Description of problem:

The %post removes the user mysql when the package is uninstalled:
postuninstall scriptlet (using /bin/sh):
[...]
if [ $1 = 0 ] ; then
        userdel mysql >/dev/null 2>&1 || :
fi

but at install time the group mysql is created, too:
preinstall scriptlet (using /bin/sh):
/usr/sbin/useradd -M -o -r -d /var/lib/mysql -s /bin/bash \
        -c "MySQL Server" -u 27 mysql > /dev/null 2>&1 || :

So when one removes mysql-server, the group mysql is left behind and the useradd
silently fails.


Version-Release number of selected component (if applicable):
5.0.27-1.fc6

How reproducible:
always

Steps to Reproduce:
1. install mysql-server
2. uninstall mysql-server
3. install mysql-server
  
Actual results:
the user mysql is not there.

Expected results:
the user mysql should be created at install time of mysql-server or the user
should be somehow warned, that there is a problem. (Other than "Using root
instead of mysql, see additionial info)

Additional info:

When I installed mysql-server on CentOS 5 after removing it, the following
warning appeared:

  Installing: mysql-server                 ######################## 
[3/4]warning: user mysql does not exist - using root

So maybe this is also a security issue, I did not investigate further due to a
lack of time. In addition, this seems to be a problem in RHEL, too.