View source for Linux-for-Sys-Ads/C2/Modifying-and-Deleting-Groups/English

'''Title of script:''' '''Modifying and Deleting Groups'''

'''Author:''' Antara Roy Choudhury

'''Keywords:''' groupmod, groupdel, change group name, change GID, delete group

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|| '''Visual Cue'''
|| '''Narration'''
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|| Slide 1: Introduction
|| Hello and welcome to the spoken tutorial on '''Modifying and Deleting Groups in Linux.'''
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|| Slide 2: Learning Objectives
|| In this tutorial we will learn about

* '''groupmod command '''and
* '''groupdel command '''

We will do this through some examples.
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|| Slide 3: System requirement
|| To record this tutorial, I am using '''Ubuntu Linux 16.04 OS'''
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|| Slide:4 Prerequisite
|| To practice this tutorial, 

* you should have gone through the '''Linux System Administration '''tutorials''' '''on this website and
* you must have '''root access''' to your computer.

|-
|| Press Ctrl+Alt+T
|| Open the '''Terminal '''by pressing '''Ctrl, Alt and T '''keys simultaneously on the keyboard.
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|| Type sudo su [Enter]
|| First, you should login as '''superuser '''or '''root user'''.
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|| Only narration
|| Here onwards, please remember to press the '''Enter''' key after typing each '''command'''.
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|| Type 

grep "electronics" /etc/group

[Enter]
|| In the series, we had created the '''group electronics.'''

Let us check the details of the '''group '''from the '''/etc/group''' file.
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|| Highlight GID in the output
|| Notice that '''group electronics''' has '''GID''' 1006.
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|| Highlight last field(list of members, it should be empty)
|| Also, the list of members field is empty.

So, no '''user''' has '''group electronics''' as a '''supplementary group'''.
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|| Type: cat /etc/passwd [Enter]
|| Let’s check the '''/etc/passwd''' file to know how many '''users''' belong to the '''primary group electronics.'''
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|| Highlight 1006 in the fourth field of the user testmod 
|| Notice that, the '''users testmod''' and '''amit''' have '''1006''' in the fourth '''field'''.

It means the users''' testmod '''and''' amit '''belong to the '''group electronics'''
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|| 
|| Let me create a document '''testfile.txt '''in the user account''' testmod'''
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|| Type su - testmod [Enter]
|| '''So, login''' as '''user testmod''' 
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|| Highlight in the output
|| Now if we create any document, then that document will be owned by the '''group electronics.'''Let's do that.
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|| Type vi testfile.txt [Enter]
|| First we’ll create a text file named '''testfile.txt'''

I am going to use '''vi text editor '''to do so. 

But you can use any other '''text editor '''of your choice.

At the command prompt type '''vi space testfile.txt '''
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|| Press i
|| Press the '''I''' key to switch to '''insert mode'''.
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|| Type: Hi I am user testmod
|| Now type this text, “'''Hi I am user testmod'''”
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|| Press Esc
|| Press the '''Escape''' key on the keyboard to exit from the '''insert mode'''.
|-
|| press wq
|| Then press '''colon w q''' 

'''w''' is used to save the typed text in the text file.

And '''q''' is used to quit the '''editor'''.
|-
|| Press Enter
|| Now press '''Enter.'''
|-
|| On getting command prompt
|| We are back to the '''command prompt'''
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|| Type ls -l testfile.txt [Enter]
|| Now type, '''ls space hyphen l space testfile.txt'''
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|| Highlight the third and fourth field
|| Notice the third and fourth '''fields'''.

The document belongs to '''user testmod''' and '''group electronics.'''
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|| Retain same screen
|| Now let us start modifying the '''group''' with the '''groupmod command.'''
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|| Slide 5
'''groupmod space [options] space groupname'''
|| 
* The '''groupmod command''' is used to''' '''modify the definition of the '''group '''specified in the''' command'''.
* This is the syntax
* Here the '''options field''' is not mandatory.
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|| Slide 6
|| '''groupmod command''' can be used to modify-
* the '''group '''name
* '''GID'''
* '''GID''' to a non-unique number

|-
|| [Terminal]

Type exit [Enter]
|| Suppose, we want to modify our '''group'''’s name from '''electronics''' to '''electrical'''.

