DevOps Command Reference Guide

Quick reference for DevOps commands

Claude and JonC 2026-02-24

Linux Commands

Navigation & File System

Command	Description	Example
`pwd`	Print working directory	`pwd`
`cd [path]`	Change directory	`cd /var/log`
`cd ..`	Go up one directory	`cd ..`
`cd ~`	Go to home directory	`cd ~`
`cd ~username`	Go to user's home directory	`cd ~devops_user`
`ls`	List files	`ls`
`ls -l`	List with details	`ls -l`
`ls -a`	List all (including hidden)	`ls -a`
`ls -la`	List all with details	`ls -la`
`ls -lah`	List all with human-readable sizes	`ls -lah`
`tree`	Display directory structure	`tree`

File & Directory Management

Command	Description	Example
`touch [file]`	Create empty file	`touch newfile.txt`
`mkdir [dir]`	Create directory	`mkdir newfolder`
`mkdir -p [path]`	Create nested directories	`mkdir -p folder/subfolder`
`cp [src] [dest]`	Copy file	`cp file1.txt file2.txt`
`cp [src]/* [dest]`	Copy all files (wildcard)	`cp folderA/* folderB/`
`mv [old] [new]`	Move/rename file	`mv oldname.txt newname.txt`
`rm [file]`	Remove file	`rm file1.txt`
`rm -d [dir]`	Remove empty directory	`rm -d emptyfolder`
`rm -rf [dir]`	Remove directory recursively (DANGEROUS)	`rm -rf oldfolder`
`cat [file]`	Display file contents	`cat /etc/passwd`

Text Editors

Command	Description	Example
`vi [file]`	Open file in vi editor	`vi config.txt`
`i`	Enter INSERT mode in vi	Press `i`
`:wq`	Save and quit vi	Type `:wq`
`:q!`	Quit without saving vi	Type `:q!`

User Management

Command	Description	Example
`sudo useradd [user] -c "Name"`	Add user with full name	`sudo useradd jenkins -c "Jenkins User"`
`sudo passwd [user]`	Set user password	`sudo passwd devops_user`
`sudo groupadd [group]`	Create group	`sudo groupadd developers`
`sudo usermod [user] -aG [group]`	Add user to group	`sudo usermod sarah -aG developers`

Permissions & Ownership

Command	Description	Example
`chmod [mode] [file]`	Change file permissions	`chmod 755 script.sh`
`chmod u=rwx [file]`	Set user permissions	`chmod u=rwx myfile`
`chmod g=rx [file]`	Set group permissions	`chmod g=rx myfile`
`chown [user] [file]`	Change file owner	`sudo chown devops_user myfile`
`chgrp [group] [file]`	Change file group	`sudo chgrp developers myfile`

Permission Octal Values

Permission	Octal	Binary	Description
`---`	0	000	No permissions
`--x`	1	001	Execute only
`-w-`	2	010	Write only
`-wx`	3	011	Write + Execute
`r--`	4	100	Read only
`r-x`	5	101	Read + Execute
`rw-`	6	110	Read + Write
`rwx`	7	111	Read + Write + Execute

Common Permission Examples:

755 = rwxr-xr-x (Owner: all, Group: r+x, Others: r+x)
750 = rwxr-x--- (Owner: all, Group: r+x, Others: none)
644 = rw-r--r-- (Owner: r+w, Group: read, Others: read)
600 = rw------- (Owner: r+w, Group: none, Others: none)

Networking

Command	Description	Example
`ifconfig`	Display network configuration	`ifconfig`
`ip addr`	Display IP addresses	`ip addr`
`ping [host]`	Test network connectivity	`ping google.com`
`curl [url]`	Download/transfer data	`curl https://example.com/file`
`wget [url]`	Download file	`wget https://example.com/file.txt`
`netstat`	Network statistics	`netstat`
`ss`	Socket statistics	`ss`

Package Management (Red Hat/CentOS)

Command	Description	Example
`sudo dnf update`	Update package list	`sudo dnf update`
`sudo dnf upgrade`	Upgrade installed packages	`sudo dnf upgrade`
`sudo dnf install [pkg]`	Install package	`sudo dnf install nginx`
`sudo dnf install -y [pkg]`	Install without prompts	`sudo dnf install -y tree`
`sudo yum install [pkg]`	Install (older systems)	`sudo yum install httpd`

Service Management (systemctl)

Command	Description	Example
`sudo systemctl enable [service]`	Enable service at boot	`sudo systemctl enable nginx`
`sudo systemctl start [service]`	Start service	`sudo systemctl start nginx`
`sudo systemctl stop [service]`	Stop service	`sudo systemctl stop nginx`
`sudo systemctl restart [service]`	Restart service	`sudo systemctl restart nginx`
`sudo systemctl status [service]`	Check service status	`sudo systemctl status nginx`

System Information

Command	Description	Example
`uname -a`	Display system information	`uname -a`
`df -h`	Display disk space (human-readable)	`df -h`
`top`	Display running processes	`top`
`ps`	Show processes	`ps aux`
`kill [pid]`	Kill process by ID	`kill 1234`
`sudo poweroff`	Shut down system	`sudo poweroff`

Git Commands

Initial Setup

Command	Description	Example
`git config --global user.name "Name"`	Set username	`git config --global user.name "John Doe"`
`git config --global user.email "email"`	Set email	`git config --global user.email "john@example.com"`

Repository Management

Command	Description	Example
`git init`	Initialize repository	`git init`
`git clone [url]`	Clone repository	`git clone git@github.com:user/repo.git`
`git remote add origin [url]`	Link remote repository	`git remote add origin git@github.com:user/repo.git`
`git remote -v`	View remote repositories	`git remote -v`

