Processes

Program running on a system is a process. Linux is a multi-processing
  (multi-tasking) system.
Attributes: Lifetime, PID, PPID, UID, GID, env variables, CWD.
Process with PID=1 is init
Monitoring: ps (for full listing, use ps -ef or ps -aux) 
  top, pstree
Signal a running processes with PID=1009:
    
    kill -HUP 1009    #Hang up; re-read config files
    kill -1   1009
 
    kill -INT 1009    #Interrupt, Ctrl-C
    kill -2   1009 

    kill -9  1009     #Kill; stop unconditionally
    kill -TERM 1009

    kill -15   1009    #Terminate gracefully
    kill -TERM 1009

    kill -TSTP 1009   #Suspend; can be continued
    kill -18   1009
   
Process can be started with lower and higher priority through nice
    (range: -20, +19)
     nice 10 matlab
Process can be re-niced at run time:
     renice 5 1009
Suspend interactive process and move it to the background:
     Ctrl-Z 
      jobs
      bg %1
      jobs
Move a background process to the foreground:
      fg %1  



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