simplesshd

Overview ¶

Command simplesshd provides a simple ssh daemon that works similar to OpenSSH. It accepts connections on port 2222 from any interface by default.

This command is not intended to be used in production. The various defaults are unsafe. It exists to demonstrate the functionality of the proxyssh package.

Overview ¶

When a connection is received no authentication is performed and it is accepted by default.

When an SSH client requests a session this daemon executes a shell command. By default, the shell used is /bin/bash, but this can be configured. This shell command is executed as the user running the simplesshd command. When arguments are provided via the ssh command, these are passed to the command. When the client requests to allocate a pty, a pty is created. The daemon then proxies the input and output streams between the connection and the executed process.

This daemon furthermore allows Port Forwarding and Reverse Port Forwarding. This is only allowed to a limited set of Network Addresses, these have to be provided via arguments.

Configuration ¶

All configuration is performed using command line flags.

-port hostname:port

By default connections on any interface on port 2222 will be accepted. This can be changed using this argument.

-shell executable

When executing a user program the '/bin/bash' shell is used by default. This argument allows to use a different shell instead. The shell is looked up in $PATH.

When an ssh session is started without a provided command, proxyssh starts the shell without any arguments. When the user provides a command to run, it is passed to the shell using a '-c' argument. For example, suppose the shell is /bin/bash and the user requests the command 'ls -alh'. Then this program will execute the command:

/bin/bash -c "ls -alh"

No escaping is performed on the user-provided shell command.

-L host:port, -R host:port

To configure the ports to allow traffic to and from certain hosts in the local network via the ssh server, the '-L' and '-R' flags can be used. '-L' enables the ssh client to send connections to the provided host:port combination. '-R' enables the reverse, enabling the ssh client to accept connections at the provided host and port. Both flags can be passed multiple times.

-hostkey prefix

Te daemon supports two kinds of ssh host keys, an RSA and an ED25519 key. By default these are stored in two files called 'hostkey.pem_rsa' and 'hostkey.pem_ed25519' in the working directory of the simplesshd process. If either of these files do not exist, they are generated when the program runs for the first time.

It is possible to customize where these files are stored. Using this argument their prefix (by default 'hostkey.pem') can be set.

-timeout time

By default, SSH connections are terminated after one hour of inactivity. This timeout can be customized using this flag. The time argument should be a sequence of numbers follows by their units. Valid units are "ns", "us", "ms", "s", "m" and "h". See also golang's time.ParseDuration function.