Guides

Linux Commands Every DevOps Engineer Uses Daily

By Ravindra Bagale, DevOps trainer · LinkedIn · Published: 28 October 2026 · Last updated: 28 October 2026

These Linux commands are the daily language of DevOps on Amazon Linux and Ubuntu. Learn names with sample output — the way Infosys, TCS and product on-call teams triage.

Language: English · मराठी · हिंदी

Why these commands matter every day

When Flipkart sale traffic or an Infosys client portal is slow, seniors do not open a textbook. They run disk, process, port and log checks.

Why: Fast triage saves MTTR. What: A short daily set with sample output. How: Practice on your own VM. Read every column.

Concept 1: Disk and memory

Why: Full disks kill apps silently. What: df, du, free, df -i. How: Check / and /var first.

Example 1: Disk free

Type this:

df -h /

You will see:

Filesystem      Size  Used Avail Use% Mounted on
/dev/nvme0n1p1   8.0G  3.1G  4.9G  39% /

What it means: Root at 39 percent. Above 90 percent needs cleanup.

Example 2: Biggest dirs

Type this:

du -h -d1 /var 2>/dev/null | sort -h | tail -3

You will see:

1.2G    /var/log
2.0G    /var/lib
3.4G    /var

What it means: /var/log often fills first on app servers.

Example 3: Inode check

Type this:

df -i / | tail -1

You will see:

/dev/nvme0n1p1  524288  81234  443054  16% /

What it means: Inode exhaustion can block creates even when bytes remain.

Concept 2: Processes and load

Why: One runaway process can starve the box. What: ps, top, uptime. How: Sort by CPU; know load averages.

Example 4: Top CPU snapshot

Type this:

ps aux --sort=-%cpu | head -n 4

You will see:

USER PID %CPU %MEM COMMAND
root 1 0.0 0.2 systemd
...

What it means: Read the COMMAND column in outages.

Example 5: Memory free

Type this:

free -h

You will see:

total used free
Mem: 3.7Gi 1.2Gi 1.1Gi

What it means: Watch available, not only free.

Example 6: Load average

Type this:

uptime

You will see:

14:02:11 up 3 days,  2 users,  load average: 0.15, 0.10, 0.05

What it means: Three numbers: 1, 5, 15 minute averages.

Concept 3: Ports and HTTP

Why: Wrong bind address wastes hours. What: ss, curl, scp pattern. How: Confirm listen ports before restart wars.

Example 7: Listen ports

Type this:

ss -tulpn | head -n 5

You will see:

Netid State Local Address:Port
tcp LISTEN 0.0.0.0:22
tcp LISTEN 0.0.0.0:80

What it means: See who owns port 80 before nginx fights.

Example 8: HTTP check

Type this:

curl -s -o /dev/null -w "%{http_code}\n" https://example.com/

You will see:

200

What it means: 200 means the edge answered. Not a full app health check.

Example 9: Copy with scp mind-set

Type this:

printf '%s\n' 'scp report.txt ec2-user@10.0.0.5:/home/ec2-user/'

You will see:

scp report.txt ec2-user@10.0.0.5:/home/ec2-user/

What it means: Use keys; never paste passwords into scripts.

Concept 4: Services and journals

Why: systemctl is the control plane for services. What: is-active, status, journalctl -u. How: Always read logs before a blind restart.

Example 10: Service active?

Type this:

systemctl is-active sshd || systemctl is-active ssh

You will see:

active

What it means: active means accepting connections.

Example 11: Recent journal

Type this:

journalctl -u sshd -n 3 --no-pager 2>/dev/null || journalctl -u ssh -n 3 --no-pager

You will see:

-- Logs begin --
... Started OpenSSH ...

What it means: journalctl is the first log stop on systemd hosts.

Example 12: Follow pattern

Type this:

printf '%s\n' 'ss -> process -> journalctl -> restart'

You will see:

ss -> process -> journalctl -> restart

What it means: Daily outage order at Infosys-style accounts.

Pocket order

1. df -h /
2. free -h
3. ss -tulpn
4. systemctl status NAME
5. journalctl -u NAME -n 50

Suppose: Pune colocated app server

Disk full at 2 a.m. du finds /var/log. Clean, then add logrotate.

Suppose: London SaaS API

ss shows nothing on 443. Fix the listen address, not the code first.

Check yourself (quiz)

Daily path: disk → process → ports → logs. Practice output, not only names. Did you understand? Let us try it once more.