Linux Commands: General Commands, System Configuration, Package Manager, Network & VLAN Configuration & Firewalls, SSH & Host Keys, Certificates, KVM & SQL

# Print the help documentation of a command
command --help

# Print the manual documentation of a command
man command

# List bash history: For current user
history

# Remove entry from history: Define entry number
history -d 1234

# Show Date (current session)
HISTTIMEFORMAT="%F "

# Show Date and Time (current session)
HISTTIMEFORMAT="%F %T "

# Show Date and Time (permanent)
echo 'HISTTIMEFORMAT="%F %T "' >>  ~/.bashrc

# Temporarily turn off the recording of commands in the bash history
bash +o history

# Turn the recording of commands in the bash history back on
bash -o history

# List all files currently open by specific user
sudo lsof -u username

# List all files currently open by specific user: Only regular files 
sudo lsof -u username | grep REG

# List incoming and outgoing SSH connections: Default SSH port 22
lsof -i TCP:22

# List all network connections
sudo lsof -i

# Compress and archive file
zip -r filezip file

# Compress and archive folder
zip -r folder.zip folder

# List files in archive
unzip -l file.zip

# List files in archive: More details
unzip -lv file.zip

# Unzip archive
unzip file.zip

# Split file into 5MB parts
split -b 5MB filename.exe

# List files
ls

# Shell output:
filename.exe  xaa  xab  xac  xad

# Restore original file
cat  xaa  xab  xac  xad > file.exe

# Split file into 5MB parts: Add prefix to fileparts
split -b 5MB filename.exe 'part-'

# List files
ls

# Shell output:
filename.exe   part-aa  part-ab  part-ac  part-ad

# Split file into 10 pieces of equal size
split -n 10 filename.exe 'part-'

# Find files and folders: Current directory (and subdirectories)
find . -name docker-compose.yml

# Find files: Specific directory (/home)
find /home -name "docker-compose" -type f

# Find folders: Specific directory (/home)
find /home -name "folder" -type d

# Find symbolic link
find / -name "file" -type l


# Find (all) files: Filenames include "kernel"
find /var | grep kernel

# Find (all) files: Save output into file
find /var > var-files.txt

# Open file in less
less filename

# Displays line numbers alongside the text
less -N /var/log/syslog

# Pipe output to less
cat /var/log/syslog | less -N

# Quit less
q

# List files modified in the last 30 days
find -mtime -30

# List files and folder with data usage
du --max-depth=1 -x -h

# List files with detailed timestamp
`ls -l --time-style="+%d %b %Y"`

# Save output to file
`ls -l --time-style="+%d %b %Y" > output.txt`

# List .log files with detailed timestamp
`find . -maxdepth 1 -type f -name "*.log" -exec ls -l --time-style="+%d %b %Y" {} \;`

