My case goes like this.

I installed bitnami redmine first with port 80 for http service, but got problems and failed. 

However, when I tried to give a second shot, I was told that port 80 was not available, so instead I used port 81. The app, redmine, worked fine with an IP addr + port 81.

but recently as I want to install bitnami wordpress upon the bitnami stack, the domain has to go with the port 81, which seems really ugly.  

so I decided to change the port 81 back to 80, the default port http used. Here are the steps to follow.

1. find the 80 port user, stop it

a couple of tools can be found in this page.

netstat -tulpn | grep :80

the output could be like:

tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      1607/apache2

kill the PID 1607 or stop the httpd service.

2. change the port in the configure files

2.1 find the bitnami http.conf file

should be in the apache2/conf/ folder

>vim httpd.conf#Listen 12.34.56.78:80Listen 80

change the linstenning port to 80.

2.2 find the bitnami.conf

should be in the /apache2/conf/bitnami/ folder

>vim bitnami.conf<IfVersion < 2.3 >  NameVirtualHost *:80  NameVirtualHost *:444</IfVersion><VirtualHost _default_:80>  DocumentRoot "/opt/redmine/apache2/htdocs"  <Directory "/opt/redmine/apache2/htdocs">

change the, NameVirtualHost, VirtualHost _default_,   into 80.

3. restart bitnami stack

ctlscript.sh restart

now the httpd port was reset to the default 80 again.

Tricky thing here is that you use bitnami stack, if you only change the httpd.conf, it won‘t work.

blog written in linux os.