By default, ssh searches for
id_rsa files. The keys do not have to be named like this, you can name it
mykey just as well, or even place it in a different directory. However, if you do either of those, then you need to explicitly reference the key in the ssh command like so:
ssh user@server -i /path/to/mykey
If a command does not accept
sshfs, use the
sshfs -o IdentityFile=/path/to/mykey user@host:/path/on/remote /mountpoint
How It Works
When generating a key, you'll get two files:
id_rsa (private key) and
id_rsa.pub (public key). As their names suggest, the private key should be kept secret and the public key can be published to the public.
Public-key authentication works with a public and a private key. Both the client and the server have their own keys. When installing
openssh-server the server public and private keys are generated automatically. For the client, you'll have to do that on your own.
When you (client) connect with a server, public keys are exchanged. You'll receive the servers one, and the server yours. The first time you receive the server public key, you'll be asked to accept it. If this public key changes over a time, you'll be warned because a possible MITM (Man in the middle) attack is going on, intercepting the traffic between the client and the server.
The server checks whether you are allowed to connect (defined in
/etc/ssh/sshd_config) and if your public key is listed in the
~/.ssh/authorized_keys file. Possible reasons why the public key is denied:
AllowGroups is specified, but your server user is not listed in the groups or users list (default not defined, placing no restriction on the users or groups from logging in).
DenyGroups is specified and you're in the users or groups list.
- You're trying to login as root, but
PermitRootLogin is set to
PubkeyAuthentication is set to
AuthorizedKeysFile is set to a different location, and the public keys are not added to that file (default
.ssh/authorized_keys, relative to home dir)
~/.ssh/authorized_keys: your public key is not added in this file (note that this file is read as root user)
Using multiple keys
It's not uncommon to use multiple keys. Instead of running
ssh user@host -i /path/to/identity_file, you can use a configuration file,
Common settings are the IdentityFile (the keys) and port. The next configuration will check "id_dsa" and "bender" only when connecting with
If you omit
Host yourhost, the settings will apply to all SSH connections. Other options can also be specified for this host match, like
Port 2222, etc. This would allow you to connect with the shorthand
ssh yourhost instead of
ssh -p2222 youruser@yourhost -i ~/.ssh/id_dsa -i ~/.ssh/bender.