Difference between revisions of "Tutorial8: Links / Process Management"

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===Main Objectives of this Practice Tutorial===
 
===Main Objectives of this Practice Tutorial===
  
:* Understand the purpose and why links are used in Unix / Linux
+
:* Define the term '''i-node''' as it relates to the Unix/Linux File System
  
:* Define the term '''inode''' number as it relates to a file on Unix / Linux
+
:* Issue the '''ls -i''' command to view '''i-node''' (index) numbers associated with Unix/Linux files
  
:* Define the terms: '''Hard''' Link and '''Symbolic''' Link
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:* Define the terms '''Hard''' and '''Symbolic''' Links
  
:* Issue the '''ln''' command to create hard and symbolic links
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:* Issue the '''<span style="font-family:courier">ln</span>''' command to create '''hard''' and '''symbolic''' links
  
:* Define and understand the purpose of a '''process''' in Unix / Linux
+
:* Define term '''process''' as it relates to the Unix/ Linux operating system
  
 
:* '''Run''' and '''terminate''' processes in the foreground and background
 
:* '''Run''' and '''terminate''' processes in the foreground and background
  
 
:* '''Display''' and '''manipulate''' background and foreground processes
 
:* '''Display''' and '''manipulate''' background and foreground processes
 +
 +
:* Use '''<span style="font-family:courier">alias</span>''' and '''<span style="font-family:courier">history</span>''' commands in Unix/Linux
 
<br>
 
<br>
  
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|- valign="top" style="padding-left:15px;"
 
|- valign="top" style="padding-left:15px;"
  
|colspan="2" |Course Notes:<ul><li>[https://ict.senecacollege.ca/~murray.saul/uli101/ULI101-Week7.pdf PDF] | [https://ict.senecacollege.ca/~murray.saul/uli101/ULI101-Week8.pptx PPTX]</li></ul>
+
|colspan="2" |Course Notes:<ul><li>[https://ict.senecacollege.ca/~murray.saul/uli101/ULI101-Week8.pdf PDF] | [https://ict.senecacollege.ca/~murray.saul/uli101/ULI101-Week8.pptx PPTX]</li></ul>
  
  
 
|  style="padding-left:15px;" |Links
 
|  style="padding-left:15px;" |Links
* Hard Links
+
* [http://www.linfo.org/hard_link.html#:~:text=A%20hard%20link%20is%20merely,created%20to%20other%20hard%20links. Hard Links]
* Symbolic Links<br>
+
* [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]<br>
 
Managing Processes
 
Managing Processes
* Process Information
+
* [https://en.wikipedia.org/wiki/Inode inode]
* Manipulating Processes
+
* [https://opensource.com/article/18/9/linux-commands-process-management Manipulating Processes]
* Running commands / programs in background with &
 
  
 
|  style="padding-left:15px;"|Linux Commands
 
|  style="padding-left:15px;"|Linux Commands
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* [http://man7.org/linux/man-pages/man1/jobs.1p.html jobs]
 
* [http://man7.org/linux/man-pages/man1/jobs.1p.html jobs]
 
* [http://man7.org/linux/man-pages/man1/kill.1.html kill]
 
* [http://man7.org/linux/man-pages/man1/kill.1.html kill]
 +
* [https://man7.org/linux/man-pages/man1/sleep.1.html sleep]
 +
* [http://linuxcommand.org/lc3_man_pages/aliash.html alias] , [https://man.linuxreviews.org/man1p/unalias.1p.html unalias]
 +
* [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>
 
|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>
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= KEY CONCEPTS =
 
= KEY CONCEPTS =
  
===Linking Files===
+
<!--
  
''Links are powerful and add flexibility to Linux filesystems because everything is a file.<br><br>There are two types of Linux filesystem links: hard and soft. The difference between the two types of links is significant, but both types are used to solve similar problems. They both provide multiple directory entries (or references) to a single file, but they do it quite differently.'' <br><br>Reference: https://opensource.com/article/17/6/linking-linux-filesystem
+
<table align="right"><tr valign="top"><td>[[Image:inode-number-1.png|thumb|right|300px|Each inode stores the attributes and disk block locations of the object's data.<br>(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]</td><td>[[Image:inode-number-2.png|thumb|right|360px|The '''inode number''' is like a '''finger-print''', and is considered to be '''unique''' for each file on the Unix / Linux file system.]]</td></tr></table>
 
 
 
 
'''inode (index) Number of a File:'''
 
 
 
<table align="right"><tr valign="top"><td>[[Image:inode-number-1.png|thumb|right|300px|Each inode stores the attributes and disk block locations of the object's data.<br>(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]</td><td>[[Image:inode-number-2.png|thumb|right|360px|The '''inode number''' is like a '''finger-print''', and usually is '''unique''' for each file on the Unix / Linux file system.]]</td></tr></table>
 
 
''The inode (index node) is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory. Each inode stores the attributes and disk block locations of the object's data. File-system object attributes may include metadata (times of last change, access, modification), as well as owner and permission data.''
 
''The inode (index node) is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory. Each inode stores the attributes and disk block locations of the object's data. File-system object attributes may include metadata (times of last change, access, modification), as well as owner and permission data.''
  
 
Reference: https://en.wikipedia.org/wiki/Inode
 
Reference: https://en.wikipedia.org/wiki/Inode
  
 +
-->
  
The '''inode number''' is like a '''finger-print''', and usually is '''unique''' for each file on the Unix / Linux file system.<br>Referring to the diagram on the far right, issuing the '''ls''' command with the '''-i''' option<br>displays the inode number for each file. You can see that <u>each</u> file<br>(whether it is a directory or regular file) has its own unique inode number.
+
===i-node (index) ID Number of a File===
  
 +
[[Image:inode-number-3.png|thumb|right|450px|The '''i-node number''' is like a '''finger-print''', and is considered to be '''unique''' for each file on the Unix / Linux file system.]]
 +
An '''i-node''' is a '''database''' containing information (e.g. ''file type'', ''owner'', ''permissions'', etc.) for all files that are created on the Unix/Linux filesystem.<br><br>The ''i-node number'' is like a '''finger-print''', and is considered to be '''unique''' for each file on the Unix / Linux file system.<br><br>Referring to the diagram on the far right, issuing the <span style="font-family:courier;font-weight:bold;">ls</span> command with the <span style="font-family:courier;font-weight:bold;">-i</span> option displays the i-node number for each file. You can see that <u>each</u> file (whether it is a directory or regular file) has its own unique<br>i-node number.
  
 +
===Hard Links===
  
'''Hard Links:'''
+
[[Image:hard-link-1.png|thumb|right|300px|A '''Hard link''' is a file which is created that shares the '''same i-node number''' with the <u>original</u> file<br>(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])<br>Image manipulated by author]]
 +
A '''Hard link''' is a '''reference''' to the physical data on a file  system.<br>It does this by creating a file that shares the '''same i-node number''' with the <u>original</u> file.
  
<table align="right"><tr valign="top"><td>[[Image:hard-link-1.png|thumb|right|300px|(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])<br>Image manipulated by author]]]</td><td>[[Image:inode-number-3.png|thumb|right|500px|'''Hard links''' share the '''same inode number'''. Hard links are very good for '''backup''' purposes.]]</td></tr></table>
 
A '''Hard link''' is a reference to the physical data on a file  system.
 
  
'''Advantages''' of hard links are that if one hard link remains (even if original file has been removed), the data in that hard linked file is NOT lost, a hard links will automatically change when a change to that original file or hard links occur since they share the same '''i-node number'''<br>and the Unix/Linux OS treats them all as the same file.
+
'''Advantages:''' If only one hard link remains (even if original file has been removed), the '''data in that hard linked file is NOT lost'''. The data in hard linked files are '''automatically updated''' when original file are updated.
  
'''Disadvantages''' of hard links are that they take-up extra space,<br>you cannot hard link directory files, and you cannot hard link files from other Unix/Linux servers<br>(since the inode number may already be used by the other Unix/Linux server).
+
'''Disadvantages:''' Hard links '''take-up extra space''', you '''cannot hard link directories''',<br>and you '''cannot hard link files from other Unix/Linux servers''' (since the inode number may already be used by the other Unix/Linux server).
  
