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Time Narration
00:01 Hello and welcome to the spoken tutorial on Modifying and Deleting Groups in Linux.
00:09 In this tutorial we will learn about

groupmod command and groupdel command

00:17 We will do this through some examples.
00:21 To record this tutorial, I am using Ubuntu Linux 16.04 OS
00:28 To practice this tutorial, you should have gone through the Linux System Administration tutorials on this website and
00:36 you must have root access to your computer.
00:41 Open the Terminal by pressing Ctrl, Alt and T keys simultaneously on the keyboard.
00:49 First, you should login as superuser or root user.
00:56 Here onwards, please remember to press the Enter key after typing each command.
01:03 In the series, we had created the group electronics.
01:07 Let us check the details of the group from the /etc/group file.
01:14 Notice that group electronics has GID 1006.
01:20 Also, the list of members field is empty.
01:25 So, no user has group electronics as a supplementary group.
01:31 Let’s check the /etc/passwd file to know how many users belong to the primary group electronics.
01:42 Notice that, the users testmod and amit have 1006 in the fourth field.
01:50 It means the users testmod and amit belong to the group electronics
01:57 Let me create a document testfile.txt in the user account testmod
02:04 So, login as user testmod
02:08 Now if we create any document, then that document will be owned by the group electronics.Let's do that.
02:17 First we’ll create a text file named testfile.txt
02:24 I am going to use vi text editor to do so.
02:28 But you can use any other text editor of your choice.
02:33 At the command prompt type vi space testfile.txt
02:41 Press I on the keyboard to insert text.
02:45 Now type this text, “Hi I am user testmod
02:50 Press the Escape key on the keyboard to exit from the insert mode.
02:55 Then press colon w q
02:59 w is used to save the typed text in the text file.
03:04 And q is used to quit the editor.

Now press Enter.

03:11 We are back to the command prompt.
03:14 Now type, ls space hyphen l space testfile.txt
03:22 Notice the third and fourth fields.
03:25 The document belongs to user testmod and group electronics.
03:31 Now let us start modifying the group with the groupmod command.
03:37 The groupmod command is used to modify the definition of the group specified in the command.
03:45 This is the syntax.
03:49 Here the options field is not mandatory.
03:54 groupmod command can be used to modify- the group name,


04:00 GID to a non-unique number
04:04 Suppose, we want to modify our group’s name from electronics to electrical.
04:10 To do so, let me switch back to the root login.
04:15 Exit from the user testmod.
04:19 Now type groupmod space hyphen n space electrical space electronics
04:28 Then type cat space /etc/group
04:34 Notice that the group with GID 1006 is now named as electrical.
04:42 You can also change the GID of a group to a new unique non-negative number.
04:50 Suppose, you are planning to use number 1100 as the new GID value.
04:57 So, first ensure, that the number 1100 is not present as GID in any other group.
05:06 From the output of /etc/group 1100 is not set as a GID value to any of the group.
05:16 This type of manual checking is not a good idea, if you have a large number of groups.
05:22 Instead we can use the grep command to check if the number is present or not.
05:30 As an assignment, try this out on your own.
05:35 Now to change GID value, type groupmod space hyphen g space 1100 space electrical
05:48 Now check the details of the file /etc/group
05:54 Notice that GID of electrical is now 1100.
06:00 We know that user testmod belongs to the group electrical.
06:05 Let’s check /etc/passwd file for the entry of the user testmod.
06:14 Notice that the GID value in the fourth field is also updated.
06:19 It is showing the current value 1100.
06:24 The group ID has changed.
06:27 But the files belonging to this group will retain the old group ID value.
06:34 So we must change their group ID manually.
06:39 To find all files belonging to the group with GID 1100, type find space slash home space hyphen gid space 1100
06:55 This may take some time.
06:58 We have not got any output.
07:01 Recall the previous command.
07:04 Change the group ID value to 1006 that is the previous group ID of electrical.
07:12 Notice, the file testfile.txt still belongs to group ID 1006.
07:20 Please note the complete path of the file testfile.txt
07:26 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.

