Error "unable to start session" instead of a proper error message

[mattab]

After upgrade to Piwik 1.6 many users are reporting "Unable to start session" messages. It seems to happen when the piwik/tmp/sessions directory is not writable.
INstead we should detect this before trying to start the session and if the directory is not writable, return the standard piwik error message showing the "chmod" help command.

[mattab]

See also a report in: http://forum.piwik.org/read.php?2,82920

Maybe the whole tmp/ folder should be checked more often?

[mattab]

Definitely a problem across the board...

 problem writing temporary file '/var/www/vhosts/..../piwik/tmp/templates_c/wrt4ebc5ba68a6af'  ```

http://forum.piwik.org/read.php?5,82929

[mattab]

(In [5587]) Fixes #2717

• Now displaying better error message including commands to type to fix the problem
• Suggesting to enable db session when piwik is already installed (in case the of webhost /user changed directory permissions)

[mattab]

(In [5588]) Refs #2717 - typo

[mattab]

Solution to problem "session has already been started by session.auto-start or session_start()"

Set session.auto_start = Off in php.ini

Source: post

[mattab]

Replying to matt:

Solution to problem "session has already been started by session.auto-start or session_start()"

Set session.auto_start = Off in php.ini

Source: post

This issue has been fixed in #5344 New system check to alert user when session.auto_start = 1