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OpenSSH Config File Examples
Taken from:
System-wide SSH client configuration files
/etc/ssh/ssh_config : This files set the default configuration for all users of OpenSSH clients on that desktop/laptop and it must be readable by all users on the system.
User-specific SSH client configuration files
~/.ssh/config or $HOME/.ssh/config : This is user’s own configuration file which, overrides the settings in the global client configuration file, /etc/ssh/ssh_config.
~/.ssh/config file rules
The rules are as follows to create an ssh config file:
You need to edit ~/.ssh/config with a text editor such as vi.
One config parameter per line is allowed in the configuration file with the parameter name followed by its value or values. The syntax is:
config value
config1 value1 value2
You can use an equal sign (=) instead of whitespace between the parameter name and the values.
config1=value1 value2
All empty lines are ignored.
All lines starting with the hash (#) are ignored.
All values are case-sensitive, but parameter names are not.
Tip : If this is a brand new Linux, Apple OS X/Unix box, or if you have never used ssh before create the ~/.ssh/ directory first using the following syntax:
mkdir -p $HOME/.ssh
chmod 0700 $HOME/.ssh
For demonstration purpose my sample setup is as follows:
Local desktop client – Apple OS X or Ubuntu Linux.
Remote Unix server – OpenBSD server running latest OpenSSH server.
Remote OpenSSH server ip/host: (
Remote OpenSSH server user: nixcraft
Remote OpenSSH port: 4242
Local ssh private key file path : /nfs/shared/users/nixcraft/keys/server1/id_rsa
Based upon the above information my ssh command is as follows:
$ ssh -i /nfs/shared/users/nixcraft/keys/server1/id_rsa -p 4242
$ ssh -i /nfs/shared/users/nixcraft/keys/server1/id_rsa -p 4242 -l nixcraft
You can avoid typing all of the ssh command parameters while logging into a remote machine and/or for executing commands on a remote machine. All you have to do is create an ssh config file. Open the Terminal application and create your config file by typing the following command:
vi ~/.ssh/config
vi $HOME/.ssh/config
Add/Append the following config option for a shortcut to server1 as per our sample setup:
Host server1
User nixcraft
Port 4242
IdentityFile /nfs/shared/users/nixcraft/keys/server1/id_rsa
Save and close the file. To open your new SSH session to by typing the following command:
$ ssh server1
Adding another host
Append the following to your ~/.ssh/config file:
Host nas01
User root
IdentityFile ~/.ssh/nas01.key
You can simply type:
$ ssh nas01
Putting it all together
Here is my sample ~/.ssh/config file that explains and create, design, and evaluate different needs for remote access using ssh client:
### default for all ##
Host *
ForwardAgent no
ForwardX11 no
ForwardX11Trusted yes
User nixcraft
Port 22
Protocol 2
ServerAliveInterval 60
ServerAliveCountMax 30
## override as per host ##
Host server1
User nixcraft
Port 4242
IdentityFile /nfs/shared/users/nixcraft/keys/server1/id_rsa
## Home nas server ##
Host nas01
User root
IdentityFile ~/.ssh/nas01.key
## Login AWS Cloud ##
Host aws.apache
User wwwdata
IdentityFile ~/.ssh/aws.apache.key
## Login to internal lan server at via our public uk office ssh based gateway using ##
## $ ssh ##
Host uk.lan
User nixcraft
ProxyCommand ssh nc %h %p 2> /dev/null
## Our Us Proxy Server ##
## Forward all local port 3128 traffic to port 3128 on the remote server ##
## $ ssh -f -N proxyus ##
Host proxyus
User breakfree
IdentityFile ~/.ssh/
LocalForward 3128
Understanding ~/.ssh/config entries
Host : Defines for which host or hosts the configuration section applies. The section ends with a new Host section or the end of the file. A single * as a pattern can be used to provide global defaults for all hosts.
HostName : Specifies the real host name to log into. Numeric IP addresses are also permitted.
User : Defines the username for the SSH connection.
IdentityFile : Specifies a file from which the user’s DSA, ECDSA or DSA authentication identity is read. The default is ~/.ssh/identity for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa and ~/.ssh/id_rsa for protocol version 2.
ProxyCommand : Specifies the command to use to connect to the server. The command string extends to the end of the line, and is executed with the user’s shell. In the command string, any occurrence of %h will be substituted by the host name to connect, %p by the port, and %r by the remote user name. The command can be basically anything, and should read from its standard input and write to its standard output. This directive is useful in conjunction with nc(1) and its proxy support. For example, the following directive would connect via an HTTP proxy at
ProxyCommand /usr/bin/nc -X connect -x %h %p
LocalForward : Specifies that a TCP port on the local machine be forwarded over the secure channel to the specified host and port from the remote machine. The first argument must be [bind_address:]port and the second argument must be host:hostport.
Port : Specifies the port number to connect on the remote host.
Protocol : Specifies the protocol versions ssh(1) should support in order of preference. The possible values are 1 and 2.
ServerAliveInterval : Sets a timeout interval in seconds after which if no data has been received from the server, ssh(1) will send a message through the encrypted channel to request a response from the server. See blogpost “Open SSH Server connection drops out after few or N minutes of inactivity” for more information.
ServerAliveCountMax : Sets the number of server alive messages which may be sent without ssh(1) receiving any messages back from the server. If this threshold is reached while server alive messages are being sent, ssh will disconnect from the server, terminating the session.
A note about shell aliases (outdated method)
Warning examples may crash your computerWARNING! This bash shell aliased based setup may work out for you. However, I recommend that you use ~/.ssh/config file for better results in a long run. SSH config file is more advanced and elegant solutions. The alias command only used here for demo purpose and it is here due to historical reasons.
An alias is nothing but shortcut to commands and you can create the alias use the following syntax in your ~/.bashrc file:
alias server1="ssh -i /nfs/shared/users/nixcraft/keys/server1/id_rsa -p 4242"
Then, to ssh into the server1, instead of typing full ssh -i /nfs/shared/users/nixcraft/keys/server1/id_rsa -p 4242 command, you would only have to type the command ‘server1’ and press the [ENTER] key:
$ server1
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