29 KiB
29 KiB
RHCSA Study Notes
Exam Information
- Exam Code: EX200
- Duration: 2.5 hours
- Passing Score: 210/300 (70%)
Core Topics
1. Essential Tools
- Access a shell prompt and issue commands
- Use input-output redirection
- Use grep and regular expressions
- Access remote systems using SSH
- Log in and switch users in multiuser targets
2. File Management
- Create, delete, copy, and move files and directories
- Create and manage hard and soft links
- Find files and directories
- Manage file permissions and ownership
3. Service Configuration
- 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
Note: Check boxes can be used to track progress on each topic as you study
CLI Commands
Networking
nmtui
nmtui # Network Manager Text User Interface
ip
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
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
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
pidof sleep # Display the PID of the sleep command
kill
kill -l # List all signals
kill -9 1234 # Kill the process with PID 1234
nice
nice -n 10 sleep 100 # Run the sleep command with a priority of 10
Partitions and Mounting
lsblk
lsblk -f # List all block devices with filesystem type
fdisk
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
sudo mkfs.xfs /dev/sda1 # Format the partition /dev/sda1 as XFS
mount
sudo mount /dev/sda1 /mnt # Mount the partition /dev/sda1 to /mnt
sudo mount -a # Mount all partitions
LVM
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
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
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
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
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
### 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
nano myscript.sh
Note: Shebang is the first line of the script that tells the system which interpreter to use.
#!/bin/bash
echo "Hello, World!"
### Variables ###
myvar="Hello, World!"
echo $myvar
### Conditionals ###
if [ -f /etc/passwd ]; then
echo "File exists"
else
echo "File does not exist"
fi
Script to create a directory
NOTE: When creating bash scripts you can use particular operators to check for the existence of a file (-f) or directory (-d). The following example uses the -d operator to check for the existence of a directory. Using conditional logic, if the script detects that the directory does not exist, the script will go ahead and create it.
#!/bin/bash
# Ask the user to enter a directory name
echo "Enter a directory name: "
# Read the user's input
read user_dir
# Check if the user_dir exists
if [ -d "$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 '$user_dir' has been created."
fi
In a similar vein, you can check for the existence of a regular file using the -f operator.
#!/bin/bash
# Ask the user to enter a filename
echo "Enter a filename: "
# Read the user's input
read user_file
# Check if the file exists
if [ -f "$user_file" ]; then
echo "The file '$user_file' exists."
else
echo "The file '$user_file' does not exist."
fi
for loop
#!/bin/bash
for i in 1..10; do
echo $i
done
while loop
#!/bin/bash
i=1
while [ $i -le 10 ]; do
echo $i
i=$((i+1))
done
until loop
#!/bin/bash
i=1
until [ $i -gt 10 ]; do
echo $i
i=$((i+1))
done
Example script to check a user's age
#!/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
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.
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.
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.
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
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
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
sudo dnf install nfs-utils # Install the NFS utilities
### Port Number ###
> Note: The port number for NFS is 2049.
### Firewall ###
sudo firewall-cmd --add-service=nfs --permanent # Add the NFS service to the firewall
sudo firewall-cmd --reload # Reload the firewall
sudo firewall-cmd --list-services # List the services in the firewall
sudo nano /etc/exports # Edit the exports file
# Add the following line to the exports file:
/mnt/nfs 192.168.1.0/24(rw,sync,no_subtree_check) # 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
### root-squash and no_root_squash
> Note: root-squash is a feature of NFS that allows the root user to access the NFS share as a regular user. no_root_squash
> is a feature of NFS that allows the root user to access the NFS share as the root user.
> Note: async is a feature of NFS that allows the NFS server to write to the NFS share asynchronously.
> sync is a feature of NFS that allows the NFS server to write to the NFS share synchronously.
