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Tutorial8: Links / Process Management

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{{Admon/caution|DO NOT USE THIS VERSION OF THE LAB. This page will no longer be updated.|'''New version here:''' https://seneca-ictoer.github.io/ULI101/A-Tutorials/tutorial8 '''Andrew's students please go here:''' http://wiki.littlesvr.ca/wiki/OPS145_Lab_7}}

=LINKING FILES / MANAGING PROCESSES=

|- valign="top" style="padding-left:15px;"

|colspan="2" |~~Course Notes~~'''Slides:'''<ul><li>Week 8 Lecture 1 Notes: [https://~~ict~~wiki.cdot.senecacollege.ca/~~~murray~~uli101/slides/ULI101-8.1.pdf PDF] | [https://wiki.~~saul~~cdot.senecacollege.ca/uli101/slides/ULI101-~~Week8~~8.1.pptx PPTX]</li><li>Week 8 Lecture 2 Notes: [https://wiki.cdot.senecacollege.ca/uli101/slides/ULI101-8.2.pdf PDF] | [https://~~ict~~wiki.cdot.senecacollege.ca/~~~murray.saul~~uli101/~~uli101~~slides/ULI101-~~Week8~~8.2.pptx PPTX] </li></ul>

| style="padding-left:15px;" |'''Links:'''

* [http://www.linfo.org/hard_link.html#:~:text=A%20hard%20link%20is%20merely,created%20to%20other%20hard%20links. Hard Links]

* [https://www.computerhope.com/jargon/s/symblink.htm#:~:text=Alternatively%20referred%20to%20as%20a,or%20directory%20using%20its%20path.&text=In%20Linux%20and%20Unix%20symbolic,created%20using%20the%20mklink%20command. Symbolic Links]

'''Managing Processes:'''

* [https://en.wikipedia.org/wiki/Inode inode]

* [https://opensource.com/article/18/9/linux-commands-process-management Manipulating Processes]

| style="padding-left:15px;"|'''Linux Commands:'''

* [http://man7.org/linux/man-pages/man1/ln.1.html ln]

* [http://man7.org/linux/man-pages/man1/ps.1.html ps]

* [https://mediatemple.net/community/products/dv/204404624/using-the-history-command history]

|colspan="1" style="padding-left:15px;" width="30%"|'''Brauer Instructional Videos:'''<ul><li>[https://www.youtube.com/watch?v=tZ94-qH9unM&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=9 Inodes and Links]</li><li>[https://www.youtube.com/watch?v=q93POTgH-aQ&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=7 Processes and Jobs]</li></ul>

|}

Users can '''manage processes''' to become more '''productive''' while working in the Unix / Linux Command-line environment. Processes that run in the terminal are known as ''~~Common~~ 'foreground''' processes. You can run or send processes currently running in the ''foreground'' to the '''background''' to free-up your terminal (e.g. issue other Linux commands / ). Below are a listing of common '''Linux commands''' and '''keyboard shortcuts ''' to manage foreground and background processes:''

<table cellpadding="5" width="80%"><tr valign="top"><th width="25%" style="border-bottom: 1px solid black;text-align:left;">Linux Command / Key Combination</th><th style="border-bottom: 1px solid black;text-align:left;">Purpose</th></tr><tr valign="top"><td>ps</td><td>Displays snapshot information about processes. ''Examples: ''ps , ps -l , ps -ef , ps -u , ps aux </td></tr><tr valign="top"><td>'''top'''</td><td>The '''top''' command provides a realtime status of running processes. '''NOTE:''' You can press '''ctrl-c''' to exit </td></tr><tr valign="top"><td>'''ctrl-c'''</td><td>'''Terminates''' a process running in the foreground</td></tr><tr valign="top"><td>'''ctrl-z'''</td><td>Sends a process running in the foreground into the '''background'''.</td></tr><tr valign="top"><td>fg</td><td>Moves a background job from the current environment into the foreground. ''Example: ''fg %job-number</td></tr><tr valign="top"><td>bg</td><td>Runs (starts) the most recent process that was placed into the background. ''Example: ''bg %job-number</td></tr><tr valign="top"><td>jobs</td><td>The '''jobs''' utility displays the '''status''' of jobs that were started in the current shell environment. ''Example: ''jobs [1]+ Stopped vim a   <-- Job #1 (+ most recent process / background) [2]  Running sleep 200 &  <-- Job #2 [3]  Running sleep 300 &  <-- Job #3 [4]- Running sleep 400 &  <-- Job #4 (- second recent process / background) </td></tr><tr valign="top"><td>kill</td><td>The kill command sends the specified signal to the specified processes or process groups. If no signal is specified, the '''TERM''' signal is sent. The default action for this signal is to terminate the process. ''Examples:'' kill PID , kill -9 PID , kill %job-number , kill -9 %job-number</td></tr></table>

===Aliases / Command History===

'''~~Alias~~Aliases:''' ~~Assigns~~ An '''alias''' is a '''nickname ''' to an existing command or group of commands. An alias existing in '''system memory''' and will be '''lost''' when your current Linux session ends, unless the alias is set in a '''start-up file''' (e.g. ~/.bashrc. You will learn about using start-up files later in this course.

