Process Management

Process Management — Quick Reference

ps — Snapshot of Running Processes

ps aux                        # all processes, full detail
ps aux | grep nginx           # find a specific process
ps -ef                        # full-format listing (alt style)
ps -p 1234                    # info for a specific PID

Column	Meaning
`USER`	Owner of the process
`PID`	Process ID
`%CPU`	CPU usage
`%MEM`	Memory usage
`STAT`	State (R=running, S=sleeping, Z=zombie)
`COMMAND`	Command that started the process

top / htop — Live Process Monitor

top                           # built-in live monitor
htop                          # better UI (may need install)

top key bindings:

Key	Action
`k`	Kill a process (enter PID)
`M`	Sort by memory
`P`	Sort by CPU
`q`	Quit

kill / killall — Terminate Processes

kill 1234                     # graceful stop (SIGTERM)
kill -9 1234                  # force kill (SIGKILL)
kill -HUP 1234                # reload config (SIGHUP)

killall nginx                 # kill all processes named nginx
killall -9 node               # force kill all node processes

Common signals:

Signal	Number	Meaning
`SIGTERM`	15	Graceful shutdown (default)
`SIGKILL`	9	Force kill, cannot be caught
`SIGHUP`	1	Reload config / restart
`SIGINT`	2	Interrupt (same as Ctrl+C)

Background & Foreground Jobs

command &                     # run in background
Ctrl+Z                        # suspend current process
bg                            # resume suspended job in background
fg                            # bring background job to foreground
fg %2                         # bring job #2 to foreground
jobs                          # list all background/suspended jobs

nohup — Survive Terminal Close

Runs a command that keeps running after you log out.

nohup ./script.sh &           # run in background, immune to hangup
nohup ./script.sh > out.log 2>&1 &   # capture stdout + stderr

Output goes to nohup.out by default unless redirected.

Redirect & Pipes

command > file.txt            # stdout to file (overwrite)
command >> file.txt           # stdout to file (append)
command 2> err.txt            # stderr to file
command > out.txt 2>&1        # stdout + stderr to same file
command 2>/dev/null           # discard stderr
command1 | command2           # pipe stdout of cmd1 into cmd2

pgrep / pkill — Find & Kill by Name

pgrep nginx                   # print PIDs of processes named nginx
pgrep -l nginx                # print PID + name
pkill nginx                   # kill all processes named nginx
pkill -9 node                 # force kill by name

lsof — List Open Files / Ports

lsof -i :8080                 # what process is using port 8080
lsof -i TCP                   # all TCP connections
lsof -p 1234                  # files opened by PID 1234
lsof -u username              # files opened by user

systemctl — Manage Services (systemd)

systemctl start nginx         # start a service
systemctl stop nginx          # stop a service
systemctl restart nginx       # restart
systemctl reload nginx        # reload config without restart
systemctl status nginx        # check status
systemctl enable nginx        # start on boot
systemctl disable nginx       # don't start on boot
systemctl list-units          # list all active units

Tips

Always try kill (SIGTERM) before kill -9 — give the process a chance to clean up.
pgrep -l is faster than ps aux | grep for finding a PID.
Use nohup + & for long-running jobs on remote servers.
lsof -i :PORT is the fastest way to find what’s occupying a port.

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