File Permissions and security - sharing with FW externally booted Linux

Question

I want to be able to access my Music folder and others on my Powerbook's internal HD from my Linux OS (Kubuntu 9.04) which boots from an external Firewire drive.
It worked fine when I changed the permissions in "Others:" to "Read Only", but I am afraid that this makes me vulnerable to having files stolen so I changed it back... Am I correct in assuming this?
Is there a way that I can add Read/Write permissions to my Linux user account?
Thanks ahead of time.

Answer 1

I did this with NFS, but I haven't tried it from a shared harddrive.
how should I do if I want the permissions to work in both OSes?
You can change the permissions of files and directories in either OS.
I suggest that you make a complete backup of your system. You should create a second administrator account from which you use to change your original account. You should log out your original account before proceeding.
Mac OS X ... harddrive -> Applications -> Utilities -> terminal
Ubuntu ... Applications > Accessories > Terminal
Your current user is:
echo $USER
Let's assume myuser
To find out your UID and GID do:
ls -ln
ls -l
Or, you can use the id command.
id
compare the output and write down what you find.
You best use the numeric value for your userid. In this case it is 500. To list all the files owned by a userid do:
sudo find / -user 500 -exec ls {} \;
# adding a -x before the / limits the search to the current file system.
Mac OS X ... harddrive -> Applications -> Utilities -> NetInfo Manager
In the middle column is the function. Pick users then select your user. Click on the lock at the bottom of the panel. Go into the property list and change UID and GID.
In the Ubuntu terminal,
man 5 passwd
... will give you the format of the passwd file.
sudo nano /etc/passwd
... the format is user-name, password, uid, gid, ...
control-o
... to save
control-x
... to quit
The groups are defined in /etc/group
cat /etc/group
Now change the UID and GID of all files:
You best use the numeric value for your userid. In this case it is 500.
sudo find / -user 500 -exec chown 1100:211 {} \;
/* Where chown has the format of chown uid:gid file-name */
/* adding -print before -exec lists the files that will be changed. */
/* You may want to leave off :211 if your uid & gid are not paired. */
/* Notice the -exec runs another command on the found file. */
sudo find / -group 20 -exec chgrp 211 {} \;
On the Mac you get into single user mode by holding down command-s when you poweron your machine. Just in case you run into problems.
On Mac OS, there are a few files that have the old uid as part of their names. The .Trashes file will be only removal media and maybe everywhere.
/.Trashes/501
/Library/Caches/com.apple.IntlDataCache.501
/Library/Caches/com.apple.IntlDataCache.sbdl.501
/Library/Caches/com.apple.user501pictureCache.tiff
On Linux, there are a few files that have the old user name as part of their file and folder names:
Here is another explaination of the procedure. ( It misses some file because the auther checks only the most likely places.
http://lissot.net/netinfo/change_user.html
Robert