it-knowledge/src/rhcsa.md

# RHCSA Study Notes

## Exam Information
- Exam Code: EX200
- Duration: 2.5 hours
- Passing Score: 210/300 (70%)

[CLI Commands](rhcsa.md#cli-commands)

## Core Topics

### 1. Essential Tools
- [x] Access a shell prompt and issue commands
- [x] Use input-output redirection
- [x] Use grep and regular expressions
- [x] Access remote systems using SSH
- [x] Log in and switch users in multiuser targets

### 2. File Management
- [x] Create, delete, copy, and move files and directories
- [x] Create and manage hard and soft links
- [x] Find files and directories
- [x] Manage file permissions and ownership

### 3. Service Configuration
- [x] Configure networking and hostname resolution
- [ ] Start, stop, and check system service status
- [ ] Configure services to start automatically at boot
- [ ] Configure time service clients

### 4. Storage Management
- [ ] List, create, delete, and modify physical storage partitions
- [ ] Create and configure filesystem
- [ ] Configure and manage swap space
- [ ] Create and manage LVM storage
- [ ] Create and manage STRATIS storage

### 5. Container Management
- [ ] Find and retrieve container images
- [ ] Create and manage containers
- [ ] Configure container storage

### 6. System Management
- [ ] Boot, reboot, and shut down a system
- [ ] Install Red Hat Enterprise Linux
- [ ] Use systemd targets for system management
- [ ] Configure system logging
- [ ] Schedule tasks using cron and systemd timers

### 7. Security
- [ ] Configure firewall settings
- [ ] Configure SELinux
- [ ] Manage users and groups
- [ ] Set file permissions and ownership

## Resources
- Official Red Hat Documentation
- Practice Environments
- Useful Commands Reference

## Progress Tracking
- [ ] Complete practice exams
- [ ] Lab environment setup
- [ ] Hands-on practice completed

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*Note: Check boxes can be used to track progress on each topic as you study*

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---

# CLI Commands

## Networking

### nmtui
```bash
nmtui # Network Manager Text User Interface
```

### ip
```bash
sudo ip addr add dev eth0 192.168.2.2/24 # Add an IP address to the interface eth0 Note: Not persistent, will be lost on reboot
```

### nmcli
```bash
nmcli connection add connection.interface-name ens160 ipv4.addresses 192.168.100.1/24 ipv4.gateway 192.168.100.254 type ethernet # Persistant IP address

sudo nmcli connection up ethernet-ens160 # Bring up the ethernet interface

sudo nmcli connection down ethernet-ens160 # Bring down the ethernet interface

sudo nmcli connection delete id "ens160" # Delete the ethernet connection

sudo nmcli connection show # Show all connections
```

## Manage and Monitor Processes

### top
```bash
top # Display running processes

top -o %MEM # Sort by memory usage

top -o %CPU # Sort by CPU usage

top -p 1234 # Display information for process 1234
```
### pidof
```bash
pidof sleep # Display the PID of the sleep command
```

### kill
```bash
kill -l # List all signals

kill -9 1234 # Kill the process with PID 1234
```

### nice
```bash
nice -n 10 sleep 100 # Run the sleep command with a priority of 10
```

## Partitions and Mounting

### lsblk
```bash
lsblk -f # List all block devices with filesystem type
```

### fdisk
```bash
sudo fdisk /dev/sda # Partition the disk /dev/sda 
# Note: n for new partition, p for primary, 1 for first partition, w for write
```

### mkfs
```bash
sudo mkfs.xfs /dev/sda1 # Format the partition /dev/sda1 as XFS
```

### mount
```bash
sudo mount /dev/sda1 /mnt # Mount the partition /dev/sda1 to /mnt

sudo mount -a # Mount all partitions
```

### LVM
```bash
sudo fdisk /dev/sda # Partition the disk /dev/sda
# Note: p for print, n for new partition, t for type, 8e for LVM, w for write

### Physical Volumes ###
sudo pvdisplay # Display all physical volumes
sudo pvs # Display all physical volumes

sudo pvcreate /dev/sda1p1 # Create a physical volume on /dev/sda1p1
sudo pvcreate /dev/sdb1p1 # Create a physical volume on /dev/sdb1p1
sudo pvcreate /dev/sdc1p1 # Create a physical volume on /dev/sdc1p1

### Volume Groups ###
sudo vgcreate vg_data /dev/sda1p1 /dev/sdb1p1 /dev/sdc1p1 # Create a volume group vg_data on /dev/sda1p1, /dev/sdb1p1, /dev/sdc1p1

sudo vgdisplay # Display all volume groups
sudo vgs # Display all volume groups

### Logical Volumes ###
sudo lvdisplay # Display all logical volumes
sudo lvs # Display all logical volumes

sudo lvcreate -n lv_data -l 100%FREE vg_data # Create a logical volume lv_data on vg_data
sudo lvcreate -n lv_data -L 100M vg_data # Create a logical volume lv_data on vg_data with a size of 100M

### Formatting and Mounting ###
sudo mkfs.xfs /dev/vg_data/lv_data # Format the logical volume lv_data as XFS
sudo mount /dev/vg_data/lv_data /mnt # Mount the logical volume lv_data to /mnt
sudo umount /mnt # Unmount the logical volume lv_data from /mnt

### Extending and Reducing ###
sudo lvextend -L +100M /dev/vg_data/lv_data # Extend the logical volume lv_data by 100M
sudo lvreduce -L -100M /dev/vg_data/lv_data # Reduce the logical volume lv_data by 100M

sudo lvremove /dev/vg_data/lv_data # Remove the logical volume lv_data
sudo vgremove vg_data # Remove the volume group vg_data
sudo pvremove /dev/sda1p1 /dev/sdb1p1 /dev/sdc1p1 # Remove the physical volumes /dev/sda1p1, /dev/sdb1p1, /dev/sdc1p1

### Interactive LVM Tool ###
sudo lvm # Interactive LVM tool
```

