3 Process Control

ps axf     # display process tree
ps axfj    # with more info
ps axfjww  # even if lines wrap around terminal

Processes

• Orphan: parents terminate before children
  • init adopts it and periodically calls waitpid()
• Zombie: child terminated, but parent never calls waitpid()
  • It will show in the process tree as <defunct>

Memory mappings

When a process fork()s, its mappings are duplicated for the child

Copy-On-Write:

• Even pieces in stack/text/code are shared and marked as read only
• Once when memory is written, OS splits it to two
• Delays duplication of memory space.
• Efficient since fork() is typically followed by exec(), which will trash the memory anyway
• exec() loads a new program code into memory by mapping its executable file to the text region of the address space

Process groups job control

proc1 | proc2

proc1 and proc2 share the same group ID (PGID)

proc1 | proc2 &    # & sends pipeline to background
# [1] 7106         # [<job number>] <leading PID>
proc3 | proc4 | proc5

All share the same session ID (SID)

If you send a signal, it’s delivered to the foreground process group

• jobs: List all jobs
• Ctrl-Z: Suspend (SIGSTOP) foreground job and send to the background
• bg <job>: Resume <job> in the background
• fg <job>: Bring backgrouded <job> into the foreground