sudo apt update && sudo apt upgrade -y    # update everything
sudo apt install build-essential curl wget git vim -y  # essentials
sudo apt install ubuntu-restricted-extras -y  # codecs, fonts
# Install proprietary drivers (NVIDIA etc.)
sudo ubuntu-drivers autoinstall
# Or manually: Software & Updates → Additional Drivers

wsl --install                  # installs Ubuntu by default
wsl --install -d Ubuntu-24.04  # specific version

# AWS: search "Ubuntu" in AMI marketplace — official Canonical AMIs
# Azure: az vm create --image Ubuntu2204 ...
# GCP: gcloud compute instances create ... --image-family ubuntu-2404-lts
# DigitalOcean, Linode, Vultr: Ubuntu available as default droplet/instance image

uname -r                       # current kernel version
uname -a                       # full kernel + system info
cat /proc/version              # kernel version + compiler
ls /boot/vmlinuz*              # installed kernels
sudo apt install linux-generic-hwe-22.04  # install HWE kernel

echo $SHELL                    # current shell
cat /etc/shells                # available shells
chsh -s /bin/zsh               # change default shell

pwd                            # print working directory
ls                             # list files
ls -la                         # detailed + hidden files
ls -lh                         # human-readable sizes
ls -lt                         # sort by modification time
cd /path  cd ~  cd ..  cd -    # navigate
touch file.txt                 # create file / update timestamp
touch file{1..5}.txt           # create file1.txt through file5.txt
mkdir dirname                  # create directory
mkdir -p a/b/c                 # create nested directories
cp source dest                 # copy file
cp -r src/ dest/               # copy directory recursively
cp -p source dest              # preserve permissions + timestamps
mv source dest                 # move or rename
rm file.txt                    # delete file
rm -rf dirname/                # delete directory (careful!)
ln -s target linkname          # create symbolic link
ln target hardlink             # create hard link
cat file.txt                   # print file
less file.txt                  # paginated view (q to quit)
head -n 20 file.txt            # first 20 lines
tail -n 20 file.txt            # last 20 lines
tail -f /var/log/syslog        # follow log live
file filename                  # show file type
wc -l file.txt                 # count lines
stat file.txt                  # detailed file info (size, inode, times)

find / -name "*.conf"          # find by name
find /home -type f -size +1M   # files > 1MB
find . -mtime -7               # modified in last 7 days
find . -perm 777               # files with 777 permissions
find . -name "*.log" -delete   # find and delete
locate filename                # fast search (uses updatedb database)
sudo updatedb                  # update locate database
which python3                  # find executable location
whereis nginx                  # find binary + man page + source
type ls                        # show if alias/builtin/file

command > file.txt     # stdout to file (overwrite)
command >> file.txt    # stdout to file (append)
command 2> error.txt   # stderr to file
command 2>&1           # stderr → stdout
command &> file.txt    # both stdout + stderr
command < file.txt     # file as stdin
cmd1 | cmd2            # pipe stdout of cmd1 to cmd2
cmd1 |& cmd2           # pipe stdout + stderr
 
# Text processing
grep "pattern" file            # search pattern
grep -r "pattern" dir/         # recursive
grep -i -v -n "pattern" file   # case-insensitive / invert / line numbers
grep -E "regex" file           # extended regex
awk '{print $1}' file          # print first column
awk -F: '{print $1}' /etc/passwd  # custom delimiter
sed 's/old/new/g' file         # replace all occurrences
sed -i 's/old/new/g' file      # in-place edit
cut -d: -f1 /etc/passwd        # cut field 1 with : delimiter
sort file                      # sort alphabetically
sort -n file                   # sort numerically
sort -rn file                  # reverse numeric sort
uniq                           # remove adjacent duplicates
sort file | uniq -c | sort -rn # count occurrences
tr 'a-z' 'A-Z'                 # translate characters
tee file.txt                   # write to file AND stdout
xargs                          # build commands from stdin

nano file.txt          # beginner-friendly
# Ctrl+O → save  Ctrl+X → exit  Ctrl+W → search  Ctrl+K → cut line
 
vim file.txt           # powerful modal editor
# Modes: Normal (default) | Insert (i) | Visual (v) | Command (:)
# :w save  :q quit  :wq save+quit  :q! force quit
# dd delete line  yy copy  p paste  /word search  n next match
# :%s/old/new/g  replace all
 
nano ~/.bashrc         # edit bash config
source ~/.bashrc       # reload without restarting terminal

