Linux Commands

Get Init Process

ps -f 1

Fork & Exec

parent (ex: bash) -> child (ex ls -l) 
     ls -l command from bash forks the new process and executing using "exec"
     parent returns back once child finishes its work (exec ends once the process completes)
     ex: exec ls -l (it will close current shell)

Suspend & Restore the running process

Suspend the current running process in foreground : ctrl + z (equivalent to below command)
Note: kill -20 means SUGTSTP and Stopped state

kill -20 [pid]

To get process with hierarchy:  

ps f 

Column: STAT values::: 
  T -> suspended state 
  S -> Running state 

Jobs

To see running jobs

jobs

To restore the suspended process as foreground : 

fg #it resume on current process, if only one job

To restore the suspended process as background : 

bg #it resume on current process, if only one job

Multiple jobs running in background and to bring foreground :

fg %{job_number} #jobs command will give job_number

Note: jobs shows + and - after job number.
  '+' means last job sent to bg
  '-' means last to previous job sent to bg
  fg / bg : equivalent to kill -18 [pid] . '-18' means SIGCONT

Kill

List of kill signals:

kill -l

Kill Processes:

sends sigterm: Terminated state in jobs queue
Gradual shutdown

kill -15 [pid]  #default - without number also same

sends sigint : 

kill -2 [pid]

sends sighup : 

kill -1 [pid]

sends sigkill : force kill
Abrupt shutdown

kill -9 [pid]