Setting up public key authentication over SSH

January 18, 2006

Every time I want to setup public key authentication over SSH, I have to look it up, and I've never found a simple guide, so here's mine.

Generate key on local machine

ssh-keygen -t rsa

It will ask you for a password but you can leave it blank.

Note you could also pick -t dsa if you prefer.

Ensure that the remote server has a .ssh directory

Make sure the server your connecting to has a .ssh directory in your home directory. If it doesn't exist you can run the ssh-keygen command above, and it will create one with the correct permissions.

Copy your local public key to the remote server

If your remote server doesn't have a file called ~/.ssh/authorized_keys2 then we can create it. If that file already exists, you need to append to it instead of overwriting it, which the command below would do:

scp ~/.ssh/

Now ssh to the remote server

Now you can ssh to the remote server without entering your password.


Now keep in mind that all someone needs to login to the remote server, is the file on your local machine ~/.ssh/id_rsa, so make sure it is secure.

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38 people found this page useful, what do you think?


I followed the instructions but when i try to access the server ssh remote-server it is still asking for a passowrd. Does the username on the localmachine and the remote need to match. Thanks a million Nav
I too followed the instructions and have to still enter a password =( any help would be appreciated. thanks, Dan
You need authorization and identification files created there as well... identification contains line like IdKey _private_key_file_name_here_ authorization contains line like Key _private_key_file_name_here_ HTH, Alex
Instead of doing the scp try this (worked for me): cat ~/.ssh/ | ssh "cat - >> ~/.ssh/authorized_keys"
As the tutorial says run ssh-keygen command if .ssh doesnt exist in your home directory on the server. It didnt work when i created .ssh myself.
Thanks for the simple, straightforward tutorial. I hate looking through pages of text just to find out how to do something simple.
it's work.. example is very simple to understand
Hi, Thanks for a quick simple guide. I understood what I needed to do, just couldn't find a quick simple guide on doing it until I saw this. Great work.
I do not know if this command is available for Apple systems but most linux distros have a very quick way to do the "Copy your local public key to the remote server" step. ssh-copy-id -i user@host
Worked like a charm on Leopard, thanks!
if it doesn't work, perhaps you need to reconfigure the /etc/ssh/ssh_config file for Public Key authentication
For those who find it still asks for a password, one thing this tutorial forgets is that on the server you need to ensure the permissions of ~/.ssh and ~/.ssh/authorized_keys are secure: server$ chmod 700 ~/.ssh server$ chmod 600 ~/.ssh/authorized_keys That should sort out most problems. More info here:
Whoops, there should have been a line-break there: server$ chmod 700 ~/.ssh server$ chmod 600 ~/.ssh/authorized_keys
How would i go about doing this in a php script. So all i have to do is like input machine details and have it send the ssh key over to the remote machine automatically. i can code it in just having a problem, when i run scp filename user@ip:.ssh . How do i send the password via the php script when it asks. I tried doing a system command with the password but it doesn't work. Nor does it produce any kinda output. I am using the System() Php Function.
Came here after following other directions that didn't work.
here is script that does it for you automatically
Worked for me only after I ran on the host, even though there was already a .ssh directory. Great tutorial. Thanks!
Hi, if you want to configure ssh passwordless authentication,we can use following articale
Very good tutorial, straight to the point. I've used and worked without problems
Many thanks for the tutorial. It was easy to follow and to the point.
This works... Thank you, it used to be soo complex for me before, now I can login all my servers.
Thanks allot it works fine for me.
there is nothing really private in the authorized_keys file because, in fact, its a public key so there is no need for that chmod
This is by far the best guide I've seen. I too get confused by other guides.
DANGEROUS command!

It will overwrite already excising keys on the destination server.

ssh_copy_id is the best way
err: ssh-copy-id
Good guide, but found the file on server needed to be authorized_keys (not authorized_keys2).

Also, in response to harry who commented that there is no need to secure the file because it's a public key: You absolutely need to make sure this file is at least not writable by any other users (or they can simply append their keys to the file). As for why it shouldn't be readable by other users, that's just the first rule of security. If they don't need access, they don't have access.
Thanks Harry, this was just the quick reference I was looking for. Like Rhys though, I was wondering why you used authorized_keys2, rather than authorized_keys?

Anyway, cheers.
To those that still receive the password prompt. Make sure you are specifying the private key rather than the public key when logging in.
thanks for posting this - worked great for me after spending 15 min googling in circles..
Correcct command
scp ~/.ssh/
Thanks for the guide!It helped me out realy well...
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pete you're right, I always have to look this up too. thankfully your page is first on google for: ssh public key auth
I always forget how to do this.. worked first shot! Thanks!
if you don't reboot you probably need to ssh-add after doing ssh-keygen
Thanks Chris, Having the right permission of 600 and 700 definitely fixed the issue.

"For those who find it still asks for a password, one thing this tutorial forgets is that on the server you need to ensure the permissions of ~/.ssh and ~/.ssh/authorized_keys are secure:

server$ chmod 700 ~/.ssh server$ chmod 600 ~/.ssh/authorized_keys

That should sort out most problems. More info here: "
not sure that I have done this correct I have the keys in /home/admin/.shh/authorized_keys
what goes in the /etc/sshd_config file and where does it go please
I have chmod 600 the files in .ssh

Worked on my Snow Leopard install and Fedora Linux box. BUT, needed to do this to get it to work - thanks Niel!

server$ chmod 700 ~/.ssh server$ chmod 600 ~/.ssh/authorized_keys
make sure the permissions for
./ssh - 700
~/.ssh/authorized_keys - 644 isn't anymore, i stored an archive of the page here :
Dude, what do you mean when you say ~/.ssh/authorized_keys2? It should be "authorized_keys" without the "2".

And as some of the other guys pointed out: Be careful not to overwrite an existing file, but concat the new public key to the end of it, e.g. with cat ... >>.
Thanks for the instructions, works very good!

regarding authorized_keys or authorized_keys2 .. please check your sshd server config file , i.e. /etc/ssh/sshd_config , prameter AuthorizedKeysFile. It will tell you what file your sshd server is using:)))
On server1
zue$ ssh zue@server2 ----- working

root$ ssh root@server2 ----- not working

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