#!/bin/bash
# Variables
name="Ubuntu"
version=24
readonly PI=3.14       # constant
 
# String operations
echo "Hello, $name"
echo "Length: ${#name}"
echo "Upper: ${name^^}"
echo "Slice: ${name:0:3}"
 
# Conditionals
if [ "$version" -ge 22 ]; then
    echo "Modern Ubuntu"
elif [ "$version" -eq 20 ]; then
    echo "Ubuntu 20"
else
    echo "Older Ubuntu"
fi
 
# File tests
[ -f file.txt ] && echo "file exists"
[ -d /etc ]     && echo "directory exists"
[ -r file.txt ] && echo "readable"
[ -x script.sh ] && echo "executable"
 
# Loops
for i in {1..5}; do echo "Item $i"; done
for file in *.txt; do echo "$file"; done
while read line; do echo "$line"; done < file.txt
 
# Functions
greet() {
    local name="$1"
    echo "Hello, ${name:-World}!"
}
greet "Ubuntu"
 
# Arrays
fruits=("apple" "banana" "cherry")
echo "${fruits[0]}"           # first element
echo "${fruits[@]}"           # all elements
echo "${#fruits[@]}"          # array length
 
# Exit codes
command && echo "success" || echo "failed"
command; echo "exit code: $?"

ps aux                         # all running processes
ps aux | grep nginx            # filter by name
ps -ef --forest                # process tree with parent info
top                            # real-time monitor (q to quit)
htop                           # improved top (sudo apt install htop)
pgrep nginx                    # get PID by name
pstree                         # visual process tree
pstree -p                      # with PIDs

kill PID                       # SIGTERM — graceful stop
kill -9 PID                    # SIGKILL — force kill
kill -HUP PID                  # SIGHUP — reload config
killall nginx                  # kill all by name
pkill -f "python script.py"    # kill by pattern
command &                      # run in background
Ctrl+Z → bg                    # suspend then background
fg                             # bring to foreground
fg %2                          # bring job 2 to foreground
jobs                           # list background jobs
nohup command &                # survive logout
disown %1                      # detach job from shell

uname -a                       # kernel + system info
hostname                       # system hostname
hostname -I                    # all IP addresses
whoami                         # current user
id                             # UID, GID, groups
uptime                         # uptime + load average
w                              # who is logged in + what they're doing
last                           # login history
df -h                          # disk space usage
df -hT                         # with filesystem type
du -sh /path                   # directory size
du -sh /* 2>/dev/null | sort -rh | head -20  # top 20 largest dirs
free -h                        # RAM + swap usage
lscpu                          # CPU info
lsblk                          # block devices
lsblk -f                       # with filesystem types
lsusb                          # USB devices
lspci                          # PCI devices
lshw -short                    # hardware summary
cat /proc/cpuinfo              # detailed CPU info
cat /proc/meminfo              # detailed memory info
cat /etc/os-release            # Ubuntu version info
lsb_release -a                 # Ubuntu release details

systemctl start nginx          # start service
systemctl stop nginx           # stop service
systemctl restart nginx        # restart service
systemctl reload nginx         # reload config (no downtime)
systemctl enable nginx         # start on boot
systemctl disable nginx        # don't start on boot
systemctl status nginx         # status + recent logs
systemctl is-active nginx      # active / inactive
systemctl is-enabled nginx     # enabled / disabled
systemctl list-units --type=service --state=running
systemctl list-units --type=service --state=failed
systemctl daemon-reload        # reload after editing unit files
systemctl reboot               # reboot system
systemctl poweroff             # shutdown

sudo nano /etc/systemd/system/myapp.service

[Unit]
Description=My Application
After=network.target
 
[Service]
Type=simple
User=www-data
WorkingDirectory=/opt/myapp
ExecStart=/usr/bin/python3 /opt/myapp/app.py
Restart=on-failure
RestartSec=5
 
