COMP 3000 2012 Week 3 Notes

Shell

• useful command line programs
  • bc -l
    • command line calculator
  • cal
    • command line calendar
  • uniq
    • filters out duplicate lines
  • sort
    • takes input on STDIN, sorts lines, prints to STDOUT
• vmlinux is the linux kernel with virtual memory [1]
  • vmlinuz is the same but compressed
• bash runs on vmlinux
  • most programs run on bash
  • ls/cd also run on vmlinux
  • ls runs as a child process of bash
• to get rid of a misbehaving child
  • the parent must kill it
  • waits for child to die
  • an unreaped child becomes a zombie
  • zombies can't be killed, must be reaped
  • to kill a zombie, must kill parent
  • orphans become a child of init (ward of state)
  • init is good at reaping children

job control

• job is a process
  • term comes from batch processing
• Useful control sequences
  • Ctrl-C
    • terminate job
  • Ctrl-Z
    • stop job
• To start a stopped job in the foreground
  • fg %n
    • where n is the job number
• To start a stopped job in the background
  • bg %n
• To determine jobs that are running
  • jobs
• Who manages jobs?
  • the shell
  • built on kernel functionality

Why we're studying unix

• all operating systems have basically the same architecture
• windows is just a variation on unix
• windows comes from vms
  • increment(vms) -> wnt

References

[1]: https://en.wikipedia.org/wiki/Vmlinux