Tested under Ubuntu 14.04.2 LTS
Add proxies in /etc/environment
$ sudo vi /etc/environment
# Proxies
http_proxy="http://proxy.server.com:port/"
https_proxy=$http_proxy
ftp_proxy=$http_proxy
rsync_proxy=$http_proxy
no_proxy="localhost,127.0.0.1,localaddress,.localdomain.com"
Add proxies in /etc/sudoers. It is to keep proxies working when execute command via sudo.
$ sudo vi /etc/sudoers
Defaults env_keep +="http_proxy"
Defaults env_keep +="https_proxy"
Defaults env_keep +="ftp_proxy"
Add proxies in /etc/apt/apt.conf
$ sudo vi /etc/apt/apt.conf
# Proxy
Acquire::http::Proxy "http://proxy.server.com:port/";
Use --http-proxy to specify proxy.
$ sudo gem install --http-proxy http://proxy.server.com:port/ tmuxinator
$ git config --global http.proxy http://proxy.server.com:port/
$ git config --global https.proxy http://proxy.server.com:port/