```bash
sudo nano /etc/exports # Edit the exports file
# Add the following line to the exports file:
/mnt/nfs 192.168.1.0/24(rw,sync,no_subtree_check,root_squash) # The directory to export
# Add the following line to the exports file:
/mnt/nfs 192.168.1.0/24(rw,async,no_subtree_check,no_root_squash) # The directory to export
Configure an NFS Client
sudo dnf install nfs-utils # Install the NFS utilities
sudo nano /etc/fstab # Edit the fstab file
# Add the following line to the fstab file:
192.168.1.1:/mnt/nfs /mnt/nfs nfs defaults 0 0
sudo mount -a # Mount the NFS shares
sudo mount 192.168.1.1:/mnt/nfs /mnt/nfs # Mount the NFS share
sudo umount /mnt/nfs # Unmount the NFS share
NTP
sudo dnf install ntp # Install the NTP utilities
sudo ntpdate time.nist.gov # Update the time
sudo ntpq -p # Display the NTP peers
sudo ntpstat # Display the NTP status
### Timezone and Time Commands ###
sudo timedatectl set-timezone America/Chicago # Set the timezone to America/Chicago
sudo timedatectl set-time "12:00:00" # Set the time to 12:00:00
sudo timedatectl set-ntp true # Enable the NTP service
sudo timedatectl set-ntp false # Disable the NTP service
### chrony
```bash
sudo dnf install chrony # Install the chrony utilities
sudo chronyc sources # Display the chrony sources
sudo chronyc tracking # Display the chrony tracking
sudo chronyc sources -v # Display the chrony sources with more detail
sudo nano /etc/chrony.conf # Edit the chrony configuration file
# Add the following line to the chrony configuration file:
server time.nist.gov iburst # Add the NIST time server
pool 2.rhel.pool.ntp.org iburst # Add the RHEL time server
sudo systemctl start chronyd # Start the chrony service
sudo systemctl enable chronyd # Enable the chrony service to start on boot
Secure Linux Systems
lsattr
lsattr # List the attributes of the files and directories
lsattr /etc/passwd # List the attributes of the /etc/passwd file
chattr
chattr +i /etc/passwd # Set the immutable attribute on the /etc/passwd file
chattr -R +i /etc/ # Set the immutable attribute on the /etc/ directory and all its contents
chattr +a /etc/passwd # Set the append only attribute on the /etc/passwd file
chattr -i /etc/passwd # Remove the immutable attribute on the /etc/passwd file
chattr -R -i /etc/ # Remove the immutable attribute on the /etc/ directory and all its contents
getfacl
getfacl /etc/passwd # Display the ACLs of the /etc/passwd file
setfacl
setfacl -m u:user:rwx /etc/passwd # Set the ACLs of the /etc/passwd file for the user user with read, write, and execute permissions
setfacl -m g:group1:r file.txt # Set the ACLs of the file.txt file for the group group1 read only
SELinux Basics
sudo sestatus # Display the SELinux status
sudo getenforce # Display the SELinux mode
sudo setenforce 0 # Set the SELinux mode to permissive
sudo setenforce 1 # Set the SELinux mode to enforcing
ls -Z # List the SELinux context of the files and directories
ps -eZ # List the SELinux context of the processes
### SELinux Port Management
# Note: SELinux will block any attempt to use a port that is not in the SELinux policy in enforcing mode.
sudo semanage port -a -t http_port_t -p tcp 8080 # Add the HTTP port to the SELinux policy
sudo semanage port -d -t http_port_t -p tcp 8080 # Remove the HTTP port from the SELinux policy
### SELinux Login Management
sudo semanage login -a -s user_t user1 # Add the user user1 to the SELinux policy
sudo semanage login -d user1 # Remove the user user1 from the SELinux policy
### getsebool
```bash
getsebool -a # List all SELinux booleans
getsebool httpd_can_network_connect # Display the SELinux boolean for the httpd_can_network_connect boolean
### setsebool
```bash
setsebool -P httpd_can_network_connect on # Set the httpd_can_network_connect boolean to on
setsebool -P httpd_can_network_connect off # Set the httpd_can_network_connect boolean to off
sudo semanage boolean -l -C # List all SELinux booleans
### sealert
```bash
sudo sealert -a /var/log/audit/audit.log # Display the SELinux alerts
journalctl | grep -i sealert # Display the SELinux alerts
Manage Packages on RHEL
rpm
rpm -q httpd # Display the installed packages
rpm -qa # Display all installed packages
rpm -qf /bin/bash # Display the package that installed the /bin/bash command
rpm -ql httpd # Display the files installed by the httpd package
rpm -ql coreutils | grep bin # Display the files installed by the coreutils package
sudo rpm -i httpd-2.4.37-1.el8.x86_64.rpm # Install the httpd package
sudo rpm -e httpd # Remove the httpd package
rpm2cpio
rpm2cpio httpd-2.4.37-1.el8.x86_64.rpm | cpio -tv # Display the contents of the httpd package
rpm2cpio httpd-2.4.37-1.el8.x86_64.rpm | cpio -idmv # Extract the contents of the httpd package
dnf
sudo dnf install httpd # Install the httpd package
sudo dnf remove httpd # Remove the httpd package
sudo dnf list # List all packages
sudo dnf search httpd # Search for the httpd package
sudo dnf info httpd # Display information about the httpd package
sudo dnf provides /bin/bash # Display the package that provides the /bin/bash command
sudo dnf deplist httpd # Display the dependencies of the httpd package
modify the .repo file to skip the GPG check
sudo nano /etc/yum.repos.d/rhel.repo
# Add the following line to the rhel.repo file:
gpgcheck=0
dnf groups
sudo dnf group list # List all groups
sudo dnf group list --hidden # List all hidden groups
sudo dnf group install "Development Tools" # Install the Development Tools group
sudo dnf group install --with-optional "Development Tools" # Install the Development Tools group with optional packages
sudo dnf group info "Development Tools" # Display information about the Development Tools group
sudo dnf group remove "Development Tools" # Remove the Development Tools group
sudo dnf history # Display the history of the packages
sudo dnf history undo 1 # Undo the last package installation
sudo less /var/log/dnf.rpm.log # Display the dnf log
dd
Note: dd is used to copy and convert files and is used to create disk images.
