Linux Networking, Process and Resource Management

sivasai papanisivasai papani
6 min read

Introduction

When your application says “connection refused”, do you know what to check?

In this guide, we’ll explore the essential Linux networking, Process and Resource Management tools every DevOps engineer should know.

Know Your IP Address and Interfaces:

Get your IP address

ip a

Look for something like:

inet 192.168.1.100/24

Check hostname

hostname

ping: Are We Even Connected?

Check if a server is reachable:

ping google.com

Press ctrl+c to exit

Stops after 4 packets

ping -c 4 google.com

Use IP to rule out DNS issues:

ping 8.8.8.8  //google ip

If IP works but domain fails, your DNS is broken.

curl: Talk to Web Services

Basic usage:

curl http://localhost:8080

#####Response#####

<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
<TITLE>301 Moved</TITLE></HEAD><BODY>
<H1>301 Moved</H1>
The document has moved
<A HREF="https://www.google.com/">here</A>.
</BODY></HTML>

Include headers:

curl -I  https://google.com

#####Response#####

HTTP/2 301 
location: https://www.google.com/
content-type: text/html; charset=UTF-8
content-security-policy-report-only: object-src 'none';base-uri 'self';script-src 'nonce-n3v5G1r1RqFCsv_MXvlk2A' 'strict-dynamic' 'report-sample' 'unsafe-eval' 'unsafe-inline' https: http:;report-uri https://csp.withgoogle.com/csp/gws/other-hp
date: Sun, 27 Jul 2025 17:16:53 GMT
expires: Tue, 26 Aug 2025 17:16:53 GMT
cache-control: public, max-age=2592000
server: gws
content-length: 220
x-xss-protection: 0
x-frame-options: SAMEORIGIN
alt-svc: h3=":443"; ma=2592000,h3-29=":443"; ma=2592000

DNS Tools:

Resolve a domain:

Gives A record, DNS server used, TTL, and more.

dig google.com

#####Response#####

; <<>> DiG 9.10.6 <<>> google.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34035
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;google.com.            IN    A

;; ANSWER SECTION:
google.com.        64    IN    A    172.217.169.14

;; Query time: 9 msec
;; SERVER: 2a0e:cb01:176:4100:7612:13ff:fe15:c780#53(2a0e:cb01:176:4100:7612:13ff:fe15:c780)
;; WHEN: Sun Jul 27 18:18:20 BST 2025
;; MSG SIZE  rcvd: 55

Firewalls:

Check if firewall is running

sudo ufw status

Allow a particular port:

sudo ufw allow 8080

Deny all incoming connections:

sudo ufw default deny incoming

Summary:

ToolPurpose
pingTest connectivity
curlInteract with web APIs and ports
digDNS lookup
ufwManage Linux firewalls

Process & Resource Monitoring

top – Real-time System Monitor

top

You’ll see something like this:

PID    COMMAND      %CPU TIME     #TH    #WQ  #PORT MEM    PURG  CMPRS  PGRP
10210  top          5.6  00:00.70 1/1    0    27    7824K  0B    0B     10210
488    WindowServer 2.2  01:53:35 22     6    2320  315M+  68M-  33M    488
0      kernel_task  1.5  67:00.20 646/10 0    0     10M    0B    0B     0
4874   Google Chrom 0.8  12:50.80 45     2    1285  195M+  32K   27M    4874
7084   Terminal     0.5  00:09.45 8      3    320-  101M+  51M-  5840K  7084
10152  Google Chrom 0.3  01:33.22 21     1    206   187M   944K  0B     487

Use this when a server is slow — find out which process is eating resources.

ps: Show Running Processes

ps

shows the running process

  PID TTY           TIME CMD
10168 ttys001    0:00.08 -zsh

free: Memory and Swap Usage

free -h

ooutput

              total  used   free  shared  buff/cache  available
Mem:           2.0G   1.4G   100M    50M      500M        300M
Swap:          1.0G   512M   488M

  • Used: What’s currently in use

  • Free: Really unused RAM

  • Available: What your system can still use

  • Swap: Virtual memory when RAM is full

  • If available RAM is low, your app may get killed (OOM error).

uptime: CPU Load Average

uptime

sample output:

18:31  up 20 days, 18:30, 2 users, load averages: 1.21 1.36 1.48

The last 3 numbers (1.21, 1.36, 1.48) are:

  • 1 minute

  • 5 minutes

  • 15 minutes load average

💡 Load average ≈ number of active processes.
If it’s > number of CPU cores, your system is under heavy load.

