Have you tried overriding the url with a url handler? 

There's the login_redirector plugin:

http://community.elgg.org/pg/plugins/project/384766/developer/jdalsem/loginredirector

It's for Elgg 1.7, so I don't know if it works for Elgg 1.8 (most likely not without some modifications). But you could use this plugin as a starting point to implement the redirect on your site. If the redirect should always go to the dashboard the plugin code can be simplified anyway.

You need to enable the dashboard plugin, then make a custom plugin that registers for the system, index hook and redirects logged users to /dashboard.

solved by add redirection url in actions/login.php 

change 

// forward to main index page

$forward_url = ' ';

TO:

// forward to main index page

$forward_url = '/profile';

adding, appeared:

'Sorry. We could not find the requested profile.'

As most developers will say -- better to do a custom plugin for such functions.
The Login Redirector should work pretty well after the 1.8 code fixes.

If you 'insist' on 'hacking' the core code...  try this :--
     $forward_url='/profile';elgg_get_logged_in_user_entity()->username;

same message:

'Sorry. We could not find the requested profile.'

There is a plugin for this? For elgg 1.8?

Just post your site's url here - so we can try it out ;)

ps: there was a typo in the code i posted ! did you catch it or did you just blindly copy the typo-ed error code ?

I copied. What is wrong in your code?