# Copy .log files
`find . -type f -name "*.log" -exec cp {} /path/to/destination \;`

# Find files that contain specific text
find /opt/* -type f -iname "*" -exec grep -i -n "specific-text" {} +

# Find word in file (Outputs whole line)
grep word file.txt

# Find files that contain specific text
sudo grep -ri "specific-text" /opt/*

# List the location of one or several executable files
which ls grep

# List all matching pathnames of each argument
which -a ls grep

# Create hard link of file
ln file file_hardlink

# Create symbolic / soft link of file
ln -s file file_softlink

# -i parameter lists inode of file
ls -li

# List the full path of a file: Syntax
realpath filename

# List the full path of a file: Example
realpath /etc/apache2/sites-enabled/000-default.conf

# Shell output:
/etc/apache2/sites-available/000-default.conf

# Calculate MD5 checksum
md5sum filename

# List Linux distribution
cat /etc/*-release

# List Kernel Version
uname -r

# Output how long the server is running
uptime

# Check for outdated processes
needrestart

# List CPU details
cat /proc/cpuinf

# List CPU details
lscpu

# Install sysstat
sudo apt install sysstat -y

# List CPU usage (all CPUs)
mpstat -P ALL

# List average CPU usage
mpstat | awk '/all/ {print 100 - $NF"%"}'

# List RAM and Swap usage
free -h

# List total RAM on system
grep MemTotal /proc/meminfo

# List services reading / writing on disk
iotop

# Quit iotop
q

# List Hostname
cat /etc/hostname

# Change Hostname
sudo hostnamectl set-hostname newname

# Also change here
/etc/hosts

# List Hardware Specs, e.g Mainboard
sudo dmidecode

# List the valid types for dmidecode
sudo dmidecode --type

# List dmidecode details for bios
sudo dmidecode --type bios

# List dmidecode details for system
sudo dmidecode --type system

# Install lshw
sudo apt install lshw -y

# List system details
sudo lshw -c system

# List system date and time
date

# List system date and time: 24-hour format
date +"%H:%M"

# Set system date
date -s "2023-05-28"

# Set system time
date -s "10:00:00"

# Set date & time
date -s "2023-05-28 10:00:00"

# List current timezone
timedatectl

# Check time & timezone
date

# List all available timezones
timedatectl list-timezones

# List timezones for europe
timedatectl list-timezones | grep Europe

# Change current timezone: To Vienna
sudo timedatectl set-timezone Europe/Vienna

# Check status 
sudo systemctl status systemd-timesyncd

# Check status: More details
sudo timedatectl timesync-status 

# Open timesyncd.conf
sudo vi /etc/systemd/timesyncd.conf

# Define time server: For example "ntp.ubuntu.com"
[Time]
NTP=ntp.ubuntu.com

# Restart ystemd-timesyncd service
sudo systemctl restart systemd-timesyncd

# Check status
sudo systemctl status chronyd

# List NTP source server
chronyc sources

# Compare "Ref time" and "System time"
chronyc tracking

# Open chrony.conf
sudo vi /etc/chrony.conf

# Restart service
sudo systemctl start chronyd

# Allow the "192.168.30.0/24" network to sync the time
sudo tee --append /etc/chrony.conf << HERE
allow 192.168.30.0/24
HERE

# Restart service
sudo systemctl restart chronyd

# Uncomment defined servers or server pools:
sudo sed -i 's/server/#server/g' /etc/chrony.conf
sudo sed -i 's/pool/#pool/g' /etc/chrony.conf

# Define NTP server
sudo tee --append /etc/chrony.conf << HERE
server 192.168.30.110 iburst
allow 192.168.30.110
HERE

# Restart service
sudo systemctl restart chronyd

# Install tcpdump
sudo apt install tcpdump

# Check NTP traffic: Define ethernet port
sudo tcpdump port 123 -i ens33

# List Crontab from current user
crontab -l

# List Crontab from specific user
crontab -u username -l

# Edit Crontab from current user
crontab -e


# User specific Crontabs are located in the following directory
/var/spool/cron/crontabs

# For example: root
cat /var/spool/cron/crontabs/root

# System Wide Crontab
cat /etc/crontab

# Individual cron files, often used by system packages like MDADM
cd /etc/cron.d/

# Other Cron directories
/etc/cron.hourly/
/etc/cron.daily/
/etc/cron.weekly/
/etc/cron.monthly/

# List processes: Static
ps aux

# List processes: Real-time
top

# List processes: Real-time, modify / kill processes
htop

# Quit htop
q

# List processes: From specific user
ps -u username

# List processes: From specific user, format output
ps -u ubuntu -o pid,ppid,%cpu,%mem,command

# Process trees
pstree

# Process trees with ID's
pstree -p

# Find ID of running process
pgrep processname

# Also search command line associated with process
pgrep -f processname

# Also works with running scripts
pgrep -f script.sh

# Terminate process: Define process ID
sudo kill ID

# Terminate process: Define process name
sudo pkill name

# Terminate process: Define process name, example "vi"
sudo pkill vi

# Terminate process: Owned by specific user
sudo pkill vi -u username

# Terminate all processes running under the specified username "username"
kill -9 $(lsof -t -u username)

# Trace system calls made by process: For example df -h (Check which mountpoint is stuck)
strace df -h

# Output summary instead of full output
strace -c df -h

# Save output to file
strace -o strace.txt df -h

# Trace already running process: Replace PID with process ID
strace -p PID

# Displays all the current ulimit settings
ulimit -a

# Set the maximum number of processes available to a single user
ulimit -u [number]

# Sets the maximum number of user processes to unlimited
ulimit -u unlimited

# Enable service at boot
sudo systemctl enable servicename

# Disable service at boot
sudo systemctl disable servicename

# Start service
sudo systemctl start servicename

# Stop service
sudo systemctl stop servicename

# Restart service
sudo systemctl restart servicename

# Reload service without interrupting normal functionality
sudo systemctl reload servicename

# Service status
sudo systemctl status servicename

# View the systemd journal logs
journalctl -xeu servicename

# List all journal log entries: Starting at the oldest entry
journalctl

# List journal log entries from the current boot
journalctl -b

# List journal log entries from the current boot: Start with newest entry
journalctl -b -e

# List journal log entries: Kernel only
journalctl -k

# List journal log entries: Kernel only, from the current boot, start with newest entry
journalctl -k -b -e

# List journal log entries for unit / service
journalctl -u nginx

# List journal log entries for unit / service: Current boot
journalctl -b -u nginx.service

# List journal log entries for unit / service: Current boot, add explanatory text & start at end
journalctl -xeu servicename

# Move through journalctl: Line by line
arrow up / down

# Move through journalctl: A page at the time
bild(page) up / down

# List services and units that are enabled to start at boot
sudo systemctl list-unit-files

# List currently loaded / active units: All currently loaded units that systemd has active or has attempted to start
sudo systemctl list-units

# List units the are active, inactive or in a failed state
sudo systemctl list-units --all

# List contents of a unit file
sudo systemctl cat nginx

# List dependency tree of a unit: Units systemd will attempt to activate when starting the unit
sudo systemctl list-dependencies nginx

