CST8177 - Lab #6

Process Management

Objectives

• To use process management tools

• To learn how to use job scheduling tools

Lab Outcome

• An understanding of how to manage running processes

In-Lab Demo: List the steps required to submit a weekly system job.

Section A - Process management

In order to manage processes on a system, you need to be able to both view and access those processes. Commands to do so include:

Process management commands

ps	to list existing processes on the local system
jobs	to list existing background jobs
fg and bg	to move jobs between the background and foreground
kill	to send a signal to a process using the PID or job number
killall	to send a signal to all processes using the process name
Ctrl-C	to kill a process currently running in the foreground (also ^C)
top	to view currently running processes and the resources associated to them (use q to quit, h for help)
pgrep	look up processes, based on the name or on other attributes
pstree	to display process relationships (hierarchy)

Resource management commands

free	to generate information about how much free memory is available on the system
vmstat	reports information about processes, memory, paging, block IO, traps, and cpu activity.

Try a variety of the commands in the questions below to locate the best one for accomplishing the tasks requested.

Exercise #1: Using process management utilities

Using the utilities above, or other suitable commands, answer the questions below:

• What is the PID of the rsyslogd daemon?
  Record the most suitable utility to use: _____________________ __________________

• Is rsyslogd a parent process or a child process?
  Record the most suitable utility to use: ______________________ _________________

• If rsyslogd is a child process, what's the
  parent process's name/PID?
  Record the most suitable utility to use: _______________________ ________________

• What is the name of the process that is
  currently using up the highest %MEM?
  Record the most suitable utility to use: ________________________ ________________

• Assume that the PID of foobar is 99. Further
  assume that the command line kill 99 has no
  effect (what is kill's default signal?). To kill
  the process foobar you have to use the

  following command line: _____________________ _________________________________

• Write the key combination that kills
  a process that runs in the foreground. _________________________________________

Exercise #2: Working with job control

• In this exercise you are working on more than one terminal window.
  Note: To determine the device name of your terminal, use the tty command.

Job control commands

jobs	to list current processes started by this particular shell
CTRL-Z or ^Z	to stop execution of a process running in the foreground
bg %jobnum	to move a suspended job into the background
fg %jobnum	to move a background job to the foreground
kill %jobnum	to terminate a background job

At terminal #1

• cat

  starts a copy of cat reading from stdin

• CTRL-Z

  suspend the cat process while it is running

• find / -name '*.conf' >& /dev/null

  starts a long-running find

• CTRL-Z

  as above, but do this fairly quickly, since it's not that long-running

• jobs

  List all the background jobs for this terminal or tty device

At terminal #2

• ps -ef | grep find

  Does this list the process you started in terminal
  #1? Determine the process state of find: __________________ __________________

• pgrep find

  compare with the ps/grep combination
  above; which do you prefer and why? __________________________________________

  _________________________________________________________________________________

• jobs

  Does this list the processes you stopped in terminal #1? _______________________

At terminal #1

• kill %1

  terminate the cat process. Press ENTER and describe what happens:

_________________________________________________________________________________

• bg %2

  check job %2; Is it still find? ___________________________________________________

• fg %2

  Is the find process still running? _____________________________________________

• cat &

  run the cat again, starting it directly in the background

• jobs

  How many jobs are listed? With what job number(s)? ____________ _____________

• Terminate all remaining jobs with a single command:

  _________________________________________________________________________________

Section B - Job Scheduling

In this section, you create and modify crontab entries to observe how the normal scheduling system works. You will find some good information about the format and content of the crontab in man 5 crontab., and information about the crontab command in man 1 crontab (yes, they are different). Be sure to check anacrontab(5) and anacrontab(8) as well.

Exercise #1: Cron scheduling

Do this exercise first as a normal user and again as root.

The crond daemon is used to schedule jobs that run periodically, using a schedule based on minute / hour / day-of-month (dom) / month / day-of-week (dow). Jobs submitted usingthe system crontab file in /etc will run at the scheduled time until they are removed from the cron queue.