For a 4-core system, a load of 3.0 is OK, 6.0 = too high.

df – Disk Free Space

df -h

output:

Filesystem        Size    Used   Avail Capacity iused ifree %iused  Mounted on
/dev/disk3s1s1   926Gi    10Gi   861Gi     2%    426k  4.3G    0%   /
devfs            201Ki   201Ki     0Bi   100%     698     0  100%   /dev
/dev/disk3s6     926Gi    20Ki   861Gi     1%       0  9.0G    0%   /System/Volumes/VM
/dev/disk3s2     926Gi   6.7Gi   861Gi     1%    1.2k  9.0G    0%   /System/Volumes/Preboot

If / is 100%, your system may crash! Always monitor this.

du – Directory Space Usage

du -sh *

Shows size of all folders in current directory:


230M    Desktop
  0B    Documents
2.3G    Downloads
7.4G    Library
 12K    Movies
740K    Music
 68K    Personal-Portfolio
7.3M    Pictures
  0B    Public

It helps find what’s filling your disk.

Kill by PID

kill 1345

Kill a stubborn process

kill -9 1345

-9 is a force kill (SIGKILL)

Kill by name

killall nginx

Use responsibly. You can crash services if used blindly.

Mastering grep, |, and awk — DevOps Superpowers for Filtering and Processing Logs

As a DevOps engineer, you'll spend a lot of time staring at logs, shell outputs, and command results. But when you're looking at thousands of lines, how do you:

  • Find errors quickly?

  • Extract just what you need?

  • Automate log parsing?

That’s where the holy trio of Linux commands comes in:

  • grep → Find what you’re looking for

  • | (pipe) → Pass output from one command to another

  • awk → Extract and transform data

Let’s learn how to use them with simple, clear examples.

grep — Search Through Text

Think: “Give me lines that match this word.”

Basic usage:

grep "error" app.log

Finds all lines that contain the word error in the app.log file.

Real-world example:

grep "ERROR" /var/log/nginx/error.log

You’ll get:

[Sat Jul 27 13:00:42] ERROR: Connection refused
[Sat Jul 27 13:02:19] ERROR: Timeout reached

grep -i "error" app.log

Matches Error, ERROR, etc.

| (Pipe) — Combine Commands Like Lego Blocks

Think: “Send the output of one command to another.”

For example:

ps aux | grep nginx

Breakdown:

  • ps aux lists all processes

  • | sends that list to grep

  • grep nginx filters only lines with “nginx”

Example:

cat /var/log/syslog | grep "docker"

Or shorter:

grep "docker" /var/log/syslog

Piping is useful when the first command doesn’t support filtering directly.

awk — Extract Specific Columns

Think: “Print the 5th column from each line.”

Basic usage:

awk '{print $1}' file.txt

This prints the first column from each line.

Example: List users running processes

ps aux | awk '{print $1}'

What’s happening:

  • ps aux → list all processes

  • awk '{print $1}' → extract user column

Output:

root
ubuntu
nginx

Example: Show only IPs from access logs

cat access.log | awk '{print $1}' | sort | uniq -c

This gives you a count of unique IPs hitting your server.

DevOps Use Cases

Use CaseCommand
Find errors in logsgrep "error" app.log
List Nginx processes`ps aux
Count failed login attempts`grep "Failed password" /var/log/auth.log
Extract memory usage`free -m
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linux networking linux for beginners

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sivasai papani
sivasai papani