Nasty human error in Zope ZEO setup

Together with my colleague Jan we today tried to fix a problem with Zope ZEO server that wouldn't start. Very strange we thought since another ZEO server on the same machine was working fine. We compared zope.conf files and found nothing obvious. Here was the error you get with 'bin/runzeo':

root@da-ovz-vm99182:/var/lib/zope-2.8.9/aragdb-zeo1# ./bin/runzeo 
Error: error opening file //var/lib/zope-2.8.9/aragdb-zeo1/etc/zeo.conf: 
[Errno ftp error] no host given

What?? ftp error??

Long story short, the error was this line in 'runzeo':

CONFIG_FILE="/${INSTANCE_HOME}/etc/zeo.conf"

which should have been this:

CONFIG_FILE="${INSTANCE_HOME}/etc/zeo.conf"

Not so easy to spot because the CONFIG_FILE line is something you rarely look closely at.