Basic Workflow

Command	Description	Example
`git status`	Check repository status	`git status`
`git add .`	Stage all changes	`git add .`
`git add [file]`	Stage specific file	`git add README.md`
`git commit -m "message"`	Commit changes	`git commit -m "Fixed bug"`
`git push`	Push to remote	`git push`
`git push origin [branch]`	Push specific branch	`git push origin main`
`git pull`	Pull from remote	`git pull`
`git pull origin [branch]`	Pull specific branch	`git pull origin main`
`git log`	View commit history	`git log`

Branching

Command	Description	Example
`git branch`	List branches	`git branch`
`git branch [name]`	Create branch	`git branch feature-login`
`git checkout [branch]`	Switch to branch	`git checkout feature-login`
`git checkout -b [branch]`	Create and switch to branch	`git checkout -b feature-login`
`git switch [branch]`	Switch to branch (newer)	`git switch feature-login`
`git merge [branch]`	Merge branch into current	`git merge feature-login`

Merge Conflicts

When conflicts occur:

Edit files to resolve conflicts (remove markers: <<<<<<<, =======, >>>>>>>)
git add [file] - Stage resolved file
git commit -m "Resolved merge conflict" - Complete merge

SSH Setup for GitHub

Command	Description	Example
`ssh-keygen -t rsa -b 4096 -C "email"`	Generate SSH key	`ssh-keygen -t rsa -b 4096 -C "user@example.com"`
`eval "$(ssh-agent -s)"`	Start SSH agent	`eval "$(ssh-agent -s)"`
`ssh-add ~/.ssh/id_rsa`	Add key to agent	`ssh-add ~/.ssh/id_rsa`
`cat ~/.ssh/id_rsa.pub`	Display public key	`cat ~/.ssh/id_rsa.pub`
`ssh -T git@github.com`	Test connection	`ssh -T git@github.com`

AWS Commands & Concepts

EC2 (Elastic Compute Cloud)

Task	Description	Details
Launch Instance	Create virtual server	Amazon Linux 2, t2.micro (free tier)
Key Pair	SSH authentication	Download .pem (Mac/Linux) or .ppk (Windows)
Connect via SSH	Access instance	`ssh -i keyfile.pem ec2-user@public-dns`
Default Username	EC2 login user	`ec2-user` (Amazon/RHEL), `ubuntu` (Ubuntu)
Security Groups	Virtual firewall	Configure inbound/outbound rules

Common EC2 Ports

Service	Port	Protocol
SSH	22	TCP
HTTP	80	TCP
HTTPS	443	TCP
ICMP (Ping)	N/A	All ICMP - IPv4

S3 (Simple Storage Service)

Task	Description	Steps
Create Bucket	Storage container	Unique name, select region
Upload Objects	Add files	Use Upload button
Public Access	Allow public viewing	Uncheck "Block Public Access" + Bucket Policy
Versioning	Keep file versions	Enable in Properties tab
Lifecycle Policies	Automate storage	Transition to Glacier (30 days), Delete (90 days)
Static Website	Host website	Enable in Properties, upload index.html

S3 Bucket Policy (Public Access)

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": "*",
      "Action": "s3:GetObject",
      "Resource": "arn:aws:s3:::BUCKET_NAME/*"
    }
  ]
}

IAM (Identity and Access Management)

Task	Description	Example
Create User	Add IAM user	Console access or Programmatic access
Attach Policy	Grant permissions	AmazonS3FullAccess, AmazonEC2FullAccess
Access Keys	API/CLI access	Access Key ID + Secret Access Key
Groups	Organize users	Create group, assign policies, add users

CloudWatch

Task	Description	Example
Monitor Metrics	View instance stats	CPU utilization, Network traffic
Create Alarm	Alert on thresholds	CPU > 70%
View Logs	Application logs	EC2 system logs

Security Groups

Task	Description	Example
Create Security Group	Define firewall rules	Allow SSH (22), HTTP (80)
Inbound Rules	Control incoming traffic	Source: 0.0.0.0/0 (anywhere) or specific IP
Outbound Rules	Control outgoing traffic	Usually allow all
Associate with Instance	Apply to EC2	Select during launch or modify later
IP Restrictions	Limit by IP	Source: Your IP only

AWS CLI Login (EC2)

# Connect to EC2 instance
ssh -i /path/to/keyfile.pem ec2-user@ec2-XX-XX-XX-XX.compute-1.amazonaws.com

# Or using PuTTY (Windows)
# Host: ec2-XX-XX-XX-XX.compute-1.amazonaws.com
# Username: ec2-user
# Private key: keyfile.ppk

Important Paths & Directories

Linux File System

Path	Description
`/`	Root of filesystem
`/root`	Root user home directory
`/home/username`	User home directory
`/etc`	Configuration files
`/var/log`	Log files
`/var/www/html`	Web server files (Apache)
`/bin`	Essential binaries
`/usr/bin`	User binaries
`/tmp`	Temporary files

Special Characters

Character	Meaning	Example
`/`	Root directory or path separator	`/home/user`
`~`	Home directory	`cd ~`
`.`	Current directory	`./script.sh`
`..`	Parent directory	`cd ..`
`*`	Wildcard (any characters)	`*.txt`

Quick Tips

The Three "Roots" in Linux

Root User - Administrator account
Root Filesystem - / at top of hierarchy
Root Home Folder - /root directory

Absolute vs Relative Paths

Absolute: Starts with / (e.g., /home/user/file.txt)
Relative: From current location (e.g., ../folder/file.txt)

Dangerous Commands

⚠️ NEVER RUN: sudo rm -rf / - Deletes entire system!

Git Workflow

Make changes
git add .
git commit -m "message"
git push origin branch-name

AWS Free Tier

EC2: t2.micro (750 hours/month)
S3: 5GB storage
Always verify free tier eligibility!