How to kill a process in Linux? What to do if 'kill pid' doesn't help?

In Linux, a process can be killed using the kill command and specifying the PID (process ID):

kill <pid>

By default, the SIGTERM (15) signal is sent, which terminates the process gracefully.

If the process does not respond to SIGTERM, a more forceful SIGKILL (9) signal can be sent, which forcibly terminates the process:

kill -9 <pid>

If even kill -9 does not work, the process might be in a "D" (uninterruptible sleep) state, for example, waiting for I/O or blocked at the kernel level. In this case, the process cannot be killed until the system call completes or the resource is freed.

For diagnostics, you can use:

• ps aux | grep <pid> — to check the process status (STAT column)
• top or htop — process monitoring
• strace -p <pid> — trace system calls of the process

If the process is stuck due to hardware or filesystem issues, the problem needs to be addressed at that level.