sudo dd if=/dev/sr0 of=/optical-rhel.iso bs=1M # Create an ISO image of the optical drive
sudo dd if=/dev/sr0 of=/optical-rhel.iso bs=1M status=progress # Create an ISO image of the optical drive with progress
### mounting an iso image using /etc/fstab
```bash
sudo nano /etc/fstab
# Add the following line to the fstab file:
/path/to/iso /mnt/iso iso9660 defaults 0 0
sudo mount -a # Mount the ISO image
sudo umount /mnt/iso # Unmount the ISO image
### dnf config-manager
sudo dnf config-manager --add-repo="file:///path/to/repo/AppStream" # Add a repository
sudo dnf config-manager --add-repo="file:///path/to/repo/BaseOS" # Add a repository
sudo dnf repolist # List all repositories
Understand and Configure Firewalls
firewall-cmd
Note: firewall-cmd is used to manage the firewall rules.
### displaying the firewall zones
sudo firewall-cmd --get-active-zones # Display the active zones
sudo firewall-cmd --get-default-zone # Display the default zone
sudo firewall-cmd --get-zones # Display the zones
### setting the default zone
sudo firewall-cmd --set-default-zone=public # Set the default zone to public
### displaying the rules in the firewall
sudo firewall-cmd --list-all # Display all the rules in the firewall
sudo firewall-cmd --list-services --zone=public # Display the services in the public zone
sudo firewall-cmd --list-ports --zone=public # Display the ports in the public zone
sudo firewall-cmd --list-protocols --zone=public # Display the protocols in the public zone
### adding rules to the firewall
sudo firewall-cmd --zone=public --add-service=http --permanent # Add the http service to the public zone
sudo firewall-cmd --zone=public --add-port=80/tcp --permanent # Add the port 80/tcp to the public zone
sudo firewall-cmd --zone=public --add-protocol=tcp --permanent # Add the tcp protocol to the public zone
### removing rules from the firewall
sudo firewall-cmd --zone=public --remove-service=http --permanent # Remove the http service from the public zone
sudo firewall-cmd --zone=public --remove-port=80/tcp --permanent # Remove the port 80/tcp from the public zone
sudo firewall-cmd --zone=public --remove-protocol=tcp --permanent # Remove the tcp protocol from the public zone
### reloading the firewall
sudo firewall-cmd --reload # Reload the firewall
port reference
sudo less /etc/services # Display the services
Manage DNS and Logging
resolv.conf
sudo nano /etc/resolv.conf # Edit the resolv.conf file
sudo systemctl restart NetworkManager # Restart the NetworkManager service
nsswitch.conf
sudo nano /etc/nsswitch.conf # Edit the nsswitch.conf file
sudo systemctl restart NetworkManager # Restart the NetworkManager service
query dns
dig www.google.com # Query the DNS server for www.google.com
dig -x 192.168.1.1 # Query the DNS server for the reverse lookup(PTR) of 192.168.1.1
nslookup www.google.com # Query the DNS server for www.google.com
nslookup -type=mx gmail.com # Query the DNS server for the MX records for gmail.com
logging
sudo journalctl # Display the journal
sudo journalctl -xe # Display the journal and show the boot messages
sudo journalctl -f # Display the journal and follow the log
sudo journalctl -u httpd # Display the journal for the httpd service
sudo journalctl --since "1 hour ago" # Display the journal for the last hour
sudo journalctl --since "1 hour ago" --until "2 hour ago" # Display the journal for the last hour and until 2 hours ago
rsyslog
sudo nano /etc/rsyslog.conf # Edit the rsyslog configuration file
sudo systemctl restart rsyslog # Restart the rsyslog service
sudo systemctl status rsyslog # Display the status of the rsyslog service
logrotate
sudo nano /etc/logrotate.conf # Edit the logrotate configuration file\
logger
logger "This is a test message" # Log a message
logger -p local0.info "This is a test message" # Log a message to the local0.info facility
sudo tail /var/log/messages # Display the messages
Troubleshoot RHEL Systems
Troubleshooting Capacity Problems
### df
sudo df -h # Display the disk space usage
sudo df -i # Display the inode usage
sudo df -T # Display the filesystem type
### dd
sudo dd if=/dev/zero of=/dev/sda1 bs=1M count=100 # Create a 100MB file on the /dev/sda1 partition
