[erlang-questions] scp subsystem

Ingela Andin <>
Tue Mar 19 15:01:57 CET 2013


Hi!

2013/3/19, Stefan Jahn <>:
> dear erlang'ers,
>
> after reading some documentation on ssh otp system I ended up with:
>
>     ssh:daemon({0,0,0,0}, 45678, [{pwdfun, fun auth/2},
> %% create server keys:
> %% ssh-keygen -f /tmp/ssh/ssh_host_rsa_key -N '' -t rsa
> %% ssh-keygen -f /tmp/ssh/ssh_host_dsa_key -N '' -t dsa
> 				  {system_dir, "/tmp/ssh"},
> 				  {user_dir, "/tmp/ssh"},
> %				  {ssh_cli,{ssh_cli, {ssh_scpd, []}}},
> 				  {auth_methods, "keyboard-interactive,password"},
> 				  {subsystems, [
> 						ssh_scpd:subsystem_spec([])
> %						ssh_sftpd:subsystem_spec([{vsn, 3}])
> 					       ]}]).
>
> whereas the ssh_scpd module is base on the ssh_sftpd module from otp, i.e.
>
> -module(ssh_scpd).
> %-behaviour(ssh_daemon_channel).
> -behaviour(ssh_channel).
>
> -define(UINT32(X), X:32/unsigned-big-integer).
>
> %% External exports
> -export([subsystem_spec/1]).
>
> %% Callbacks
> -export([init/1, handle_ssh_msg/2, handle_msg/2, terminate/2,
> code_change/3]).
>
> implementing the callbacks similar to what we have in ssh_sftpd...
>
> now, when I start
>
> $ scp -P 45678 README :README
>
> authentification works fine as implemented in auth/2, but somehow
> the ssh channel behaviour is not used at all.
>
> 's password:
> {error,{1,erl_parse,["syntax error before: ",[]]}}
> $ Received disconnect from 127.0.0.1: 11: Application shutdown
>
> It seems like scp commands are send into the standard erlang shell (which
> I did not specify) and not into the channel.
>
> I am using R15B2.
>
> Could please someone help out here and give me some hint where to
> proceed reading?
>
> Also an abstract description of the difference between the purposes of
> ssh_cli and subsystems options would be appriciated.

ssh_cli is to customize the shell I do not think you want to use
ssh_cli at all. You should write your scp-deamon as subsystem and then
use an existing scp client to connect to it or
write your own erlang client that opens an ssh connection, requests
the ssh-scp subsystem and then sends scp commands on the channel along
the lines;

ssh:connect ...
ssh_connection:session_channel...
ssh_connection:subsystem...
ssh_connection:send...

The client can use the ssh_channel behavior.

Regards Ingela Erlang/OTP team Ericsson AB



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