  
 
''Examples:''
 
''Examples:''
  
<span style="font-family:courier">'''touch myfile.txt<br>ln myfile.txt myfile1.hard.lnk<br>ln myfile.txt myfile2.hard.lnk<br>ln myfile.txt ~/backups/myfile.hard.lnk<br>'''</span>
+
<span style="font-family:courier">ln myfile.txt myfile1.hard.lnk<br>ln myfile.txt ~/backups/myfile.hard.lnk<br>'''</span>
  
 +
===Symbolic Links===
  
 +
[[Image:symbolic-link-1.png|thumb|right|300px|A '''Symbolic Link''' is an indirect '''pointer''' to a file and are also known as '''soft''' link or '''symlink'''. The symbolic link file contains the pathname to the original file. (Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]
 +
A '''Symbolic Link''' is an indirect '''pointer''' to a file and are also known as '''soft''' link or '''symlink'''. The symbolic link file contains the '''pathname''' to the original file.
  
'''Symbolic Links:'''
 
  
<table align="right"><tr valign="top"><td>[[Image:symbolic-link-1.png|thumb|right|300px|(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]</td><td>[[Image:inode-number-4.png|thumb|right|500px|Symbolic links do NOT share the same i-node number. '''Symbolic links''' are very good for short-cuts to other files (including directories) but NOT for backup purposes.]]</td></tr></table>
+
'''Advantages:''' symbolic links are '''shortcuts''' to other files, where the symbolic link only contains the pathname to the original file, you '''can create symbolic links'''<br>'''on different Unix/Linux servers''', and that you '''can create symbolic links for directories'''.
A '''Symbolic Link''' is an indirect pointer to a file and are also known as '''soft link''' or '''symlink'''.
 
  
'''Advantages''' of symbolic links are that they are shortcuts to other files, where the symbolic link only contains the pathname to the original file, you can create symbolic links<br>on different Unix/Linux servers, and that you can create symbolic links for directories.
+
'''Disadvantages:''' Symbolic links are NOT good for backup purposes<br>since a symbolic link can point to a nonexistent file  (referred to as a "broken link").
 
 
'''Disadvantages''' of symbolic links are that they are NOT good for backup purposes<br>since a symbolic link can point to a nonexistent file  (referred to as a "broken link").
 
  
  
 
''Examples:''
 
''Examples:''
  
<span style="font-family:courier">'''touch otherfile.txt<br>ln -s otherfile.txt otherfile1.sym.lnk<br>ln -s otherfile.txt otherfile2.sym.lnk<br>ln -s otherfile.txt ~/backups/otherfile.sym.lnk<br>'''</span>
+
<span style="font-family:courier">ln -s otherfile.txt otherfile1.sym.lnk<br>ln -s otherfile.txt ~/backups/otherfile.sym.lnk<br>'''</span>
 
<br><br>
 
<br><br>
  
 
===Managing Processes===
 
===Managing Processes===
  
 +
All '''commands/programs''' ('''tasks''') that are '''running''' on a Unix/Linux computer system are referred to as '''processes'''.
 +
<br><br>
 +
'''Characteristics of Processes:'''
  
[[Image:process-diagram-1.png|thumb|right|300px|(Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]
+
* Each process has an '''owner'''
All programs that are executing on a Unix/Linux computer system are referred to as '''processes''':
+
* Each process has a unique ID ('''PID''')
 
+
* Processes keep their ''PID'' for their '''entire life'''.
* Each process has an '''owner'''
+
* Usually a parent sleeps (''suspends'') when a child is running (the exception is when the child process is running in the background)
* Each process has a unique ID ('''PID''') Processes in UNIX can run in the '''foreground''' or '''background'''
+
*UNIX / Linux processes are '''hierarchical'''. The process structure can have '''child processes''', '''great grandchild processes''', etc.
* Programs / Commands can be run in the '''background''' by placing an '''ampersand''' '''&''' after the command<br>(eg. '''program-name  &''')
 
 
 
UNIX processes are '''hierarchical''':
 
  
* The process structure has a '''root''', '''parents''', and '''children'''
 
* Creation of a new process is called '''forking''' or  '''spawning'''
 
* The Parent process can spawn a child and children can spawn their own children
 
* Processes keep their '''PID''' for their entire life
 
* Usually a parent sleeps when a child is executing<br>(the exception is when the child process  is executing in the background)
 
  
Users can learn to manage processes to become more productive while working in the Unix / Linux Command-line environment.
+
Users can '''manage processes''' to become more '''productive''' while working in the Unix / Linux Command-line environment.<br>Processes that run in the terminal are known as '''foreground''' processes. You can run or send processes currently running<br>in the ''foreground'' to the '''background''' to free-up your terminal (e.g. issue other Linux commands).<br><br>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 /<br>Key Combination</th><th style="border-bottom: 1px solid black;text-align:left;">Purpose</th></tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold;">ps</span></td><td>Displays snapshot information about processes.<br>''Examples: ''<span style="font-family:courier;font-weight:bold">ps , ps -l , ps -ef , ps -u , ps aux</span><br></td></tr><tr valign="top"><td>'''<span style="font-family:courier;font-weight:bold;">top</span>'''</td><td>The '''top''' command provides a realtime status of running processes.<br>'''NOTE:''' You can press '''ctrl-c''' to exit<br></td></tr><tr valign="top"><td><span style="font-family:courier;">'''ctrl-c'''</span></td><td>'''Terminates''' a process running in the foreground</td></tr><tr valign="top"><td><span style="font-family:courier;">'''ctrl-z'''</span></td><td>Sends a process running in the foreground into the '''background'''.</td></tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold;">fg</span></td><td>Moves a background job from the current environment into the foreground.<br>''Example: ''<span style="font-family:courier;font-weight:bold">fg %job-number</span></td></tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold;">bg</span></td><td>Runs (starts) the most recent process that was placed into the background.<br>''Example: ''<span style="font-family:courier;font-weight:bold">bg %job-number</span></td></tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold;">jobs</span></td><td>The '''jobs''' utility displays the '''status''' of jobs that were started in the current shell environment. ''Example:<br>''<span style="font-family:courier;">jobs<br>[1]+  Stopped  vim a <span style="font-size:8pt;">&nbsp; &lt;-- Job #1 (+ most recent process / background)</span><br>[2]&nbsp; Running          sleep 200 & <span style="font-size:8pt;">&nbsp;&lt;-- Job #2</span><br>[3] &nbsp;Running              sleep 300 & <span style="font-size:8pt;">&nbsp;&lt;-- Job #3</span><br>[4]-  Running                sleep 400 &<span style="font-size:8pt;">&nbsp; &lt;-- Job #4 (- second recent process / background)</span><br><br></span></td></tr><tr valign="top"><td><span style="font-family:courier;font-weight:bold;">kill</span></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.<br>''Examples:''<br><span style="font-family:courier;font-weight:bold;">kill PID , kill -9 PID , kill %job-number , <br>kill -9 %job-number</span></td></tr></table>
Below are common Linux commands / keyboard shortcuts to manage 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>The '''ps''' (''process status'') command displays snapshot information about processes. By default, the ps command displays information only about the current terminal ('''ps -l''' provides a detailed listing, '''ps -U''' username shows all)<br><br>''Examples: ''<span style="font-family:courier;font-weight:bold">ps , ps -l , ps -ef , ps -u , ps aux</span><br></td></tr><tr valign="top"><td>'''top'''</td><td>The '''top''' command provides a continuous  update including resource usage<br>'''NOTE:''' You can press '''ctrl-c''' to exit<br></td></tr><tr valign="top"><td>'''fg'''</td><td>The '''fg''' (foreground) command moves a background job from the current environment into the foreground. The fg command issued without arguments will place the most recent process in the background to the foreground. ''Example: ''<span style="font-family:courier;font-weight:bold">fg %job-number</span></td></tr><tr valign="top"><td><span style="font-family:courier;">'''&lt;ctrl&gt;&lt;c&gt;'''</span></td><td>'''Terminates''' a process running in the foreground</td></tr><tr valign="top"><td><span style="font-family:courier;">'''&lt;ctrl&gt;&lt;z&gt;'''</span></td><td>Sends a process running in the foreground into the '''background'''.</td></tr><tr valign="top"><td>'''bg'''</td><td>The '''bg''' utility shall resume suspended jobs from the current environment. The bg command issued without arguments will run the most recent process that was placed into the background.<br>''Example: ''<span style="font-family:courier;font-weight:bold">bg %job-number</span></td></tr><tr valign="top"><td>'''jobs'''</td><td>The '''jobs''' utility shall display the status of jobs that were started in the current shell environment<br>''Examples:<br>''<span style="font-family:courier;">jobs<br>[1]+  Stopped  vim a <span style="font-size:8pt;">&nbsp; &lt;-- Job #1 (+ means most recent process sent to background)</span><br>[2]&nbsp; Running          sleep 200 & <span style="font-size:8pt;">&nbsp;&lt;-- Job #2</span><br>[3] &nbsp;Running              sleep 300 & <span style="font-size:8pt;">&nbsp;&lt;-- Job #3</span><br>[4]-  Running                sleep 400 &<span style="font-size:8pt;">&nbsp; &lt;-- Job #4 (- means second recent process sent to background)</span><br><br></span></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.<br>''Examples:''<br><span style="font-family:courier;font-weight:bold;">kill PID , kill -9 PID , kill %job-number , <br>kill -9 %job-number</span></td></tr></table>
 