# Modify unit file: Add snippet, changes are kept separate from the original file
sudo systemctl edit nginx

# Modify unit file: Edit entire file
sudo systemctl edit --full nginx

# Reload systemd after modifying a unit file
sudo systemctl daemon-reload

# List all active targets
sudo systemctl list-units --type=target

# List all available targets
sudo systemctl list-unit-files --type=target

# List default target that the system is configured to use at boot
sudo systemctl get-default

# Set default target
sudo systemctl set-default target-name

# Swtich to different Target (Immediately)
sudo systemctl isolate target-name

# Mask service
sudo systemctl mask service_name.service

# Unmask service
sudo systemctl unmask service_name.service

# Disable service after boot
sudo update-rc.d servicename disable

# Remove service from the system's startup sequence
sudo update-rc.d -f nginx remove

# Enable service after boot
sudo update-rc.d servicename defaults

# Start service
sudo service servicename start

# Stop service
sudo service servicename stop

# Restart service
sudo service servicename restart

# Reload service
sudo service servicename reload

# Service status
sudo service servicename status

# Init.d scripts directory
/etc/init.d/

# Start service script
sudo /etc/init.d/servicename start

# Stop service script
sudo /etc/init.d/servicename stop

# Restart service script
sudo /etc/init.d/servicename restart

# Reload service script
sudo /etc/init.d/servicename reload

# Display the previous and current runlevel
runlevel

# Shell output:
N 2

# Change runlevel: Change to runlevel 1
sudo init 1

# or
telinit 1

# Install needrestart
sudo apt install needrestart

# Check if a reboot is necessary
needrestart

# Shut down
sudo shutdown now

# Shut down: Older distributions
sudo shutdown -h now

# Systemctl command
sudo systemctl poweroff

# Reboot
sudo shutdown now -r
# or
sudo reboot

# Cancel reboot
sudo shutdown -c


# Systemctl command
sudo systemctl reboot

sudo systemctl rescue

#!/bin/sh
printf "\n$(cat /etc/update-motd.d/mytext.asc)\n"

# Open YaST GUI
sudo yast

# Check status
sestatus

# Enable SELinux passive mode: Log policy violations but don't enforce them
sudo setenforce 0

# Reenable SELinux back to enforcing mode
sudo setenforce 1

# Open SELinux configuration
sudo vi /etc/selinux/config

# Disable SELinux
SELINUX=disabled

# Enable SELinux
SELINUX=enforcing

# Reboot
sudo reboot

# Start Kdump
sudo systemctl start kdump

# Stop Kdump
sudo systemctl stop kdump

# Check status
sudo systemctl status kdump

# Enable service after boot
sudo systemctl enable kdump

# Disbale service after boot
sudo systemctl disable kdump

# Kdump configuration
sudo vi /etc/kdump.conf

# Default default crash dump location
/var/crash

# Crash dump will be save into a sub directory with hostname and date:
/var/crash/127.0.0.1-2023-12-26-13:39:35

# Switch to root user
sudo su

# Intentionally initiate a kernel panic and capture a crash dump: For debugging and testing purposes
echo c > /proc/sysrq-trigger

# Install crash package
sudo dnf install crash

# Manual
crash -h

# List installed packages:
dpkg -l


# List details of specific package
dpkg -l | grep apache2

# Shell output:
rc  apache2                               2.4.52-1ubuntu4.7                       amd64        Apache HTTP Server

# Update package index
sudo apt update

# List upgradeable packages
apt list --upgradable

# Upgrade installed packages
sudo apt upgrade

# Upgrade installed packages, dependencies & kernel: Install & remove packages
sudo apt dist-upgrade

# Install package
sudo apt install packagename

# Reinstall package
sudo apt install --reinstall packagename

# Remove package but not the data and configuration files
sudo apt remove packagename

# Remove software package and the related data and configuration files
sudo apt purge packagename

# Remove dependency packages that are not required any more
sudo apt autoremove

# Package version, size, installed size, dependencies
sudo apt info packagename

# List package version in repository
sudo apt show packagename

# List of software repositories
sudo vi /etc/apt/sources.list

# Unattended upgrades configuration
sudo vi /etc/apt/apt.conf.d/50unattended-upgrades

# Check configuration
sudo unattended-upgrade --dry-run

# Enable unattended-upgrades after reboot
sudo systemctl enable unattended-upgrades

# Start unattended-upgrades service
sudo systemctl start unattended-upgrades

# List GPG keys
sudo apt-key list

# Shell output:
Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
/etc/apt/trusted.gpg
--------------------
pub   rsa4096 2015-09-15 [SC]
      08B7 3419 AC32 B4E9 66C1  A330 E84A C2C0 460F 3994
uid           [ unknown] Ceph.com (release key) <security@ceph.com>

/etc/apt/trusted.gpg.d/ubuntu-keyring-2012-cdimage.gpg
------------------------------------------------------
pub   rsa4096 2012-05-11 [SC]
      8439 38DF 228D 22F7 B374  2BC0 D94A A3F0 EFE2 1092
uid           [ unknown] Ubuntu CD Image Automatic Signing Key (2012) <cdimage@ubuntu.com>

/etc/apt/trusted.gpg.d/ubuntu-keyring-2018-archive.gpg
------------------------------------------------------
pub   rsa4096 2018-09-17 [SC]
      F6EC B376 2474 EDA9 D21B  7022 8719 20D1 991B C93C
uid           [ unknown] Ubuntu Archive Automatic Signing Key (2018) <ftpmaster@ubuntu.com>

