the Fictionalrealm / Coding

If you’re a real geek, you might want to make an ssh client… using  php, well, this is something that no one will probably ever need to do… but if you’re reading this, maybe it happens so that you need it

So, to start with, there is a php extension called libssh2, and it’s really tricky to install it on some server configurations. I’m not going to discuss that part here because it’s purely server administration issue. I will just get to the coding part.

What we want to do here is to create php script that would run from console, will connect to remote ssh server, execute commands, and display output just like every ssh client does. The first problem is – libssh2 documentation on php site really sucks.

Connecting to remote server is easy:

$connection = ssh2_connect($host, 22);
ssh2_auth_password($connection, $user, $password);
$stream = ssh2_shell($connection);

What you do here is basically connect to remote server, and fetch a stream from ssh2_shell function which you will use to do IO operations.

Now here comes the tricky part, according to the manual, the way you do an output to ssh (like execute a command) is to call ssh2_exec function, but this doesn’t really work well. When you do output using that command,  your ssh stream gets reset, and you can’t just continue writing new commands that will work based on previous command. It’s like this – you cant do a “cd” command and then “ls”, cause “ls” will show contents of folder that was shown before you did “cd” (the logged in users home folder). Anyway here is the way I solved it:

You can use simple fwrite() function to work with your $stream variable,  like this

fwrite($stream, $command."\n");

Now getting to the fetching output part, it might sound weird but don’t use fread() here To get the server’s output you should use stream_get_contents function instead of fread. If you do – it works perfectly. Just keep in mind that server output will not appear immediately,  you need to wait for it (do a loop).

So this is nearly all you need to know to setup and maintain a simple ssh2 connection, execute commands, and get output in one session.

Here are some other aspects you might have problems with:

First of all, the obvious one, what if you typed a command like ping or top or something that is going to end only if you press, the Ctr+C keys? the way to imitate the Ctr+C combination is pretty easy, this combination actually sends a signal to the system that’s terminating the current process, and it’s just….. number 3 character in ASCII table (Bingo! )

It’s one of so called ETX signals (like end of text)

fwrite($stream, chr(3));

You do this command, and ping or top or whatever it is – terminates.

Next thing, I want to tell you is that in ANSI terminal there is not only text, you can have Midnight Commander ( mc ) which is nice and coloured, and htop and lot’s of others, how does that work?

Very simple! There’s an ANSI mode for terminal which is getting some other types of signals, like not only text but “go to next line” or “set foreground colour to green” e.g. I’m not going to go through the aspects of ANSI terminal, I will just explain how to enable it on libssh2 because by default it is using simple text mode and output of htop command will be more than weird.

And again it’s not explained in the manual in any imaginable way, but here is how you do it:

$stream = ssh2_shell($connection, 'ansi');

PHP Manual says that it’s possible to give the ANSI parameter to ssh2_exec, but in our case we do not use it (we had problems with the library when trying to implement this) so it appears, through not discussed in manual, that you can pass that parameter to ssh2_shell function as well and when using that stream you will get output in “ANSI” way. You just need to make sure you parse it correctly and display to end user as it’s supposed to be.

So that’s mainly it about creating this stuff using PHP, feel free to ask if you had any issues, or discovered some other methods