  
 
===Aliases / Command History===
 
===Aliases / Command History===
  
 +
<br>
 +
'''Aliases:'''
 +
<br><br>
 +
An '''alias''' is a '''nickname''' to an existing command or group of commands.<br><br>An alias existing in '''system memory''' and will be '''lost''' when your current Linux session ends,<br>unless the alias is set in a '''start-up file''' (e.g. <span style="font-family:courier;font-weight:bold;">~/.bashrc</span>. You will learn about using start-up files <u>later</u> in this course.<br><br>
  
'''Alias:'''
+
''Examples:''
 
 
Assigns a new name to an existing utility
 
 
 
''Example:''
 
  
 
<span style="font-family:courier;font-weight:bold;>alias</span> (Alias command without an argument will display all the aliases currently set)
 
<span style="font-family:courier;font-weight:bold;>alias</span> (Alias command without an argument will display all the aliases currently set)
 
''Other Examples:''
 
  
 
<span style="font-family:courier;font-weight:bold;>alias dir=ls<br>alias ls='ls -al'<br>alias clearfile='cat /dev/null >'</span>
 
<span style="font-family:courier;font-weight:bold;>alias dir=ls<br>alias ls='ls -al'<br>alias clearfile='cat /dev/null >'</span>
  
 +
'''<span style="font-family:courier;font-weight:bold;>unalias alias-name</span>'''  (removes alias from memory)
  
  
 
'''Command History:'''
 
'''Command History:'''
 +
<br><br>
 +
The filename <span style="font-family:courier;font-weight:bold;>~/.bash_history</span> stores recently executed command lines
 +
<br><br>
 +
''Examples of commands that use command history:''
  
'''~/.bash_history''' stores recently executed command lines
+
<table width="80%"><tr valign="top"><td width="30%"><span style="font-family:courier;font-weight:bold;>up arrow</span> or <span style="font-family:courier;font-weight:bold;>down arrow</span>      </td><td>move to '''previous''' command or '''next''' command within Bash shell prompt</td></tr><tr><td><span style="font-family:courier;font-weight:bold;>fc -l</span></td><td>  display last '''16''' commands</td></tr><tr><td><span style="font-family:courier;font-weight:bold;>history | more</span></td><td>display all stored commands</td></tr><tr><td><span style="font-family:courier;font-weight:bold;>!num</span></td><td>'''re-execute''' an issued command number by command number (determined from ''history'' command)</td></tr><tr><td><span style="font-family:courier;font-weight:bold;>!xxx</span></td><td>'''re-run''' a most recent previously-issued command beginning with string "xxx"</td></tr></table><br><br>
  
<table width="60%"><tr><td><span style="font-family:courier;font-weight:bold;><up></span> or <span style="font-family:courier;font-weight:bold;><down></span>      </td><td>move to previous command or next command</td></tr><tr><td><span style="font-family:courier;font-weight:bold;>fc -l</span></td><td>  display last 16 commands</td></tr><tr><td><span style="font-family:courier;font-weight:bold;>history</span></td><td>display all stored commands</td></tr><tr><td><span style="font-family:courier;font-weight:bold;>!num</span></td><td>re-execute command number "num"</td></tr><tr><td><span style="font-family:courier;font-weight:bold;>!xxx</span></td><td>re-execute last command beginning with string "xxx"</td></tr></table>
+
=INVESTIGATION 1: LINKING FILES=
  
=INVESTIGATION 1: LINKING FILES=
+
<span style="color:red;">'''ATTENTION''': Depending on your ULI101 instructor, you may be required to complete this tutorial for '''marks''' in this course.<br>Please refer to your instructor's course notes and lecture notes regarding evaluation for this course.<br><br>The due date for successfully completing this tutorial (i.e. '''tutorial 8''') is by '''Friday by midnight''' next week (i.e. '''Week 8''').<br>If your instructor has NOT assigned marks for completing this tutorial, you can perform it for '''practice'''.</span><br><br>
  
<br>
+
In this investigation, you will learn how to create '''hard links''' and '''symbolic links''' on your Matrix account,<br>and observe the <u>advantages</u> and <u>limitations</u> of using both types of links.
In this section, you will learn how to create hard links and symbolic links on your Matrix account.
 
  
  
 
'''Perform the Following Steps:'''
 
'''Perform the Following Steps:'''
  
# '''Login''' your matrix account.<br><br>
+
# '''Login''' to your matrix account.<br><br>
# Issue a command to '''confirm''' you are located in your home directory.<br><br>
+
# Issue a Linux command to '''confirm''' you are located in your '''home''' directory.<br><br>'''NOTE:''' You will remain in your '''home''' directory to get practice using pathnames.<br><br>
 
# Issue the following Linux command to create a directory called '''~/links''':<br><span style="color:blue;font-weight:bold;font-family:courier;">mkdir ~/links</span><br><br>
 
# Issue the following Linux command to create a directory called '''~/links''':<br><span style="color:blue;font-weight:bold;font-family:courier;">mkdir ~/links</span><br><br>
# Issue the '''ls''' command to confirm that the directory called '''~/links''' exists.<br><br>
+
# Issue the '''ls -ld''' command to confirm that the directory '''~/links''' exists.<br><br>
# Use a text editor to create a file called '''~/links/data-file.txt'''<br><br>
+
# Use a text editor to create a file called <span style="font-weight:bold;font-family:courier;">~/links/data-file.txt </span><br>(i.e. <u>without</u> changing to the links directory).<br><br>
# Enter the following text displayed below:<br><br><span style="font-family:courier;font-weight:bold;">This is line 1<br>This is line 2<br>This is line 3<br><br></span>
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# Enter the following text displayed below:<br><br><span style="font-family:courier;font-weight:bold;">This is line 1<br>This is line 2<br>This is line 3<br><br></span>[[Image:hard-link-inode1.png|thumb|right|450px|'''Hard links''' <u>share</u> the same '''i-node''' with regular files on a Unix / Linux filesystem.]]
# Issue the following Linux command:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -li ~/links/data-file.txt</span><br><br>Note the '''i-node''' number for this file. What does this i-node number represent?<br><br>
 
# Issue the following Linux command to create the following hard link in the same directory: <br><span style="color:blue;font-weight:bold;font-family:courier;">ln ~/links/data-file.txt ~/links/data-file.hard.lnk<br><br>
 
