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Tutorial8: Links / Process Management

324 bytes added, 17:52, 25 February 2021

→‎INVESTIGATION 3: ALIASES / COMMAND HISTORY

# Make certain that you are logged into your Matrix account.

# Issue a Linux command to confirm that you are located in your '''home''' directory. The '''sleep''' command '''pauses for a specified number of seconds''' before returning to the shell prompt. In the tutorial, we will be using this command to '''simulate "long-running" processes''' for us to manage.

# Issue the following Linux command: sleep 700 Notice that this process will run for '''700 seconds''', and is forcing the user to wait until this process finishes. A process that is '''running in the terminal''' is referred to as a '''foreground ~~process~~processes'''. The Unix/Linux system is designed to allow users to send '''preemptive signals''' to manage those processes. # Press the following '''key combination''' to '''terminate''' the command running on the terminal: ctrl-c 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''' - which is signal '''#2''') signal to ''terminate '' a process~~ ~~that is running on the terminal (i.e. the '''foreground''').

# Reissue the Linux command: sleep 700

# Press the '''key combination''': ctrl-z

# You should now see output similar to what is displayed below: [1]+ Stopped sleep 700 '''NOTE:''' This indicates that this process has been placed into the '''background'''. This is useful in order to "'''free-up'''" the terminal to run other Linux commands~~. # Clear your bash shell terminal screen~~.

# Issue the following Linux command: jobs You should see the following output similar that was displayed above: [1]+ Stopped sleep 700 This display indicates that this process (that is now in the background) has '''stopped'''. In other words, the ''sleep'' command is NOT counting-down to zero to terminate. '''NOTE:''' You need to use the '''bg''' command to '''run''' that process that was sent into the '''background'''.

# Issue the following Linux command: bg '''NOTE:''' You can use the bg command WITHOUT arguments to specify the most recent process that was placed into the background. From the '''jobs''' command, the process that has a plus sign "+" indicates the most recent process placed into the background.

# Issue the following Linux command: jobs You should see the following output similar that was displayed above: [1]+ sleep 700 & This display indicates that this process in the background is '''running in the background''' (denoted by the ampersand character "&"). Now the command is counting-down to zero.

# Issue the following Linux command: fg You should notice that the ''sleep'' command is now running in the '''foreground'''. # Press the '''key combination''' to '''terminate'''~~TIP:~~the process running in the '''foreground''' : ctrl-c You can issue Linux commands with ampersand "'''&'''" in your terminal to '''run''' processes automatically in the '''background''' ~~automatically~~ without having to issue ''ctrl-z'' and ''bg'' short-cut keys.~~ ~~ ~~# Press the '''key combination''' to '''terminate''' the process running in the '''foreground''': ctrl-c~~ # Issue the following Linux ~~command~~commands: sleep 500 & sleep 600 & sleep 700 &

# Issue the '''jobs''' command. What do you notice? In the jobs command output, jobs that display a plus sign ('''+''') indicates the '''most recent''' process placed in to the background, and a minus sign ('''-''') indicates the '''second most recent''' process placed into the background. The '''kill''' command issued to terminate processes that are running in the '''foreground''' or '''background'''. Issuing the kill command without options would send the '''SIGTERM''' signal (eg. ''signal terminate'' - which is signal '''#15''').

# Issue the following Linux command to '''terminate''' the '''first''' job running in the background: kill %1 '''NOTE:''' You can specify job number preceded by percent % with the '''kill''', '''bg''', and '''fg''' commands to specify the processes' job number.

# Issue the '''jobs''' command. What do you notice?

# Issue the following Linux commands: kill %2 kill %3

# Issue the '''jobs''' command (you may have to issue the ''jobs'' command several times to get final result). What do you notice?~~ You can also manipulate processes by their '''PID''' ('''process ID''').~~

# Let's use '''grouping''' to run several commands in sequence within a single process.

# Issue the following Linux command: (sleep 400; sleep 500; sleep 600) &

# Issue the '''jobs''' command. What do you notice? You should notice all commands are run in a group as just one process.

# Issue the following Linux command to terminate the first job running in the '''background''': kill %1 NOTE: If issuing the kill command does not work, then you would need to send a STRONGER signal to "'''kill'''" (not "''SIGTERM'' - which is signal ''#15''") the process. The '''SIGKILL''' signal (signal '''#9''') would be required to do this by issuing the '''kill''' command with the option: '''-9'''.

# Issue the '''jobs''' command and make certain there are no processes that are running in the '''background'''. You can also manipulate processes by their '''PID''' ('''process ID'''). Let's terminate our Matrix Bash shell process by using the '''kill''' command using that ~~process~~processes' '''PID'''.

# Issue the following Linux command: ps

#Note in the '''ps''' command output the PID of the process called '''bash'''. You will be using that PID when issuing the next Linux command.

# Issue the following Linux command (using the bash ~~process~~processes' PID number instead of "PID"): kill PID What did you notice? '''It did not work''' since you need to send a STRONGER signal (eg. '''SIGKILL''', not ''SIGTERM''). # Issue the following Linux command (using the bash ~~process~~processes' PID number instead of "PID"): kill -9 PID What did you notice? You should have been '''logged off''' of your Matrix session!

:In the next investigation, you will learn how to '''create aliases''' and '''view command history''' on your Matrix server.

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: alias | grep "lh"

# Issue the following alias: lh What do you think this command does?

# '''Logout ''' of your Matrix account, than log into your Matrix account. # Reissue the '''lal''' alias. What happened?

# Reissue the '''lh''' alias. What happened?

# Issue the '''alias | grep lh''' command without any arguments to see if it is stored in memory.

# Run the '''lh''' alias to confirm that it is properly set in memory.

# Issue the following Linux command to edit your ~/.bashrc startup file: nano ~/.bashrc

# Add the following line at the '''bottom ''' of this file: alias lh='ls --human-readable --size -1 -S --classify'

# Save your editing changes and exit your text editor.

# '''Logout ''' of your Matrix account, ~~than log into~~ then '''login''' to your Matrix account.

# Reissue the '''lh''' alias. What happened?

# Issue the following Linux command: unalias lh

# Run the '''lh''' alias to see what happens. What happenned?

# '''Logout ''' of your Matrix account, ~~than log into~~ then '''login''' to your Matrix account.

# Reissue the '''lh''' alias. What happened? Why?

# Reissue the '''lal''' alias. Why '''didn't''' this alias work? The checking script below is designed to act as a '''filter''' with a '''pipeline command'''. This will allow to check if your '''lh''' alias exists when it is checked in this program. # Issue the following Linux pipeline command ~~to check your work~~: alias | bash /home/murray.saul/scripts/week8-check-3 If you encounter errors, then view the feedback to make corrections, and then re-run the checking script. If you receive a congratulation message that there are no errors, then proceed with this tutorial.

# Issue the following Linux command: history | grep "lh" What do you notice?

# ~~Press~~ Type an exclamation mark '''! ~~immediately~~ ''' followed by the number by one of those commands listed in the '''history list ''' and press ENTER What happened?

# Type the following: !unalias and press ENTER What happened?

# Issue the following Linux command: history | grep "lh" What happened?

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