# Linux commands: kill

> Learn how the Linux kill command sends signals to a process by PID, defaulting to TERM, and how to send others like KILL, HUP, or STOP, by name or number.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2020-09-09 | Topics: [CLI](https://flaviocopes.com/tags/cli/) | Canonical: https://flaviocopes.com/linux-command-kill/

Linux processes can receive **signals** and react to them.

That's one way we can interact with running programs.

The `kill` program can send a variety of signals to a program.

It's not just used to terminate a program, like the name would suggest, but that's its main job.

We use it in this way:

```bash
kill <PID>
```

By default, this sends the `TERM` signal to the process id specified.

We can use flags to send other signals, including:

```bash
kill -HUP <PID>
kill -INT <PID>
kill -KILL <PID>
kill -TERM <PID>
kill -CONT <PID>
kill -STOP <PID>
```

`HUP` means **hang up**. It's sent automatically when a terminal window that started a process is closed before terminating the process.

`INT` means **interrupt**, and it sends the same signal used when we press `ctrl-C` in the terminal, which usually terminates the process.

`KILL` is not sent to the process, but to the operating system kernel, which immediately stops and terminates the process.

`TERM` means **terminate**. The process will receive it and terminate itself. It's the default signal sent by `kill`.

`CONT` means **continue**. It can be used to resume a stopped process.

`STOP` is not sent to the process, but to the operating system kernel, which immediately stops (but does not terminate) the process.

You might see numbers used instead, like `kill -1 <PID>`. In this case,

`1` corresponds to `HUP`.
`2` corresponds to `INT`.
`9` corresponds to `KILL`.
`15` corresponds to `TERM`.
`18` corresponds to `CONT`.
`15` corresponds to `STOP`.

> This command works on Linux, macOS, WSL, and anywhere you have a UNIX environment