Search not working!

Hello, the search engine hasn't been operative for a couple of days. Also, the contact form doesn't work (captcha won't pass despite entering the correct letters) and there's a suspicious error message at the bottom of the page: Warning: Unknown: write failed: No space left on device (28) in Unknown on line 0 Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/lib/php/sessions) in Unknown on line 0