Configuring OpenSSH ssh configuration files

Configuring OpenSSH

⁠14.2.1. Configuration Files

There are two different sets of configuration files: those for client programs (that is, ssh, scp, and sftp), and those for the server (the sshd daemon).

System-wide SSH configuration information is stored in the /etc/ssh/ directory as described in Table 14.1, “System-wide configuration files”. User-specific SSH configuration information is stored in ~/.ssh/ within the user's home directory as described in Table 14.2, “User-specific configuration files”.

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Table 14.1. System-wide configuration files

File	Description
/etc/ssh/moduli	Contains Diffie-Hellman groups used for the Diffie-Hellman key exchange which is critical for constructing a secure transport layer. When keys are exchanged at the beginning of an SSH session, a shared, secret value is created which cannot be determined by either party alone. This value is then used to provide host authentication.
/etc/ssh/ssh_config	The default SSH client configuration file. Note that it is overridden by ~/.ssh/config if it exists.
/etc/ssh/sshd_config	The configuration file for the sshd daemon.
/etc/ssh/ssh_host_dsa_key	The DSA private key used by the sshd daemon.
/etc/ssh/ssh_host_dsa_key.pub	The DSA public key used by the sshd daemon.
/etc/ssh/ssh_host_key	The RSA private key used by the sshd daemon for version 1 of the SSH protocol.
/etc/ssh/ssh_host_key.pub	The RSA public key used by the sshd daemon for version 1 of the SSH protocol.
/etc/ssh/ssh_host_rsa_key	The RSA private key used by the sshd daemon for version 2 of the SSH protocol.
/etc/ssh/ssh_host_rsa_key.pub	The RSA public key used by the sshd daemon for version 2 of the SSH protocol.
/etc/pam.d/sshd	The PAM configuration file for the sshd daemon.
/etc/sysconfig/sshd	Configuration file for the sshd service.

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Table 14.2. User-specific configuration files

File	Description
~/.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.
~/.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. This file is very important for ensuring that the SSH client is connecting the correct SSH server.

For information concerning various directives that can be used in the SSH configuration files, see the