Comment 120 for bug 349469

If you want to see this in action I have a set of provisioning scripts that reprocuce the problem in an automated way...

On a brand new Debian 8.1 linode, if you run my script it will prompt you for a mysql password-- the thing is I tried to pre-set the mysql password with debconf.

git clone https://github.com/bradchesney79/2015DebianJessieWebserverProject.git
pushd 2015DebianJessieWebserverProject-master/
git checkout ef2dd6e396c0b88652c47c39f2cf692d562d9d23
popd
mkdir -p /root/bin
cp -R /root/2015DebianJessieWebserverProject-master/* /root/bin/
./root/bin/build-script.sh

The system will begin to build.

<CTRL> + <Z> the password prompt to get back to the command line.

I try to run the debconf command after the fact:

root@server/root/# echo "mysql-server mysql-server/root_password select passw0rd" | debconf-set-selections

<Output>
debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable
</Output>

root@server/root/# fuser -v /var/cache/debconf/config.dat

<Output>
                     USER PID ACCESS COMMAND
/var/cache/debconf/config.dat:
                     root 19165 F.... frontend
</Output>

root@server/root/# kill 19165

Succeeds.

root@server/root/# echo "mysql-server mysql-server/root_password select passw0rd" | debconf-set-selections

Succeeds.