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

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, GID
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
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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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