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*We can understand '''group''' as a '''collection of users'''.
 
*We can understand '''group''' as a '''collection of users'''.
 
*In a college system, a '''group '''can be '''different departments''' like '''CSE''', '''Electrical''' etc.
 
*In a college system, a '''group '''can be '''different departments''' like '''CSE''', '''Electrical''' etc.
−
*Groups can also be different clubs like '''music club''',''' sports club, literature club,''' etc.
+
*'''Groups''' can also be different clubs like '''music club''',''' sports club, literature club,''' etc.
  
 
|-
 
|-
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|-
 
|-
 
|| Slide 7:
 
|| Slide 7:
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|| *Every '''user''' must belong to one and only one''' primary group'''.
+
||  
 +
*Every '''user''' must belong to one and only one''' primary group'''.
 
*This is the default''' group''' for the '''user''' when the '''user '''logs in.  
 
*This is the default''' group''' for the '''user''' when the '''user '''logs in.  
 
*For example: a student must belong to one and only one '''department'''.
 
*For example: a student must belong to one and only one '''department'''.
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|-
 
|-
 
|| Slide 8:
 
|| Slide 8:
−
|| *A '''user''' can be a member of more than one '''group'''.  
+
||  
 +
*A '''user''' can be a member of more than one '''group'''.  
 
*Those '''groups '''are called '''supplementary groups'''.
 
*Those '''groups '''are called '''supplementary groups'''.
 
*These '''groups '''are assigned to the '''user''', to provide him additional '''access''' to resources.
 
*These '''groups '''are assigned to the '''user''', to provide him additional '''access''' to resources.
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|-
 
|-
 
|| Slide 9
 
|| Slide 9
−
|| Let’s take an example.*'''User radha '''belongs to the '''CSE department'''.
+
|| Let’s take an example.
 +
*'''User radha '''belongs to the '''CSE department'''.
 
*She is also a member of the '''music club '''and '''sports club'''.
 
*She is also a member of the '''music club '''and '''sports club'''.
 
*In this scenario, '''CSE''' is the '''primary group '''for '''radha'''.
 
*In this scenario, '''CSE''' is the '''primary group '''for '''radha'''.
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|-
 
|-
 
|| Slide 10
 
|| Slide 10
−
|| *Alternatively, we can mention a '''GID '''of our choice.
+
||  
 +
*Alternatively, we can mention a '''GID '''of our choice.
 
*For this, we need to use '''hyphen gid''' option along with the '''addgroup command'''.
 
*For this, we need to use '''hyphen gid''' option along with the '''addgroup command'''.
 
*'''GIDs''' in the range of''' 0 '''to''' 999''' are '''reserved''' for the '''system users'''.
 
*'''GIDs''' in the range of''' 0 '''to''' 999''' are '''reserved''' for the '''system users'''.
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|| Notice,  
 
|| Notice,  
  
−
User '''radha''' is in group '''cse''' which has '''GID''' 1002
+
'''User radha''' is in group '''cse''' which has '''GID''' 1002
  
 
That is the''' primary group''' for '''radha'''.
 
That is the''' primary group''' for '''radha'''.
  
−
Next, there is the list of '''groups''',where '''user radha '''is member of.
+
Next, there is the list of '''groups''', where '''user radha '''is member of.
  
 
Notice, along with '''primary group cse, radha''' is also a member of two '''supplementary groups music underscore club''' and '''sports underscore club.'''
 
Notice, along with '''primary group cse, radha''' is also a member of two '''supplementary groups music underscore club''' and '''sports underscore club.'''
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|-
 
|-
 
|| Slide 13:
 
|| Slide 13:
−
|| So, remember*'''/etc/passwd''' shows '''primary group ID '''for a '''user'''
+
|| So, remember
 +
*'''/etc/passwd''' shows '''primary group ID '''for a '''user'''
 
*'''/etc/group file''' shows list of '''usernames''' who have the''' group '''as a '''supplementary group'''
 
*'''/etc/group file''' shows list of '''usernames''' who have the''' group '''as a '''supplementary group'''
  
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|| As an assignment-
 
|| As an assignment-
  
−
#Create two '''groups: '''
+
1)Create two '''groups: '''
−
##'''cultural '''
+
#'''cultural '''
−
##'''literature'''
+
#'''literature'''
  
 
|-
 
|-
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Assignment(Cont.)
 