''Examples:''

'''Command History:'''

The filename ~~'''~~~/.bash_history~~'''~~ stores recently executed command lines

''Examples of commands that use command history:''

<table width="80%"><tr valign="top"><td width="30%">up arrow or down arrow </td><td>move to '''previous''' command or '''next''' command within Bash shell prompt</td></tr><tr><td>fc -l</td><td> display last '''16''' commands</td></tr><tr><td>history | more</td><td>display all stored commands</td></tr><tr><td>!num</td><td>'''re-execute''' an issued command number by command number (determined from ''history'' command)</td></tr><tr><td>!xxx</td><td>'''re-~~execute~~run''' an a most recent previously-issued command beginning with string "xxx"</td></tr></table>

=INVESTIGATION 1: LINKING FILES=

'''ATTENTION''': This online tutorial will be required to be completed by '''Friday in week 9 by midnight''' to obtain a grade of '''2%''' towards this course In this ~~section~~investigation, you will learn how to create '''hard links''' and '''symbolic links''' on your Matrix account, and observe the advantages and limitations of using both types of links.

# Issue the following Linux command to create a hard-linked file in your '''home''' directory: ln ~/links/data-file.txt ~/data-file.hard.lnk

# Issue the following Linux command to compare all file's ''i-node'' numbers: ls -li ~/links/data-file.txt ~/links/data-file.hard.lnk ~/data-file.hard.lnk What do you notice about all of those file's ''i-node'' numbers?

# Issue the following Linux command to check that you created those hard links: ~~bash /home/murray.saul/myscripts~~~uli101/week8-check-1 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 to remove the '''~/links''' directory and its contents: rm -rf ~/links

# Issue a Linux command to confirm that the '''~/links''' directory has been removed.

# Save your editing session and exit your text editor.

# Issue the following Linux command to view the contents of the '''symbolic''' linked file: cat ~/links2/text-file.sym.lnk What did you notice? Again, when you view the contents of the symbolic-linked file, you are redirected (via ''pathname'') to the original file.

# Issue the following Linux command to check that you created those symbolic links: ~~bash /home/murray.saul/myscripts~~~uli101/week8-check-2 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 to remove the '''~/links2''' directory: rm -rf ~/links2

# Issue a Linux command to confirm that the '''~/links2''' directory has been removed.

# Issue the following Linux command: ls -l ~/text-file.sym.lnk This output indicates a "'''broken link'''" and indicates this is not an effective method of backing up files.

# Issue a command to delete the ~/text-file.sym.lnk file which is a ''broken link''.

# Issue the following Linux command: ln -s ~~~murray~~jason.~~saul~~carman/~~myscripts checking-scripts~~example t8example [[Image:symbolic-link-inode2.png|thumb|right|500px|'''Symbolic links''' can be used to point to '''directories''' as well as regular files. Symbolic links can also point to files on '''other''' Unix/Linux filesystems.]]# Issue the following Linux command: ls -ld ~~checking-scripts~~t8example What do you notice? Symbolic links are good for creating "short-cuts" to both '''regular files''' and '''directories'''.

=INVESTIGATION 2: MANAGING PROCESSES =

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

In this ~~section~~investigation, you will learn how to '''manage aliases''' and '''Linux command history''' on 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: alias | ~~bash /home/murray.saul/myscripts~~~uli101/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. We will complete this investigation by learning to execute p'''reviously issued commands''' by using '''command history'''.

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

# Type an exclamation mark '''!''' 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?

# 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 =

simulate a quiz:

https://~~ict~~wiki.cdot.senecacollege.ca/~~~murray.saul~~uli101/~~uli101~~files/uli101_week8_practice.docx

Your instructor may take-up these questions during class. It is up to the student to attend classes in order to obtain the answers to the following questions. Your instructor will NOT provide these answers in any other form (eg. e-mail, etc).

# Aliases / History:<ol type="a"><li>Write a linux command to create an '''alias''' called '''ld''' that issues the command: '''ls -ld'''</li><li>Write a linux command to unset the '''alias''' created in the previous question.</li><li>Issue a Linux command to list '''history''' of commands that match the pattern called '''touch'''.</li></ol>

# Create a '''table''' listing each Linux command, useful options and command purpose for the following Linux commands: '''ln''' , '''ps''' , '''top''' , '''fg''' , '''bg''' , '''jobs''' , '''kill''' , '''alias''' , '''unalias''' , '''history'''

_________________________________________________________________________________

Author: Murray Saul

License: LGPL version 3

Link: https://www.gnu.org/licenses/lgpl.html

_________________________________________________________________________________

[[Category:ULI101]]

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