[Install]
WantedBy=multi-user.target

sudo systemctl daemon-reload
sudo systemctl enable --now myapp

journalctl -f                  # follow live (like tail -f)
journalctl -u nginx            # logs for specific service
journalctl -u nginx -f         # follow service logs
journalctl -b                  # since last boot
journalctl -b -1               # previous boot
journalctl -p err              # errors only
journalctl -p warning          # warnings and above
journalctl --since "1 hour ago"
journalctl --since "2024-01-01" --until "2024-01-02"
journalctl -n 50               # last 50 lines
journalctl --disk-usage        # log disk usage
journalctl --vacuum-time=7d    # delete logs older than 7 days

adduser username               # interactive: creates home dir + sets password
useradd -m -s /bin/bash user   # manual: -m=home dir, -s=shell
passwd username                # set/change password
passwd -l username             # lock account
passwd -u username             # unlock account
usermod -aG sudo username      # add to sudo group (grant sudo)
usermod -aG docker username    # add to docker group
usermod -s /bin/zsh username   # change shell
usermod -d /new/home username  # change home directory
userdel username               # delete user (keep home dir)
userdel -r username            # delete user + home dir
su - username                  # switch user (load their environment)
sudo -i                        # root shell
sudo -u username command       # run command as another user
id username                    # show UID, GID, groups
who                            # who is logged in
w                              # who + what they're doing
last                           # login history

sudo visudo                    # safely edit /etc/sudoers
# Add user to sudoers file:
username ALL=(ALL:ALL) ALL
# Allow without password:
username ALL=(ALL) NOPASSWD: ALL
# Allow specific command only:
username ALL=(ALL) NOPASSWD: /usr/bin/apt

groupadd groupname             # create group
groupdel groupname             # delete group
groupmod -n newname oldname    # rename group
usermod -aG group1,group2 user # add user to groups
gpasswd -a user group          # add user to group
gpasswd -d user group          # remove user from group
groups username                # show user's groups
getent group groupname         # group details
newgrp groupname               # switch active group (current session)

sudo apt update                        # refresh package lists
sudo apt upgrade -y                    # upgrade installed packages
sudo apt full-upgrade -y               # upgrade + handle dependency changes
sudo apt install package               # install package
sudo apt install package1 package2     # install multiple
sudo apt install ./local.deb           # install local .deb file
sudo apt remove package                # remove (keep config files)
sudo apt purge package                 # remove + config files
sudo apt autoremove                    # remove unused dependencies
sudo apt autoclean                     # clean old downloaded packages
sudo apt clean                         # clear entire package cache
apt search keyword                     # search packages
apt show package                       # package details
apt list --installed                   # list installed packages
apt list --upgradable                  # list upgradable packages
dpkg -l | grep package                 # check if installed
dpkg -l                                # list all installed packages
dpkg -i package.deb                    # install .deb directly
dpkg -r package                        # remove package
dpkg --get-selections                  # list all installed

cat /etc/apt/sources.list              # main package sources
ls /etc/apt/sources.list.d/            # additional sources
 
# Add PPA (Personal Package Archive)
sudo add-apt-repository ppa:user/ppa-name
sudo apt update && sudo apt install package
 