# Remove APT GPG key: For example Ceph key
sudo apt-key del 460F3994

# Install Nala
sudo apt install nala -y

# Nala command overview
nala -h

# Find fastest mirror / update mirrors
sudo nala fetch

# Update package index
sudo nala update

# List upgradeable packages
nala list --upgradable

# Upgrade packages
sudo nala upgrade

# Install package 
sudo nala install packagename

# Remove package but not the data and configuration files
sudo nala remove packagename

# Remove software package and the related data and configuration files
sudo nala purge packagename

# Remove dependency packages that are not required any more
sudo nala autoremove

# List recently run nala commands
nala history

# Shell outpuit:
ubuntu@ubuntu:~$ nala history
  ID    Command                                                                                                                             Date and Time              Altered    Requested-By
  1     install nginx                                                                                                                       2023-12-30 12:07:22 UTC         20    ubuntu (1000)
  2     upgrade cryptsetup cryptsetup-bin cryptsetup-initramfs libcryptsetup12 libssh-4 openssh-client openssh-server openssh-sftp-serv…    2023-12-30 12:11:54 UTC         14    ubuntu (1000)


# Details about a history event
nala history info 1

# Undo history element (upgrade / install)
sudo nala history undo 1

# Install snap
sudo apt install snapd

# Check snap version
snap --version

# Upgrade package
sudo snap refresh packagename

# Upgrade all installed snap packages
sudo refresh

# Install package
sudo snap install packagename

# Uninstall package
sudo snap remove packagename

# Info for snap package
sudo nap find packagename

# Find available packages to install
sudo snap find packagename

# List installed packages
snap list

# List installed and disabled packages
snap list --all

# Update & upgrade
sudo apt update && sudo apt upgrade -y

# Install flatpak
sudo apt install flatpak -y

# Add the Flathub repository
sudo flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo

# Optional: Reboot the system
sudo reboot

# Verify installation / check version
flatpak --version

# Search for package
sudo flatpak search packagename

# Install package
flatpak install flathub application-id -y

# Start & run package
flatpak run <application-id>

# Update package index
sudo dnf makecache

# List upgradeable packages
sudo dnf check-update
# or
sudo dnf list updates

# Upgrade packages
sudo dnf update

# Upgrade specific package
sudo dnf update httpd

# Install package
sudo dnf install packagename

# Uninstall package
sudo dnf remove packagename

# List enabled repositories
sudo dnf repolist

# List available repositories
sudo dnf repolist --all

# Enable repository
sudo dnf config-manager --enable reponame

# Disable repository
sudo dnf config-manager --disable reponame

# Add repository from URL
sudo dnf config-manager --add-repo="URL"

# Upgrade to newer OS release 
sudo do-release-upgrade

# Install prerequisites
sudo apt install unzip wget -y

# Change directory
cd /usr/local/src

# Download source code: tar or zip
wget https://github.com/htop-dev/htop/archive/refs/tags/3.3.0.zip

# Unpack: tar
tar -xvzf 3.3.0.tar.gz

# Unpack: zip
sudo unzip 3.3.0.zip

# Download source code
git clone https://github.com/htop-dev/htop.git

# Change owner
sudo chown -R `whoami`:`whoami` htop/

# Change directory
cd htop

# Open readme file
less README

# Install htop dependencies
sudo apt install libncursesw5-dev autotools-dev autoconf automake build-essential

# Compile the package from source
./autogen.sh && ./configure && make

# Install package: In "/usr/local" directory
sudo make install

# Run htop
htop

# Create User
sudo adduser username

# Create User: Without PW
sudo adduser --disabled-password  username

# Create User: Without PW
sudo adduser username && sudo passwd -d username

# Switch user
sudo su username

# Exit user session
exit

# Change password of actual user
passwd

# Output username
whoami

# Delete user without home directory
sudo deluser username

# Delete user and home directory
sudo deluser --remove-home username

# Delete user without home directory
sudo userdel username

# Delete user and home directory
sudo userdel -r username

# Lock / Deactivate User:
sudo passwd -l username

# Unlock / Reactivate
sudo passwd -u username

# Shell Output: (Lock and unlock)
passwd: password expiry information changed


#Check User Status:
passwd -S username

# Expire account immediately
sudo chage -E 0 username

