Admin group can sudo, but my user in admin group can't

Question

I'm having trouble giving a user sudo access. I have Ubuntu 12.04 LTS on my new VPS.

I made a user named portaljacker, added it to the admin group, and admin group is in the sudoers file as

%admin ALL=(ALL) ALL

yet when I use sudo as portaljacker it says:

sudo: must be setuid root

I have no idea what's wrong since I did this a while ago on a previous VPS (not accessible, long story) and can't remember what I did differently.

Answer 1

It seems like your sudo executable has the wrong permissions. Try ls -l /usr/bin/sudo and see what it says. It should look like -rwsr-xr-x (or ---s--x--x; the s needs to be there in that position, though). If the s is not there, try running chmod u+s /usr/bin/sudo as root.