fork() and exec()

• fork() creates a new process by duplicating the current process. The new process is referred as child and existing process from which duplicate is created is referred as parent
  • Child will its own unique PID (Process ID),
  • The childs parent process ID will be same as parents process ID
  • Child doesn’t inherit parents memory locks and semaphore adjusments
  • Child doesn’t intherit outstanding I/O operations from parent.
  • On success, the PID of the child process is returned to parent and 0 is returned to child. On failure, -1 is returned to parent
• exec() replaces the current process with new one.

Viewing Processes

• The most commonly used command to view processes is ps

ps --help
man ps

• Lets execute ps
• The result in this example lists two process process 1736 and 1809 which are bash and ps.
• To get bigger picture lets try to execute ps x
• Adding the x opts tells ps to show all of the our processes regardless of what terminal they are controlled by. The presence of ? in the TTY column indicates no controlling terminal
• State Meaning
  • R: Running
  • S: sleeping
  • D: Uninterruptible sleep
  • T: stopped
  • <: A high priority process
  • N: A low priority process
• Lets get into more details of the process by executing ps aux
• Header Meaning
  • USER: USER ID. This is owner of process
  • %CPU: Cpu usage in percent
  • %MEM: Memory usage in percent
  • VSZ: Virtual Memory Size
  • RSS: Resident Set size. This is amount physical memory(RAM) the process is using in kilobytes
  • START: Time when the process started.
• Ps command can tell you lot about what machine is doing at the moment when you typed the ps command
• To get dynamic view of machines activity use top clear
• Also try htop
• PS command shows static info, whereas top and htop commands show us dynamic info