# Account never expires
sudo chage -E -1 username


# Display Current Expiry Information
sudo chage -l username

# Switch to sudo: Maintain current shell environment
su

# Switch to sudo: Invokes login shell 
su -

# Install Sudo (Debian)
apt install sudo

# Edit sudoers file
sudo visudo

# Sudoers Path: Edit with visudo
/etc/sudoers

# Create a user specific sudoers file
vi /etc/sudoers.d/username

# Change permissions
chmod 440 /etc/sudoers.d/username

# Run any command as any user, including root: Password required
username ALL=(ALL) ALL

# Run any command as any user, including root: No password required
username ALL=(ALL) NOPASSWD:ALL

# Open .bashrc of current user
cd && vi .bashrc

# Add "sbin" & "/usr/sbin" to search system administration utilities when using sudo
PATH=$PATH:/usr/sbin:/sbin

# Run several Commands as sudo
sudo sh -c 'command1 && command2 >> file'

# Create RSA Key: 4096 bit
ssh-keygen -t rsa -b 4096

# Create RSA Key: With comment
ssh-keygen -t rsa -b 4096 -C "user1"

# Create RSA Key: With custom file name
ssh-keygen -t rsa -b 4096 -f ~/.ssh/keyname

# Connect to Server
ssh user@IP

# Connect to Server: Custom port
ssh -p 2222 user@IP

# Connect to Server: Define specific SSH Key
ssh -i /path/to/private_key user@IP`

# Connect to Server: Verbose for debugging
ssh -v -i /path/to/private_key user@IP

# Connect to Server: Define Encryption Key
ssh -v -i /path/to/private_key -o PubkeyAcceptedKeyTypes=ssh-rsa user@IP

# Connect to a remote Server without SSH Key
ssh -o PasswordAuthentication=yes -o PreferredAuthentications=keyboard-interactive,password -o PubkeyAuthentication=no user@IP

# Copy SSH Key to Server
ssh-copy-id -i ~/.ssh/keyename user@IP

# Create directory
mkdir ~/.ssh

# Change permission
chmod 700 ~/.ssh

# Manually add SSH Keys
vi .ssh/authorized_keys

# Change permission
chmod 600 ~/.ssh/authorized_keys


# Change permission of SSH Key (in case the key was copied)
chmod 400 ~/.ssh/keyname

# Define specific SSH port for host: Syntax
Host DNS or IP
  Port 2222

# Define specific SSH port for host: Example
Host 192.168.30.70
  Port 2222

# Define specific SSH port & oint to a specific SSH Key
Host DNS or IP
  Preferredauthentications publickey
  IdentityFile ~/.ssh/id_rsa
  Port 2222

# Open the SSH daemon configuration
sudo vi /etc/ssh/sshd_config

# Define the port
Port 2280

# Restart sshd service
sudo systemctl restart sshd

    # Check if SSH Agent is running
if [[ "$SSH_AUTH_SOCK" = "" ]]; then
    # Start SSH Agent
    exec ssh-agent bash
else
    # Add SSH Keys
    ssh-add
fi

sudo vi /etc/ssh/sshd_config

# Allow SSH root login: Only Key Authentication 
PermitRootLogin prohibit-password

# Allow SSH root login: Allow Passowrd
PermitRootLogin yes

# Disable SSH root login
PermitRootLogin no

# Reload SSH Service
sudo systemctl reload ssh

# Check known_hosts file
cat ~/.ssh/known_hosts

# Host keys directory
/etc/ssh

# Create backup directory
sudo mkdir /etc/ssh/backup_keys_$(date +%F)

# Backup the existing host keys
sudo cp /etc/ssh/ssh_host_* /etc/ssh/backup_keys_$(date +%F)/

# Remove the old host keys
sudo rm /etc/ssh/ssh_host_*

# Create new host keys: For all key types for which host keys do not already exist
sudo ssh-keygen -A

# Restart SSH service (Should not be necessary)
sudo systemctl restart ssh

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

# Remove host key: Current user
ssh-keygen -R 192.168.30.60

# Remove host key: Specific user
ssh-keygen -f "/home/debian/.ssh/known_hosts" -R "192.168.30.60"

# Connect to target host: Syntax
ssh -J jumpuser@jump-host targetuser@target-host

# Verbose Mode
ssh -v -J jumpuser@jump-host targetuser@target-host

# Connect to target host: Example
ssh -J debian@192.168.30.61 debian@192.168.30.62

# Shell output:
debian@192.168.30.61's password:
debian@192.168.30.62's password:

vi ~/.ssh/config

# Define jump host
Host jump-host
  HostName 192.168.30.61
  User debian

# Define final target host using the jump host
Host target-host
  HostName 192.168.30.62
  User debian
  ProxyJump jump-host

# Connect to target host: The connection will automatically be routed through jump-host
ssh target-host

# Verbose Mode
ssh -v target-host

# Establish Socks Proxy connection: Permanent
ssh -fN -D 9999 debian@192.168.30.61

# Establish Socks Proxy connection: 2 minutes
ssh -f -D 9999 debian@192.168.30.61 sleep 120

# Test the connection
all_proxy="socks5://127.0.0.1:9999" curl 127.0.0.1:80

# List SSH processes
ps aux | grep ssh

# Shell output:
debian     22892  0.0  0.0  14284  5264 ?        Ss   20:00   0:00 ssh -f -D9999 debian@192.168.30.61 sleep 120

