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→INVESTIGATION 2: MANAGING PROCESSES
In this section, you will learn how to manage processes on a Unix / Linux server.
# Make certain that you are logged into your Matrix account.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">sleep 700</span><br><br>'''NOTE:''' The '''sleep''' command just waits for a specified number of seconds before completing<br>in order to return returning to the shell prompt. It is useful in order to force a pause in a sequence of commands.<br><br># Notice that this process will run for '''700 seconds''', and is forcing the user to wait until this process finishes.<br>A process that is running in the terminal is referred to as a '''foreground process'''.<br><br>The Unix/Linux system is designed to allow users to send '''preemptive signals''' to manage those processes.<br><br># Press the key combination: <span style="color:blue;font-family:courier;font-weight:bold"><ctrl><c></span><br><br>You should notice that the process that was running in the foreground has been '''interrupted ''' (i.e. terminated). '''NOTE:''' The '''ctrl-c''' key combination sends '''SIGINT''' ('''Signal Interrupt''') to terminate a process that is running.<br><br>
# Reissue the Linux command: <span style="color:blue;font-family:courier;font-weight:bold">sleep 700</span><br><br>
# Press the key combination: <span style="color:blue;font-family:courier;font-weight:bold"><ctrl><z></span><br><br>
# You should now see output similar to what is displayed below:<br><span style="font-family:courier;font-weight:bold">[1]+ Stopped sleep 700</span><br><br>'''NOTE:''' This indicates that this process has been placed into the '''background'''.<br>This is useful in order to "'''free-up'''" the terminal to run other commands.<br><br>
# Clear your bash shell terminal screen.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">jobs</span><br><br>You should see the following output similar that was displayed above:<br><span style="font-family:courier;font-weight:bold">[1]+ Stopped sleep 700</span><br><br>This display indicates that this process (that is now in the background) has '''stopped'''.<br>In other words, the ''sleep '' command is NOT counting-down to zero to terminate.<br><br>'''NOTE:''' You need to use the '''bg''' command to run that process that was sent into the background.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">bg</span><br><br>'''NOTE:''' You can use the bg command WITHOUT arguments to specify the most recent process<br>that was placed into the background. From the '''jobs''' command, the process that has a plus sign "+"<br>indicates the most recent process placed into the background.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">jobs</span><br><br>You should see the following output similar that was displayed above:<br><span style="font-family:courier;font-weight:bold">[1]+ sleep 700 &</span><br><br>This display indicates that this process in the background is '''running in the background'''<br>(denoted by the ampersand character "&"). Now the command is counting-down to zero.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">fg</span><br><br>You should notice that the ''sleep '' command is now running in the '''foreground'''.<br><br>You can run commands with ampersand "'''&'''" to run processes in the background.<br><br> # Press the key combination: <span style="color:blue;font-family:courier;font-weight:bold"><ctrl><c></span> to stop '''terminate''' the process running in the foreground.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">sleep 500 & sleep 600 & sleep 700 &</span><br><br>
# Issue the '''jobs''' command. What do you notice?<br><br>
# Issue the following Linux commands:<br><span style="color:blue;font-family:courier;font-weight:bold">kill %2</span><br><span style="color:blue;font-family:courier;font-weight:bold">kill %3</span><br><br>
# Issue the '''jobs''' command. What do you notice?<br><br>You can also manipulate processes by their '''PID''' ('''process ID''').<br><br>
# Let's use '''grouping ''' to run several commands in sequence within a single process.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">(sleep 400; sleep 500; sleep 600) &</span><br><br>
# Issue the '''jobs''' command. What do you notice?<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">ps</span><br><br>What is the PID of the previously issued Linux command in the background?<br><br>
# Issue the following Linux command (using the PID number instead of "PID"):<br><span style="color:blue;font-family:courier;font-weight:bold">kill PID</span><br><br>
# Issue the '''jobs''' command. Is the sleep process still running?<br><br>'''NOTE:''' You need to issue the ''kill -9 PID '' command if the previous commands did not work.<br><br>
# Issue the following Linux command (using the PID number instead of "PID"):<br><span style="color:blue;font-family:courier;font-weight:bold">kill -9 PID</span><br><br>
# Issue the '''jobs''' and '''ps''' commands to confirm there are no processes running in the background.<br><br>
