Process States and Kill command

Last Blog Review →

In the last blog we understood, what is process management, parent process, forking, example of it and command for knowing the process id.

Process States →

1. Running - In this state the process is in running state or ready to run

2. Waiting - A process is waiting for a resource

3. Stopped - A process is stopped for example after receiving signal

4. Zombie - A process is exited successfully, but its state change is not yet acknowledge by the parent.

What is process termination →

In general scenarios, when a process terminates it free’s up allocated resources. If a shell has forked a subprocess, then it wait for them to finish it’s task first (other than background process).

In other cases the process may not behave normally and can be in waiting state or consuming resources for a longer time.

In some other cases, if process is not required we can kill the process and free up resources.

KILL command →

The kill command sends a specific signal to the specified process, if no signal is provided the default sigterm signal is sent.

Syntax

kill PID or kill -signal PID

How to kill a process →

1. To kill a process we will get the PID first

    $$ pidof google      #GEtting PID of google
    1002
   
    $$ kill 1002         #Google will be terminated
   
    $$ touch new.txr     #starting a new process
    $$ pidof touch         
    1434
   
    $$ kill -SIGSTOP 1434 #Sending signal to stop touch process
    [1]+ Stopped
   

2. Here we used SIGSTOP signal to stop the touch process instead of directly killing it. If we want to kill the process we can use SIGKILL signal

    kill -SIGKILL 1434
   

Conclusion →

In this blog we understood, multiple process states, what it means to terminate a process. KILL command and how to use a KILL command to terminate a process.