All users, including root, appear to have lost admin privileges

run the following command in terminal. It will list the current members of the admin group. who is in there?

dscl . read /groups/admin GroupMembership

that's what I thought. the Directory service entry for the admin group got corrupted and needs to be recreated.

This has to be done from single user mode now. Restart and hold command+S at the chime. you'll see a black screen with some white text.
There are a bunch of commands for you to enter. Please make sure you enter them EXACTLY as I give them. That's very important.



At the prompt enter

/sbin/fsck -fy
\\

Let it work (it will take a while). that's the command to repair the drive. if it reports any errors run it again till there are none. If you can't get rid of errors do not proceed with other commands and enter

reboot

This will reboot the computer. Post back.
If there are no errors you can proceed.
enter

/sbin/mount -uw /

Then enter

launchctl load /System/Library/LaunchDaemons/com.apple.DirectoryServices.plist

and next


rm /var/db/dslocal/nodes/Default/groups/admin.plist

This will delete the corrupt entry for the admin group. The next command will create it correctly.
\\
dseditgroup -o create -i 80 admin

Next we need to add your user and the root user to the newly created admin group.
That's done with the following two commands:

dscl . append /groups/admin GroupMembership root

dscl . append /groups/admin GroupMembership short-user-name

Put the short name of your user instead of short-user-name in the above. Note that there is a space before and after "." in the above commands.

That ought to do it. Now restart by entering

reboot

Your admin group should be back with you in it. Post back if there are any problems. Also, none of above command except the very first one should produce any feedback. If they do you've done something wrong. do not proceed and reenter them correctly.

Message was edited by: V.K.

This totally worked in my case. I can't thank you enough.

you are welcome! I"m glad it worked.

you sir are a god! I am not sure if this is a coincidence but the only meaningful thing i did between the last time i remember using the admin account and now was installing a mcafee virus scan app. I couldn't find anything online that would attribute the admin group corruption on the virus scan but I have disabled it just to be safe.

Carlos