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Hey there! I'm currently working as an Associate DevOps Engineer, and I'm diving into popular DevOps tools like Azure Devops,Linux, Docker, Kubernetes,Terraform and Ansible. I'm also on the learning track with AWS certifications to amp up my cloud game. If you're into tech collaborations and exploring new horizons, let's connect!
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DevOps Journey with M Hassan
174 posts
I am writing these blogs because I recently completed a comprehensive DevOps course where I gained in-depth knowledge of the topics mentioned. As I progressed through the course, I realized the importance of having a concise and accessible resource to revise and reinforce my understanding of each topic. Therefore, I decided to create cheat sheets in the form of blog posts. These cheat sheets will not only serve as a handy reference for myself but also benefit others who are also interested in mastering DevOps concepts. By documenting each topic and providing concise explanations, I aim to create a valuable resource that simplifies complex concepts and facilitates hands-on practice. This way, I can solidify my own understanding while helping others on their DevOps journey.
On this page
RHCSA stands for Red Hat Certified System Administrator.
Industry-recognized Linux certification
Required for Linux system administration jobs
Builds strong foundation in:
Linux OS
Users & permissions
Filesystems
Networking
Services & processes
Useful for DevOps, SysAdmin, Cloud, and Server roles
We do not install Linux directly on our main system. Instead, we use Virtualization.
We use VMware (or VirtualBox)
A VM allows us to run an OS inside another OS
Example:
Host OS: Windows
Guest OS: RHEL / CentOS / Rocky Linux
Install VMware
Create a new Virtual Machine
Attach Linux ISO file
Allocate:
RAM
CPU
Disk
Install Linux OS inside VM
✅ This method is safe and widely used for learning and testing
/Linux has a single root directory /. Everything starts from here.
| Directory | Purpose |
/ | Root of the filesystem |
/root | Home directory of root user |
/home | Home directories of normal users |
/bin | Essential user commands (ls, cp, mv) |
/sbin | System/admin commands |
/etc | Configuration files |
/var | Logs, mail, variable data |
/tmp | Temporary files |
/boot | Bootloader & kernel files |
whoami
➡ Shows current logged-in user
ls
➡ Lists files and directories
cd
➡ Changes directory
Examples:
cd /etc
cd ..
cd ~
Example:
hassan@server1:/home/hassan$
| Part | Meaning |
hassan | Username |
server1 | Hostname |
/home/hassan | Current directory |
$ | Normal user |
# | Root user |
✅ Correction:
$ → normal user
# → root (admin) user
Correct boot order:
BIOS / UEFI
Bootloader (GRUB2)
Loads the kernel
Allows selecting different OS
Kernel
Core of OS
Manages CPU, memory, devices
init / systemd
Login Screen
✅ Correction:
BIOS does not load the OS directly
BIOS/UEFI loads the bootloader
Bootloader loads the kernel
Kernel starts the OS
If multiple OS are installed
GRUB menu allows choosing which OS to boot
Linux:
UEFI → GRUB → Kernel → systemd → Services → Ready
Windows:
UEFI → Boot Manager → Kernel → Services → Login → Ready
cp source destination
➡ Copy files or directories
Examples:
cp file1 file2
cp -r dir1 dir2
mv source destination
➡ Move or rename files
Examples:
mv file1 /tmp
mv oldname newname
Temporary:
hostname newname
Permanent (Recommended):
hostnamectl set-hostname newname
| BIOS | UEFI |
| Old technology | Modern |
| Slow boot | Fast boot |
| MBR partition | GPT partition |
| Limited disk size | Supports large disks |
| Text-based | GUI support |
✅ UEFI is used in modern systems
Linux has command-line editors.
nano file.txt
Easy to use
Shortcuts shown at bottom
Save: CTRL + O
Exit: CTRL + X
vim file.txt
Modes:
Normal mode (default)
Insert mode → i
Command mode → :
Common commands:
i # insert mode
:w # save
:q # quit
:wq # save and quit
:q! # quit without saving
Create files
Edit files using nano & vim
Copy and move files
Rename files
Change hostname
Navigate directories
You learned:
RHCSA basics and importance
Linux installation using VMware
Linux directory structure
Basic Linux commands
Boot process (BIOS → GRUB → Kernel → OS)
BIOS vs UEFI
File operations
Nano & Vim editors
cp -r source_directory destination_directory
-r → recursive (copy directory and all its contents)
Example:
cp -r /home/hassan/docs /home/hassan/backup_docs
rm filename
rm -i filename
rmdir directory_name
rm -r directory_name
rm -rf directory_name
Removes directory and contents without warning
⚠️ Use carefully! Can delete important data
** is used to represent all files or directories
Example:
rm *.txt
.txt files in current directorycommand [options] [arguments]
Command → what to do (ls, cp, rm)
Options → modify behavior (-l, -r, -f)
Arguments → files or directories to operate on
Example:
ls -l /home/hassan
Files starting with . are hidden
Create a hidden file:
touch .hiddenfile
clear
mkdir folder_name
mkdir -p parent_folder/child_folder
-p → create parent directories if they don’t existmkdir folder{1..10}
folder1, folder2, … folder10touch file{1..10}.txt
file1.txt → file10.txttree directory_name
cat /etc/services
more /etc/fstab
Better alternative to more
Scroll forward/backward
less /etc/fstab
head -n 10 /etc/services
tail -n 10 /etc/services
nl /etc/services
grepgrep "pattern" filename
Search for specific text in a file
Example:
grep "ftp" /etc/services
-i → ignore case
-c → show count of matching lines
-v → show non-matching lines
-n → show line numbers
Example:
grep -i "ftp" /etc/services
grep -c "ssh" /etc/services
wcwc filename
Options:
-l → number of lines
-w → number of words
-c → number of bytes
-m → number of characters
Example:
wc -l /etc/services
wc -w /etc/services
ls > file.txt
Overwrites file.txt with output of ls
Append output to a file
ls >> file.txt
Adds output to the end of file.txt
Pipes (send output of one command to another)
cat /etc/services | grep ftp
✅ Correction:
> → overwrite
>> → append
| → pipe (send output to another command)
You learned:
Copying, moving, deleting files and directories
Wildcards * for multiple files
Command structure (command → options → arguments)
Hidden files and creating them
Creating folders/files in bulk
Reading files (cat, more, less, head, tail, nl)
Searching in files (grep with options)
Word count (wc)
Redirection (>, >>) and pipes (|)
Linux allows combining commands and controlling execution flow using operators.