### STRATIS
```bash
sudo dnf install stratisd stratis-cli # Install the STRATIS storage service and CLI

sudo stratis pool create pool1 /dev/sda1p1 # Create a pool named pool1 on /dev/sda1p1
sudo stratis pool add-data pool1 /dev/sdb1p1 # Add a data volume to the pool named pool1 on /dev/sdb1p1

sudo stratis pool delete pool1 # Delete the pool named pool1

sudo stratis pool list # List all pools
sudo stratis blockdev list # List all block devices

sudo stratis fs create pool1 fstest # Create a filesystem named fstest on the pool named pool1
sudo stratis fs list # List all filesystems # Note: UUID is the UUID of the filesystem
mkdir /mnt/fsmount # Create a mount point for the filesystem
sudo nano /etc/fstab # Add the following line to the fstab file: UUID=1234567890 /mnt/fsmount xfs x-systemd.requires=stratisd.service 0 0
sudo mount -a # Mount all filesystems
```

## Automatic Services & Task Scheduling

### cron
```bash
sudo crontab -e # Edit the cron table

sudo crontab -l # List the cron table

### crontab format ###

* * * * * command # Run the command every minute

0 12 * * * command # Run the command at 12:00 PM

0 0 * * * command # Run the command at 12:00 AM
```

### at
```bash
at 12:00 PM # Schedule a command to run at 12:00 PM

at -l # List all scheduled jobs

atq # List all scheduled jobs

atrm 1 # Remove the scheduled job with ID 1
```

### systemd

```bash
sudo systemctl start sshd # Start the sshd service
sudo systemctl stop sshd # Stop the sshd service
sudo systemctl restart sshd # Restart the sshd service

sudo systemctl enable sshd # Enable the sshd service to start on boot
sudo systemctl disable sshd # Disable the sshd service from starting on boot
sudo systemctl status sshd # Check the status of the sshd service

sudo systemctl daemon-reload # Reload the systemd daemon

sudo systemctl mask sshd # Mask the sshd service
sudo systemctl unmask sshd # Unmask the sshd service
```

### systemd service and timer commands

```bash
### Creating a service ###
sudo nano /etc/systemd/system/myapp.service
# [Unit]
# Description=My App

# [Service]
# Type=simple
# ExecStart=/usr/bin/myapp
# User=myuser

### Creating a timer ###
sudo nano /etc/systemd/system/myapp.timer
# [Unit]
# Description=My App Timer

# [Timer]
# OnBootSec=10min # Run the timer 10 minutes after the system starts
# OnCalendar=*-*-* 10:00:00 # Run at 10:00 AM every day
# OnCalendar=*-*-* *:*:0 # Run at every minute

# [Install]
# WantedBy=graphical.target # Run the timer on the graphical target

### Tying the timer to the service ###
sudo systemctl link /etc/systemd/system/myapp.timer 

### Starting a service ###
sudo systemctl start myapp
sudo systemctl start myapp.timer
```

## Bash Scripting

### Basic Script
```bash
nano myscript.sh
```

> Note: Shebang is the first line of the script that tells the system which interpreter to use.
```bash
#!/bin/bash
echo "Hello, World!"

### Variables ###
myvar="Hello, World!"
echo $myvar

### Conditionals ###
if [ -f /etc/passwd ]; then
    echo "File exists"
else
    echo "File does not exist"
fi
```

### Script to create a directory
> NOTE: When creating bash scripts you can use particular operators to check for the existence of a file (-f) or directory (-d). The 
> following example uses the -d operator to check for the existence of a directory. Using conditional logic, if the script detects 
> that the directory does not exist, the script will go ahead and create it.

```bash
#!/bin/bash

# Ask the user to enter a directory name
echo "Enter a directory name: "

# Read the user's input 
read user_dir

# Check if the user_dir exists
if [ -d "$user_dir" ]; then
  echo "The directory '$user_dir' already exists."
else
  # Create the user_dir directory if it doesn't exist
  mkdir "$user_dir"
  echo "The directory '$user_dir' has been created."
fi
```