Assignment(Cont.)
−
|| #Now create a''' user ajay''' with  
+
||  
−
##'''Home directory''' as '''/home/ajay underscore dir '''
+
2)Now create a''' user ajay''' with  
−
##'''User id '''as''' 1090'''
+
#'''Home directory''' as '''/home/ajay underscore dir '''
−
##'''Primary group '''as '''cultural'''
+
#'''User id '''as''' 1090'''
−
##'''Supplementary group '''as '''literature'''
+
#'''Primary group '''as '''cultural'''
−
##Add '''comments "Native: Mumbai"'''
+
#'''Supplementary group '''as '''literature'''
 +
#Add '''comments "Native: Mumbai"'''
  
 
|-
 
|-

Latest revision as of 16:52, 31 August 2018

Title of script: Assigning Groups on User Creation

Author: Antara Roy Choudhury

Keywords: group, primary group, supplementary group, assigning group, specify GID, /etc/group file


Visual Cue Narration
Slide 1: Introduction Hello and welcome to the spoken tutorial on Assigning Groups on User Creation in Linux.
Slide 2: Learning Objectives In this tutorial we will learn about
  • Creating a user group
  • /etc/group file
  • Assigning groups to users at the time of account creation

We will do this through some examples.

Slide 3: System requirement To record this tutorial, I am using Ubuntu Linux 16.04 OS
Slide:4 Prerequisite To practice this tutorial,
  • you should have gone through Linux System Administration tutorials on this website.
  • you must have root access to your computer.
Slide 5: What is a group in Linux?
  • We can understand group as a collection of users.
  • In a college system, a group can be different departments like CSE, Electrical etc.
  • Groups can also be different clubs like music club, sports club, literature club, etc.
Slide 6: Linux supports two types of groups.
  • Primary group and
  • Supplementary group
Slide 7:
  • Every user must belong to one and only one primary group.
  • This is the default group for the user when the user logs in.
  • For example: a student must belong to one and only one department.
Slide 8:
  • A user can be a member of more than one group.
  • Those groups are called supplementary groups.
  • These groups are assigned to the user, to provide him additional access to resources.

More on access mechanism or permission will be discussed in subsequent tutorials.

Slide 9 Let’s take an example.
  • User radha belongs to the CSE department.
  • She is also a member of the music club and sports club.
  • In this scenario, CSE is the primary group for radha.
  • And she is a member of two supplementary groups - music club and sports club.

Let’s create this scenario in our system.

First, we will create group CSE.

And we will use addgroup command in order to create this group.

Press Ctrl+Alt+T Open the Terminal by pressing Ctrl, Alt and T keys simultaneously on the keyboard.
Type

sudo su

[Enter]

Now, we should login as superuser or root user.

To do so type: sudo space su and press Enter.

Type

Password of your account

[Enter]

Type the admin password and then press Enter.
Highlight # prompt Notice, our login prompt has changed to a hash symbol.

This indicates that we are in the root user mode.

Only narration Here onwards, please remember to press the Enter key after typing each command.
Type

addgroup cse [Enter]

Now type addgroup space cse
Show the output

{Suppose output is

Adding group cse (GID 1009)}

This will create group cse.

Linux automatically allocates a Unique ID for each group that is created.

Here, GID, that is Group ID is 1002.

Slide 10
  • Alternatively, we can mention a GID of our choice.
  • For this, we need to use hyphen gid option along with the addgroup command.
  • GIDs in the range of 0 to 999 are reserved for the system users.
  • So, always choose a number greater than or equal to 1000 as GID
Let’s us create a group Music_club with the GID 1012.
Type:

addgroup -gid 1012 Music_club

[Enter]

On the terminal type:

addgroup space hyphen gid 1012 space Music underscore club

Here type M is in capital letter.

Show the output Notice, it is showing some error.

Actually, we should have written m in lowercase letter.

Let’s try that.

Press Up key Press the Up arrow key to get the previously executed command.
Change Music_club to music_club [Enter] Change capital M to m in lowercase letter.
Show the output The command is working now.

So, always remember to use lowercase letters while writing group names.

Type

addgroup sports_club

[Enter]

Similarly let’s create another group sports underscore club.

This time no need to mention the GID.

Now we have three groups cse, music underscore club and sports underscore club.
cat /etc/group

[Enter]

How can we check the details of the created group?


Type cat space /etc/group

Show file opened There will be an entry in this file for every user on the system.
slide

Highlight on the slide

Each line has four fields separated by a colon symbol.

The first field is the name of the group.

The second field is the encrypted password for the group.

Third field shows the GID as a number.

Highlight on the slide

Fourth field contains the list of users that belong to that group separated by commas.

This list contains all users who have this group as a secondary group.

