# SYSTEM

hostname                         # Show hostname
hostnamectl                     # Show system hostname and OS information
uptime                           # Show system uptime and load
uname -a                         # Show kernel information
cat /etc/os-release              # Show Linux distribution information
whoami                           # Show current username
id                               # Show current user and group IDs
date                             # Show current date and time
timedatectl                      # Show system time and timezone
free -h                          # Show memory usage
nproc                            # Show number of CPU cores
lscpu                            # Show CPU information

# STORAGE

df -h                            # Show filesystem disk usage
df -hT                           # Show filesystem usage and filesystem types
du -sh *                         # Show sizes of items in current directory
lsblk                            # List block devices
lsblk -f                         # List block devices with filesystem information
blkid                            # Show block device UUIDs and filesystem types
findmnt                          # Show mounted filesystems
mount                            # Show mounted filesystems
sudo fdisk -l                    # List disk partitions

# NETWORK

ip addr                          # Show network interfaces and IP addresses
ip -br addr                      # Show concise network interface information
ip route                         # Show routing table
ip -br link                      # Show concise link status
ss -tulpn                        # Show listening TCP and UDP ports
ss -tunap                        # Show active network connections
ping -c 4 8.8.8.8                # Test network connectivity
curl -I https://example.com      # Show HTTP response headers
dig example.com                  # Query DNS
resolvectl status                # Show DNS resolver status
hostname -I                      # Show local IP addresses

# SYSTEMD

systemctl --failed               # Show failed systemd units
systemctl list-units --type=service --state=running  # Show running services
systemctl list-units --type=service --state=failed   # Show failed services
systemctl status docker          # Show Docker service status
journalctl -xe                   # Show recent system journal errors
journalctl -b                    # Show logs from current boot
journalctl -p err -b             # Show errors from current boot
journalctl --disk-usage          # Show journal disk usage

# PROCESSES

ps aux                           # Show all running processes
ps aux --sort=-%cpu | head       # Show top CPU-consuming processes
ps aux --sort=-%mem | head       # Show top memory-consuming processes
top                              # Interactive process monitor
htop                             # Interactive process monitor
pgrep -a process-name            # Find processes by name
lsof -i                          # Show network connections by process

# PACKAGES

apt list --upgradable            # Show available package updates
apt policy package-name          # Show package version information
dpkg -l                          # List installed packages
dpkg -l | grep package-name      # Search installed packages
apt-cache search package-name    # Search available packages

# FILES

ls -lah                          # List files with details
pwd                              # Show current directory
find . -maxdepth 1 -type f       # Find files in current directory
find . -type f -name "*.log"     # Find log files recursively
du -sh ./*                       # Show sizes of items in current directory
stat filename                    # Show file metadata
file filename                    # Identify file type
namei -l /path/to/file           # Show path permissions

# USERS

who                              # Show logged-in users
w                                # Show logged-in users and activity
last                             # Show recent logins
getent passwd                    # List local and directory users
getent group                     # List groups
groups                           # Show current user's groups
sudo -l                          # Show current user's sudo privileges

# DOCKER

docker ps                        # List running containers
docker ps -a                     # List all containers
docker images                    # List Docker images
docker volume ls                 # List Docker volumes
docker network ls                # List Docker networks
docker stats                     # Show container resource usage
docker system df                 # Show Docker disk usage
docker compose ps                # Show Compose container status
docker compose images            # Show Compose images
docker compose logs -f           # Follow Compose logs

# GIT

git status                       # Show repository status
git log --oneline -10            # Show last 10 commits
git log --oneline --decorate -10 # Show recent commits with branch information
git branch                       # Show local branches
git branch -a                    # Show all branches
git remote -v                    # Show Git remote URLs
git diff                         # Show uncommitted changes

# HARDWARE

lspci                            # List PCI devices
lsusb                            # List USB devices
lsmem                            # Show memory information
lsblk -o NAME,SIZE,TYPE,FSTYPE,MOUNTPOINTS  # Show detailed storage layout
sudo dmidecode -t system         # Show system hardware information

# SSH

sshd -T                          # Show effective SSH server configuration
ssh -v localhost                 # Test SSH connection with verbose output
lastlog                          # Show last login for users

# DISK / FILESYSTEM DIAGNOSTICS

sudo dmesg -T | tail -50         # Show recent kernel messages
sudo dmesg -T | grep -i error    # Search kernel messages for errors
sudo journalctl -k -b            # Show kernel logs from current boot
sudo smartctl --scan             # Detect available SMART devices
sudo smartctl -H /dev/sdX        # Show SMART health status
sudo smartctl -a /dev/sdX        # Show complete SMART information