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SSH config tips

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ssh DevOps

SSH config file
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~/.ssh/config file can be very useful to configure settings for your ssh connections.

For example you may configure default User and IdentityFile for a domain using.

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Host example.com
   IdentityFile /path/to/identityfile
   User defaultUserName

Multiple Identities on same server
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I use trick for configuring multiple identities on Bitbucket server.

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Host personal.bitbucket.org
   HostName bitbucket.org
   User git
   IdentityFile ~/.ssh/id_rsa

Host work.bitbucket.org
   HostName bitbucket.org
   User git
   IdentityFile ~/.ssh/id_rsa_work

And you need to use personal.bitbucket.org and work.bitbucket.org when you want to ssh into them.

Bitbucket has wild card domain redirection, that’s why this works for Bitbucket.

For other domains, you may need to add an entry into /etc/hosts.

Specify Port
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If you have configured your SSH server to use a different port instead of 22, lets say 2222

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Host my.server.fqdn
   Port 2222

Force password authentication
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You can force Password Authentication by using

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ssh -o PreferredAuthentications=password -o PubkeyAuthentication=no user@host

Port forwarding
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This is my favourite of all.

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ssh -L 9000:mydb.host:9000 [email protected]

This can be very useful for accessing a port behind a firewall, may be for database.

If you are using AWS EMR or Hortworks Sanbdox, then you will need access to more than one port through ssh.

Using -L command line option can be very lengthy, instead you could use LocalForward directive in the ~/.ssh/config

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# This will allow us to use port 8080 on the local machine
# in order to access example.com at port 80 from the remote machine
Host local_to_remote
    LocalForward 8080 example.com:80

# This will allow us to offer access to internal.com at port 443
# to the remote machine through port 7777 on the other side
Host remote_to_local
    RemoteForward 7777 internal.com:443

References
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