# Issue the '''ls -li''' command for the '''~/links''' directory.<br><br>What do you notice about both of these file's i-node numbers?<br><br>
 
# Use a text editor to edit the file '''~/links/data-file.txt''' and add some additional lines to this file.<br><br>
 
 
# Save your editing session and exit your text editor.<br><br>
 
# Save your editing session and exit your text editor.<br><br>
# Issue the following Linux command: <br><span style="color:blue;font-weight:bold;font-family:courier;">cat ~/links/data-file.hard.lnk</span><br><br>What do you noticed what happened to this linked file?<br><br>
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# Issue the following Linux command:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -li ~/links/data-file.txt</span><br><br>View the '''i-node''' number for this file. What does this ''i-node'' number represent?<br><br>We will now create a '''hard link''' file to demonstrate how creating hard links are useful for '''back-ups'''.<br><br>
# Use a text editor to edit the hard-linked file '''~/links/data-file.txt.hard.lnk''' and add some additional lines to this file.<br><br>
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# Issue the following Linux command to create the following '''hard link''' in the same directory: <br><span style="color:blue;font-weight:bold;font-family:courier;">ln ~/links/data-file.txt ~/links/data-file.hard.lnk</span><br><br>
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# Issue the following Linux command to display ''i-node'' ID numbers for <u>both</u> files:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -li ~/links/data-file.txt ~/links/data-file.hard.lnk</span><br><br>What do you notice about both of those file's ''i-node'' numbers?<br><br>
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# Use a text editor to edit <span style="font-weight:bold;font-family:courier;">~/links/data-file.txt</span><br>and '''add some lines of text''' to the <u>bottom</u> of that file.<br><br>
 
# Save your editing session and exit your text editor.<br><br>
 
# Save your editing session and exit your text editor.<br><br>
# Issue the following Linux command: <br><span style="color:blue;font-weight:bold;font-family:courier;">cat ~/links/data-file.hard.lnk</span><br><br>What do you noticed what happened to this original file?<br><br>
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# Issue the following Linux command: <br><span style="color:blue;font-weight:bold;font-family:courier;">cat ~/links/data-file.hard.lnk</span><br><br>You should notice that the hard linked file also contains the additional line(s) that you added to the <u>original</u> file.<br>This is very useful for backing up your files <u>without</u> using the '''cp''' command!<br><br>
 +
# Use a text editor to edit the hard-linked file <span style="font-weight:bold;font-family:courier;">~/links/data-file.hard.lnk</span><br>and add some lines to the bottom of this file.<br><br>
 +
# Save your editing session and exit your text editor.<br><br>
 +
# Issue the following Linux command: <br><span style="color:blue;font-weight:bold;font-family:courier;">cat ~/links/data-file.txt</span><br><br>What happened to this '''original''' file?</u> file?<br>What does this mean in terms of creating hard-linked files for back-ups?<br><br>
 
# Issue the following Linux command to create a hard-linked file in your '''home''' directory:<br><span style="color:blue;font-weight:bold;font-family:courier;">ln ~/links/data-file.txt ~/data-file.hard.lnk<br><br>
 
# Issue the following Linux command to create a hard-linked file in your '''home''' directory:<br><span style="color:blue;font-weight:bold;font-family:courier;">ln ~/links/data-file.txt ~/data-file.hard.lnk<br><br>
# Issue the '''ls -i''' command to determine the i-node number for the file called '''~/data-file.hard.lnk'''<br><br>What do you notice about this file's ''i-node'' number?
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# Issue the following Linux command to compare all file's ''i-node'' numbers:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -li ~/links/data-file.txt ~/links/data-file.hard.lnk ~/data-file.hard.lnk</span><br><br>What do you notice about all of those file's ''i-node'' numbers?<br><br>
# Make certain you are currently located in your '''home''' directory.<br><br>
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# Issue the following Linux command to check that you created those hard links: <br><span style="color:blue;font-weight:bold;font-family:courier;">~uli101/week8-check-1</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 to remove the ~/links directory and its contents: <br><span style="color:blue;font-weight:bold;font-family:courier;">rm -rf ~/links</span><br><br>
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# Issue the following Linux command to remove the '''~/links''' directory and its contents: <br><span style="color:blue;font-weight:bold;font-family:courier;">rm -rf ~/links</span><br><br>
 
# Issue a Linux command to confirm that the '''~/links''' directory has been removed.<br><br>
 
# Issue a Linux command to confirm that the '''~/links''' directory has been removed.<br><br>
# Issue the following Linux command to view the contents of your linked file in your '''home''' directory:<br><span style="color:blue;font-weight:bold;font-family:courier;">cat ~/data-file.hard.lnk</span><br><br>What do you notice? What does this tell you about hard links?<br><br>
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# Issue the following Linux command to view the contents of your linked file in your '''home''' directory:<br><span style="color:blue;font-weight:bold;font-family:courier;">cat ~/data-file.hard.lnk</span><br><br>What do you notice? What does this tell you about hard links?<br><br>We will now learn how to create '''symbolic links'''.<br><br>
# Issue the following Linux command to create a directory called '''~/links2''':<br><span style="color:blue;font-weight:bold;font-family:courier;">mkdir ~/links</span><br><br>
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# Issue the following Linux command to create a directory called '''~/links2''':<br><span style="color:blue;font-weight:bold;font-family:courier;">mkdir ~/links2</span><br><br>'''NOTE:''' You will remain in your '''home''' directory to get practice using pathnames.<br><br>
# Issue the '''ls''' command to confirm that the directory called '''~/links2''' exists.<br><br>
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# Issue the <span style="font-weight:bold;font-family:courier;">ls -ld</span> command to confirm that the directory called '''~/links2''' exists.<br><br>
# Use a text editor to create a file called '''~/links2/text-file.txt'''<br><br>
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# Use a text editor to create a file called <span style="font-weight:bold;font-family:courier;">~/links2/text-file.txt</span><br>(i.e. <u>without</u> changing to the '''links2''' directory). <br><br>[[Image:symbolic-link-inode1.png|thumb|right|500px|'''Symbolic links''' are '''pointers''' (i.e. pathnames) to '''regular files''' and '''directories'''.<br>They do '''NOT''' share the same '''i-node'''.]]
 
# Enter the following text displayed below:<br><br><span style="font-family:courier;font-weight:bold;">This is line one<br>This is line two<br>This is line three<br><br></span>
 