;Purpose: Run multiple commands sequentially, regardless of whether previous commands succeed or fail
Syntax:
command1; command2; command3
echo "Hello"; ls; pwd
Output:
Prints “Hello”
Lists files
Shows current directory
✅ Note: Commands run one by one even if one fails.
|Purpose: Sends output of first command as input to second command
Syntax:
command1 | command2
cat /etc/services | grep ftp
cat prints file → grep filters only lines containing “ftp”&&Purpose: Run second command only if the first command succeeds
Syntax:
command1 && command2
mkdir test && cd test
test folder if folder creation succeeds&Purpose: Run command in background
Syntax:
command &
gedit file.txt &
gedit in background, so terminal is free to use||Purpose: Run second command only if the first command fails
Syntax:
command1 || command2
cd nonexistfolder || echo "Folder does not exist"
cd fails, prints warning| Operator | Purpose |
; | Run commands sequentially, ignore errors |
&& | Run next command only if previous succeeds |
| ` | |
& | Run command in background |
| ` | ` |
Linux manages users and groups for access control and permissions.
| User Type | Description | UID |
| Root user | Super admin, full privileges | 0 |
| System user | Used by OS services, limited login | 1–999 |
| Regular user | Normal human user, limited privileges | 1000+ |
| Group Type | Description |
| Root group | Associated with root user, admin group |
| System group | For OS processes and services |
| Regular group | For normal users, sharing resources |
whoami
groups username
cat /etc/passwd
cat /etc/group
✅ Corrections / Clarifications
UID ranges for system vs regular users:
System: 1–999
Regular: 1000+
Background operator: single & runs command in background, not a chain.
Pipes and logical operators (&&, ||) are different:
| → sends output to input
&& / || → controls execution flow
# Sequential execution
echo "Start"; ls; echo "End"
# Logical AND
mkdir demo && cd demo
# Logical OR
cd nofolder || echo "Folder not found"
# Background process
gedit file.txt &
# Pipe
cat /etc/services | grep ftp
This covers Day 7 operators + intro to user & group management.
User and group management is a core topic in RHCSA and very important for real-world Linux administration. On Day 8, we focused on creating users, managing passwords, understanding user IDs (UIDs), group IDs (GIDs), and how Linux stores user and group information internally.
To create a new user in Linux, we use the useradd command.
useradd username
Example:
useradd ali
This command:
Creates the user
Assigns a UID automatically
Creates a home directory /home/ali
Assigns a default shell
⚠️ By default, the user does not have a password yet.
To set or change a password, use:
passwd username
Example:
passwd ali
You will be prompted to enter and confirm the password.
id username
Example:
id ali
Output shows:
UID (User ID)
GID (Primary Group ID)
Secondary groups
whoami
Linux has three main types of users:
| User Type | Description | UID Range |
| Root User | Superuser with full access | 0 |
| System User | Used by services and processes | 1–999 |
| Regular User | Normal human users | 1000+ |
The usermod command is used to modify user properties.
usermod -e 2026-12-31 ali
usermod -L ali
usermod -U ali
We can control password policies using chage.
chage username
Example:
chage ali
To view password aging info:
chage -l ali
You can:
Set password expiry
Force password change
Set warning days
An individual account
Has its own UID
Can log in
Collection of users
Used to manage permissions easily
Identified by GID
Groups make permission management easier instead of assigning permissions user by user.
groupadd groupname
Example:
groupadd developers
Each user has one primary group
Assigned at user creation
Used by default when creating files
Additional groups a user belongs to
Used for extra permissions
usermod -aG groupname username
Example:
usermod -aG developers ali
⚠️
-ais very important. Without it, existing groups will be removed.
Linux stores user and group information in /etc directory.
/etc/passwdcat /etc/passwd
Contains:
Username
UID
GID
Home directory
Shell
Passwords are not stored here.
/etc/shadowcat /etc/shadow
Contains:
Encrypted passwords
Password expiry info
Only readable by root user.
/etc/groupcat /etc/group
Contains:
Group name
GID
Group members
On Day 8, we learned:
How to add users and set passwords
How to check UID, GID, and group membership
Difference between users and groups
Primary vs secondary groups
How to add users to groups
User modification and password expiry
Internal Linux files: /etc/passwd, /etc/shadow, /etc/group
This topic is very important for RHCSA exam and real Linux administration.