sudo dd if=/dev/zero of=/dev/sda1 bs=1M count=100 status=progress # Create a 100MB file on the /dev/sda1 partition with progress
### du
sudo du -hs /home/user1 # Display the disk space usage of the /home/user1 directory
sudo du -h file.txt # Display the disk space usage of the file.txt file
Troubleshooting CPU Issues
### uptime
sudo uptime # Display the uptime of the system
### lscpu
sudo lscpu # Display the CPU information
### stress test cpu with stress-ng
sudo stress-ng --cpu 2 --timeout 10s # Stress test the CPU for 10 seconds
### vmstat
sudo vmstat 1 5 # Display the VM statistics every 1 second for 5 seconds
### top
sudo top # Display the top processes
Troubleshooting Memory Issues
### free
sudo free -h # Display the memory usage
### vmstat
sudo vmstat 1 5 # Display the VM statistics every 1 second for 5 seconds
### top
sudo top # Display the top processes then press m to sort by memory
Troubleshooting Network Issues
### nmtui
sudo nmtui # Network Manager Text User Interface
### nmcli
sudo nmcli connection show # Display the network connections
### ip route
ip route show # Display the routes
### ip addr
ip -c addr # Display the network interfaces
Troubleshooting DNS Issues
### check dns resolution with dig
dig google.com # Query the DNS server for google.com
### check dns resolution with resolv.conf
sudo vim /etc/resolv.conf # Edit the resolv.conf file
### change the nameserver to 8.8.8.8
nameserver 8.8.8.8
Recovering the Root Password
### reboot the system
sudo reboot
### press esc to get to the grub menu
### press e to edit the grub menu
### go to the line that starts with linux16
### scroll down to the end of the line
### delete rhgb quiet
### add the init=/bin/bash to the end of the line
... init=/bin/bash
### press ctrl+x to boot into single user mode
### mount the root filesystem
mount -o remount,rw /
### change the root password
passwd root
### inform selinux to allow the root password change
touch /.autorelabel
exec /usr/lib/systemd/systemd
### the system may take a while to boot
Manage Containers on RHEL
podman
sudo dnf install podman # Install podman
podman pull nginx:latest # Pull the latest nginx image
podman images # Display the images
podman run --name mynginx -d -p 8080:80 nginx:latest # Run the nginx container
podman ps # Display the running containers
podman logs mynginx # Display the logs of the mynginx container
podman exec -it mynginx bash # Execute a command in the mynginx container
podman start mynginx # Start the mynginx container
podman stop mynginx # Stop the mynginx container
podman rm mynginx # Remove the mynginx container
podman rmi nginx:latest # Remove the nginx image
Building Custom Images with Podman
FROM fedora:latest
RUN dnf install -y vim
COPY welcome.txt /root/welcome.txt
CMD ["/bin/bash"]
Note: You can build the image with podman build -t myimage .
Running Containers with Podman
### build the image
podman build -t myimage -f Containerfile .
### run the container
podman run -it --name mycustomcontainer myimage
Persistent Storage
### create a volume
podman volume create myvolume
### list the volumes
podman volume ls
### run the container with the volume
podman run --name mywebserver -d -p 8080:80 -v myvolume:/var/www/html:Z nginx
Scheduling Containerised Services with Systemd
Note: You can use systemd to schedule containerised services.
configure the service to run under a user's account even when the user is not logged into the system
### enable linger for the user
sudo loginctl enable-linger user1
### create a systemd service
mkdir -p /home/user1/.config/systemd/user
podman pull nginx
### run the container
podman run -d --name mynginx -p 8080:80 nginx
### cd into the user's home directory
cd /home/user1/.config/systemd/user
podman generate systemd --name mynginx --files --new # generate the systemd service file
### ensure the service file is wantedby default.target
[Install]
WantedBy=default.target
systemctl --user daemon-reload # reload the systemd user daemon
systemctl --user enable container-mynginx.service # enable the mynginx service
systemctl --user status container-mynginx.service # check the status of the mynginx service
### after rebooting the system, the service will start automatically