Pietro Battiston

reachme and reachthem are two python programs which simplify the operation of logging in to a remote machine without a public address.

Notice that in order to do so, a machine with public address is needed.

So here are the ingredients:

• a machine A which cannot be reached from the net
• a machine B which can be reached from the net
• a machine C from which you want to reach A

If this sounds complicated, think to it as “LogMeIn except that you, not LogMeIn, provide B”.

And this is how you use it:

• reachme is run on A
• reachthem is run on C, sees there is a connection to A available, and allows the user of C to connect to A.

There is nothing very new or complicated in this: it just uses SSH port forwarding, a classic (and pretty safe) tool. reachme and reachthem make the process just a bit simpler, in particular if the user of A is technically not very sophisticated.

• A is a computer in your office which you always want to be able to reach from anywhere. Unfortunately, it is behind a NAT. B is a server of your company which instead has a public IP.
• A is your boyfriend/girlfriend/mother/grandmother/father/grandfather/sister/brother's¹⁾ computer, on which you installed Ubuntu some months ago. Now he/she needs to install a package, and he/she has no idea of how to do. B is your cheap VPS somewhere.

• Install reachme (or reachme-light, if it is a server) on A, and create a file ~/.config/reachme/force_config with content

{'IP': 'example.com',
 'uname': 'piero',
 'port': '1333',
 'check_every': '30'}

• Install reachthem (and reachme, on which it depends) on C (replace “example.com” with the IP or address of B)
• Set up SSH keys²⁾ such that C is allowed passwordless access to A, and both A (with the username mentioned in the above configuration file, which you will probably want to be an ad-hoc user, with limited rights!) and C are allowed passwordless access to B (this is the only operation which must be done manually on B; things may change in the future).
• (Tell your loved one to) start reachme on A
• Start reachthem on B, and fill the fields Address (of B) and Username (on B) (as well as Sshd port if it is different than 22). Then retrieve the list of “Available hosts”. A should appear: click on it, and then click Open shell

Download the above packages for Ubuntu/Debian, or clone the git repo:

git clone https://gitlab.com/pbat/reachme.git

(both reachme and reachthem can be ran from the repo, without installing them).

In order to reach a server at any time, you will presumably want to add a crontab line (with crontab -e) such as

    */10 * * * * reachme --daemon

Currently, probably screen access. Terminal, filesystem access and port forwarding should work.