Process and Task Scheduling Labs

Lab: ps

  1. ps
ps
  1. Check manual pages:
man ps
  1. Run with “every” and “full format” flags:
ps -ef
  1. Produce an output with the command name in column 1, PID in column 2, PPID in column 3, and owner name in column 4, run it as follows:
ps -o comm,pid,ppid,user
  1. Check how many sshd processes are currently running on the system:
ps -C sshd

Lab: top

  1. top
top
  1. View manual page:
man top

Lab: List a specific process

  1. list the PID of the rsyslogd daemon
pidof rsyslogd
or
pgrep rsyslogd

Lab: Listing Processes by User and Group Ownership

  1. List processes owned by user1:
ps -U user1
  1. List processes owned by group root:
ps -G root

Lab: nice

  1. View the default nice value:
nice
  1. List priority and niceness for all processes:
ps -efl

Lab: Start Processes at Non-Default Priorities (2 terminals)

  1. Run the top command at the default priority/niceness in Terminal 1:
top
  1. Check the priority and niceness for the top command in Terminal 2 using the ps command:
ps -efl | grep top
  1. Terminate the top session in Terminal 1 by pressing the letter q and relaunch it at a lower priority with a nice value of +2:
nice -n 2 top
  1. \Check the priority and niceness for the top command in Terminal 2 using the ps command:
ps -efl | grep top
  1. Terminate the top session in Terminal 1 by pressing the letter q and relaunch it at a higher priority with a nice value of -10. Use sudo for root privileges.
sudo nice -n -10 top
  1. Check the priority and niceness for the top command in Terminal 2 using the ps command:
ps -efl | grep top
  1. Terminate the top session by pressing the letter q.

Lab: Alter Process Priorities (2 terminals)

  1. Run the top command at the default priority/niceness in Terminal 1:
top
  1. Check the priority and niceness for the top command in Terminal 2 using the ps command:
ps -efl | grep top
  1. While the top session is running in Terminal 1, increase its priority by renicing it to -5. Use the command substitution to get the PID of top. Prepend the renice command by sudo. The output indicates the old (0) and new (-5) priorities for the process.
sudo renice -n -5 $(pidof top)
  1. Validate the above change with ps. Focus on columns 7 and 8.
ps -efl | grep top
  1. Repeat the above but set the process to run at a lower priority by renicing it to 8: The output indicates the old (-5) and new (8) priorities for the process.
sudo renice -n 8 $(pidof top)
  1. Validate the above change with ps. Focus on columns 7 and 8.
ps -efl | grep top

Lab: Controlling Processes with Signals

  1. Pass the soft termination signal to the crond daemon, use either of the following:
sudo pkill crond
# or
sudo kill $(pidof crond)
  1. Confirm:
ps -ef | grep crond
  1. Forcefully kill crond:
sudo pkill -9 crond
# or
sudo pkill -s SIGKILL crond
# or
sudo kill -9 $(pgrep crond)
  1. Kill all crond processes:
sudo killall crond
  1. View manual pages:
man kill
man pkill
man killall

Lab: cron and atd

  1. View log files for cron and atd
sudo cat /var/log/cron

Lab: at and crond

  1. run /home/user1/.bash_profile file for user1 2 hours from now:
at -f ~/.bash_profile now + 2 hours
  1. Consult crontab manual pages:
man crontab

Lab: Submit, View, List, and Erase an at Job

1.Run the at command and specify the correct execution time and date for the job. Type the entire command at the first at> prompt and press Enter. Press Ctrl+d at the second at> prompt to complete the job submission and return to the shell prompt.

at 11:30pm 3/31/20
date &> /tmp/date.out

The system assigned job ID 5 to it, and the output also pinpoints the job’s execution time.

2.List the job file created in the /var/spool/at directory:

sudo ls -l /var/spool/at/

3.List the spooled job with the at command. You may alternatively use atq to list it.

at -l
# or
atq

4.Display the contents of this file with the at command and specify the job ID:

at -c 5

5.Remove the spooled job with the at command by specifying its job ID. You may alternatively run atrm 5 to delete it.

at -d 5

This should erase the job file from the /var/spool/at directory. You can

  1. confirm the deletion by running atq or at -l.
atq

Lab: Add, List, and Erase a Cron Job

assume that all users are currently denied access to cron

  1. Edit the /etc/cron.allow file and add user1 to it:
sudo vim /etc/cron.allow
user1
  1. Switch to user1 Open the crontable and append the following schedule to it. Save the file when done and exit out of the editor.
crontab -e
*/5 10-11 5,20 * * echo "Hello, this is a cron test." > /tmp/hello.out
  1. Check for the presence of a new file by the name user1 under the /var/spool/cron directory:
sudo ls -l /var/spool/cron
  1. List the contents of the crontable:
crontab -l
  1. Remove the crontable and confirm the deletion:
crontab -r
crontab -l

Lab: Anacron

  1. View the default content of /etc/anacrontab without commented or empty lines:
cat /etc/anacrontab | grep -ve ^# -ve ^$
  1. View anacron man pages:
man anacron

Lab 8-1: Nice and Renice a Process

  1. As user1 with sudo on server1, open two terminal sessions. Run the top command in terminal 1. Run the pgrep or ps command in terminal 2 to determine the PID and the nice value of top.
ps -efl | grep top
  1. Stop top on terminal 1 and relaunch at a lower priority (+8).
nice -n 8 top
  1. Confirm the new nice value of the process in terminal 2.
ps -efl | grep top
  1. Issue the renice command in terminal 2 and increase the priority of top to -10:
renice -n -10 $(pidof top)
  1. Confirm:
ps -efl | grep top

Lab 8-2: Configure a User Crontab File

As user1 on server1, run the tty and date commands to determine the terminal file (assume /dev/pts/1) and current system time.

tty
date

Create a cron entry to display “Hello World” on the terminal. Schedule echo “Hello World” > /dev/tty/1 to run 3 minutes from the current system time.

crontab -e
*/3 * * * * echo "Hello World" > /dev/pts/2

As root, ensure user1 can schedule cron jobs.

sudo vim /etc/cron.allow
user1