# Enter the following text displayed below:<br><br><span style="font-family:courier;font-weight:bold;">This is line one<br>This is line two<br>This is line three<br><br></span>
# Issue the following Linux command to create the following symbolic link in the same directory: <br><span style="color:blue;font-weight:bold;font-family:courier;">ln -s ~/links2/text-file.txt ~/links2/text-file.sym.lnk</span><br><br>
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# Save your editing session and exit your text editor.<br><br>
# Issue the '''ls -li''' command for the '''~/links2''' directory.<br><br>What do you notice about both of these file's i-node numbers?<br>What do you notice about the size of the file ~/links2/text-file.sym.lnk?<br>What pathname do you think it represents?<br><br>
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# Issue the following Linux command to create the following '''symbolic''' link in the same directory: <br><span style="color:blue;font-weight:bold;font-family:courier;">ln -s ~/links2/text-file.txt ~/links2/text-file.sym.lnk</span><br><br>
# Change to your '''home''' directory.<br><br>
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# Issue the following Linux command to display ''i-node'' numbers for <u>both</u> files:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -li ~/links2/text-file.txt ~/links2/text-file.sym.lnk</span><br><br>What do you notice about both of these file's ''i-node'' numbers?<br>What do you notice about the size of the file <span style="font-weight:bold;font-family:courier;">~/links2/text-file.sym.lnk''</span>?<br>What '''pathname''' do you think this ''symbolic-linked'' file represents?<br><br>
# Issue the following Linux command to create the following symbolic link in your home directory: <br><span style="color:blue;font-weight:bold;font-family:courier;">ln -s ~/links2/text-file.txt ~/text-file.sym.lnk</span><br><br>
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# Issue the following Linux command to create the following '''symbolic link''' in your '''home''' directory: <br><span style="color:blue;font-weight:bold;font-family:courier;">ln -s ~/links2/text-file.txt ~/text-file.sym.lnk</span><br><br>
# Issue the ls -l command for the ~/text-file.txt.sym.lnk file.<br><br>What do you notice? What is the file size?<br>What pathname do you think this file contains?<br><br>
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# Issue the following Linux command to display ''i-node'' numbers for all of those files:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -li ~/links2/text-file.txt ~/links2/text-file.sym.lnk ~/text-file.sym.lnk</span><br><br>What do you notice about all of those file's i-node numbers?<br>What is the file size of <span style="font-weight:bold;font-family:courier;">~/text-file.sym.lnk</span>?<br>What '''pathname''' do you think this ''symbolic-linked'' file contains?<br><br>
# Issue the following Linux command:<br><span style="color:blue;font-weight:bold;font-family:courier;">cat ~/text-file.txt.sym.lnk</span><br><br>What did you notice?<br><br>
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# Use a text editor to edit the '''symbolic''' link file called <span style="font-weight:bold;font-family:courier;">~/links2/text-file.sym.lnk</span><br>and add some lines to the bottom of that file.<br><br>
# Issue the following Linux command to remove the ~/links2 directory: <br><span style="color:blue;font-weight:bold;font-family:courier;">rm -rf ~/links2</span><br><br>
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# Save your editing session and exit your text editor.<br><br>
# Re-issue the Linux command you performed in '''step #34'''.<br><br>What happened? Why?<br><br>
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# Issue the following Linux command to view the contents of the '''original''' file:<br><span style="color:blue;font-weight:bold;font-family:courier;">cat ~/links2/text-file.txt</span><br><br>What did you notice? This happened because when you edited the symbolic-linked file,<br>you were redirected (via ''pathname'') to the <u>original</u> file.<br><br>
# Issue the following Linux command: <br><span style="color:blue;font-weight:bold;font-family:courier;">ls -l ~/text-file.txt.sym.lnk</span><br><br>What do you notice?<br><br>
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# Use a text editor to edit the '''original''' file called <span style="font-weight:bold;font-family:courier;">~/links2/text-file.txt</span><br>and add some lines to the bottom of that file.<br><br>
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">ln -s ~uli101 linux</span><br><br>
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# Save your editing session and exit your text editor.<br><br>
# Issue the following Linux command: <span style="color:blue;font-weight:bold;font-family:courier;">linux/assign1</span><br><br>What happened? Why?
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# Issue the following Linux command to view the contents of the '''symbolic''' linked file:<br><span style="color:blue;font-weight:bold;font-family:courier;">cat ~/links2/text-file.sym.lnk</span><br><br>What did you notice? Again, when you view the contents of the symbolic-linked file,<br>you are redirected (via ''pathname'') to the <u>original</u> file.<br><br>
 +
# Issue the following Linux command to check that you created those symbolic links: <br><span style="color:blue;font-weight:bold;font-family:courier;">~uli101/week8-check-2</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 to remove the '''~/links2''' directory: <br><span style="color:blue;font-weight:bold;font-family:courier;">rm -rf ~/links2</span><br><br>
 +
# Issue a Linux command to confirm that the '''~/links2''' directory has been removed.<br><br>
 +
# Issue the following Linux command to view the contents of the<br>'''original''' file called <span style="font-weight:bold;font-family:courier;">~/links2/text-file.txt:</span><br><span style="color:blue;font-weight:bold;font-family:courier;">cat ~/text-file.sym.lnk</span><br><br>What happened? Why did does this happen?<br><br>[[Image:symbolic-link-inode3.png|thumb|right|500px|Example of a '''broken link''' when a symbolic link points to a '''non-existent file'''.]]
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# Issue the following Linux command: <br><span style="color:blue;font-weight:bold;font-family:courier;">ls -l ~/text-file.sym.lnk</span><br><br>This output indicates a "'''broken link'''" and indicates this is not an effective method of backing up files.<br><br>
 +
# Issue a command to delete the <span style="font-weight:bold;font-family:courier;">~/text-file.sym.lnk</span> file which is a ''broken link''.<br><br>
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# Issue the following Linux command:<br><span style="color:blue;font-weight:bold;font-family:courier;">ln -s ~murray.saul/myscripts checking-scripts</span><br><br>[[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:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -ld checking-scripts</span><br><br>What do you notice? Symbolic links are good for creating "short-cuts" to <u>both</u> '''regular files''' and '''directories'''.
  
  
:In the next investigation, you will learn how to manage processes on your Matrix server.<br><br>
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:In the next investigation, you will learn how to '''manage processes''' on your Matrix server.<br><br>
  
 
=INVESTIGATION 2: MANAGING PROCESSES =
 
=INVESTIGATION 2: MANAGING PROCESSES =
  
In this section, you will learn how to manage processes on a Unix / Linux server.
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In this investigation, you will learn how to '''manage processes''' on a Unix / Linux server.
 
 
  
  
Line 210: Line 213:
  
 
# Make certain that you are logged into your Matrix account.<br><br>
 
# Make certain that you are logged into your Matrix account.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">sleep 700</span><br><br>'''NOTE:''' The sleep command just waits for a specified number of seconds before completing<br>in order to return to the shell prompt. It is useful in order to force a pause in a sequence of commands.<br><br>
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# 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 this tutorial, we will be using this command to '''simulate''' the management of "long-running" processes.<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 process'''.<br><br>The Unix/Linux system is designed to allow users to send preemptive signals to manage those processes.<br><br>
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# 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 processes'''.<br><br>The Unix/Linux system is designed to allow users to send '''preemptive signals''' to manage those processes.<br><br>
# Press the key combination: <span style="color:blue;font-family:courier;font-weight:bold">&lt;ctrl&gt;&lt;c&gt;</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''') to terminate a process that is running.<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''')<br>to ''terminate'' a process that is running on the terminal (i.e. a '''foreground''' process).<br><br>
 
