HOWTO Create SSH Config file

HOWTO CREATE config FOR SSH PRE-DEFINED INFORMATION

The config file is located in your ~/.ssh directory and hold specific

variables for your ssh connections. One example is ssh into a non-standard

port, or to always attempt to use -X for X11 forwarding.

Adding info for encryption types and an example of howto automatically

forward through computer B into C.

The basic layout of the config file is as follows:

Host	ANY_URL
	Port		22222
. ## note ignore the ., this is just for wiki formatting to keep the space without creating a new code block
Host	<IP_ANY_URL>
	Port		22222
. ## note ignore the ., this is just for wiki formatting to keep the space without creating a new code block
Host	*
	Protocol	        2
	ForwardAgent	        yes
	ForwardX11	        yes
	ServeraliveInterval	30
	ServerAliveCountMax	5
	TCPKeepAlive	        yes
. ## note ignore the ., this is just for wiki formatting to keep the space without creating a new code block
Host	Server_C
       User	server_c_user
       ProxyCommand ssh -qax -W %h:%p URL_Server_B
       Ciphers aes256-ctr,aes256-cbc

The first "Host" is the fully qualified domain name ie: google.com. For this connection

we are defining port 22222 as the standard port for this connection. Now instead of typing:

[user@server ~]$ ssh -p 22222 user@ANY_URL

You can now just type:

[user@server ~]$ ssh user@ANY_URL

This is real handy for scp and other options like ssh-copy-id that can be a royal pain for

non-standard ports.

The second "Host" is the IP address of the fully qualified domain name of the first "Host".

Always better safe then sorry. It is not required, but if for some reason your DNS is not working 100%, this will be a way around said issue. Great in LANs as well as WWW connections.

The third "Host" in the above example is for all connections. We are stating use protocol vs. 2

over 1. Always attempt to use X11 forwarding.

The fourth "Host" in the above example is for forwarding your ssh connection from the outside facing computer into a 2nd system that is NOT directly accessible via a straight ssh from the WWW. This is used like the following...

[user@server_A ~]$ ssh Server_C
Last login: Sun Jul 27 15:36:26 2014 from user_server_A
[server_C_user@Server_C ~]$ 

Once you have created this file you will need to verify the permissions and that it is locaed

in the correct directory.

[user@server ~]$ ls -laF .ssh
total 48
drwx------.  2 user user 4096 Mar 14 15:23 ./
drwx------. 17 user user 4096 Mar 29 19:40 ../
-rw-------.  1 user user 4466 Mar 12 10:30 authorized_keys
-rw-r--r--.  1 user user  175 Jan  5 12:23 config
-r--------.  1 user user 3243 Jan  5 12:14 id_rsa
-rw-r--r--.  1 user user  741 Jan  5 12:14 id_rsa.pub
-rw-r--r--.  1 user user 1447 Mar 14 15:23 known_hosts

Without these permissions your config file will fail. This will work in both Linux and OSx.