> In a similar vein, you can check for the existence of a regular file using the -f operator.

```bash
#!/bin/bash

# Ask the user to enter a filename
echo "Enter a filename: "

# Read the user's input
read user_file

# Check if the file exists
if [ -f "$user_file" ]; then
  echo "The file '$user_file' exists."
else
  echo "The file '$user_file' does not exist."
fi
```

### for loop
```bash
#!/bin/bash

for i in 1..10; do
    echo $i
done
```

### while loop
```bash
#!/bin/bash

i=1
while [ $i -le 10 ]; do
    echo $i
    i=$((i+1))
done
```

### until loop
```bash
#!/bin/bash

i=1
until [ $i -gt 10 ]; do
    echo $i
    i=$((i+1))
done
```

### Example script to check a user's age
```bash
#!/bin/bash
echo "Please provide me your age: "

read age

if [ "$age" -le 17 ]; then
	echo "You cannot enter bars or vote."
elif [ "$age" -ge 18 ] && [ "$age" -le 20 ]; then
	echo "You can vote but not enter bars."
else
	echo "You are old enough to vote and enter bars."
fi
```

## Boot Process & Targets

### Change the grub2 configuration
```bash
sudo grub2-mkconfig -o /boot/grub2/grub.cfg # Create a new grub configuration file

sudo nano /etc/default/grub # Edit the grub configuration file

# Add the following line to the grub configuration file:
GRUB_CMDLINE_LINUX="quiet splash"
```

### dmesg

> Note: The boot process is the process by which a system starts up. It is a sequence of events that occur when a system is powered on or rebooted.

```bash
sudo dmesg # Display the kernel messages
sudo dmesg | tail # Display the last 10 lines of the kernel messages
sudo dmesg | grep "kernel" # Display the kernel messages that contain the word "kernel"

### /var/log/messages ###
sudo less /var/log/messages # Display the kernel messages
```

### systemd targets

> Note: Systemd targets are a way to manage the boot process of a system. They are a way to manage the boot process of a system.
>> multi.target is the default target for the system.
>> graphical.target is the target for the graphical interface.
>> basic.target is the target for the minimal system.
>> rescue.target is the target for the rescue mode.
>> emergency.target is the target for the emergency mode.
>> multi-user.target is the target for the multi-user mode.
>> reboot.target is the target for the reboot mode.
>> poweroff.target is the target for the poweroff mode.

```bash
systemctl list-units --type=target

### Changing the default target ###
sudo systemctl set-default multi-user.target # Set the default target to multi-user.target
sudo systemctl set-default graphical.target # Set the default target to graphical.target
sudo systemctl set-default basic.target # Set the default target to basic.target
```

### Run Level

> Note: Run level is a way to manage the boot process of a system. It is a way to manage the boot process of a system.
> 0 is the emergency mode. 
> 1 is the single user mode.
> 2 is the multi-user mode. 
> 3 is the multi-user mode. 
> 4 is the multi-user mode. (unused)
> 5 is the graphical mode.
> 6 is the reboot mode.

```bash
runlevel # Display the current run level
sudo systemctl get-default # Display the default target
sudo systemctl set-default runlevel3.target # Set the default target to runlevel3.target
sudo telinit 3 # Change to runlevel 3
```

## Manage SSH Connections

### ssh
```bash
ssh user@host # Connect to the host as the user

ssh -p 2222 user@host # Connect to the host as the user on port 2222

ssh -i /path/to/private_key user@host # Connect to the host as the user using a private key

ssh-copy-id user@host # Copy the user's public key to the host

ssh-keygen -t ed25519 -C "comment" -f ~/.ssh/id_ed25519 -N "" # Generate a new ed25519 key

ssh-keygen -t rsa -b 4096 -C "comment" -f ~/.ssh/id_rsa -N "" # Generate a new rsa key
```

### sshd_config
```bash
sudo nano /etc/ssh/sshd_config # Edit the sshd configuration file

# Add the following line to the sshd configuration file:
Port 2222

sudo systemctl restart sshd # Restart the sshd service
```

## NFS & NTP

### NFS
```bash
sudo dnf install nfs-utils # Install the NFS utilities

sudo nano /etc/exports # Edit the exports file

# Add the following line to the exports file:
/mnt/nfs # The directory to export

sudo exportfs -r # Export the NFS shares
sudo exportfs # Display the NFS shares

sudo systemctl start nfs-server # Start the NFS server
```

### Configure an NFS Client
```bash
sudo dnf install nfs-utils # Install the NFS utilities

sudo mount 192.168.1.1:/mnt/nfs /mnt/nfs # Mount the NFS share
sudo umount /mnt/nfs # Unmount the NFS share
```