# Remove PPA
sudo add-apt-repository --remove ppa:user/ppa-name
 
# Add third-party repo (example: Docker)
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker.gpg
echo "deb [arch=amd64 signed-by=/usr/share/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list
sudo apt update && sudo apt install docker-ce

snap find package              # search snap store
sudo snap install package      # install snap
sudo snap install code --classic  # install with classic confinement
sudo snap remove package       # remove snap
snap list                      # list installed snaps
sudo snap refresh              # update all snaps
sudo snap refresh package      # update specific snap
snap info package              # package details + versions
snap connections package       # snap interfaces/permissions

sudo apt install flatpak -y
flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
flatpak install flathub org.gimp.GIMP
flatpak run org.gimp.GIMP
flatpak update
flatpak list
flatpak uninstall org.gimp.GIMP

ip a                           # all interfaces + IPs
ip addr show eth0              # specific interface
ip route                       # routing table
ip route show default          # default gateway
hostname -I                    # all IP addresses
cat /etc/hosts                 # local DNS overrides
cat /etc/resolv.conf           # DNS servers
ss -tulnp                      # listening ports + processes
ss -tulnp | grep :80           # filter by port
lsof -i :80                    # what uses port 80
netstat -tulnp                 # (older, needs net-tools)

ping -c 4 google.com           # ping 4 times
ping -i 0.2 google.com         # fast ping
traceroute google.com          # trace route
mtr google.com                 # real-time traceroute (sudo apt install mtr)
dig google.com                 # DNS lookup
dig google.com MX              # MX records
dig google.com ANY             # all records
nslookup google.com            # simple DNS lookup
curl -I https://example.com    # HTTP headers only
curl -L https://example.com    # follow redirects
wget https://example.com/file  # download file
wget -r -np https://site.com   # recursive download
nc -zv host 80                 # test TCP port connectivity
nc -zvu host 53                # test UDP port

ls /etc/netplan/               # netplan config files
sudo nano /etc/netplan/01-netcfg.yaml

# Static IP example
network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      addresses:
        - 192.168.1.100/24
      routes:
        - to: default
          via: 192.168.1.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]
      dhcp4: false
 
# DHCP example
network:
  version: 2
  ethernets:
    eth0:
      dhcp4: true

sudo netplan try               # test config (auto-reverts if no confirm)
sudo netplan apply             # apply config
sudo netplan generate          # generate backend config

ssh user@host                  # connect
ssh user@host -p 2222          # custom port
ssh -i ~/.ssh/id_rsa user@host # with private key
ssh-keygen -t ed25519 -C "email@example.com"  # generate key (recommended)
ssh-keygen -t rsa -b 4096      # RSA 4096-bit key
ssh-copy-id user@host          # copy public key to remote host
ssh -L 8080:localhost:80 user@host   # local port forward
ssh -R 8080:localhost:80 user@host   # remote port forward
ssh -D 1080 user@host               # SOCKS5 proxy
ssh -N -f user@host -L 8080:localhost:80  # background tunnel
 
# SSH server
sudo apt install openssh-server
sudo systemctl enable --now ssh
sudo nano /etc/ssh/sshd_config
# Key settings:
#   Port 22
#   PermitRootLogin no
#   PasswordAuthentication no   (after setting up key auth)
#   PubkeyAuthentication yes
sudo systemctl restart ssh

sudo ufw status                # check status
sudo ufw status verbose        # detailed status with rules
sudo ufw enable                # enable firewall
sudo ufw disable               # disable firewall
sudo ufw allow 22              # allow SSH
sudo ufw allow 80/tcp          # allow HTTP
sudo ufw allow 443/tcp         # allow HTTPS
sudo ufw allow 8080            # allow custom port
sudo ufw deny 23               # deny telnet
sudo ufw allow from 192.168.1.0/24  # allow subnet
sudo ufw allow from 192.168.1.10 to any port 22  # specific IP + port
sudo ufw delete allow 80/tcp   # delete rule
sudo ufw reset                 # reset all rules
sudo ufw logging on            # enable logging → /var/log/ufw.log
# Default policies
sudo ufw default deny incoming
sudo ufw default allow outgoing

sudo apt install fail2ban -y
sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local
sudo nano /etc/fail2ban/jail.local
# Key settings:
#   [sshd]
#   enabled = true
#   maxretry = 3
#   bantime = 3600
#   findtime = 600
sudo systemctl enable --now fail2ban
sudo fail2ban-client status        # overall status
sudo fail2ban-client status sshd   # SSH jail status
sudo fail2ban-client set sshd unbanip 1.2.3.4  # unban IP