Show file /etc/group


Highlight groups cse, music_club, sports_club

We can see the entries for cse, music underscore club and sports underscore club groups.

Notice, music underscore club has Gid 1012 which we mentioned during group creation.

Here, the fourth field is empty for all the groups.

This is because there are no members in these groups, as of now.

The password field is x.

We will discuss about the password field and list of members field in detail, in a separate tutorial on groups.

Retain same screen Now, how can we specify the primary and supplementary groups while creating the user?

Let us see an example.

Type

adduser -ingroup cse radha

[Enter]

To specify that user radha belongs to the primary group cse, type:

adduser space hyphen ingroup space cse space radha

Type

pass_radha

[enter]

Type the password as pass underscore radha and press Enter.

Retype the same password and press Enter.

Type name as Radha with capital R.

And proceed as we have done before.

Show output We have successfully created user radha with primary group cse.
Highlight ingroup So, you should use ingroup option to specify primary group’s name while creating the user.
adduser radha music_club

[Enter]

As we know, radha is a member of music underscore club.

So music underscore club will be the supplementary group for the user radha.

Type adduser space radha space music underscore club

Retain same screen Remember.

To add supplementary groups using adduser command, you should have an existing user.

Highlight

adduser -ingroup cse radha

command executed previously

Here, we have first created the user radha.
Highlight

adduser radha music_club

Then added radha to the supplementary group using adduser command.
adduser radha sports_club If you need to specify that radha is also a member of sports club type:

adduser space radha space sports underscore club

id radha Let’s check user radha’s details using id command.

Type id space radha

Show the output Notice,

User radha is in group cse which has GID 1002

That is the primary group for radha.

Next, there is the list of groups, where user radha is member of.

Notice, along with primary group cse, radha is also a member of two supplementary groups music underscore club and sports underscore club.

Type

grep radha /etc/group

[Enter]

Now let’s check our /etc/group file for the entry of radha

Type: grep space radha space /etc/group

Highlight appropriately in the output Notice, you can see user radha is the member of groups music underscore club and sports underscore club

But not as a member of the primary group that is cse.

So the group file will list only the supplementary groups in which the user is associated.

Type

grep radha /etc/passwd

[Enter]

Check the /etc/passwd file for the details of the username radha.

Type grep space radha space /etc/passwd

Show the output Notice, the fourth field is 1002

It is the GID for the group cse.

It is the primary group for radha.

Slide 13: So, remember
  • /etc/passwd shows primary group ID for a user
  • /etc/group file shows list of usernames who have the group as a supplementary group
Slide 14: Command id space username shows the details of both primary and supplementary groups
Retain same screen You can also specify the group id instead of group’s name while creating the user.

Let us create a user suraj and assign him to the group cse using the gid.

We know group cse has GID 1002

Type

adduser -gid 1009 suraj

[Enter]

So type: adduser space hyphen gid space 1002 space suraj

You should use hyphen gid option to specify the group ID.

Use pass underscore suraj as the password

Retype the password

Full Name as Suraj with S in capital letter.

Proceed as we have done for the previous users.

Highlight the output We have successfully created user suraj with primary group cse.
Type

exit and press Enter

To exit from the root user access, type exit
Retain same screen This brings us to the end of this tutorial.

Let us summarize.

Display Slide 15

Summary

In this tutorial we learnt about-
  • Creating primary group
  • Assigning user to the primary group
  • Assigning user to the supplementary group
  • /etc/group file
  • Assigning groups to users at the time of account creation
Display Slide 16

Assignment

As an assignment-

1)Create two groups:

  1. cultural
  2. literature
Slide 17

Assignment(Cont.)

2)Now create a user ajay with

  1. Home directory as /home/ajay underscore dir
  2. User id as 1090
  3. Primary group as cultural
  4. Supplementary group as literature
  5. Add comments "Native: Mumbai"
Slide 18

Assignment(Cont.)

3) Use the command id to check the user details

4) Check the details of user ajay in /etc/passwd and /etc/group files

Slide 19: About Spoken Tutorial project The video at the following link summarises the Spoken Tutorial project.

Please download and watch it.

Slide 20: Spoken Tutorial workshops The Spoken Tutorial Project team conducts workshops and gives certificates.

For more details, please write to us.

Slide 21: Forum for specific questions: Please post your timed queries in this forum.
Slide 22: Acknowledgement Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.

More information on this mission is available at this link.

Slide 23: Thank You The script has been contributed by Antara and this is Praveen from IIT Bombay signing off.

Thank you for joining.

Contributors and Content Editors

Nancyvarkey, Pravin1389

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