Verify that the cron daemon, crond, is
running and show the command used: ______________ ________________________________

Analyzing a cron job

# min hour dom month dow [userid] command

0,*/15 8-20 24,25 12 * root echo "From crontab" > /root/out

What does this cron job do? Change the date/time in order to execute it now.

_______________________________________________________________________________________

_______________________________________________________________________________________

Creating / submitting a cron job as a user

The crontab utility is used to allow users to submit jobs to cron. The crontab utility can perform a number of actions, such as:

-l	list current cron job file
-e	edit/create cron job file
-r	remove cron job file

See man 1 crontab for the switches to perform crontab command actions. For more details on cron syntax, see man 5 crontab.

Creating/Modifying a cron job

• Create a cron job with the crontab command. You are now in a specialized vi (see? I told you!) set to edit only your userid's own crontab file.

  Note: The su command will cause the crontab command to operate on the crontab file for root. If root, specify the user name in the command, as:

  crontab -u userid -e.

• Create a cron job, based on the example above. (you must follow cron syntax) to create a file in your ~/cron directory (which you must first create). Make your time delay only a minute or two for the current day.

  Tip: Put in a comment with the crontab syntax as your first entry :

  # min hour dom month dow command

• After leaving the crontab command, verify that you now have a crontab file with your input (as root, look at
  /var/spool/cron/userid; now cat the file and
  verify the content. Is that what you put in?). ___________________________________

• View the result of the entry executing. Did it work? _____________________________

  Note: You don't have to restart the service for the new configuration to take effect. The crond daemon checks each of its directories every minute)

Removing a cron job

• Now remove the cron job(s).

• Verify that the job(s) have been removed.
  Is it gone from /var/spool/cron/? ___________________________________________

Crontab access

You should experiment with the files /etc/cron.allow and /etc/cron.deny to control who can submit cron jobs using the crontab command.

The format of both access control files is one line per user, specifying the userid. The cron control files are read each time a user tries to create/modify a cron job. If the file cron.allow exists, only users listed in it are allowed to use cron, and the cron.deny file is ignored. If cron.allow does not exist, all users listed in cron.deny are not allowed to use cron. Note: The root user can always use cron.

Exercise #2: Viewing the system cron jobs

• View the cron configuration file that lists the cron jobs used for system maintenance with the anacron daemon: less /etc/anacrontab.

  Historically the file /etc/crontab contained configuration entries like those we've seen above which called the run-parts command on all the files in the cron.{daily,weekly,monthly} directories. These jobs are now run indirectly through anacron to prevent conflicts between cron and anacron. See man 5 anacron and man 8 anacron on how to managethe job execution.

• Describe the purpose of any one of the anacrontab entries.

  Note: The utility /usr/bin/run-parts is a shell script that takes a directory name as an argument. Its purpose is to execute every executable file that is located in the given directory. Therefore, no extra entry needs to be added into the system files.

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

• Describe your own crontab entries (both user and root), whether each was successful or not, and why.

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

Section C - Service management

Supporting commands

runlevel	display the previous and current runlevels
telinit n,	switch to runlevel n
uname	display basic system information
chkconfig	manage runlevel services with the following options

--list [service]	list the state of one or all services in all runlevels; a state can be on or off
--level n service on	change the state of a runlevel service on in the specified runlevel
--level n service off	change the state of a runlevel service off in the specified runlevel
--add service	add the service to the runlevels based on the defaults
--del service	remove the service from all runlevels

Exercise #1: Viewing a runlevel service

• List all runlevels where the crond service runs: ________________________________

  Record the command line: ________________________________________________

• Record the name of the crond startup
  script (show the absolute path) used
  in the directory for runlevel 3
  (/etc/rc.d/rc3.d/ for runlevel 3): _____________________________________________
  Tip: use ls with grep

  Record the command line: ________________________________________________

• Record the name of the crond startup
  script (show the absolute path) that is
  executed when the service is activated: _________________________________________

  Record the command line: ________________________________________________

Exercise #2: Turning a service on & off

• Deactivate the crond service in runlevel 3.

Record the command line: ________________________________________________

• Verify that the changes you made are in effect.

Record the command line: ________________________________________________

• Reactivate the crond service in runlevel 3.

Record the command line: ________________________________________________