ps / top / htop

# Inspect — modern alternatives in parens
ps aux                    # everyone's processes
ps -ef                    # similar, BSD vs SysV style
ps -p $$                  # current shell
ps --forest               # tree view
top                       # live, refresh
htop                      # nicer top (install: brew/apt install htop)
btop                      # newer, prettier

# Filtering
ps aux | grep -v grep | grep nginx
pgrep -af nginx           # PIDs matching a name
pgrep -u ada              # PIDs of a user

# Resource usage on a PID
ps -p $PID -o pid,user,%cpu,%mem,etime,cmd

# Signals
kill <PID>                # default = SIGTERM (15)
kill -9 <PID>             # SIGKILL — last resort, no cleanup
kill -HUP <PID>           # SIGHUP — reload config in many daemons
kill -INT <PID>           # SIGINT — like Ctrl+C
pkill -f myscript.sh      # kill by command-line match
killall nginx

# Foreground / background
longrun.sh &              # run in background
jobs                       # list current shell's jobs
fg %1                      # bring job 1 back
bg %1                      # send to background
Ctrl + Z, then bg          # pause + send to background

# Survive a logout
nohup longrun.sh > out.log 2>&1 &
disown                     # detach from the shell
# Modern alternative: tmux / screen / systemd-run --user --scope

# Open files / sockets a process holds
lsof -p $PID
lsof -i :8080              # who's on this port?
ss -ltnp | grep :8080      # modern replacement

# Memory + CPU details (Linux)
cat /proc/$PID/status
cat /proc/$PID/limits

ps aux | head
top
htop                            # nicer, if installed