significantly improve your productivity and troubleshooting skills. In this blog, we’ll explore 10 essential Linux commands that every engineer should know.

1. Monitor System Performance

top & htop

Displays real-time system performance, including CPU and memory usage, running processes, and overall resource utilization.

Checking running processes and CPU usage

top

Output

👉 Use htop for a more user-friendly version with color-coded output.

2. Process Management

1. ps - Process Status

Lists all currently running processes along with their Process IDs (PIDs) and resource consumption.

Example: List all running processes

ps aux

Output

👉 Use ps aux | grep python to filter processes related to Python.

ps aux | grep python

2. pgrep - Find Process IDs

Searches for specific processes by name and retrieves their PIDs.

Find the PID of a running process

pgrep nginx

Output

2593
2594

👉 Use pgrep -l nginx to display both the PID and process name.

pgrep -l nginx

3. pstree - Process Hierarchy

Displays the hierarchical relationship between processes, showing which process triggered others.

View process tree for a specific process

pstree

Output

3. Network Connection Inspection

Shows active network connections, listening ports, and protocol usage, helping diagnose network-related issues.

netstat

List active TCP connections

netstat -tuln

Output

👉 Use netstat -ltn to check listening ports.

netstat -ltn

4. Capture & Analyze Network Traffic

tcpdump

Captures packets traveling through the network, helping identify latency issues and packet loss.

Capture HTTP packets

First, you need to find out the primary network interface.
To do this, run the command ifconfig.

In this case, it's - eth0

sudo tcpdump -i eth0 port 80

Output

And suppose you are trying to check port 80, then

sudo tcpdump -i eth0 port 80

👉 Use tcpdump -w capture.pcap to save packets for analysis.

5. Connectivity Troubleshooting

ping & traceroute

Ping a website

Tests network connectivity by sending packets to a remote host and measuring response time.

ping google.com -c 5

Output

Trace the route of a website

Shows the path packets take between your system and a target server, identifying network bottlenecks.

traceroute google.com

Output

6. Disk Space Analysis

df & du

Check disk space usage

df: Displays available and used disk space for each mounted file system.

df -h

Output

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       50G   30G   20G  60% /

To check disk space usage of a particular folder

du: Shows the space used by a specific directory or file, useful for pinpointing large storage consumers.

du -sh /var/log

Output

7. Memory Usage Inspection

free

Displays memory usage statistics, including total, used, and free RAM, helping manage resource allocation.

Check RAM usage

free -h

Output

              total        used        free      shared  buff/cache   available
Mem:           16G         8G         4G         1G         4G         7G
Swap:          2G         1G         1G

👉 Use watch free -h to continuously monitor RAM usage.

watch free -h

8. System Log Analysis

journalctl

Retrieves logs for services managed by systemd, allowing troubleshooting of crashes and errors.

View logs for a service

journalctl -u nginx

Output (Partial)

May 26 22:00:15 server nginx[2584]: Starting nginx service...
May 26 22:01:00 server systemd[1]: nginx.service: Main process exited, code=exited, status=1/FAILURE

👉 Use journalctl -b to all the logs.

journalctl -b

👉 Use journalctl -n 50 to fetch the last 50 logs.

journalctl -n 50

9. Identify Port & File Usage

lsof

Lists open files or identifies processes using specific ports, useful in resolving port conflicts.

Find processes using port 8080

lsof -i :8080

Output

COMMAND   PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
python3   1024  root   16u  IPv4 104857 0t0      TCP *:http-alt (LISTEN)

👉 Use lsof -p $(pgrep nginx) to check files opened by Nginx.

10. Log File Analysis

tail & head

View the last 10 lines of a log file

Displays the last few lines of a file, commonly used to monitor logs in real time.

tail -n 10 /var/log/nginx/error.log

Output

[error] 3456#3456: *12 directory index of "/var/www/html/" is forbidden, client: 192.168.1.12
[error] 3456#3456: *15 File not found: /var/www/html/favicon.ico

👉 Use tail -f /var/log/syslog to stream logs in real time.

tail -f /var/log/syslog

Viewing the first 10 lines of a file

Viewing the first 10 lines of a file

head -n 10 /var/log/syslog

Expected Output

May 28 04:00:01 server systemd[1]: Starting Daily Cleanup Service...
May 28 04:00:02 server kernel: [123456.789012] eth0: Link is Up - 1Gbps Full Duplex
May 28 04:00:03 server sshd[5678]: Accepted password for user from 192.168.1.10 port 54321 ssh2
May 28 04:00:04 server systemd[1]: Started Apache Web Server.
May 28 04:00:05 server apache2[6789]: [notice] Apache/2.4.41 (Ubuntu) started successfully.
May 28 04:00:06 server systemd[1]: Started MySQL Database Server.
May 28 04:00:07 server mysqld[7890]: [info] MySQL server ready for connections.
May 28 04:00:08 server systemd[1]: Finished Daily Cleanup Service.
May 28 04:00:09 server systemd[1]: Running scheduled tasks...
May 28 04:00:10 server systemd[1]: System maintenance completed.

👉 Use head -n 20 /var/log/syslog to view the first 20 lines instead.

Bonus 1: Linux Shortcut

Reverse search (Ctrl + R)

Quickly retrieve past commands

Press the right arrow key to select the command.

Bonus 2: Customizing terminal prompt

Modify your shell prompt.

export PS1="Hey There $ "

Conclusion

These Linux commands are indispensable for software engineers working with servers, applications, and troubleshooting environments. Mastering them ensures better system performance, quicker issue resolution, and efficient resource management.