SAAM 1

• Characteristics of a Process


  1. It can be started from the GUI or the command line

  2. It can start another process

  3. It can only be created by another process
• Commands Used in Viewing and Controlling Processes


  • ps
  • top
  • jobs
  • bg
  • fg
• Controlling Processes

  1. To interrupt a process, press Ctrl + C

  2. Putting a process in the background

  3. The jobs Command

  4. Returning a process to the foreground

  5. Moving a process to the background
• ps 


  It reports a snapshot of current processes.
• top


  It displays tasks.
• jobs


  This lists active jobs
• bg


  It places a job in the background
• fg


  This places a job in the foreground
• r


  running
• s 


  Sleeping This process is not running; it is waiting for an event.
• d


  Uninterruptible sleep Process is waiting for I/O such as a disk drive
• t


  Traced or stopped
• z


  A defunct or “zombie” process This is a child process that has been terminated, but has not been cleaned up by its parent.
• <


  A high priority process
• N


  A low priority process
• L


  Has pages locked into memory This is for real-time and custom I/O
• s


  A session leader
• l


  Multi-threaded
• +


  In the foreground process group
• USER


  User ID This is the owner of the process.
• %CPU


  CPU usage in percent
• %MEM


  Memory usage in percent
• VSZ


  Virtual Memory Size
• RSS


  Resident Set Size This is the amount of physical memory (in kilobytes) the process is using
• START

  This is the time when the process has started.

  For values over 24 hours, a date is used.
• top


  program name
• 15:59:48

  Current time of the day
• up 3:00


  This is the uptime. It is the amount of time since the machine was last booted. In the above screenshot, the system has been up for three (3) hours.
• 1 user

  There is one (1) user logged in.
• load average


  refers to the number of processes that are waiting to run; that is, the number of processes that are in a runnable state and are sharing the CPU. There are three (3) values shown: average for the last 60 seconds, for the previous 5 minutes, and for the previous 15 minutes.
• Tasks


  It is the summary of the number of processes and their various process states.
• %Cpu(s):


  It describes the activities that the CPU is performing
• us


  The % of time the CPU is being used for user processes
• sy


  The % of time the CPU is being used for system (kernel) processes
• ni


  The % of time the CPU is being used by “nice” (low priority) processes Nicenessindicates the priority of a Linux process. The higher the niceness, the more willing the process will voluntarily give some of its cycles to other processes, thus lowering its priority.
• id


  The % of time the CPU has been idle
• wa


  The % of time the CPU has been waiting for I/O
• hi


  The % of CPU time spent servicing hard interrupts
• si


  The % of CPU time spent servicing soft interrupts
• st


  The % of CPU time stolen from the current vm by the hypervisor