# Reissue the Linux command:  <span style="color:blue;font-family:courier;font-weight:bold">sleep 700</span><br><br>
 
# Reissue the Linux command:  <span style="color:blue;font-family:courier;font-weight:bold">sleep 700</span><br><br>
# Press the key combination: <span style="color:blue;font-family:courier;font-weight:bold">&lt;ctrl&gt;&lt;z&gt;</span><br><br>
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# Press the '''key combination''': <span style="color:blue;font-family:courier;font-weight:bold">ctrl-z</span><br><br>[[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:<br><span style="font-family:courier;font-weight:bold">[1]+  Stopped                sleep 700</span><br><br>'''NOTE:''' This indicates that this process has been placed into the background.<br>This is useful in order to "free-up" the terminal to run other commands.<br><br>
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# You should now see output similar to what is displayed below:<br><span style="font-family:courier;font-weight:bold">[1]+  Stopped                sleep 700</span><br><br>'''NOTE:''' This indicates that this process has been placed into the '''background'''.<br>This is useful in order to "'''free-up'''" the terminal to run other Linux commands.<br><br>
# Clear your bash shell terminal.<br><br>
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# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">jobs</span><br><br>You should see the following output similar that was displayed above:<br><span style="font-family:courier;font-weight:bold">[1]+  Stopped                sleep 700</span><br><br>This display indicates that this process (that is now in the background) has '''stopped'''.<br>In other words, the ''sleep'' command is NOT counting-down to zero to terminate.<br><br>'''NOTE:''' You need to use the '''bg''' command to '''run''' that process that was sent into the '''background'''.<br><br>[[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: <span style="color:blue;font-family:courier;font-weight:bold">jobs</span><br><br>You should see the following output similar that was displayed above:<br><span style="font-family:courier;font-weight:bold">[1]+  Stopped                sleep 700</span><br><br>This display indicates that this process (that is now in the background) has stopped.<br>In other words, the sleep command is NOT counting-down to zero to terminate.<br><br>NOTE: You need to use the '''bg''' command to run that process that was sent into the background.<br><br>
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# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">bg</span><br><br>'''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.<br><br>
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">bg</span><br><br>'''NOTE:''' You can use the bg command WITHOUT arguments to specify the most recent process<br>that was placed into the background. From the '''jobs''' command, the process that has a plus sign "+"<br>indicates the most recent process placed into the background.<br><br>
+
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">jobs</span><br><br>You should see the following output similar that was displayed above:<br><span style="font-family:courier;font-weight:bold">[1]+ sleep 700 &</span><br><br>This display indicates that this process in the background is '''running in the background'''<br>(indicated by the ampersand character "'''&'''"). Now this command has resume pausing until '''700 seconds'''.<br><br>[[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: <span style="color:blue;font-family:courier;font-weight:bold">jobs</span><br><br>You should see the following output similar that was displayed above:<br><span style="font-family:courier;font-weight:bold">[1]+ sleep 700 &</span><br><br>This display indicates that this process in the background is running in the background<br>(denoted by the ampersand character "&"). Now the command is counting-down to zero.<br><br>
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# 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>  
# 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>You can run commands with ampersand "&" to run processes in the background.<br><br>  
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# Press the '''key combination''' to '''terminate''' the process running in the '''foreground''':<br><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 '''background''' <u>without</u> having to issue ''ctrl-z'' and ''bg'' short-cut keys.<br><br>  
# Press the key combination: <span style="color:blue;font-family:courier;font-weight:bold">&lt;ctrl&gt;&lt;c&gt;</span> to stop the process running in the foreground.<br><br>  
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# Issue the following Linux commands:<br><span style="color:blue;font-family:courier;font-weight:bold">sleep 500 & sleep 600 & sleep 700 &</span><br><br>
# Issue the following Linux command: <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>[[Image:process-jobs4.png|thumb|right|300px|Using the '''kill %1''' command to '''terminate''' job #1.]]
# Issue the '''jobs''' command. What do you notice?<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 following Linux command: <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 '''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 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. What do you notice?<br><br>You can also manipulate processes by their '''PID''' ('''process ID''').<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>[[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.<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 following Linux command:<br><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><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: <span style="color:blue;font-family:courier;font-weight:bold">ps</span><br><br>What is the PID of the previously issued Linux command in the background?<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 following Linux command (using the PID number instead of "PID"):<br><span style="color:blue;font-family:courier;font-weight:bold">kill PID</span><br><br>'''NOTE:''' You may need to issue the kill -9 PID command if the previous commands did not work.<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 processes' '''PID'''.<br><br>
# Issue the '''jobs''' command to confirm there are no processes running in the background.<br><br>
+
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">ps</span><br><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 processes' 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?<br><br>'''FYI:''' If the command did NOT work, issue the following Linux command (using the bash processes' PID number instead of "PID"):<br><span style="color:blue;font-family:courier;font-weight:bold">kill -9 PID</span><br><br>
 +
 
 +
:In the next investigation, you will learn how to '''create aliases''' and '''view command history''' on your Matrix server.<br><br>
  
 
=INVESTIGATION 3: ALIASES / COMMAND HISTORY=
 
=INVESTIGATION 3: ALIASES / COMMAND HISTORY=
  
 
<br>
 
<br>
In this section, you will learn how to ...
+
In this investigation, you will learn how to '''manage aliases''' and '''Linux command history''' on your Matrix account.
  
  
 
'''Perform the Following Steps:'''
 
'''Perform the Following Steps:'''
  
# x<br><br>
+
# Make certain that you are logged into your Matrix account.<br><br>[[Image:alias-1.png|thumb|right|400px|Issuing the '''alias''' command (<u>without</u> arguments) will display a list of existing aliases on your Unix / Linux system.]]
 
+
# Issue a Linux command to confirm that you are located in your '''home''' directory.<br><br>
 
+
# Issue the following Linux command: <span style="color:blue;font-family:courier;font-weight:bold">alias | more</span><br><br>Observe those <u>existing</u> aliases that have previously been declared. Take a few moments to run those aliases to see what happens.<br><br>
 
+
# Issue the following to create an alias: <span style="color:blue;font-family:courier;font-weight:bold">alias lal='ls -al'</span><br><br>
 
+
# Issue the following alias: <span style="color:blue;font-family:courier;font-weight:bold">lal</span><br><br>What do you notice?<br><br>
# After you complete the Review Questions sections to get additional practice, then work on your<br>online assignment 2 and complete section4 labelled: '''Linking files and directories'''.
+
# Issue the following to create another alias (lowercase l and h):<br><span style="color:blue;font-family:courier;font-weight:bold">alias lh='ls --human-readable --size -1 -S --classify'</span><br><br>
 +
# 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 and then '''login''' to 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>
 +
# Reissue the command to create the '''lh''' alias in '''step #6'''.<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, 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, 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:<br><span style="color:blue;font-weight:bold;font-family:courier;">alias | ~uli101/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>We will complete this investigation by learning to execute p'''reviously issued commands''' by using '''command history'''.<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>
 +
# Type an exclamation mark '''!''' 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>
 +
# After you complete the Review Questions sections to get additional practice, then work on your<br>'''online assignment 2''' and complete '''section4''' labelled: '''Linking files and directories'''.<br><br>
  
 
= LINUX PRACTICE QUESTIONS =
 
= LINUX PRACTICE QUESTIONS =
Line 265: Line 294:
 
'''Review Questions:'''
 
'''Review Questions:'''
  
# Write a single Linux command to create a hard link called '''~/backup/myfile.txt.lnk''' to the existing file called '''~/myfile.txt'''<br>Write a single Linux command to display detailed information for those files above displaying their i-node numbers.<br>In this case, will the inode numbers for those files above be the same or different?<br><br>
+
# Hard Links:<ol type="a"><li>What is the purpose of creating a hard-link?</li><li>What is a limitation of a hard link?<li>Write a single Linux command to create a hard link called '''~/backup/myfile.txt.lnk''' for the <u>existing</u> file called '''~/myfile.txt'''</li><li>Write a single Linux command to display the '''i-node''' number for both files. Are the '''i-node''' numbers identical?</li></ol><br>
# Write a single Linux command to create a symbolic link called '''~/shortcuts/murray.saul.lnk''' to the existing directory called '''~murray.saul'''<br>Write a single Linux command to display detailed information for those files above displaying their i-node numbers.<br>In this case, will the inode numbers for those files above be the same or different?<br><br>What data is contained in the file called '''~/shortcuts/murray.saul.lnk'''?<br>What would be the size of the file called '''~/shortcuts/murray.saul.lnk'''?<br><br>
+
# Symbolic (Soft) Links:<ol type="a"><li>What is the purpose of creating a symbolic (soft) link?</li><li>What is a limitation of a symbolic (soft) link?</li><li>Write a single Linux command to create a symbolic link called '''~/shortcuts/murray.saul.lnk'''<br>to the <u>existing</u> directory called '''~murray.saul'''</li><li>Are the i-node numbers identical for both of those files?</li><li>What data is contained in the file called '''~/shortcuts/murray.saul.lnk'''?</li></ol><br>
# Write a single Linux command to run the program called '''~/clean.sh''' in the background.<br>What command would you issue to place the previously issued program in the foreground?<br>What command would you issue to confirm that this program is running in the background?<br>What key-combination would you issue to send that program again into the background?<br><br>
+
# Background / Foreground Processes:<ol type="a"><li>Write a single Linux command to run the program called '''~/clean.sh''' in the '''background'''.</li><li>Write a single Linux command to place the previously issued program in the '''foreground'''.</li><li>Write a single Linux command to '''confirm''' that this program is running in the background.</li><li>What '''key-combination''' would you issue to send that program again into the '''background'''?</li><li>Write a single Linux command to have that process sent into the background to '''continue running'''?</li></ol><br>
 +
# Managing Background processes:<br><span style="text-indent:120px;">Use the following diagram to answer the accompanying questions.<br>Each of the following questions will use the diagram below and are treated as independent situations.<br><br><span style="font-family:courier;font-weight:bold;">[1]&nbsp;  Stopped                vim a<br>[2]-  Stopped                vim b<br>[3]+  Stopped                vim c</span></span><ol type="a"><li>Write a single Linux command to bring the second-recently process placed in the background into the '''foreground'''.</li><li>Write a single Linux command to '''terminate job #3'''.</li></ol><br>
 