# Terminalte process
kill 22892

# Install cpu-checker / kvm-ok utility
sudo apt install cpu-checker -y

# check if KVM virtualization is supported
kvm-ok

# Shell output
INFO: /dev/kvm exists
KVM acceleration can be used

# Install packages
sudo apt install qemu-kvm virt-manager virtinst libvirt-clients bridge-utils libvirt-daemon-system -y

# Add user to groups
sudo usermod -aG libvirt ubuntu
sudo usermod -aG kvm ubuntu

# Start Virt Manager
virt-manager

# List running VMs
virsh list

# List running & stopped VMs
virsh list --all

# Start VM
virsh start vmname

# Stop VM
virsh shutdown vmname

# Shutdown VM
virsh destroy vmname

# VM logs
cat /var/log/libvirt/qemu/vm-name.log

# Define VM: Create VM from XML file
virsh define file.xml

# Undefine VM: XML file will not be deleted
virsh undefine vmname

# Edit undefined XML file
vi vmname.XML

# Edit defined XML file
virsh edit vmname

# List VM details
virsh dominfo vmname

# List VM details: List XML details
virsh dumpxml vmname

# List VM details: Save XML details into file
virsh dumpxml vmname > filename.txt

# Default XML path
/etc/libvirt/qemu

# Default qcow2 path
/var/lib/libvirt/images/


# Grep for "source"
virsh dumpxml vmname | grep source

# Or grep for "qcow"
virsh dumpxml vmname | grep qcow

# Open qcow dir
cd /path/to/qcow_files

# List reserved storage of qcow file
ls -alh

# List actual storage used for qcow file
du -alh

# Expand qcow file (Stop VM first)
sudo qemu-img resize /path/to/vmname.qcow2 +10G

# Check disk size with fdisk
sudo fdisk -l /path/to/vmname.qcow2

# Shrink qcow file (Stop VM first): New size = 100G
qemu-img resize --shrink /path/to/vmname.qcow2 100G

# Note: the VM partition must first be shrinked from within the VM

# Convert qcow2 image to vmdk image
qemu-img convert -p -f qcow2 -O inputfile.qcow2 outputfile.vmdk

# Help
ip help

# List interfaces: With IP Addresses
ip a
# List interfaces / colored output
ip -c a
# List interface: Only IPv4 Addresses
ip -c -4 a


# List interfaces: Show status up/down
ip link # or
ip link show

# Check specific interface status
ip link show eth0


# Set interface status: Up
ip link set dev eth0 up
ip link set dev eth0 down


# List physical interfaces
sudo lshw -class network


# List details of physical interface
sudo ethtool -k eth0

#  Assign IP address (till reboot)
ip addr add dev eth0 192.198.30.15/24

# Check IP for eth0 
ip addr list eth0

# Release current DHCP lease
dhclient -r

# Request a new DHCP lease
dhclient

# List routing tables 
ip route show

# List specific routing table
sudo ip route show table 101


# Add entry to routing table: Set up Default Gateway
ip route add default via 192.168.0.1

# Add entry to routing table: Route IP range through specific interface
ip route add 192.0.2.0/24 via 192.168.0.2 dev eth1

# Install package
apt install net-tools -y

# List ARP tables: Use DNS names
arp

# List ARP tables: Use IP
arp -n

# List all network interfaces and their status
networkctl

# List detailed information about interface
networkctl status br30

# Path to Netplan Configuration Files
/etc/netplan/

# Default Configuration File
sudo vi /etc/netplan/00-installer-config.yaml

# Apply Netplan Changes (Reboot after severe changes)
sudo netplan apply

network:
  ethernets:
    ens33:
      dhcp4: true
  version: 2

network:
  renderer: networkd
  ethernets:
    ens33:
      dhcp4: true
      dhcp4-overrides:
        use-dns: false
      nameservers:
        addresses:
          - "1.1.1.1"
          - "8.8.8.8"
  version: 2

network:
  ethernets:
    eno1:
      addresses:
      - 192.168.10.80/24 # Define IPv4
      nameservers:
        addresses:
        - 1.1.1.1 # Primary DNS Server
        - 8.8.8.8 # Secondary DNS Server
        search: []
      routes:
      - to: default
        via: 192.168.10.1 # Default Gateway
  version: 2

# Install VLAN package:  Necessary to create and manage VLANs in Ubuntu
sudo apt install vlan -y

# Load 8021q Kernel Module: Responsible for VLAN tagging in the Linux kernel
sudo modprobe 8021q

# Load Kernel Module: After reboot
echo "8021q" | sudo tee -a /etc/modules

# VLANs from switch
192.168.10.0/24 Untagged
192.168.30.0/24 Tagged
192.168.70.0/24 Tagged

network:
  ethernets:
    eno1:
      addresses:
      - 192.168.10.80/24
      nameservers:
        addresses:
        - 1.1.1.1
        - 8.8.8.8
      routes:
      - to: default
        via: 192.168.10.1
  vlans:
    eno1.30: # VLAN 1
      id: 30
      link: eno1
      dhcp4: true
      nameservers:
        addresses:
        - 1.1.1.1
        - 8.8.8.8
    eno1.70: # VLAN 2
      id: 70
      link: eno1
      dhcp4: true
      nameservers:
        addresses:
        - 1.1.1.1
        - 8.8.8.8
  version: 2

network:
  ethernets:
    eno1:
      addresses:
      - 192.168.10.80/24
      nameservers:
        addresses:
        - 1.1.1.1
        - 8.8.8.8
        search: []
      routes:
      - to: default
        via: 192.168.10.1
  vlans:
    eno1.30: # VLAN 1
      id: 30
      link: eno1
      addresses:
        - 192.168.30.80/24 # Define IP address
      nameservers:
        addresses:
          - 1.1.1.1
          - 8.8.8.8
    eno1.70: # VLAN 2
      id: 70
      link: eno1
      addresses:
        - 192.168.70.80/24 # Define IP address
      nameservers:
        addresses:
          - 1.1.1.1
          - 8.8.8.8
  version: 2

