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Tutorial8: Links / Process Management

374 bytes added, 17:52, 25 February 2021
INVESTIGATION 3: ALIASES / COMMAND HISTORY
# Make certain that you are logged into your Matrix account.<br><br>
# Issue a Linux command to confirm that you are located in your '''home''' directory.<br><br>The '''sleep''' command '''pauses for a specified number of seconds''' before returning to the shell prompt.<br>In the tutorial, we will be using this command to '''simulate "long-running" processes''' for us to manage.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">sleep 700</span><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 processprocesses'''.<br><br>The Unix/Linux system is designed to allow users to send '''preemptive signals''' to manage those processes.<br><br>
# Press the following '''key combination''' to '''terminate''' the command running on the terminal: <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).<br>'''NOTE:''' The '''ctrl-c''' key combination sends '''SIGINT''' ('''Signal Interrupt''' - which is signal '''#2''') signal to<br>''terminate'' a process that is running on the terminal (i.e. the '''foreground''').<br><br>
# Reissue the Linux command: <span style="color:blue;font-family:courier;font-weight:bold">sleep 700</span><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>
# Press the '''key combination''' to '''terminate''' the process running in the '''foreground''': <span style="color:blue;font-family:courier;font-weight:bold">ctrl-c</span> <br><br>You can issue Linux commands with ampersand "'''&'''" in your terminal to '''run''' processes automatically in the<br>'''background''' <u>without</u> having to issue ''ctrl-z'' and ''bg'' short-cut keys.<br><br>
# Issue the following Linux commandcommands: <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>In the jobs command output, jobs that display a plus sign ('''+''') indicates the '''most recent''' process<br>placed in to the background, and a minus sign ('''-''') indicates the '''second most recent''' process<br>placed into the background.<br><br>The '''kill''' command issued to terminate processes that are running in the '''foreground''' or '''background'''.<br>Issuing the kill command <u>without</u> options would send the '''SIGTERM''' signal (eg. ''signal terminate'' - which is signal '''#15''').<br><br>
# Issue the following Linux command to '''terminate''' the '''first''' job running in the background:<br><span style="color:blue;font-family:courier;font-weight:bold">kill %1</span><br><br>'''NOTE:''' You can specify job number preceded by percent % with the<br>'''kill''', '''bg''', and '''fg''' commands to specify the processes' job number.<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 (you may have to issue the ''jobs'' command several times to get final result).<br> 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>You should notice all commands are run in a group as just one process.<br><br>
# Issue the following Linux command to terminate the first job running in the '''background''':<br><span style="color:blue;font-family:courier;font-weight:bold">kill %1</span><br><br>NOTE: If issuing the kill command does not work, then you would need to send a STRONGER signal<br>to "'''kill'''" (not "''SIGTERM'' - which is signal ''#15''") the process. The '''SIGKILL''' signal (signal '''#9''')<br>would be required to do this by issuing the '''kill''' command with the option: '''-9'''.<br><br>
# Issue the '''jobs''' command and make certain there are no processes that are running in the '''background'''.<br><br>You can also manipulate processes by their '''PID''' ('''process ID'''). Let's terminate our Matrix Bash shell process <br>by using the '''kill''' command using that processprocesses' '''PID'''.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">ps</span><br><br>
#Note in the '''ps''' command output the PID of the process called '''bash'''.<br><br>You will be using that PID when issuing the <u>next</u> Linux command.<br><br>
# Issue the following Linux command (using the bash processprocesses' PID number instead of "PID"):<br><span style="color:blue;font-family:courier;font-weight:bold">kill PID</span><br><br>What did you notice? '''It did not work''' since you need to send a STRONGER signal (eg. '''SIGKILL''', not ''SIGTERM'').<br><br># Issue the following Linux command (using the bash processprocesses' PID number instead of "PID"):<br><span style="color:blue;font-family:courier;font-weight:bold">kill -9 PID</span><br><br>What did you notice? You should have been '''logged off''' of your Matrix session!<br><br>
:In the next investigation, you will learn how to '''create aliases''' and '''view command history''' on your Matrix server.<br><br>
<br>
In this section, you will learn how to '''manage aliases ''' and Linux '''command history ''' on your Matrix account.
# Issue the following command to confirm that this newly-created alias is stored in memory:<br><br><span style="color:blue;font-family:courier;font-weight:bold">alias | grep "lh"</span><br><br>
# Issue the following alias: <span style="color:blue;font-family:courier;font-weight:bold">lh</span> <br><br>What do you think this command does?<br><br>
# '''Logout ''' of your Matrix account, than log into your Matrix account.<br><br># Reissue the '''lal''' alias. What happened?<br><br>
# Reissue the '''lh''' alias. What happened?<br><br>
# Issue the '''alias | grep lh''' command without any arguments to see if it is stored in memory.<br><br>
# Run the '''lh''' alias to confirm that it is properly set in memory.<br><br>
# Issue the following Linux command to edit your ~/.bashrc startup file:<br><span style="color:blue;font-family:courier;font-weight:bold">nano ~/.bashrc</span><br><br>
# Add the following line at the '''bottom ''' of this file:<br><span style="font-family:courier;font-weight:bold;>alias lh='ls --human-readable --size -1 -S --classify'</span><br><br>
# Save your editing changes and exit your text editor.<br><br>
# '''Logout ''' of your Matrix account, than log into then '''login''' to your Matrix account.<br><br>
# Reissue the '''lh''' alias. What happened?<br><br>
# Issue the following Linux command: <span style="font-family:courier;font-weight:bold;>unalias lh</span><br><br>
# Run the '''lh''' alias to see what happens.<br><br>What happenned?<br><br>
# '''Logout ''' of your Matrix account, than log into then '''login''' to your Matrix account.<br><br>
# Reissue the '''lh''' alias. What happened? Why?<br><br>
# Reissue the '''lal''' alias. Why '''didn't''' this alias work?<br><br>The checking script below is designed to act as a '''filter''' with a '''pipeline command'''.<br>This will allow to check if your '''lh''' alias exists when it is checked in this program.<br><br># Issue the following Linux pipeline command to check your work: <br><span style="color:blue;font-weight:bold;font-family:courier;">alias | bash /home/murray.saul/scripts/week8-check-3</span><br><br>If you encounter errors, then view the feedback to make corrections, and then re-run the checking script.<br>If you receive a congratulation message that there are no errors, then proceed with this tutorial.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">history | grep "lh"</span><br><br>What do you notice?<br><br>
# Press Type an exclamation mark '''! immediately ''' followed by the number by one of those commands <br>listed in the '''history list ''' and press <span style="color:blue;font-family:courier;font-weight:bold">ENTER</span><br><br>What happened?<br><br>
# Type the following: <span style="color:blue;font-family:courier;font-weight:bold">!unalias</span> and press <span style="color:blue;font-family:courier;font-weight:bold">ENTER</span><br><br>What happened?<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">history | grep "lh"</span><br><br>What happened?<br><br>
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