lsblk                          # list block devices
lsblk -f                       # with filesystem types + UUIDs
fdisk -l                       # all disks and partitions (sudo)
df -h                          # disk space usage
df -hT                         # with filesystem type
du -sh /path                   # directory size
du -sh /* 2>/dev/null | sort -rh | head -20  # top 20 largest dirs
blkid                          # UUIDs and filesystem types

sudo fdisk /dev/sdb            # partition disk (MBR/GPT)
sudo parted /dev/sdb           # partition disk (GPT preferred)
sudo parted /dev/sdb mklabel gpt
sudo parted /dev/sdb mkpart primary ext4 0% 100%
sudo mkfs.ext4 /dev/sdb1       # format as ext4
sudo mkfs.xfs /dev/sdb1        # format as XFS
sudo mkfs.vfat /dev/sdb1       # format as FAT32

sudo mount /dev/sdb1 /mnt      # mount partition
sudo mount -o ro /dev/sdb1 /mnt  # read-only
sudo mount -t ext4 /dev/sdb1 /mnt
sudo umount /mnt               # unmount
 
# Permanent mount — add to /etc/fstab
sudo blkid /dev/sdb1           # get UUID
sudo nano /etc/fstab
# UUID=xxxx-xxxx  /mnt/data  ext4  defaults  0  2
sudo mount -a                  # test fstab without reboot

swapon --show                  # show swap
free -h                        # RAM + swap usage
# Create swap file
sudo fallocate -l 4G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab
# Adjust swappiness (0-100, default 60)
sudo sysctl vm.swappiness=10
echo 'vm.swappiness=10' | sudo tee -a /etc/sysctl.conf

# Physical Volumes
sudo pvcreate /dev/sdb         # create PV
sudo pvdisplay                 # show PVs
# Volume Groups
sudo vgcreate myvg /dev/sdb    # create VG
sudo vgdisplay                 # show VGs
sudo vgextend myvg /dev/sdc    # add disk to VG
# Logical Volumes
sudo lvcreate -L 20G -n mylv myvg   # create 20GB LV
sudo lvcreate -l 100%FREE -n mylv myvg  # use all free space
sudo lvdisplay                 # show LVs
sudo mkfs.ext4 /dev/myvg/mylv  # format LV
sudo lvextend -L +10G /dev/myvg/mylv  # extend LV
sudo resize2fs /dev/myvg/mylv  # resize filesystem after extend

sudo apt install gnome-tweaks -y       # GNOME Tweaks tool
sudo apt install gnome-shell-extensions -y
# Install extensions from: extensions.gnome.org
# Popular extensions:
#   Dash to Dock     → macOS-style dock
#   AppIndicator     → system tray icons
#   Blur my Shell    → blur effects
#   GSConnect        → KDE Connect for GNOME (phone integration)

xrandr                         # list displays + resolutions
xrandr --output HDMI-1 --mode 1920x1080 --rate 60  # set resolution
xrandr --output HDMI-1 --off   # disable display
# Wayland (Ubuntu 22.04+ default):
# Settings → Displays → Resolution / Refresh Rate
echo $XDG_SESSION_TYPE         # check: x11 or wayland

# GNOME Tweaks → Appearance → Shell / Applications / Icons
# Popular themes:
sudo apt install yaru-theme-gtk yaru-theme-icon  # Ubuntu default Yaru
# Papirus icons:
sudo add-apt-repository ppa:papirus/papirus
sudo apt install papirus-icon-theme

# Create autostart entry
nano ~/.config/autostart/myapp.desktop

[Desktop Entry]
Type=Application
Name=MyApp
Exec=/usr/bin/myapp
Hidden=false
NoDisplay=false
X-GNOME-Autostart-enabled=true

