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