To do so, let me switch back to the '''root''' login

Exit from the user testmod
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|| Type groupmod -n electrical electronics [Enter]
|| Now type '''groupmod space hyphen n space electrical space electronics'''
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|| cat /etc/group [Enter]
|| Then type '''cat space /etc/group'''
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|| Highlight the entry with GID value 1006
|| Notice that the '''group''' with '''GID''' '''1006''' is now named as '''electrical.'''
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|| Slide 7
|| 
* You can also change the '''GID''' of a '''group''' to a new unique non-negative number.
* Suppose, you are planning to use number '''1100''' as the new '''GID''' value.
* So, first ensure, that the number '''1100''' is not present as '''GID''' in any other '''group'''.

|-
|| Switch to terminal

Highlight GID values in group file
|| From the output of '''/etc/group 1100''' is not set as a '''GID''' value to any of the group.

This type of manual checking is not a good idea, if you have a large number of '''groups'''.

Instead we can use the '''grep command''' to check if the number is present or not.

As an assignment, try this out on your own.
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|| Type: groupmod -g 1050 electrical [Enter]
|| Now to change '''GID''' value, type

'''groupmod space hyphen g space 1100 space electrical'''
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|| cat /etc/group [Enter]
|| Now check the details of the file''' /etc/group'''
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|| Highlight 1100 for electrical
|| Notice that '''GID''' of '''electrical''' is now '''1100.'''
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||  grep "testmod " /etc/passwd [Enter]
|| We know that '''user testmod''' belongs to the '''group electrical.'''

Let’s check '''/etc/passwd '''file for the entry of the '''user testmod'''.
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|| Highlight the fourth field
|| Notice that the '''GID''' value in the fourth '''field''' is also updated.

It is showing the current value '''1100.'''
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|| Slide 8
|| 
* The '''group ID''' has changed.
* But the files belonging to this '''group''' will retain the old '''group ID''' value.
* So we must change their '''group ID''' manually.
|-
|| 

Type find /home -gid 1100 [Enter]
|| To find all files belonging to the '''group''' with '''GID 1100''', type

'''find space slash home space hyphen gid space 1100'''
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|| Show the output
|| This may take some time. 

We have not got any output.

So, it is clear that file '''testfile'''.'''txt''' has not automatically set to the '''group ID 1100.'''
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|| Change 1100 to 1006

find /home -gid 1006 [Enter]
|| Recall the previous '''command'''.

Change the '''group ID''' value to '''1006''' that is the previous '''group ID'''.
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|| Highlight in the output
|| Notice, the file '''testfile.txt''' still belongs to '''group ID 1006.'''

Please note the complete path of the file '''testfile.txt'''
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|| Type chgrp 1100 /home/newdir/testfile.txt [Enter]
|| To change the '''group ID''' for the file '''testfile.txt''' to '''1100''', type

'''chgrp space 1100 space '''

Then type the full''' path '''of file''' testfile.txt.'''

The full '''path '''can be seen by the previous''' command''' that is''' /home/newdir/testfile.txt'''

'''chgrp command''' is used to change the '''group''' of the file.
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|| On getting # prompt back
|| The '''command''' has executed without any error.
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|| Type find /home -gid 1100 [Enter]
|| Recall the '''command''' to display all files belonging to''' group ID 1100.'''
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|| Highlight the output
|| Notice the output shows '''testfile.txt '''file.

Please note, you may have multiples file belonging to old '''group ID''' value.

Changing '''group ID''' manually one by one will be a tedious job in that case.

Try writing '''shell script '''for this. 
|-
|| Retain same screen
|| Now we know how to change the '''GID''' of a '''group''' to another unique value.

Let’s move on.
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|| cat /etc/group [Enter]
|| Recall the '''command''' to display '''/etc/group'''.
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|| Show the entry of the group literature_club

Type groupmod -g 1007 electrical [Enter]
|| Notice, '''literature club''' has '''GID 1007'''

Let us try to assign this '''1007''' as the new '''GID''' of '''electrical.'''
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|| Show the output
|| Notice, it is showing an error, '''GID 1007 already exists.'''

So, we cannot change the '''group ID '''to a non-unique value with only '''hyphen g''' option.
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|| Slide 9
|| 
* To change the '''group ID''' to a non-unique value, 
* you will need '''hyphen o option''' along with '''hyphen g option'''

|-
|| Type groupmod -g 1007 electrical [Enter]
|| Let me try to set the '''GID''' to '''1007''' now.

