[TYPO3] Call to undefined function session_start() in /var/www/localhost/htdocs/typo3/index.php on line 240

[Martin S]

After the install routine went through on my PHP 5 box I got the error
message

Call to undefined function session_start()
in /var/www/localhost/htdocs/typo3/index.php on line 240

when trying to access the BE. How do I fix this? I can't find anything in
the archive - but I might have miss searched.

Martin S