CP1300 UNIX Processes and Resources

Processes

• Foreground and background processes
  • The program running on your screen is called the foreground process
  • If you have another program you wish to run at the same time, it is possible to run this in the background, while still running another process in the foreground
  • A command followed by an & runs the process in background (output still to the screen)
  • Usually the foreground process is something interactive you want to work with, while background processes are programs which take a while to run and require little interaction

• Monitoring processes
  • ps lists the processes you have running, and related information
    • ps -f gives more information
    • ps -l gives even more information
    • ps -u login gives information about processes owned by login
  • The top command lists the processes that are using most CPU time
  • The jobs command lists the processes you have running in the background
  • The time command allows us to determine how long a program took, both in real time and in CPU time
    • There are two varieties: time and /bin/time
  • The which command allows us to determine where the executable for a program came from (since there may be different programs with the same name in different directories)
    • The directories the system searches (and the order it searches them) to look for commands is set up in your .cshrc or .login file in your home directory.

• Controlling processes
  • ^C kills the foreground process
  • kill -9 PID kills the process with that PID
  • ^Z suspends the foreground process
  • fg reactivates the suspended process
  • bg activates the suspended process in the background
  • jobs lists your background processes by number
  • kill %job number kills the background job with that job number
  • nice and renice alter the scheduling priority of a process
    • Higher scheduling priority means lower priority, the default is 0 out of -20 to 20.
    • If you have a long number-crunching job, be nice to other users and run it in the background with low priority
    • Parameter structure and meaning depends on UNIX variant and which nice or renice is used
    • On barra
      /usr/bin/nice -n change command runs command at scheduling priority change (must be positive)

      /usr/sbin/renice -n change PID adds change to the scheduling priority of process PID (must be positive)

• Starting a process from within C++
  • The system(command) call in C++ runs the command as if from the prompt
  • The C++ program waits until the command completes
  • stdlib.h must be included
  • RunACommand.cpp - Running a chosen command

• Passing data into a C++ process
  • Use parameters to main
    int main(int argc, char* argv[])
  • argc is the number of parameters
  • argv is an array of strings containing the paramters
  • argv[0] is the name of the program
  • argv[1] is the first user supplied parameter
  • WriteArguments.cpp - Writing out the arguments
  • Note that the arguments are strings. To convert to numberic use atoi or atof in stdlib.h
  • AddArguments.cpp - Adds integer arguments

• Processes and Resources
• Program I/O

Tutorial Questions

• Processes and Resources (Answers)
• Program IO (Answers)

Exam style questions