SSH config files and commands

ssh_config - OpenSSH SSH client configuration files

List of Configuration files

For Key purposes

~/.ssh/id_dsa          Contains the DSA private key of the user.

~/.ssh/id_dsa.pub   The DSA public key of the user.

~/.ssh/id_rsa           The RSA private key used by ssh for version 2 of the SSH protocol.

~/.ssh/id_rsa.pub    The RSA public key used by ssh for version 2 of the SSH protocol.

~/.ssh/identity          The RSA private key used by ssh for version 1 of the SSH protocol.

~/.ssh/identity.pub   The RSA public key used by ssh for version 1 of the SSH protocol.

~/.ssh/known_hosts Contains DSA host keys of SSH servers accessed by the user. 

For Configuration purposes

a) ssh_config  - SSH client configuration file (i.e. is used by the ssh program itself). 

b) sshd_config - SSH daemon configuration file (i.e. is used by sshd)

c) /etc/pam.d/sshd- The PAM configuration file for the sshd daemon.

d) /etc/sysconfig/sshd  - Configuration file for the sshd service.

User-specific configuration files

a) ~/.ssh/authorized_keys      Holds a list of authorized public keys for servers. When the client connects to a server, the server authenticates the client by checking its signed public key stored within this file.

More info About configuration files

ssh_config: configuration file for the ssh client on the host machine you are running. For example, if you want to ssh to another remote host machine, you use a SSH client. Every settings for this SSH client will be using ssh_config, such as port number, protocol version and encryption/MAC algorithms.

sshd_config: configuration file for the sshd daemon (the program that listens to any incoming connection request to the ssh port) on the host machine. That is to say, if someone wants to connect to your host machine via SSH, their SSH client settings must match your sshd_config settings in order to communicate with you, such as port number, version and so on.

For example, most times we change the SSH port number for security reason. Take an example as follows:

For the SSH port number, ssh_config is manually set to be 1000 (decided by the remote host), sshd_config is set to be 5555. If anyone wants to connect to your host, they MUST set their ssh client port always to 1000. However, you will always use port 5555 as the default port (instead of the 22) to connect to a remote machine. If the remote machine uses another port or the standard port, you need to specify the port number in the command line,

ssh is the command you use to connect to remote machines - the client.

sshd is the daemon that is running and allows others to connect to the machine - the server.

Table 14.2. User-specific configuration files

You can edit the /etc/sysconfig/sshd file and change the AUTOCREATE_SERVER_KEYS variable:

AUTOCREATE_SERVER_KEYS=NO

or

AUTOCREATE_SERVER_KEYS=RSAONLY

Table 14.2. User-specific configuration files

1) ssh-copy-id

ssh-copy-id - install your public key in a remote machine’s authorized_keys

ssh-copy-id [-i [identity_file]] [user@]machine

ssh-copy-id  is  a  script that uses ssh to log into a remote machine (presumably using a login password, so password authentication should be enabled, unless you’ve done some clever use of multiple identiies) It also changes the permissions of the remote user’s home, ~/.ssh, and ~/.ssh/authorized_keys to remove group writability (which would otherwise prevent you from logging in.

1) sshYou can edit the /etc/sysconfig/sshd file and change the AUTOCREATE_SERVER_KEYS variable:

AUTOCREATE_SERVER_KEYS=NO

or

AUTOCREATE_SERVER_KEYS=RSAONLY