LinuxQuestions.org
Help answer threads with 0 replies.
Go Back   LinuxQuestions.org > Forums > Linux Forums > Linux - Distributions > Slackware
User Name
Password
Slackware This Forum is for the discussion of Slackware Linux.

Notices


Reply
  Search this Thread
Old 08-29-2006, 05:44 PM   #1
Woodsman
Senior Member
 
Registered: Oct 2005
Distribution: Slackware 14.1
Posts: 3,482

Rep: Reputation: 546Reputation: 546Reputation: 546Reputation: 546Reputation: 546Reputation: 546
Modifying User and Group IDs


Bit and pieces for answering this question are available online, but I'm trying to coordinate the information cohesively. I suspect I am not the first person to run into this cute little challenge and I think a thread will benefit many people.

When I installed Slack on my first box I created various user accounts and group names. When I acquired a second box, I repeated the routine. All was well until I decided to network the boxes. I then discovered what is probably a common problem in this type of expansion project. I had established unique user and group names, but allowed the system to automagically assign the underlying UIDs and GIDs. For stand alone boxes this is fine, but on a network, as I have discovered, this is called an Oops. My approach created the interesting problem in that UID 100 on Box 1 can see and modify the files on Box 2 owned by UID 100, although the human readable user names are different. The reason is that to the system the UID and GID are the true identifiers, not the human readable names.

I now realize that in large networks various options are available to create, synchronize, and maintain unique account and group IDs, such as LDAP, NIS, etc. Those options probably are overkill for a small home LAN. Probably a simple rsync script would suffice. For now, however, I am trying to better understand how to correct my current problem in a methodical manner. Fortunately I need only modify a couple of accounts and groups.

I know about the usermod, chown, etc. Therefore my focus in this thread is creating a proper punch list to modify the user and group accounts on Box 2 without destroying files, home directories, etc., while maintaining the same human readable identities.

Do I understand correctly that usermod -u modifies the file ownership of the /home directory? Or does usermod not even do that? Regardless, seems that after modifying the UID I also have to search the entire system to update file ownership from the old UID to the new UID.

What about non-system GIDs? Should they also be unique with respect to all networked boxes? I suspect the system GIDs should all remain the same, but should I modify the non-system GIDs?

With all that said, what would be a safe methodical way to update Box 2? Here is my best guess from what I have read so far:

1. Create a written table of the user names, groups names, current IDs and new IDs.
2. Modify each user-based primary group GID: groupmod -g newgid userprimarygroupname.
3. Modify each user's UID: usermod -u newuid username.
4. Modify all system files to the appropriate UID/GID:
find / -uid olduid -exec chown username: {} \;
find / -gid oldgid -exec chown :userprimarygroupname {} \;
5. Test each account by logging in.

FWIW, I tried using kuser in KDE 3.4.3, but on testing the user's login, login/bash reported no home directory found. I suspect kuser did not modify the home directory file ownership or I do not know the appropriate way to instruct kuser to do this.

Anything else? Any caveats?

Thanks again.
 
Old 09-01-2006, 03:59 PM   #2
Woodsman
Senior Member
 
Registered: Oct 2005
Distribution: Slackware 14.1
Posts: 3,482

Original Poster
Rep: Reputation: 546Reputation: 546Reputation: 546Reputation: 546Reputation: 546Reputation: 546
My preceding proposed sketch is close to being accurate although some of the syntax is incorrect. After additional reading and some testing I wrote a mini how-to explaining the process of updating user and group IDs:

Modifying User and Group IDs to Support a Home Network

Hopefully this information will help future visitors to this thread.
 
Old 09-01-2006, 04:38 PM   #3
dive
Senior Member
 
Registered: Aug 2003
Location: UK
Distribution: Slackware
Posts: 3,467

Rep: Reputation: Disabled
Nice

One more thing though. From man usermod:

"You must change the owner of any crontab files manually. You must change the owner of any
at jobs manually. You must make any changes involving NIS on the NIS server."
 
Old 09-01-2006, 11:34 PM   #4
Woodsman
Senior Member
 
Registered: Oct 2005
Distribution: Slackware 14.1
Posts: 3,482

Original Poster
Rep: Reputation: 546Reputation: 546Reputation: 546Reputation: 546Reputation: 546Reputation: 546
Quote:
One more thing though. From man usermod...
I added a line at the end of the document. Thank you!
 
  


Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off



Similar Threads
Thread Thread Starter Forum Replies Last Post
User IDs DarReNz Solaris / OpenSolaris 4 08-16-2006 07:13 AM
Wildest thing with group IDs verl Fedora 2 03-16-2005 09:57 PM
Samba mount, user/group IDs fennec Linux - Networking 0 08-22-2004 03:54 PM
user and group ids - individual permissions? LooseCanon Linux - General 2 09-14-2003 01:57 PM
User IDs confuse me. davee Linux - Newbie 1 02-11-2003 06:42 AM

LinuxQuestions.org > Forums > Linux Forums > Linux - Distributions > Slackware

All times are GMT -5. The time now is 11:24 AM.

Main Menu
Advertisement
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Open Source Consulting | Domain Registration