[SOLVED] Permission problem in a shared partition among several Linux OSes

shva · 07-22-2012, 05:32 PM

I have a Ubuntu and a Scientific Linux installed on the same computer so that I can switch back and forth, and I intend to use a third partition to host the common files. For example, I mount this partition as /common_files in both systems. However, each time I change from one system to the other, I am no longer the owner of /common_files. So I have to do

Code:

sudo chown -R myname: /common_files

to change the ownership. How can I avoid doing that?

Note that the username for both Ubuntu and Scientific Linux is "myname". I just want to keep the ownership of /common_files on both systems. Thanks.

fogpipe · 07-22-2012, 05:44 PM

I have a shared /home partition and at any given time at least two bootable linux distros and when i run into that problem i use

Code:

chown -R myusername.myusergroup /home/myusername

This will work if your user name is the same on all the distros that you boot and if there is a group named for your user name.

For instance if your user is hal:

Code:

chown -R hal.hal $PATHTODIR

If you dont have a group on all the distros you boot to that is named after your username you will have to create that group using groupadd.

Code:

man groupadd

chrism01 · 07-22-2012, 07:17 PM

Ownerships are actually done by uid (see /etc/passwd), not username.
SL starts normal users at uid=500, Ubuntu at uid=1000 http://manpages.ubuntu.com/manpages/...er.conf.5.html http://scientificlinuxforum.org/inde...showtopic=1640
(SL is based off RHEL)

suicidaleggroll · 07-22-2012, 07:25 PM

To expand on chrism's post:

Linux does ownership by user ID, not user name. Your user IDs are different on the two machines, so when you boot one or the other, they don't recognize the UID from the other system. You need to change the UID for your username on one of the systems to match the other. If you log out, and access a terminal through Ctrl + Alt + F2-6 and log in as root, you should be able to change the UID for your username to whatever you want. You should probably do this in SL, because changing your UID in SL from 500 to 1000 is safe, changing your UID from 1000 to 500 in Ubuntu is not (1-999 in Ubuntu is reserved for system).

Code:

id username # write down the UID and GID for your user, from here on out this will be referred to as oldUID and oldGID
usermod -u newUID "username"
groupmod -g newGID "groupname"
find / -user oldUID -exec chown newUID {} \;
find / -group oldGID -exec chgrp newGID {} \;

shva · 07-22-2012, 09:32 PM

Thanks guys. After changing the user id and group id in Scientific Linux to the one used in Ubuntu, the problem is resolved.

chrism01 · 07-22-2012, 09:51 PM

Good; FYI, this also applies to NFS ie server & client must use same uids.