How to use a proxy for common applications

Global environment
Set the HTTP_PROXY environment variable

export HTTP_PROXY=http://username:password@proxy.server:port/  

apt
Create the file /etc/apt/apt.conf.d/43proxy and place the line below (be sure to provide the appropriate proxy information):

Acquire::http::Proxy "http://username:password@proxy.server:port/";

wget
Set the proxy settings in /etc/wgetrc

http_proxy=http://server_ip:port

git
Use the command below:

git config --global http.proxy http://username:password@proxy.server:port/

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SSH without user-known hosts checking

If the IP address of the host you are connecting to frequently changes, as in the case of cloud instances, but you are sure that that you are connecting to the correct host, you can use the following ssh command to disable known host checking (Note: This may lead to MITM attacks).

ssh -o UserKnownHostsFile=/dev/null user@10.0.3.x 

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