Access a shell prompt and issue commands with correct syntax

Understand and Use Essential Tools

📘Red Hat Certified System Administrator (RHCSA – EX200)

1. What is a Shell Prompt?

In Linux, the shell is a program that lets you interact with the operating system. Think of it as the interface where you type commands to make the system do tasks like:

List files
Copy or move files
Check system status

The shell prompt is where you type these commands. A typical shell prompt looks like:

[user@hostname ~]$

user – the username you are logged in as
hostname – the name of the system
~ – your current directory (here it means your home directory)
$ – indicates a normal user (if it is #, it means root user)

Important: For RHCSA, you must be comfortable working both as a regular user and as root (administrator) using the shell.

2. Accessing a Shell Prompt

You can access a shell in several ways:

Locally on the system:
- Login to a Linux system via GUI and open Terminal.
- The terminal opens a shell session.
Remotely using SSH (Secure Shell):
- Command to connect from another machine: ssh username@ip_address
- Example: ssh alice@192.168.1.100
Switching to root (administrative user):
- Using su (switch user): su - Then enter the root password.
- Or using sudo (execute commands as root): sudo command Example: sudo yum update

Tip: RHCSA exam often requires running commands with root privileges, so knowing su and sudo is essential.

3. Issuing Commands

3.1 Basic Command Structure

A Linux command typically has this format:

command [options] [arguments]

command – the program or utility you want to run (e.g., ls, cat)
options – modify the behavior of the command (e.g., -l, -a)
arguments – the target of the command (file, directory, user, etc.)

Example:

ls -l /etc

ls → list files
-l → show detailed info
/etc → directory to list

3.2 Commonly Used Commands for the Exam

Here are essential commands you must know:

Command	Purpose	Example
`pwd`	Print current directory	`pwd` → `/home/alice`
`ls`	List files	`ls -l /var/log`
`cd`	Change directory	`cd /etc`
`cat`	View file content	`cat /etc/passwd`
`more` / `less`	View large files page by page	`less /var/log/messages`
`cp`	Copy files	`cp file1.txt /tmp/`
`mv`	Move or rename files	`mv file1.txt file2.txt`
`rm`	Remove files	`rm file1.txt`
`mkdir`	Create a directory	`mkdir /tmp/testdir`
`rmdir`	Remove empty directory	`rmdir /tmp/testdir`
`touch`	Create an empty file	`touch /tmp/file1`
`echo`	Display text	`echo "Hello"`
`man`	Show manual page	`man ls`
`uname`	Show system info	`uname -a`
`whoami`	Show current user	`whoami`

RHCSA Exam Tip: You need to type commands correctly. Even small mistakes in syntax (like missing a space) can cause failure.

3.3 Understanding Options and Arguments

Single-dash options (short options): ls -l
Double-dash options (long options): ls --human-readable

Remember: Many commands combine multiple options:
ls -la /etc
-l for long listing, -a to show hidden files

3.4 Command Execution Rules

Commands are case-sensitive.
- ls ≠ LS
Commands must be typed in the correct order: command → options → arguments
Use Tab completion to save time:
- Start typing a filename or directory and press Tab to auto-complete
Use Up/Down arrows to recall previous commands

4. Viewing Command Output and Errors

Normal output → standard output (stdout)
Errors → standard error (stderr)

Example:

ls /nonexistent

Output:

ls: cannot access '/nonexistent': No such file or directory

Use redirection to handle output: ls -l /etc > filelist.txt # Save output to a file ls /nonexistent 2> error.txt # Save error to a file

5. Using `man` and `--help`

Every command has a manual: man command
Or quick help: command --help