I have a Redmine installed on CentOS without GUI. I changed email configuration and a reboot is necessary.
How to restart redmine from command line?
Restarting Apache (if you use passenger) sometimes does not make desired effect. You can restart Redmine with creating a file:
<redmineHomeDir>/tmp/restart.txt
with content "restart". Anytime you want to restart Redmine, just "touch" this file to change its time-stamp.
touch <redmineHomeDir>/tmp/restart.txt
Redmine will restart at the next page request. This solution can be found on Redmine forums or user blogs (e.g. http://texdex.blogspot.com/2011/03/restarting-redmine-without-restarting.html)