Fix Shellinabox "rhostsrsaauthentication" and "rsaauthentication" errors

ShellInABox is a tidy little app that works well, but when you configure it to connect via SSH directly instead of using its internal shell, it throws up a couple minor errors when logging in:

command-line line 0: unsupported option "rhostsrsaauthentication"
command-line line 0: unsupported option "rsaauthentication"

You can safely ignore these two notices, but if you want to remove them, here's how to do it:

Stop the currently running service.

sudo service shellinabox stop

Install git, nano, and some tools needed during compiling code:

sudo apt install git nano autoconf dh-autoreconf libssl-dev

Pull the current shellinabox code down from the github repository:

git clone

Change directory into the folder you just created:

cd shellinabox

Open the service.c file for editing with nano:

sudo nano shellinabox/service.c

Scroll down or use CTRL-W to find and comment these two lines by placing // in front of the lines:

"-oPubkeyAuthentication=no -oRhostsRSAAuthentication=no "
"-oRSAAuthentication=no -oStrictHostKeyChecking=no -oTunnel=no "

Replace those two lines with this single line, placing it immediately below:

"-oPubkeyAuthentication=no -oStrictHostKeyChecking=no -oTunnel=no "

It will look like this in the file; you can see we've removed the two items which throw the errors:

//"-oPubkeyAuthentication=no -oRhostsRSAAuthentication=no "
//"-oRSAAuthentication=no -oStrictHostKeyChecking=no -oTunnel=no "
"-oPubkeyAuthentication=no -oStrictHostKeyChecking=no -oTunnel=no "

Ctrl-X to exit, save the file. Then configure and compile the code with these 3 commands:

autoreconf -i
./configure --disable-runtime-loading

(You can research issues with disable-runtime-loading if you want to use runtime loading.)
Overwrite the existing shellinaboxd binary file with the one you just created:

sudo cp shellinaboxd /usr/bin

Start the service:

sudo service shellinabox start

Now when you log in via SSH you'll see no errors.

Posted in Developing Software on Jun 27, 2021

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