# List network interfaces with their IPv4 addresses
ip -4 a

# Shell output:
2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    altname enp0s31f6
    inet 192.168.10.80/24 brd 192.168.10.255 scope global eno1
       valid_lft forever preferred_lft forever
4: eno1.30@eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    inet 192.168.30.80/24 brd 192.168.30.255 scope global eno1.30
       valid_lft forever preferred_lft forever
5: eno1.70@eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    inet 192.168.70.80/24 brd 192.168.70.255 scope global eno1.70
       valid_lft forever preferred_lft forever

network:
  ethernets:
    eno1:
      addresses:
      - 192.168.10.80/24
      nameservers:
        addresses:
        - 1.1.1.1
        - 8.8.8.8
      routes:
      - to: default
        via: 192.168.10.1
  vlans:
    eno1.30: # VLAN 1
      id: 30
      link: eno1
    eno1.70: # VLAN 2
      id: 70
      link: eno1
  bridges:
    br30: # Bridge 1
      interfaces: [eno1.30]
      dhcp4: true
      nameservers:
        addresses:
        - 1.1.1.1
        - 8.8.8.8
      parameters:
        forward-delay: 0
        stp: true
    br70: # Bridge 2
      interfaces: [eno1.70]
      dhcp4: true
      nameservers:
        addresses:
        - 1.1.1.1
        - 8.8.8.8
      parameters:
        forward-delay: 0
        stp: true
  version: 2

network:
  ethernets:
    eno1:
      addresses:
      - 192.168.10.80/24
      nameservers:
        addresses:
        - 1.1.1.1
        - 8.8.8.8
      routes:
      - to: default
        via: 192.168.10.1
  vlans:
    eno1.30: # VLAN 1
      id: 30
      link: eno1
    eno1.70: # VLAN 2
      id: 70
      link: eno1
  bridges:
    br30: # Bridge 1
      interfaces: [eno1.30]
      addresses:
        - 192.168.30.80/24 # Define IP address
      nameservers:
        addresses:
        - 1.1.1.1
        - 8.8.8.8
      parameters:
        forward-delay: 0
        stp: true
    br70: # Bridge 2
      interfaces: [eno1.70]
      addresses:
        - 192.168.70.80/24 # Define IP address
      nameservers:
        addresses:
        - 1.1.1.1
        - 8.8.8.8
      parameters:
        forward-delay: 0
        stp: true
  version: 2

# List all available Network Interfaces
ip link show

# Path to Network Configuration
vi /etc/network/interfaces

# Apply Changes to Network Interface
ifdown enp1s0 && ifup enp1s0

# Reinitialize network configuration (After fundamental changes)
systemctl restart networking

# Check status
systemctl status networking

# It's better to reboot after compley network changes!
reboot

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug enp2s0
iface enp2s0 inet dhcp

# The primary network interface
auto enp2s0 # Auto up after boot
allow-hotplug enp2s0
iface enp2s0 inet dhcp

# The primary network interface
auto enp2s0
iface enp2s0 inet static
    address 192.168.30.10/24
    gateway 192.168.30.1 # Define gateway to WAN
    dns-nameservers 1.1.1.1 8.8.8.8 # Define DNS server

# The primary network interface
auto enp2s0
iface enp2s0 inet static
    address 192.168.70.20/24
    gateway 192.168.70.1

# Second network interface
auto enp1s0f1
iface enp1s0f1 inet static
    address 192.168.30.20/24

# Install bridge-utils
sudo apt install bridge-utils

## DHCP ip config file for br0 ##
auto vmbr1
 
# Bridge setup
iface vmbr1 inet dhcp
    bridge_ports enp2s0

# The primary network interface
auto enp2s0
iface enp2s0 inet manual

auto vmbr0
iface vmbr0 inet static
        address 192.168.30.10/24
        gateway 192.168.30.10
        bridge-ports enp1s0 # Define ports
        bridge-stp off # Panning Tree Protocol (STP) off
        bridge-fd 0 # Sets bridge forwarding delay to 0

# The primary network interface
auto enp2s0
iface enp2s0 inet manual

auto vmbr0
iface vmbr0 inet static
    address 192.168.70.20/24
    gateway 192.168.70.1
    bridge_ports enp2s0
    bridge_stp off
    bridge_fd 0

# Second network interface
auto enp1s0f1
iface enp1s0f1 inet manual

auto vmbr1
iface vmbr1 inet static
    address 192.168.30.20/24
    bridge_ports enp1s0f1
    bridge_stp off
    bridge_fd 0

