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Tutorial8: Links / Process Management

174 bytes added, 10:53, 2 September 2020

→‎INVESTIGATION 3: ALIASES / COMMAND HISTORY

# Use a text editor to create a file called '''~/links/data-file.txt'''

# Enter the following text displayed below: This is line 1 This is line 2 This is line 3

# Save your editing session and exit your text editor.

# Issue the following Linux command: ls -li ~/links/data-file.txt View the '''i-node''' number for this file. What does this i-node number represent?

# Issue the following Linux command to create the following hard link in the same directory: ln ~/links/data-file.txt ~/links/data-file.hard.lnk

# Use a text editor to create a file called '''~/links2/text-file.txt'''

# Enter the following text displayed below: This is line one This is line two This is line three

# Save your editing session and exit your text editor.

# Issue the following Linux command to create the following symbolic link in the same directory: ln -s ~/links2/text-file.txt ~/links2/text-file.sym.lnk

# Issue the '''ls -li''' command for the '''~/links2''' directory. What do you notice about both of these file's i-node numbers? What do you notice about the size of the file ''~/links2/text-file.sym.lnk''? What pathname do you think it represents?

# Change to your '''home''' directory.

# Issue the following Linux command to create the following symbolic link in your home directory: ln -s ~/links2/text-file.txt ~/text-file.sym.lnk

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.

# Issue the following Linux command: sleep 700 '''NOTE:''' The '''sleep''' command ~~just~~ waits for a specified number of seconds before ~~completing in order to return~~ returning to the shell prompt. It is useful in order to force a pause in a sequence of commands. # 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'''. The Unix/Linux system is designed to allow users to send '''preemptive signals''' to manage those processes. # Press the key combination: <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''') to terminate a process that is running.

# 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 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'''. You can run commands with ampersand "'''&'''" to run processes in the background. # Press the key combination: <ctrl><c> to ~~stop~~ '''terminate''' the process running in the foreground.

# Issue the following Linux command: sleep 500 & sleep 600 & sleep 700 &

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

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

# Issue the '''jobs''' command. 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?

# Issue the following Linux command: ps What is the PID of the previously issued Linux command in the background?

# Issue the following Linux command (using the PID number instead of "PID"): kill PID

# Issue the '''jobs''' command. Is the sleep process still running? '''NOTE:''' You need to issue the ''kill -9 PID '' command if the previous commands did not work.

# Issue the following Linux command (using the PID number instead of "PID"): kill -9 PID

# Issue the '''jobs''' and '''ps''' commands to confirm there are no processes running in the background.

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

~~ ~~

=INVESTIGATION 3: ALIASES / COMMAND HISTORY=

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

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

# After you complete the Review Questions sections to get additional practice, then work on your '''online assignment 2 ''' and complete '''section4 ''' labelled: '''Linking files and directories'''.

= LINUX PRACTICE QUESTIONS =

Msaul

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Tutorial8: Links / Process Management

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