Fast user switching bugs: Display color profile; iPod problems; Old desktops after switch; more

We'd like to revisit a group of issues that occur when fast user switching is invoked under Mac OS X 10.4.x.

Most fast user switching issues have to do with process ownership: when one user is the first to access a particular systemwide process, fast user switching sometimes does not handle the switch well to enable secondary users to access that process with full rights and privileges. In other cases, permissions are properly transferred to the new user, but experiencing problems transferring back to the original user.

MacFixIt reader Michael is the latest to report such issues:

"I have had multiple problems crop up with fast user switching once I upgraded to Tiger earlier this year. The main two were in the Display preferences (after switching between accounts I can't make any changes to the preferences and the screen gets all washed out) and in the Audio MIDI drivers (incorrect response from my MIDI controller). Over time, the second user account got increasingly corrupted, resulting in kernel panics and actually having data disappear from my hard drive. I have performed a clean reinstall this week, and everything worked properly for a few days, but now the problem has returned. If I restart or shut down everything works alright until I switch users, then it happens again."

Display profile problem The issue mentioned by Michael with display profiles is one we've covered before. In order to alleviate the display profile issue for all user accounts, use the "Go to folder" command under the "Go" menu in the Finder, and enter the following (on one line):

/System/Library/Frameworks/ApplicationServices.framework/ Versions/A/Frameworks/CoreGraphics.framework/Versions/A/Resources/

Find the "DMProxy" binary, then open System Preferences, go to the "Accounts" pane, then click on "Login Items". Drag the "DMProxy" binary into the "Login Items" field for each affected account.

iPod problems Another issue with Fast user switching involves iPods. If an iPod is left connected, the message "An iPod has been connected that is associated with another iTunes Music Library..." will appear when each user account is switched into. This can lead to accidental erasure of an iPod.

This problem can be bypassed by simply using an AC adapter, disconnecting the iPod before switching accounts, or ignoring the iTunes message.

Improper switching/old desktops, other problems If you are experiencing assorted fast user switching issues, including old desktop information appearing after a switch, or blank screens when switching, try deleting the following file:

• ~/Library/Preferences/com.apple.desktop.plist

then log out and back in and check for persistence of the issue(s)

If you are experiencing issues with fast user switching please drop us a line at late-breakers@macfixit.com.

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