INFORMACION DE PROCESOS

Running processes

• "Nmonic" : ProceSses Top Tree

To see every process on the system using BSD syntax:

ps aux

• all processes (a)
• the user (u)
• processes not associated with a terminal (x)

To see every process on the system using standard syntax:

ps -ef
ps -eF

Dynamic real-time view of a running system

top

Display a tree of processes

pstree -capl

Process priority

• -20 is highest priority
• 19 is lowest priority

nice -n -20 <command>

renice <nice-value> <pid>

• Nmonic /proc/... : ve

Memory map for a process

 cat /proc/1234/maps

gdb
info proc mappings

pmap -d 1234

/proc

• Nmonic /proc/... : de,ve,me

• Nmonic /proc/<id>/... : cm,en,ma

• /proc/<id>/environ environment variables

• /proc/<id>/cmdline command line args/command used to run the process

• /proc/<id>/maps memory map

• /proc/<id>/fd open file descriptors

System and library calls

• ltrace
• strace

Access control

• access - Check permissions for the UID and GID of the process (executable file owner / group)
  • Check is done using the calling process's real UID and GID, rather than the effective IDs as is done when actually attempting an operation (e.g., open(2)) on the file.

Other

killall <name>
kill -9 <pid>
kill <pid>

fg
bg
[Ctrl+Z]

Controlling Processes

gedit
ps-------------------Show Running Processe
Jobs ----------------Show Running Jobs
gedit & -------------Starts Job without Keeping terminal in Listning and Gives Pid
bg %1 --------------Resume a Paused Programm
kill 2973 ----------Kill Process with pID 2973
killall gedit ------Kill all gedit processes
pstree --------------Give a Relatioship Grid of all the processes
xload ---------------Load of Your system 

Process Management

• Process info:

  ps
  # print all running processes for current user
  
  ps aux
  # shows all running processes
  
  ps -eH
  # -e for processes of all users
  # -H for hierarchical format
  
  pstree
  # easier view for process hierarchy
  
  top
  # real-time updated view of processes and resources consumed
  

• Foreground & background processes:

  • We can run only one foreground process at a time in a shell; however, we can run multiple background processes at the same time:

    xeyes
    # foreground process
    # this does not allow to run other commands
    
    xeyes &
    # background process
    

  • We can also move a running process from foreground to background, and vice-versa:

    xeyes
    # foreground
    
    # Ctrl+Z to suspend/pause process
    
    jobs
    # shows suspended processes
    
    bg
    # move job to background
    
    jobs
    # xeyes is now running in background
    
    fg
    # move job to foreground
    
    # for fg and bg, we can also use job id
    # in case of multiple jobs
    

• Managing processes:

  • A process can be in one of these states:

    • Running - CPU executing a process

    • Sleeping - waiting on a resource; when it gets the resource, it will get into running state again

    • Stopped - when stop signal is sent to running process, CPU stops executing the process

    • Terminated - cause a process to die

    • Zombie - remains of the process when it was not cleaned up after dying; does not respond to normal signals used to shut a process down

  • Processes change their states in response to signals; kill command used to send these signals to processes:

    kill -l
    # shows full list of signals
    
    # SIGHUP used to signal to process that it should reread its config
    
    # SIGSTOP used to stop a process from running; Ctrl+Z
    
    # SIGTERM is default signal sent by kill to terminate process
    
    # SIGKILL used if process does not respond to SIGTERM
    
    xeyes &
    # program running in background
    
    ps -ef | grep xeyes
    # shows PID of process
    
    kill 55092
    # SIGTERM sent to process, terminated
    
    kill -9 55092
    # SIGKILL can be sent as well, if process does not respond to SIGTERM
    
    # pkill can be used if we do not know pid
    # kills any process which matches the criteria
    
    pkill xeyes
    # kills multiple instances of program
    
    sleep 5
    # pauses execution in shell for some time, adds delays
    

• Scheduling processes:

  less /etc/crontab
  # contains processes scheduled at system level
  
  crontab -e
  # personal crontab file
  
  # follow format 'm h dom mon dow  command'
  
  5 1 2 * * touch /home/bob/cron/crontab-ran.txt
  # runs the command at 1:05 every second day of each month
  
  */5 * * * * touch /home/bob/cron/crontab-ran.txt
  # runs the command every 5 minutes
  
  crontab -l
  # prints crontab file contents
  
  crontab -r
  # deletes cronjobs
  

  # init.d used to run scripts at system bootup
  
  ls -la /etc/init.d
  # view scripts running at startup
  
  ls -la /etc/rc*.d
  # shows different run-levels