After installing FogBugz on Ubuntu 12.04 LTS, you may receive the following error when trying to access your FogBugz site:
Service Temporarily Unavailable
The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

Additionally, you may see errors like the following in [Your FogBugz installation directory]/logs/error.log:

[crit] (22)Invalid argument: Failed to set mutex permissions for /tmp/fogbugz_dashboard_XXGLOBAL_1.lock
[emerg] (22)Invalid argument: Couldn't set permissions on cross-process lock; check User and Group directives

To resolve this error, add a Group directive to [Your FogBugz installation directory]/conf/httpd.conf:

Group [Your FogBugz user]

Then, restart FogBugz:

sudo [Your FogBugz installation directory]/bin/restart-fogbugz