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Tutorial 8 - Links / Process Management

8,433 bytes added, 20:17, 25 October 2021

→‎INVESTIGATION 2: MANAGING PROCESSES

= INVESTIGATION 2: MANAGING PROCESSES =

In this investigation, you will learn how to '''manage processes''' on a Unix / Linux server.

'''Perform the Following Steps:'''

# 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 this tutorial, we will be using this command to '''simulate''' the management of "long-running" processes.

# 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 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''') to ''terminate'' a process that is running on the terminal (i.e. a '''foreground''' process).

# Reissue the Linux command: sleep 700

# Press the '''key combination''': ctrl-z [[Image:process-jobs1.png|thumb|right|300px|Running a command in the terminal, pressing '''ctrl-z''' to place into the background, and issuing the '''jobs''' command to view processes in the background.]]

# 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.

# 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'''. [[Image:process-jobs2.png|thumb|right|300px|Using the '''bg''' command to '''run recent process''' that was placed into background from using '''ctrl-z''' keys.]]

# Issue the following Linux command: bg '''NOTE:''' You can use the bg command WITHOUT arguments to run recent in 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''' (indicated by the ampersand character "'''&'''"). Now this command has resume pausing until '''700 seconds'''. [[Image:process-jobs3.png|thumb|right|300px|Using the '''ampersand''' character '''&''' to run a '''series of processes''' in the background.]]

# 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''' 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''' without having to issue ''ctrl-z'' and ''bg'' short-cut keys.

# Issue the following Linux 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'''). [[Image:process-jobs4.png|thumb|right|300px|Using the '''kill %1''' command to '''terminate''' job #1.]]

# 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? [[Image:process-jobs5.png|thumb|right|300px|Using round brackets to '''group''' a series of commands to be run as '''one process'''.]]

# 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 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 processes' PID number instead of "PID"): kill PID What did you notice? '''FYI:''' If the command did NOT work, issue the following Linux command (using the bash processes' PID number instead of "PID"): kill -9 PID

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

= INVESTIGATION 3: ALIASES / COMMAND HISTORY =

= LINUX PRACTICE QUESTIONS =

Jason Michael Carman

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Tutorial 8 - Links / Process Management

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