linux

Common Linux commands organized by category for quick reference. Commands adapt to your selected distro's init system and package manager.

service management — systemd

bash# view service status
sudo systemctl status nginx -l --no-hostname

# tail logs in real-time
journalctl -u nginx -f --no-hostname

# list all running services
systemctl list-units --type=service --state=running

# restart without blocking
sudo systemctl restart nginx

# enable at boot
sudo systemctl enable --now nginx

disk & filesystem

bash# disk usage summary
df -h

# largest directories
du -sh /* 2>/dev/null | sort -h

# largest files (>100MB)
find / -type f -size +100M -exec ls -lh {} \; 2>/dev/null | sort -k5 -h

# filesystem info
lsblk -f
blkid

# check disk health
sudo smartctl -a /dev/sda

processes & memory

bash# top processes by CPU
top -o %CPU

# top processes by memory
ps aux --sort=-%mem | head -10

# memory overview
free -h

# open file descriptors per process
lsof -n | awk '{{print $1}}' | sort | uniq -c | sort -rn | head -10

# find which process uses a port
ss -tlnp | grep :3000

network

bash# listening ports
ss -tulpn

# active connections
ss -tn state established

# quick network scan
nmap -sn 192.168.1.0/24

# resolve DNS
dig +short google.com

# wireguard status
sudo wg show

# speed test through tunnel
curl --interface wg0 -o /dev/null -s -w '%{speed_download}' \
  'https://speed.cloudflare.com/__down?bytes=50000000'

logs & journal

bash# view logs for a service
journalctl -u nginx -f --no-hostname

# last boot logs
journalctl -p err -b --no-hostname

# disk usage by logs
journalctl --disk-usage

# clean up old logs
sudo journalctl --vacuum-time=7d

system info

bash# kernel and architecture
uname -a

# cpu info
lscpu
cat /proc/cpuinfo | grep 'model name' | head -1

# memory
cat /proc/meminfo | grep MemTotal

# pci devices
lspci | grep -E 'VGA|Audio|Network'

# dmesg kernel messages
dmesg | tail -20

# uptime
uptime