Ports and Processes Management

1. See what ports are in use

Often you need to know if a service is running or what program is occupying a specific port.

1.1 Using ss (Socket Statistics)

The modern command to view sockets is ss.

# -t: TCP, -u: UDP, -l: listening, -n: numeric ports
sudo ss -tuln

1.2 Using lsof (List Open Files)

If you want to know exactly which process is listening on a port (for example, 8080):

sudo lsof -i :8080

This will return something like:

COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
node    12345 root   20u  IPv6 123456      0t0  TCP *:8080 (LISTEN)

Here, the PID (Process ID) is 12345.

2. Process Management

Once you have the PID or the process name, you can control it.

2.1 Search processes with ps and grep

If you know the program name but not its PID:

ps aux | grep nginx

2.2 Interactive monitoring with htop

For a friendlier view, install and use htop:

sudo apt install htop
htop

You can search with F3 and kill processes with F9.

2.3 Kill processes

If you need to stop a process:

By PID (following the previous example):

# Sends SIGTERM signal (polite termination request)
kill 12345

# If it doesn't respond, force close (SIGKILL)
kill -9 12345

By name:

# Kills all processes with this name
killall nginx

With these tools, you can keep your services under control and free up ports when you need to!