UNIX Processes

Prof. Brian D. Davison

Computer Science & Engineering, Lehigh University

Announcements

• SQ1: Low was 1, high 10, median 5, mean 5.4.
• Office hours: Mon/Thu 11-noon
• Why are man and info better than other alternatives?
• Lessons from first lab?

Announcements

• SQ1: Low was 1, high 10, median 5, mean 5.4.
• Office hours: Mon/Thu 11-noon
• Why are man and info better than other alternatives?
• Lessons from first lab:
  • There are many windowing environments (visual interfaces)
  • Paths are important for figuring out what to run
  • Many Sun keyboards have keys in positions different than what you expect
• Yes, printing was fixed later Monday morning.
• Programming Assignment #1 is online, due Monday.
• Review UNIX commands for Friday's quiz.

Processes

• A process is the memory, open files, and other system resources needed while a program runs. The kernel creates a process when you run a program.
• For example, try:
  io:~% more /etc/termcap (e.g., view a large file with more)
  
  Then, press CTRL-Z to suspend the process.
  [1]+ Stopped more /etc/termcap
  io:~% ps
     PID TTY   TIME CMD
    2556 pts/7 0:00 more
    2540 pts/7 0:00 bash
  io:~%
  
• ps reports information about processes (owner, cpu/memory usage, etc.)
• The top command can also be used to see what programs are running, their memory and cpu usage, etc.

Managing Processes

• Normally, running a program in a shell will stop the shell while the other program runs.
• To allow both to run, start the program and put it into the background.
io:~% emacs &
io:~%
• Pressing CTRL-Z in a running program will suspend that process.
• The jobs will show you what processes are running or stopped from this shell:
  io:~% jobs
  [1]+ Stopped more /etc/termcap
  
• The fg and bg commands can move the currently stopped program into the foreground or background (and change status of other jobs currently stopped or running).

Killing Processes

• Sometimes, you get a program that you can't stop with CTRL-C.
• To kill your process that won't otherwise stop, type

  kill <processid>

  or if needed,

  kill -9 <processid>

• The killall command can be used to kill a process using its name.

C Programming

• There are many more useful UNIX utilities that we will discuss in the future, but let's consider building one.
• We saw previously that cat can display the contents of a file.
• Let's write our own version in class. Since cat reads from files, we'll need to use the open(2), read(2), and close(2) system calls.
• Note that the man system also has entries for system calls and standard library functions as well as for programs.