5.1.1. HOWTO Customize Settings for SSH

By default, SIMP includes the ssh class from the simp/ssh module under most of the SIMP scenarios. If it is absent from the scenario you have selected, add the following to Hiera to include the class:

  - 'ssh'

To exclude the SIMP ssh class so that you can manage SSH configuration by other means, refer to Disable SSH Management.

The SIMP ssh class is configured to automatically include the ssh::server and ssh::client classes. These classes, in turn, manage the SSH daemon settings for incoming connections and the SSH client settings for outgoing connections, respectively. They configure SSH with reasonable defaults for the OS and environment.

If you want to disable SIMP management of either the SSH server or client settings, you can do so through Hiera. For example, to disable SIMP management of both:

ssh::enable_client: false
ssh::enable_server: false Managing Settings for the SSH Server

The ssh::server class is responsible for configuring sshd. It delegates configuration of specific sshd settings found in sshd_config to ssh::server::conf. Detailed descriptions of the these settings are provided in the sshd_config(5) man page.

The ssh::server::conf class uses a number of SIMP-specific parameters, such as whether the system is FIPS enabled, has a firewall, or utilizes LDAP. This allows seamless integration of SSH with other SIMP-managed applications in the larger SIMP environment. For example, ssh::server::conf ensures the appropriate fallback ciphers are used, ensures proper authentication is configured, and allows SSH traffic through the firewall. More detailed information is provided in the simp/ssh module README file. Configuring ssh::server::conf from Hiera

ssh::server::conf provides default configuration for key sshd_config settings and a mechanism to set most other settings.

To customize the SSH server, edit the parameters of ssh::server::conf using Hiera or ENC.


Unlike many SIMP modules, these customizations cannot be made directly with a resource-style class declaration ― they must be made via automatic parameter lookup provided by Hiera or an ENC. Examples using Hiera are provided for illustrative purposes.

In Hiera:

ssh::server::conf::port: 2222
ssh::server::conf::passwordauthentication: false

Starting with version 6.8.0 of the simp/ssh module, multiple ports can be specified to listen for incoming SSH connections. So the ssh::server::conf::port parameter in the previous example could be set as follows in Hiera to listen on multiple ports:

ssh::server::conf::port: [22, 2222, 22222] Managing Additional Settings with sshd_config

Starting with version 6.7.0 of the simp/ssh module, you can manage additional settings not explicitly mapped to ssh::server::conf parameters, using the ssh::server::conf::custom_entries parameter. For example, to specify configuration for AllowAgentForwarding and AuthorizedPrincipalsCommand sshd settings, you would include Hiera such as the following:

  AllowAgentForwarding: "yes"
  AuthorizedPrincipalsCommand: "/usr/local/bin/my_command"

There are a few limitations with ssh::server::conf::custom_entries that need to be noted:

  • No setting validation:
    This parameter is not validated. Be careful to only specify settings that are allowed for your particular SSH daemon and avoid duplicate declaration of settings already specified. Invalid options may cause the sshd service to fail on restart. Duplicate settings will result in duplicate Puppet resources (i.e., manifest compilation failures).
  • No direct MATCH entry support:
    Due to their complexity, Match entries are not supported. However, you can add them using the sshd_config_match resource from the herculesteam-augeasproviders_ssh module. Since simp/ssh uses this module internally, the sshd_config_match resource will be available to you on any node using simp/ssh. Managing Settings for the SSH Client

The ssh::client class is responsible for configuring default client settings for outgoing SSH sessions to all hosts (Host *). Managing Settings for the Default Host Entry (Host *)

If you want to customize the default settings, you must prevent ssh::client from declaring them automatically and then declare Host * settings manually. You do this by setting ssh::client::add_default_entry to false and using the defined type ssh::client::host_config_entry. For example:

In Hiera:

ssh::client::add_default_entry: false

In Puppet:

ssh::client::host_config_entry{ '*':
  gssapiauthentication      => true,
  gssapikeyexchange         => true,
  gssapidelegatecredentials => true,
} Managing Client Settings for Specific Hosts

Different settings for particular hosts can be managed by using the defined type ssh::client::host_config_entry:

# `ancient.switch.fqdn` only understands old ciphers:
ssh::client::host_config_entry { 'ancient.switch.fqdn':
  ciphers => [ 'aes128-cbc', '3des-cbc' ],
} Managing Additional Settings with ssh_config

Starting with version 6.4.0 of the simp/ssh module, you can use the ssh_config resource from the herculesteam-augeasproviders_ssh module to manage settings that the module does not cover.

For instance, to ensure that the default host entry’s RequestTTY option is set to auto:

# RequestTTY is not managed by ssh::client::host_config_entry
ssh_config { 'Global RequestTTY':
  ensure => present,
  key    => 'RequestTTY',
  value  => 'auto',