Monitoring processes using ps

We have used the command ps in the introduction. Let's learn more about it:

• To list the process associated with our current Bash shell terminal, enter the following command:

  $ ps
  

  
• To list processes along with the parent process ID associated with the current terminal, enter the following command:

  $ ps –f
  

  

  We can see the process ID in the PID column and the parent process ID in the PPID column in the preceding output.

• To list processes with the parent process ID along with the process state, enter the following command:

  $ ps –lf
  

  

  In the preceding output, the column with S (state) shows the current state of a process, such as R for running and S for suspended state.

• To list all the processes running in the operating system including system processes, enter the following command:

  $ ps –ef
  

  

  The process names in [] are kernel threads. If you are interested in more options to learn about the ps command, you can use the following command:

  $ man ps.
  

  To find a particular process, you can use the following command:

  $ ps –ef | grep "process_name"
  

  The command with grep will display the process with process_name.

• If we want to terminate the running process, enter following command:

  $ kill pid_of_process_to_be_killed
  

  
• Many a time, if the process is not killed by the $ kill command, you may need to pass additional option to ensure that the required process is killed, which is shown as follows:

  $ kill -9 pid_of_process_to_be_killed
  

• We can terminate the process by the name of a process instead of using the process ID as follows:

  $ pkill command_name
  $ pkill sleep
  

  Or:

  $ pkill -9 command_name
  

  
• To know more about various flags of kill, enter following command:

  $ kill –l
  

  This displays all the signals or software interrupts used by the operating system. When we enter the $ kill command, the operating system sends the SIGTERM signal to the process. If the process is not killed by this command, then we enter the following command:

  $ kill -9 process_name
  

  This sends SIGKILL to the process to be killed.