# Update system
sudo apt update && sudo apt upgrade -y
# Create non-root sudo user
adduser deploy
usermod -aG sudo deploy
# Set up SSH key auth
mkdir -p /home/deploy/.ssh
nano /home/deploy/.ssh/authorized_keys  # paste public key
chmod 700 /home/deploy/.ssh
chmod 600 /home/deploy/.ssh/authorized_keys
chown -R deploy:deploy /home/deploy/.ssh
# Harden SSH
sudo nano /etc/ssh/sshd_config
# Set: PermitRootLogin no, PasswordAuthentication no, Port 2222
sudo systemctl restart ssh
# Enable firewall
sudo ufw allow 2222/tcp && sudo ufw enable

sudo apt install apache2 -y
sudo systemctl enable --now apache2
sudo ufw allow 'Apache Full'
 
sudo apt install mysql-server -y
sudo mysql_secure_installation    # secure MySQL setup
sudo mysql -u root -p             # connect to MySQL
 
sudo apt install php libapache2-mod-php php-mysql -y
sudo systemctl restart apache2
# Test: create /var/www/html/info.php with <?php phpinfo(); ?>

sudo apt install nginx -y
sudo systemctl enable --now nginx
sudo ufw allow 'Nginx Full'
 
sudo apt install mysql-server -y
sudo mysql_secure_installation
 
sudo apt install php-fpm php-mysql -y
# Configure Nginx to use PHP-FPM:
sudo nano /etc/nginx/sites-available/default
# Add: location ~ \.php$ { include snippets/fastcgi-php.conf; fastcgi_pass unix:/run/php/php8.1-fpm.sock; }
sudo nginx -t && sudo systemctl reload nginx

sudo nano /etc/nginx/sites-available/mysite

server {
    listen 80;
    server_name example.com www.example.com;
    root /var/www/mysite;
    index index.html index.php;
 
    location / {
        try_files $uri $uri/ =404;
    }
 
    location ~ \.php$ {
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/run/php/php8.1-fpm.sock;
    }
 
    # Redirect HTTP to HTTPS
    return 301 https://$host$request_uri;
}

sudo ln -s /etc/nginx/sites-available/mysite /etc/nginx/sites-enabled/
sudo nginx -t                  # test config
sudo systemctl reload nginx    # apply

sudo apt install certbot python3-certbot-nginx -y
sudo certbot --nginx -d example.com -d www.example.com
sudo certbot renew --dry-run   # test auto-renewal
# Auto-renewal is set up automatically via systemd timer
systemctl status certbot.timer

sudo apt install unattended-upgrades -y
sudo dpkg-reconfigure --priority=low unattended-upgrades
sudo nano /etc/apt/apt.conf.d/50unattended-upgrades
# Enable: Unattended-Upgrade::Automatic-Reboot "true";
sudo unattended-upgrades --dry-run  # test

sudo aa-status                 # show AppArmor status + profiles
sudo aa-enforce /etc/apparmor.d/usr.sbin.nginx  # enforce profile
sudo aa-complain /etc/apparmor.d/usr.sbin.nginx # complain mode (log only)
sudo aa-disable /etc/apparmor.d/usr.sbin.nginx  # disable profile
sudo apparmor_parser -r /etc/apparmor.d/usr.sbin.nginx  # reload profile

# AIDE — file integrity monitoring
sudo apt install aide -y
sudo aideinit                  # initialize database
sudo aide --check              # check for changes
 
