Working with Ubuntu Server (Lucid Lynx) the wheel group has been changed slightly.
Firstly, there doesn’t seem to be any wheel group at all – not by name. The group is now called root by default, and is enabled the same as before: uncomment the appropriate line in /etc/pam.d/su so it looks like this:
auth required pam_wheel.so
The system uses the root group because that is the group name for group 0, and because there is no group named wheel. However, if you want to maintain the original standard – make the entry look like this instead:
auth required pam_wheel.so group=wheel
Then rename (or duplicate) the group in /etc/group with id 0:
root:x:0:root
wheel:x:0:root
This maintains the highest level of compatibility: the group root remains as before, but the name wheel is also available. Having two groups with the same group ID is not typically recommended, but it doesn’t necessarily break anything either as long as the two groups are seen as completely equivalent. The first group in the list will normally be used when names are given for GIDs, but both names will be recognized from the user.
According to the documentation, this is overkill – but it does force the issue and make su work with the actual wheel group rather than a renamed one.
What pam_wheel actually does is search for group wheel first, then if it can’t find that, searches for group 0 (zero) next. It is this configuration that allows the renaming of the wheel group.
Apparently Debian or Ubuntu named the group sudo at one point, now root. The best thing to do – when there is no distinct advantage to change – is to go with the status quo: in doing so, any administrator that comes along will be able to learn and adapt to the system rapidly, leading to quicker completion of administration tasks, simple and complex.
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