# Install VLAN package
apt install vlan -y

# Load VLAN module & enable startup
modprobe 8021q && echo "8021q" >> /etc/modules

# Delete VLAN interface
ip link set eno1.50 down
ip link delete eno1.50

# Default untagged network
auto eno1
iface eno1 inet static
    address 192.168.30.40/24
    gateway 192.168.30.1

# VLAN 1: (Tagged) DHCP
auto eno1.50
iface eno1.50 inet dhcp

# VLAN 2: (Tagged) DHCP
auto eno1.70
iface eno1.70 inet dhcp

# Default untagged network
auto eno1
iface eno1 inet static
    address 192.168.30.40/24
    gateway 192.168.30.1

# VLAN 1: (Tagged) Static IPv4
auto eno1.50
iface eno1.50 inet static
    address 192.168.50.40/24

# VLAN 2: (Tagged) Static IPv4
auto eno1.70
iface eno1.70 inet static
    address 192.168.70.40/24

# Edit network configuration
sudo vi /etc/sysconfig/network/ifcfg-eth0

# Apply new configuration
sudo systemctl restart wicked

# Interface up
sudo wicked ifup eth0

# Interface down
sudo wicked ifdown eth0

# Interface status: All interfaces
sudo wicked ifstatus all

# Interface status: Specific interface
sudo wicked ifstatus eth0

# Shell output:
eth0            up
      link:     #2, state up, mtu 1500
      type:     ethernet, hwaddr 00:0c:29:36:84:e3
      config:   compat:suse:/etc/sysconfig/network/ifcfg-eth0 # Path to interface config
      leases:   ipv4 static granted
      addr:     ipv4 192.168.30.85/24 [static]

BOOTPROTO='dhcp'
STARTMODE='auto'
ZONE=public

BOOTPROTO='static'
STARTMODE='auto'
ZONE=public
IPADDR='192.168.30.85'
NETMASK='255.255.255.0'
BROADCAST='192.168.30.255'
GATEWAY='192.168.30.1'

# List network interfaces / status
nmcli dev status

# Shell output:
DEVICE  TYPE      STATE                   CONNECTION
ens160  ethernet  connected               ens160
lo      loopback  connected (externally)  lo


# List inferface details (IP, Gateway,...): All interfaces
nmcli con show 

# List inferface details (IP, Gateway,...): Specific interface
nmcli con show ens160

# Start interfaces
sudo nmcli con up id ens160

# Stop interfaces
sudo nmcli con down id ens160

# Set to static IPv4
sudo nmcli con modify ens160 ipv4.method manual
# Set to DHCP
sudo nmcli con modify ens160 ipv4.method auto


# Define IPv4 address
sudo nmcli con modify ens160 ipv4.address 192.168.30.85/24

# Define default gateway
sudo nmcli con mod ens160 ipv4.gateway 192.168.30.1

# Define DNS server
sudo nmcli con mod ens160 ipv4.dns "1.1.1.1 8.8.8.8"

# Set static IPv4 configuration: Define IPv4 address & gateway
nmcli con modify ens160 ipv4.method manual ipv4.address 192.168.30.85/24 ipv4.gateway 192.168.30.1

# Add Connection-Profile
nmcli con add con-name ens160-con2 type ethernet ifname ens160 ipv4.method auto

# Delete Connection-Profile
nmcli con del ens160-con2

# Enable Connection-Profile
nmcli con up id ens160

# Configuration directory
cd /etc/NetworkManager/system-connections/

# Open configuration: 
sudo vi /etc/NetworkManager/system-connections/ens160.nmconnection

# Apply changes
sudo systemctl restart NetworkManager

# Alternative: Reboot to apply the settings
sudo reboot

# Create a VLAN interface eth0.99 on top of eth0 with VLAN ID 99
sudo nmcli con add type vlan con-name eth0.99 ifname eth0.99 dev eth0 id 99

# Configure the IP Address
sudo nmcli con mod eth0.99 ipv4.addresses 10.10.99.11/24 ipv4.gateway 10.10.99.1 ipv4.dns "1.1.1.1,8.8.8.8" ipv4.method manual

# Enable the interface
sudo nmcli con up eth0.99

# Delete VLAN interface
sudo nmcli connection delete eth0.99

# Install NetworkManager package
sudo zypper install NetworkManager-tui

# Status
sudo systemctl status NetworkManager

# Start NetworkManager
sudo systemctl start NetworkManager

# Enable NetworkManager
sudo systemctl enable NetworkManager


# Start network editor (GUI)
sudo nmtui

# Apply the new configuration
sudo service network restart

# Saved NetworkManager configuration
sudo vi /etc/NetworkManager/system-connections/eth0.nmconnection

[connection]
id=eth0
uuid=6e19a7c4-bea3-4bc1-b9bd-bc2b0c1b8853
type=ethernet
autoconnect=false
interface-name=eth0
timestamp=1694360823

[ethernet]
mac-address=00:0C:29:36:84:E3

[ipv4]
method=auto

[ipv6]
addr-gen-mode=stable-privacy
method=link-local

[proxy]

[connection]
id=eth0
uuid=6e19a7c4-bea3-4bc1-b9bd-bc2b0c1b8853
type=ethernet
autoconnect=false
interface-name=eth0
timestamp=1694360823

[ethernet]
mac-address=00:0C:29:36:84:E3

[ipv4]
address1=192.168.30.85/24,192.168.30.1
dns=1.1.1.1;8.8.8.8;
method=manual

[ipv6]
addr-gen-mode=stable-privacy
method=link-local

[proxy]

# Output current DNS server
cat /etc/resolv.conf

# Output current DNS server
resolvectl status

# Resolve DNS to IP
nslookup hostname.com

# Resolve DNS to IP: Define DNS server
nslookup hostname.com 192.168.70.1


# Resolve IP to DNS
nslookup IP

# Resolve IP to DNS: Define DNS server
nslookup IP 192.168.70.1