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Reference Manual
Version 4.0

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The ssh application implements the Secure Shell (SSH) protocol and provides an SSH File Transfer Protocol (SFTP) client and server.


The ssh application is an implementation of the SSH protocol in Erlang. ssh offers API functions to write customized SSH clients and servers as well as making the Erlang shell available over SSH. An SFTP client, ssh_sftp, and server, ssh_sftpd, are also included.


The ssh application uses the applications public_key and crypto to handle public keys and encryption. Hence, these applications must be loaded for the ssh application to work. In an embedded environment this means that they must be started with application:start/[1,2] before the ssh application is started.


The ssh application does not have an application- specific configuration file, as described in application(3). However, by default it use the following configuration files from OpenSSH:

  • known_hosts
  • authorized_keys
  • authorized_keys2
  • id_dsa
  • id_rsa
  • ssh_host_dsa_key
  • ssh_host_rsa_key

By default, ssh looks for id_dsa, id_rsa, known_hosts, and authorized_keys in ~/.ssh, and for the host key files in /etc/ssh. These locations can be changed by the options user_dir and system_dir.

Public key handling can also be customized through a callback module that implements the behaviors ssh_client_key_api and ssh_server_key_api.

Public Keys

id_dsa and id_rsa are the users private key files. Notice that the public key is part of the private key so the ssh application does not use the id_<*>.pub files. These are for the user's convenience when it is needed to convey the user's public key.

Known Hosts

The known_hosts file contains a list of approved servers and their public keys. Once a server is listed, it can be verified without user interaction.

Authorized Keys

The authorized_key file keeps track of the user's authorized public keys. The most common use of this file is to let users log in without entering their password, which is supported by the Erlang ssh daemon.

Host Keys

RSA and DSA host keys are supported and are expected to be found in files named ssh_host_rsa_key and ssh_host_dsa_key.


The ssh application uses the default OTP error logger to log unexpected errors or print information about special events.