07:44 chgrp command is used to change the group of the file.
07:49 The command has executed without any error.
07:53 Recall the command to display all the files belonging to group ID 1100.
08:00 Notice the output shows testfile.txt file.
08:05 Please note, you may have multiple files belonging to old group ID value.
08:12 Changing group ID manually one by one will be a tedious job in that case.
08:18 Try writing shell script for this.
08:22 Now we know how to change the GID of a group to another unique value.

Let’s move on.

08:30 Recall the command to display /etc/group.
08:36 Notice, literature club has GID 1007.
08:42 Let us try to assign this 1007 as the new GID of electrical.
08:49 Notice, it is showing an error, GID 1007 already exists.
08:56 So, we cannot change the group ID to a non-unique value with only hyphen g option.
09:04 To change the group ID to a non-unique value, you will need hyphen o option along with hyphen g option
09:14 Let me try to set the GID to 1007 now.
09:19 Recall the previous command.
09:22 Now, after 1007, give space and then type hyphen o
09:30 The command has executed successfully.
09:34 Next, execute the cat /etc/group command
09:41 Notice that both electrical and literature_club now have same GID 1007.
09:50 So, we have learnt about groupmod command.
09:54 Now let’s learn about groupdel command.
09:58 groupdel command is used by the root or the superuser to remove a group.
10:05 Syntax is groupdel space groupname
10:10 Let me remove the group named electrical.
10:14 Type groupdel space electrical
10:19 Notice that Linux has thrown some error.
10:23 It is telling that cannot remove primary group of the user amit
10:29 So, you cannot delete electrical because it is the primary group of an existing user amit.
10:37 You must first delete the user amit and then you can remove electrical.

Let’s try this.

10:46 For deleting user amit, type userdel space hyphen r space amit
10:54 The command may report that the user's mail spool was not found.

This warning can be ignored.

11:03 Now execute the groupdel command.
11:07 Once again we got the error.

Says, cannot remove the primary group of the user testmod

11:15 Let me delete the user testmod.
11:19 Once again we got the user's mail spool error.
11:24 Now execute the groupdel command for the group electrical.
11:29 This time we did not get any error.
11:33 Now execute the cat /etc/group command
11:40 We can see that there is no entry for electrical.
11:44 The group named electrical is deleted now.
11:48 The important point you have to keep in mind is:

You are not permitted to remove the primary group of any existing user.

11:58 You must remove the user first. Then you can remove that user's primary group.
12:05 Now what about the files owned by the deleted group?
12:09 groupdel will not automatically check for files owned by the deleted group.
12:15 You should manually search all file systems for such files.
12:21 You can use the find command for this search.
12:25 You should ensure that no files remain owned by this deleted group.
12:31 You can either delete those files or change the group ownership using chgrp command.

I leave it as an exercise for you.

12:43 Switch to the terminal.
12:45 Exit from the root user access.
12:49 This brings us to the end of this tutorial.

Let us summarize.

12:55 In this tutorial we learnt about-

groupmod command to modify the group name

13:02 GID

GID to a non-unique number

13:08 groupdel command to delete a group
13:11 As an assignment: Create two new groups

civil with GID 1201, mechanical with GID 1202

13:24 Add a user suman with primary group civil
13:29 Let suman create a document test.txt and type any text of your choice.
13:36 Modify the GID of the group civil to 1203
13:42 Change the group ownership of the file test.txt.
13:47 Delete group civil
13:49 Delete file test.txt
13:53 The video at the following link summarises the Spoken Tutorial project.

Please download and watch it.

14:01 The Spoken Tutorial Project team conducts workshops using spoken tutorials and gives certificates.

For more details, please write to us.

14:13 Pls post your timed queries in this Forum.
14:17 Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.
14:23 The script has been contributed by Antara. And this is Praveen from IIT Bombay signing off.

Thanks for joining.

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