# Write a single Linux command to display running processes in “real-time”.
 
# Write a single Linux command to display running processes in “real-time”.
# Write a single Linux command to terminal a process that has the following PID: '''22384'''
+
# Write a single Linux command to terminate a process that has the following PID: '''22384'''<br><br>
# Use the following diagram to answer the accompanying questions.<br>Each of the following questions will use the diagram below and are treated as independent situations.<br><br><span style="font-family:courier;font-weight:bold;">[1]&nbsp;  Stopped                vim a<br>[2]- Stopped                vim b<br>[3]+  Stopped                vim c</span><br><br>Write a single Linux command to bring the second-recently process placed in the background into the foreground.<br>Write a single Linux command to terminate the '''job #3'''.<br><br>
+
# 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><br>
# Create a '''table''' listing each Linux command, useful options  and command purpose for the following Linux commands: '''ln''' , '''ps''' , '''top''' , '''fg''' , '''bg''' , '''jobs''' , '''kill'''
+
# Create a '''table''' listing each Linux command, useful options  and command purpose for the following Linux commands:<br>'''ln''' , '''ps''' , '''top''' , '''fg''' , '''bg''' , '''jobs''' , '''kill''' , '''alias''' , '''unalias''' , '''history'''
  
  
 
[[Category:ULI101]]
 
[[Category:ULI101]]

Latest revision as of 03:11, 17 May 2021

LINKING FILES / MANAGING PROCESSES


Main Objectives of this Practice Tutorial

  • Define the term i-node as it relates to the Unix/Linux File System
  • Issue the ls -i command to view i-node (index) numbers associated with Unix/Linux files
  • Define the terms Hard and Symbolic Links
  • Issue the ln command to create hard and symbolic links
  • Define term process as it relates to the Unix/ Linux operating system
  • Run and terminate processes in the foreground and background
  • Display and manipulate background and foreground processes
  • Use alias and history commands in Unix/Linux


Tutorial Reference Material

Course Notes
Concepts / Commands
YouTube Videos
Course Notes:


Links

Managing Processes

Linux Commands Brauer Instructional Videos:

KEY CONCEPTS

i-node (index) ID Number of a File

The i-node number is like a finger-print, and is considered to be unique for each file on the Unix / Linux file system.

An i-node is a database containing information (e.g. file type, owner, permissions, etc.) for all files that are created on the Unix/Linux filesystem.

The i-node number is like a finger-print, and is considered to be unique for each file on the Unix / Linux file system.

Referring to the diagram on the far right, issuing the ls command with the -i option displays the i-node number for each file. You can see that each file (whether it is a directory or regular file) has its own unique
i-node number.

Hard Links

A Hard link is a file which is created that shares the same i-node number with the original file
(Image licensed under cc)
Image manipulated by author

A Hard link is a reference to the physical data on a file system.
It does this by creating a file that shares the same i-node number with the original file.


Advantages: If only one hard link remains (even if original file has been removed), the data in that hard linked file is NOT lost. The data in hard linked files are automatically updated when original file are updated.

Disadvantages: Hard links take-up extra space, you cannot hard link directories,
and you cannot hard link files from other Unix/Linux servers (since the inode number may already be used by the other Unix/Linux server).


Examples:

ln myfile.txt myfile1.hard.lnk
ln myfile.txt ~/backups/myfile.hard.lnk

Symbolic Links

Symbolic Link is an indirect pointer to a file and are also known as soft link or symlink. The symbolic link file contains the pathname to the original file. (Image licensed under cc)

Symbolic Link is an indirect pointer to a file and are also known as soft link or symlink. The symbolic link file contains the pathname to the original file.


Advantages: symbolic links are shortcuts to other files, where the symbolic link only contains the pathname to the original file, you can create symbolic links
on different Unix/Linux servers, and that you can create symbolic links for directories.

Disadvantages: Symbolic links are NOT good for backup purposes
since a symbolic link can point to a nonexistent file (referred to as a "broken link").


Examples:

ln -s otherfile.txt otherfile1.sym.lnk
ln -s otherfile.txt ~/backups/otherfile.sym.lnk


Managing Processes

All commands/programs (tasks) that are running on a Unix/Linux computer system are referred to as processes.

Characteristics of Processes:

  • Each process has an owner
  • Each process has a unique ID (PID)
  • Processes keep their PID for their entire life.
  • Usually a parent sleeps (suspends) when a child is running (the exception is when the child process is running in the background)
  • UNIX / Linux processes are hierarchical. The process structure can have child processes, great grandchild processes, etc.


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 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:

Linux Command /
Key Combination
Purpose
psDisplays snapshot information about processes.
Examples: ps , ps -l , ps -ef , ps -u , ps aux
topThe top command provides a realtime status of running processes.
NOTE: You can press ctrl-c to exit
ctrl-cTerminates a process running in the foreground
ctrl-zSends a process running in the foreground into the background.
fgMoves a background job from the current environment into the foreground.
Example: fg %job-number
bgRuns (starts) the most recent process that was placed into the background.
Example: bg %job-number
jobsThe 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)

killThe 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

Aliases / Command History


Aliases:

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:

alias (Alias command without an argument will display all the aliases currently set)

alias dir=ls
alias ls='ls -al'
alias clearfile='cat /dev/null >'

unalias alias-name (removes alias from memory)


Command History:

The filename ~/.bash_history stores recently executed command lines

Examples of commands that use command history:

up arrow or down arrow move to previous command or next command within Bash shell prompt
fc -l display last 16 commands
history | moredisplay all stored commands
!numre-execute an issued command number by command number (determined from history command)
!xxxre-run a most recent previously-issued command beginning with string "xxx"


INVESTIGATION 1: LINKING FILES

ATTENTION: Depending on your ULI101 instructor, you may be required to complete this tutorial for marks in this course.
Please refer to your instructor's course notes and lecture notes regarding evaluation for this course.

The due date for successfully completing this tutorial (i.e. tutorial 8) is by Friday by midnight next week (i.e. Week 8).
If your instructor has NOT assigned marks for completing this tutorial, you can perform it for practice.


In this 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.


Perform the Following Steps:

  1. Login to your matrix account.

  2. Issue a Linux command to confirm you are located in your home directory.

    NOTE: You will remain in your home directory to get practice using pathnames.

  3. Issue the following Linux command to create a directory called ~/links:
    mkdir ~/links

  4. Issue the ls -ld command to confirm that the directory ~/links exists.

  5. Use a text editor to create a file called ~/links/data-file.txt
    (i.e. without changing to the links directory).

  6. Enter the following text displayed below:

    This is line 1
    This is line 2
    This is line 3

    Hard links share the same i-node with regular files on a Unix / Linux filesystem.
  7. Save your editing session and exit your text editor.

  8. 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?

    We will now create a hard link file to demonstrate how creating hard links are useful for back-ups.

  9. 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

  10. Issue the following Linux command to display i-node ID numbers for both files:
    ls -li ~/links/data-file.txt ~/links/data-file.hard.lnk

    What do you notice about both of those file's i-node numbers?

  11. Use a text editor to edit ~/links/data-file.txt
    and add some lines of text to the bottom of that file.

  12. Save your editing session and exit your text editor.

  13. Issue the following Linux command:
    cat ~/links/data-file.hard.lnk

    You should notice that the hard linked file also contains the additional line(s) that you added to the original file.
    This is very useful for backing up your files without using the cp command!

  14. Use a text editor to edit the hard-linked file ~/links/data-file.hard.lnk
    and add some lines to the bottom of this file.

  15. Save your editing session and exit your text editor.

  16. Issue the following Linux command:
    cat ~/links/data-file.txt

    What happened to this original file?</u> file?
    What does this mean in terms of creating hard-linked files for back-ups?

