Redmine

I've just discovered Redmine and I'm trying to install it on an Ubuntu 10.04 box to get an idea of what it can do. But I'm having some problems with the install, so I'd like to feed back the issues I'm having (and also get a working system :) Apologies if this is the wrong place or there's some documentation that I've missed.

I installed redmine from the Ubuntu repositories using Synaptic. That seemed to work OK. I already have Apache running on the box. I first tried to get Redmine to work with Apache, but hit various issues. So then I tried to get it to work with webrick but I hit problems with that too. So here I am ... !

To use webrick, I'm following the instructions in /usr/share/doc/redmine/README.Debian.gz and specifically

QUICK LAUNCH USING WEBRICK
  To test redmine without installing a web server, run as root :
  cd /usr/share/redmine/
  sudo -u www-data X_DEBIAN_SITEID="default" ruby script/server webrick -e production

but that gives an error:

=> Booting WEBrick...
 /usr/lib/ruby/1.8/fileutils.rb:243:in `mkdir': Permission denied - /usr/share/redmine/tmp (Errno::EACCES)
        from /usr/lib/ruby/1.8/fileutils.rb:243:in `fu_mkdir'
        from /usr/lib/ruby/1.8/fileutils.rb:217:in `mkdir_p'
        from /usr/lib/ruby/1.8/fileutils.rb:215:in `reverse_each'
        from /usr/lib/ruby/1.8/fileutils.rb:215:in `mkdir_p'
        from /usr/lib/ruby/1.8/fileutils.rb:201:in `each'
        from /usr/lib/ruby/1.8/fileutils.rb:201:in `mkdir_p'
        from /usr/share/redmine/vendor/rails/railties/lib/commands/server.rb:48
        from /usr/share/redmine/vendor/rails/railties/lib/commands/server.rb:48:in `each'
        from /usr/share/redmine/vendor/rails/railties/lib/commands/server.rb:48
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `require'
        from script/server:3

All the directories and files in /usr/share/redmine appear to be owned by root and nobody else has write permission. There's no tmp directory, so I'm not surprised by the error, but what should the permissions be?

I also notice that the README says

These folders are owned by www-data:www-data and have 750 permissions :
 /var/log/redmine/*
 /var/lib/redmine/*
 /var/cache/redmine/*

But they don't, they have 755. I don't know whether that matters.

I thought I'd check here before I started gaily adjusting the permissions of the standard package!