LinuxFloat

I had similar problems and did some digging to find out the cause.

I use a separate /Home partition with my existing Ubuntu Maverick 10.10 x64 installation. I set up a new partition for Ubuntu Natty 11.04 x64, sharing /swap and /home, following the notes at https://help.ubuntu.com/community/Partitioning/Home/Moving which I recommend - with one caveat, see below.

This gave .ICEauthority errors from the beginning, so I replaced it with a standalone installation. This worked, but when I switched to using the /Home partition I ran into the same user-right problems. And after logging into my 10.10 and 11.04 installations, I was unable to access either.

Using a 10.04 live-cd I was able to access the file system and eventually correct the problems.

The cause of my problem was that the users on the original 10.10 system and the 11.04 system were entered (exactly the same names and passwords) in a different order, and therefore had different User IDs - not an issue which I've seen mentioned before in connection with sharing /home partitions.

Ubuntu assigns user IDs starting with 1000 for the installer, 1001 for the second user account and so on. Ownership and permissions are stored on files against these User IDs which are translated into names when you view the permissions dialog box (right-click on the file). The System - Administration - Users and Groups - Advanced Settings button, Advanced tab shows the User ID on the system.

The 10.10 system had been installed by someone else, and I was a subsequent user. I installed the 11.04 system so I had User ID 1000 on that. The /Home partition held ownership and permissions for my user folder against User ID 1001 so when I accessed it from 11.04 it changed the ownership of /home/[myself] to 1001, also the hidden file .ICEauthority. This meant that 10.10 could no longer access /home and after that 11.04 was also stopped.

It is possible to swap User IDs if you access the system with an undamaged setup. In 10.10, before logging on to the new system, I could have gone to System - Administration - Users and Groups - Select [User] - Advanced Settings button - Advanced tab to change the User ID to match the expected value in the new system. Care not to pick one that's already in use - I'm not sure if it checks for duplicates. When you finish, you should have aligned all the users in both systems.

This implies that users of multi-boot systems sharing /home have to be co-ordinated across installations - accounts created in the same order, otherwise it will lead to problems with permissions.

Since it was too late for this, I corrected the problem by using the 10.04 Live-CD and Nautilus with root access to edit the ownership of the following files:
[MyUser] folder - Right-click for Properties and go to the Permissions tab.
- Set ownership back to (my original) User ID, Folder access: Create and delete files, File access blank.
- Set Group to (my original) user group (seems to be the same number as the User ID), Folder access 'Access files' and File access blank.
- Set Others Folder access 'Access files' and File access blank
- Check the 'Execute: Allow executing file as program' box.

ICEauthority files - one per user
Location is /home/[user]/.ICEauthority and hidden so set Nautilus: View - Show Hidden Files. Right-click on the file to open Properties, then the Permissions tab and set:
- Owner as [UserID] with Read/Write access
- Group as [User ID group - same as User ID] with access 'None'
- Others Access 'None'
- Leave the 'Execute: Allow executing file as program' box unchecked.

You may need to set up the User ID and Group you want to assign on the Live CD before you can do it.

The last ICEauthority file is the Gnome Display Manager (gdm) file (or whichever other display manager you are running) which is /var/lib/gdm/.ICEauthority. If this gets altered, you won't be able to login to a desktop - which is what happened to me.
- Owner: gdm - Gnome Display Manager with Access: Read and write
- Group: gdm - Access: None (User Id is 114)
- Others Access: None
- Leave the 'Execute: Allow executing file as program' box unchecked.

After which I reinstalled 11.04, entering users in the correct order to generate a matching set of User IDs between the two systems. Although I could have swapped the IDs around in the original system to match the new one.

I've read a lot of comments about resetting ICEauthority files, and various methods attempted, but the above got my system back to its original state via the GUI. I hope it's helpful.

By the way, a couple of snippets for checking file ownership:
sudo ls -alR /home/[User] | grep [non-User]
will check for files or folders (including hidden ones) in the User's home folder which are owned by the [non-User]
sudo ls -alR / | grep ICEauthority
searches the root filesystem for files with ICEauthority in the name

John

For my case ,I fixed this problem :~

sudo apt-get install gnome-session

Login in Shell (ALT+F1) and install lxde:
sudo apt-get install lxde

restart and everything should work

Does that file actually exist? If it does, you can try this:

chmod 777 ~/.ICEauthority; chmod 1777 /tmp
or this:

rm ~/.ICEauthority

sudo chown $USER:$USER /home/$USER/.ICEauthority
sudo chmod 644 /home/$USER/.ICEauthority

# ls -l /home/username
drwxr-xr-x 4 root root 4096 2008-05-31 10:40 home

try

1. Ctrl+Alt+F3 or boot into recovery mode
press ESC while loading grub

2. sudo chown user:user /home/user/.ICEauthority

3. sudo chmod 644 /home/user/.ICEauthority

4. shutdown -r now
restart.......ok!