[TUHS] x/y/zmodem on Unix

Serge Burjak sburjak at systech.com.au
Tue Sep 19 13:42:39 AEST 2023

Chuck Forsberg wrote Zmodem as a sliding Window transfer protocol
alternative to Kermit and superkermit. It was very high performance
over slow links. He provided source code support for the protocol
driver on the server and client end, in various versions. His client
programs  were Yam (yet another modem) and ProYam. You could shell out
of the client, run other programs. Other client platforms supported
parts of the protocol. Available as binaries and source when licenced.
It had a scripting language and out of the box had the zmodem protocol
which has the ability to send commands, resume transfers, traverse non
8 bit or unreliable links, remove or rename source file, deal with
conflicting file names, synchronise folders and lots of other things.
I have written many scripts to help dial up users into a unix box and
download financial research data. Scripts still work across the
internet. He made the code very portable, clean and I believe it is
open source now. Chuck is no longer with us.

SecureCRT ssh client from VanDyke.com still has native support. To
send a file from the unix host, typically sz filename and it just
arrives. Sz- u and it will remove the source file after successful
transfer, plus lots of other options. The binary was typically linked
so if you type sx it would try to do a transfer with xmodem, even
though it's the same binary.

Hope this helps.


On Tue, 19 Sept 2023 at 12:47, Jonathan Gray <jsg at jsg.id.au> wrote:
> On Tue, Sep 19, 2023 at 12:31:30AM +0200, Paul Ruizendaal wrote:
> > I had always associated x/y/zmodem with CP/M and MSDOS, not so much with Unix. Last December Clem already pointed out that it was popular for file exchange in the Unix scene as well, along with several other similar tools. Also, the ymodem approach to file metadata is very unix oriented, suggesting it originated on Unix or at least that Unix users were an important user demographic. Yet, I could find little trace of x/y/zmodem in the TUHS Unix Tree. The search tool finds it in 2.11BSD, in Minix 1.5 and 2.0 and in V10. Kermit is in those as well, and in 4.3BSD and 4.4BSD on top.
> have a look at
> tuhs/Applications/Shoppa_Tapes/usenix878889.tar.gz
> usenix87/Comm/
> usenix89/Comm/
> also appears in
> 386bsd/othersrc/public/zmodem-3.03/
> where the license was changed to prohibit commercial use after
> the RLE changes in April 1989
> https://www.ohse.de/uwe/software/lrzsz.html
> is derived from an earlier version with the license changed to GPLv2

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