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Kermit is one of those things I'm fond of that's really hard to describe. It is:
2: https://www.kermitproject.org/ckscripts.html
You can download kermit for dozens of platforms[3], many of which are decades out of date. They all interoperate. It is rather impressive. In fact, a new version of Kermit for TOPS-20[4] was released in June 2023! (TOPS-20 was active between 1976 and 1988).
3: http://www.columbia.edu/kermit/archive.html
4: https://kermitproject.org/kermit-20.html
There are many Kermit implementations; this page is primarily about CKermit, the most up-to-date and featureful implementation for *nix. For many years, CKermit wasn't fully open-source, but since 2011, has been released under a BSD license.
I operate the quux.org Kermit Server[5] - open to the public for you to experiment with!
The author's About Kermit[6] page gives a lot of detail about the program.
6: https://www.kermitproject.org/kermit.html
Kermit is an example of Old and Small Technology[7]. I wrote about it in Try the Last Internet Kermit Server[8].
8: /try-the-last-internet-kermit-server/
You can very easily use something like this:
kermit -C 'ssh user@host'
Now, you are logged in to the remote host, using the same OpenSSH you always use. You can happily do all your work as usual. Now let's say you're at the shell, you've been editing a file on the remote end, and you'd like to copy it to your local machine.
In a traditional setup, you'd open a new local window, then have to copy the full path name and run scp to bring it across. With Kermit, you can just type this at your shell prompt:
kermit -Iis filename.tar.gz
It will send a special byte sequence that your local kermit will pick up on, and enter transfer mode. The file will be transferred, complete with integrity checking. Then you'll be right back at your shell.
You can even send directories:
cd /usr/share/doc kermit -Ii -C 'send /recursive libthreadar-dev, exit'
Here we gave a short Kermit script with `-C`. `send` is a Kermit command, and this tells it to send the file, then exit.
Kermit has these modes:
You can flip between modes:
Kermit also has a feature where it will automatically start server mode on the remote. Here's an example:
jgoerzen@hephaestus:/tmp/t$ kermit C-Kermit 10.0 Beta.08, 15 Dec 2022, for Linux+SSL (64-bit) Copyright (C) 1985, 2022, Trustees of Columbia University in the City of New York. Open Source 3-clause BSD license since 2011. Type ? or HELP for help. (/tmp/t/) C-Kermit>
OK, I've launched kermit. Here I am in command mode with my local user. Let's ssh to the remote; that will put me into connect mode:
(/tmp/t/) C-Kermit>ssh auxuser@localhost Connecting via command "ssh -e none auxuser@localhost" Escape character: Ctrl-\ (ASCII 28, FS): enabled Type the escape character followed by C to get back, or followed by ? to see other options. ---------------------------------------------------- auxuser@hephaestus:~$
OK, now I'm in connect mode. I can send a file:
auxuser@hephaestus:~$ kermit -Iis /bin/sh Return to your local Kermit and give a RECEIVE command. KERMIT READY TO SEND... ---------------------------------------------------- ---------------------------------------------------- SENT: [/usr/bin/dash] To: [/tmp/t/sh] (OK) auxuser@hephaestus:~$
I didn't actually have to give the receive command, because my local kermit saw the special sequence to initiate a transfer, and automatically jumped into transfer mode.
Now let's go into command mode and do some stuff. I'll hit Ctrl-\ and then press c.
(/tmp/t/) C-Kermit>rpwd /home/auxuser
So we see the current working directory on the remote. But wait a minute, `rpwd` (aka `remote pwd`) uses the kermit protocol, but at the remote I was just at the shell. What happened?
Kermit was smart enough to know there wasn't a kermit connection running, so it just sent `kermit -x` to the remote, placing it in server mode. Clever!
I can even do something like this:
(/tmp/t/) C-Kermit>get /usr/bin/bzip2
Since all these transfers are on my local machine, they're so fast I don't even see the transfer-in-progress status screen. Rest assured it does exist and you'll see it on slower connections.
Now, I could type `connect` (or just `c`) to return to the remote. But the remote is in server mode, so I'd be greeted by silence if I did that. I have two ways to get the remote out of server mode:
1. I could just connect and send a few Ctrl-Cs
2. I can send the `finish` (or just `f`) comand before returning.
Let's do the second:
(/tmp/t/) C-Kermit>finish (/tmp/t/) C-Kermit>c Connecting via command "ssh -e none auxuser@localhost" Escape character: Ctrl-\ (ASCII 28, FS): enabled Type the escape character followed by C to get back, or followed by ? to see other options. ---------------------------------------------------- C-Kermit server done auxuser@hephaestus:~$ history | tail -n 3 799 kermit -Iis /bin/sh 800 kermit -x 801 history | tail -n 3
Look at that - it's the `kermit -x` invocation right there in history even.
You can of course do something like this:
1. Fire up local `kermit`
2. Run `ssh hostname`
3. While you're in ssh over there, fire up `kermit` on the remote. Now, when you're in connect mode, you're sending commands to the remote kermit, and when you're in command mode, you're sending commands to the local kermit. Potentially confusing -- and also potentially useful.
This is what you will encounter if you use the quux.org Kermit Server[9] - try it out!
These settings make kermit fast over a reliable (ssh, etc) connection. You can add them to your `~/.kermrc` if you never need to use unreliable serial links:
set reliable on set clearchannel on set receive packet-length 9000 set window 32 set control unprefix all set transfer slow-start off
The kermit protocol, by default, can work in either direction.
If you connect to untrusted remote systems, I recommend running `disable all` to prevent the remote from doing much to your local system other than sending files. For instance, `rcd` is enabled by default and allows the remote to change the directory for you to receive files.
* I also have instructions: How to Run an Internet Kermit Server[17]
10: https://www.kermitproject.org/ck10commandref.html
11: https://www.kermitproject.org/ckscripts.html
12: https://www.kermitproject.org/ck90.html
13: https://www.kermitproject.org/k95.html
14: https://www.kermitproject.org/ckw10beta.html
16: /try-the-last-internet-kermit-server/
17: /how-to-run-an-internet-kermit-server/
18: http://www.columbia.edu/kermit/hp48.html
19: https://www.kermitproject.org/hp48filetransfer.html
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Sometimes we want better-than-firewall security for things. For instance:
21: /how-to-run-an-internet-kermit-server/
This page will describe how to run an Internet Kermit[22] server, like the quux.org Kermit Server[23] that was featured in my article Try the Last Internet Kermit Server[24].
24: /try-the-last-internet-kermit-server/
25: /try-the-last-internet-kermit-server/
What is this mysterious protocol? Who uses it and what is its story?
This is a Kermit server maintained by me, John Goerzen[27].
The old sense of the word "modem" in computing referred to a device that would let two computers communicate over telephone lines. It was quite slow and unreliable by modern standards. Nowadays, the term is more broad.
29: /old-and-small-technology/
Old technology is any tech that's, well... old.
(c) 2022-2024 John Goerzen