Difference between revisions of "Linux-for-Sys-Ads/C2/Assigning-groups-on-user-creation/English"

• Creating a user group
• /etc/group file
• Assigning groups to users at the time of account creation

We will do this through some examples.

• you should have gone through Linux System Administration tutorials on this website.
• you must have root access to your computer.

• 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.

• Primary group and
• Supplementary 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.
• For example: a student must belong to one and only one department.

• 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.

• 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.

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

sudo su

[Enter]

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

Password of your account

[Enter]

This indicates that we are in the root user mode.

addgroup cse [Enter]

{Suppose output is

Adding group cse (GID 1009)}

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

Here, GID, that is Group ID is 1002.

• 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

addgroup -gid 1012 Music_club

[Enter]

addgroup space hyphen gid 1012 space Music underscore club

Here type M is in capital letter.

Actually, we should have written m in lowercase letter.

Let’s try that.

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

addgroup sports_club

[Enter]

This time no need to mention the GID.

[Enter]

Type cat space /etc/group

Highlight on the slide

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

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

Highlight groups cse, music_club, sports_club

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.

Let us see an example.

adduser -ingroup cse radha

[Enter]

adduser space hyphen ingroup space cse space radha

pass_radha

[enter]

Retype the same password and press Enter.

Type name as Radha with capital R.

And proceed as we have done before.

[Enter]

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

Type adduser space radha space music underscore club

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

adduser -ingroup cse radha

command executed previously

adduser radha music_club

adduser space radha space sports underscore club

Type id space radha

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.

grep radha /etc/group

[Enter]

Type: grep space radha space /etc/group

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.

grep radha /etc/passwd

[Enter]

Type grep space radha space /etc/passwd

It is the GID for the group cse.

It is the primary group for radha.

• /etc/passwd shows primary group ID for a user
• /etc/group file shows list of usernames who have the group as a supplementary group

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

We know group cse has GID 1002

adduser -gid 1009 suraj

[Enter]

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.

exit and press Enter

Let us summarize.

Summary

• 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

Assignment

1)Create two groups:

1. cultural
2. literature

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"

Assignment(Cont.)

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

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