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

  18. 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?

  19. Issue the following Linux command to check that you created those hard links:
    ~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.

  20. Issue the following Linux command to remove the ~/links directory and its contents:
    rm -rf ~/links

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

  22. Issue the following Linux command to view the contents of your linked file in your home directory:
    cat ~/data-file.hard.lnk

    What do you notice? What does this tell you about hard links?

    We will now learn how to create symbolic links.

  23. Issue the following Linux command to create a directory called ~/links2:
    mkdir ~/links2

    NOTE: You will remain in your home directory to get practice using pathnames.

  24. Issue the ls -ld command to confirm that the directory called ~/links2 exists.

  25. Use a text editor to create a file called ~/links2/text-file.txt
    (i.e. without changing to the links2 directory).

    Symbolic links are pointers (i.e. pathnames) to regular files and directories.
    They do NOT share the same i-node.
  26. Enter the following text displayed below:

    This is line one
    This is line two
    This is line three

  27. Save your editing session and exit your text editor.

  28. 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

  29. Issue the following Linux command to display i-node numbers for both files:
    ls -li ~/links2/text-file.txt ~/links2/text-file.sym.lnk

    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 this
    symbolic-linked file represents?

  30. 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

  31. Issue the following Linux command to display i-node numbers for all of those files:
    ls -li ~/links2/text-file.txt ~/links2/text-file.sym.lnk ~/text-file.sym.lnk

    What do you notice about all of those file's i-node numbers?
    What is the file size of ~/text-file.sym.lnk?
    What pathname do you think this symbolic-linked file contains?

  32. Use a text editor to edit the symbolic link file called ~/links2/text-file.sym.lnk
    and add some lines to the bottom of that file.

  33. Save your editing session and exit your text editor.

  34. Issue the following Linux command to view the contents of the original file:
    cat ~/links2/text-file.txt

    What did you notice? This happened because when you edited the symbolic-linked file,
    you were redirected (via pathname) to the original file.

  35. Use a text editor to edit the original file called ~/links2/text-file.txt
    and add some lines to the bottom of that file.

  36. Save your editing session and exit your text editor.

  37. 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.

  38. Issue the following Linux command to check that you created those symbolic links:
    ~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.

  39. Issue the following Linux command to remove the ~/links2 directory:
    rm -rf ~/links2

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

  41. Issue the following Linux command to view the contents of the
    original file called ~/links2/text-file.txt:
    cat ~/text-file.sym.lnk

    What happened? Why did does this happen?

    Example of a broken link when a symbolic link points to a non-existent file.
  42. 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.

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

  44. Issue the following Linux command:
    ln -s ~murray.saul/myscripts checking-scripts

    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.
  45. Issue the following Linux command:
    ls -ld checking-scripts

    What do you notice? Symbolic links are good for creating "short-cuts" to both regular files and directories.


In the next investigation, you will learn how to manage processes on your Matrix server.

INVESTIGATION 2: MANAGING PROCESSES

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


Perform the Following Steps:

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

  2. 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.

  3. 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.

  4. 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).

  5. Reissue the Linux command: sleep 700

  6. Press the key combination: ctrl-z

    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.
  7. 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.

  8. 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.

    Using the bg command to run recent process that was placed into background from using ctrl-z keys.
  9. 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.

  10. 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.

    Using the ampersand character & to run a series of processes in the background.
  11. Issue the following Linux command: fg

    You should notice that the sleep command is now running in the foreground.

  12. 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.

  13. Issue the following Linux commands:
    sleep 500 & sleep 600 & sleep 700 &

  14. 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).

    Using the kill %1 command to terminate job #1.
  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.

  16. Issue the jobs command. What do you notice?

  17. Issue the following Linux commands:
    kill %2
    kill %3

  18. Issue the jobs command (you may have to issue the jobs command several times to get final result).
    What do you notice?

    Using round brackets to group a series of commands to be run as one process.
  19. Let's use grouping to run several commands in sequence within a single process.

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

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

  22. 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.

  23. 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.

  24. Issue the following Linux command: ps

  25. 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.

  26. 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


In this investigation, you will learn how to manage aliases and Linux command history on your Matrix account.


Perform the Following Steps:

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

    Issuing the alias command (without arguments) will display a list of existing aliases on your Unix / Linux system.
  2. Issue a Linux command to confirm that you are located in your home directory.

  3. Issue the following Linux command: alias | more

    Observe those existing aliases that have previously been declared. Take a few moments to run those aliases to see what happens.

  4. Issue the following to create an alias: alias lal='ls -al'

  5. Issue the following alias: lal

    What do you notice?

  6. Issue the following to create another alias (lowercase l and h):
    alias lh='ls --human-readable --size -1 -S --classify'

  7. Issue the following command to confirm that this newly-created alias is stored in memory:

    alias | grep "lh"

  8. Issue the following alias: lh

    What do you think this command does?

  9. Logout of your Matrix account and then login to your Matrix account.

  10. Reissue the lal alias. What happened?

  11. Reissue the lh alias. What happened?

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

  13. Reissue the command to create the lh alias in step #6.

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

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

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

  17. Save your editing changes and exit your text editor.

  18. Logout of your Matrix account, then login to your Matrix account.

  19. Reissue the lh alias. What happened?

  20. Issue the following Linux command: unalias lh

  21. Run the lh alias to see what happens.

    What happenned?

  22. Logout of your Matrix account, then login to your Matrix account.

  23. Reissue the lh alias. What happened? Why?

  24. 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.

  25. Issue the following Linux pipeline command:
    alias | ~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 previously issued commands by using command history.

  26. Issue the following Linux command: history | grep "lh"

    What do you notice?

  27. Type an exclamation mark ! followed by the number by one of those commands
    listed in the history list and press ENTER

    What happened?

  28. Type the following: !unalias and press ENTER

    What happened?

  29. Issue the following Linux command: history | grep "lh"

    What happened?

  30. 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

The purpose of this section is to obtain extra practice to help with quizzes, your midterm, and your final exam.

Here is a link to the MS Word Document of ALL of the questions displayed below but with extra room to answer on the document to simulate a quiz:

https://ict.senecacollege.ca/~murray.saul/uli101/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).


Review Questions:

  1. Hard Links:
    1. What is the purpose of creating a hard-link?
    2. What is a limitation of a hard link?
    3. Write a single Linux command to create a hard link called ~/backup/myfile.txt.lnk for the existing file called ~/myfile.txt
    4. Write a single Linux command to display the i-node number for both files. Are the i-node numbers identical?

  2. Symbolic (Soft) Links:
    1. What is the purpose of creating a symbolic (soft) link?
    2. What is a limitation of a symbolic (soft) link?
    3. Write a single Linux command to create a symbolic link called ~/shortcuts/murray.saul.lnk
      to the existing directory called ~murray.saul
    4. Are the i-node numbers identical for both of those files?
    5. What data is contained in the file called ~/shortcuts/murray.saul.lnk?

  3. Background / Foreground Processes:
    1. Write a single Linux command to run the program called ~/clean.sh in the background.
    2. Write a single Linux command to place the previously issued program in the foreground.
    3. Write a single Linux command to confirm that this program is running in the background.
    4. What key-combination would you issue to send that program again into the background?
    5. Write a single Linux command to have that process sent into the background to continue running?

  4. Managing Background processes:
    Use the following diagram to answer the accompanying questions.
    Each of the following questions will use the diagram below and are treated as independent situations.

    [1]  Stopped vim a
    [2]- Stopped vim b
    [3]+ Stopped vim c
    1. Write a single Linux command to bring the second-recently process placed in the background into the foreground.
    2. Write a single Linux command to terminate job #3.

  5. Write a single Linux command to display running processes in “real-time”.
  6. Write a single Linux command to terminate a process that has the following PID: 22384

  7. Aliases / History:
    1. Write a linux command to create an alias called ld that issues the command: ls -ld
    2. Write a linux command to unset the alias created in the previous question.
    3. Issue a Linux command to list history of commands that match the pattern called touch.

  8. 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