Recall the previous '''command.'''
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|| Type groupmod -g 1007 -o electrical] [Enter]
|| Now, after '''1007''', give '''space''' and type '''hyphen o'''
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|| On getting command prompt back
|| The '''command''' has executed successfully.
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|| cat /etc/group [Enter]
|| Next, execute the '''cat /etc/group command'''
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|| Highlight GID of both electrical and literature_club
|| Notice that both '''electrical''' and '''literature_club''' now have same '''GID 1007.'''
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|| Retain same screen
|| So, we have learnt about '''groupmod command'''.

Now let’s learn about '''groupdel command.'''
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|| Slide 10
|| 
* '''groupdel command''' is used by the '''root''' or the '''superuser''' to remove a '''group'''.
* Syntax is '''groupdel space groupname'''
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|| Type: groupdel electrical [Enter]
|| Let me remove the '''group''' named '''electrical'''.

Type '''groupdel space electrical'''
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|| Show the output and highlight appropriately
|| Notice that '''Linux''' has thrown some error.

It is telling - '''cannot remove primary group of the user amit'''

So, you cannot delete '''electrical''' because it is the '''primary group''' of any existing '''user amit.'''

You must first delete the '''user amit''' and then you can remove '''electrical'''.

Let’s try this.
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|| Type: userdel -r amit [Enter]
|| For deleting user '''testmod''', type 

'''userdel space hyphen r space amit''' 
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|| Highlight 

"userdel: testmod mail spool (/var/mail/testmod) not found"
|| The '''command''' may report that the '''user's mail spool''' file was not found. 

This warning can be ignored.
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|| Type: groupdel electrical [Enter]
|| Now execute the '''groupdel command.'''
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|| Show the output and highlight appropriately
|| Once again we got the error.

Says, '''cannot remove primary group of the user testmod'''
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|| Type: userdel -r testmod [Enter]
|| Let me delete the user '''testmod'''
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|| Highlight 

"userdel: testmod mail spool (/var/mail/testmod) not found"
|| Once again we got the '''user's mail spool''' file was not found. 
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|| Type: groupdel electrical [Enter]
|| Now execute the '''groupdel command '''for the '''group''' '''electrical'''.
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|| On getting back command prompt
|| This time we did not get any error.

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|| cat /etc/group [Enter]
|| Now execute the '''cat /etc/group command'''
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|| Show the file opened
|| We can see that there is no entry for '''electrical'''.

The '''group''' named '''electrical''' is deleted now.
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|| Slide 11
|| The important point you have to keep in mind is:
* You are not permitted to remove the '''primary group''' of any existing '''user'''.
* You must remove the '''user''' first.
* Then you can remove that '''user's primary group'''.

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|| Slide 12
|| Now what about the files owned by the deleted '''group'''?

* '''groupdel''' will not automatically check for files owned by the deleted '''group'''.
* You should manually search all '''file systems''' for such files.
* You can use the '''find command''' for this search.
* You should ensure that no files remain owned by this deleted '''group'''. 
* You can either delete those files or change the '''group ownership''' using '''chgrp command.'''

I leave it as an exercise for you.
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|| Type: exit [Enter]
|| Switch to the terminal.

Exit from the '''root user access'''
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|| 
|| This brings us to the end of this tutorial.

Let us summarize.
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|| Slide 13: Summary
|| In this tutorial we learnt about-

* '''groupmod command '''to modify
** the '''group '''name
** '''GID'''
** '''GID '''to a non-unique number
* and '''groupdel command''' to delete a '''group'''

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|| Slide 14: Assignment 
|| As an assignment:

# Create two new '''groups''' 
## '''civil''' with '''GID 1201'''
## '''mechanical''' with '''GID 1202'''
# Add a '''user suman''' with '''primary group civil'''
# Let '''suman''' create a document '''test.txt''' and type any text of your choice.

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|| Slide 14: Assignment (Cont.)
|| 
# Modify the '''GID''' of the '''group civil''' to '''1203'''
# Change the '''group ownership''' of the file '''test.txt'''.
# Delete '''group civil '''
# Delete file '''test.txt'''

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|| Slide 15: About Spoken Tutorial project
|| The video at the following link summarises the Spoken Tutorial project.

Please download and watch it.
|-
|| Slide 16: Spoken Tutorial workshops
|| The Spoken Tutorial Project team conducts workshops using spoken tutorials and gives certificates.

For more details, please write to us.
|-
|| Slide 17: Forum for specific questions:
|| Pls post your timed queries in this Forum.
|-
|| Slide 18: Acknowledgement
|| Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.

More information on this mission is available at this link.
|-
|| 
|| The script has been contributed by Antara.

And this is Praveen from IIT Bombay signing off.

Thanks for joining.
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