# auditd — system call auditing
sudo apt install auditd -y
sudo systemctl enable --now auditd
sudo auditctl -l               # list audit rules
sudo ausearch -k passwd        # search audit logs
sudo aureport --summary        # audit summary report

sudo apt install lynis -y
sudo lynis audit system        # full system security audit
# Generates hardening suggestions + score

sudo apt install clamav clamav-daemon -y
sudo freshclam                 # update virus definitions
sudo clamscan -r /home         # scan home directory
sudo clamscan -r --remove /tmp # scan + remove infected files
sudo systemctl enable --now clamav-daemon

sudo apt install unattended-upgrades -y
sudo dpkg-reconfigure --priority=low unattended-upgrades

top                            # real-time process monitor
htop                           # improved top (sudo apt install htop)
btop                           # modern resource monitor (sudo apt install btop)
glances                        # all-in-one monitor (sudo apt install glances)
iotop                          # disk I/O per process (sudo apt install iotop)
nethogs                        # network usage per process (sudo apt install nethogs)
iftop                          # network bandwidth monitor (sudo apt install iftop)
vmstat 1                       # virtual memory stats every 1 second
iostat -x 1                    # disk I/O stats (sudo apt install sysstat)
sar -u 1 5                     # CPU usage 5 times every 1 second

# Check CPU governor
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
# Set to performance mode
sudo apt install cpufrequtils -y
sudo cpufreq-set -g performance
 
# Disable unnecessary services
systemctl list-units --type=service --state=running
sudo systemctl disable bluetooth  # if not needed
 
# Adjust swappiness
sudo sysctl vm.swappiness=10
echo 'vm.swappiness=10' | sudo tee -a /etc/sysctl.conf
 
# Increase file descriptor limits
echo '* soft nofile 65536' | sudo tee -a /etc/security/limits.conf
echo '* hard nofile 65536' | sudo tee -a /etc/security/limits.conf

crontab -e                     # edit current user's crontab
crontab -l                     # list current user's crontab
sudo crontab -e                # edit root's crontab
crontab -r                     # remove crontab
 
# Cron syntax: minute hour day month weekday command
# *  *  *  *  *  command
# ┬  ┬  ┬  ┬  ┬
# │  │  │  │  └── weekday (0-7, 0=Sun)
# │  │  │  └───── month (1-12)
# │  │  └──────── day (1-31)
# │  └─────────── hour (0-23)
# └────────────── minute (0-59)
 
# Examples:
0 2 * * *  /usr/bin/backup.sh          # daily at 2:00 AM
*/15 * * * * /usr/bin/check.sh         # every 15 minutes
0 0 * * 0   /usr/bin/weekly.sh         # every Sunday midnight
@reboot     /usr/bin/startup.sh        # on every reboot
@daily      /usr/bin/daily.sh          # once a day
 
# System-wide cron directories
ls /etc/cron.daily/
ls /etc/cron.weekly/
ls /etc/cron.monthly/
ls /etc/cron.d/

sudo apt install build-essential git curl wget vim -y
sudo apt install python3 python3-pip python3-venv -y
sudo apt install nodejs npm -y
# Or use nvm for Node.js version management:
curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.0/install.sh | bash
nvm install --lts
nvm use --lts

# Install Docker
sudo apt install ca-certificates curl gnupg -y
sudo install -m 0755 -d /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list
sudo apt update && sudo apt install docker-ce docker-ce-cli containerd.io docker-compose-plugin -y
sudo usermod -aG docker $USER   # run docker without sudo (re-login required)
docker run hello-world          # test

git config --global user.name "Your Name"
git config --global user.email "email@example.com"
git config --global core.editor vim
git config --global init.defaultBranch main
git config --list               # view all config
# Generate SSH key for GitHub/GitLab
ssh-keygen -t ed25519 -C "email@example.com"
cat ~/.ssh/id_ed25519.pub       # copy this to GitHub SSH keys

python3 -m venv myenv           # create virtual environment
source myenv/bin/activate       # activate
deactivate                      # deactivate
pip install package             # install in venv
pip freeze > requirements.txt   # export dependencies
pip install -r requirements.txt # install from file

export MYVAR="hello"            # set for current session
echo $MYVAR                     # print variable
printenv                        # list all env vars
unset MYVAR                     # remove variable
 
# Permanent — add to ~/.bashrc or ~/.profile
echo 'export MYVAR="hello"' >> ~/.bashrc
source ~/.bashrc
 
# System-wide — add to /etc/environment
sudo nano /etc/environment
# MYVAR="hello"