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Authors: Bill Catchings, Bob Cattani, Chris Maio, Columbia University
Modified from UNIX Kermit to Os9 Kermit By Glean Seaton and Robert
A. Larson
with fixes and contributions from many others.
Documentation:
Walter Underwood, Ford Aerospace (Palo Alto, CA)
Changed for Os9 Kermit by Robert A. Larson
Version: 1.5
Date: July 1985
A sample, working implementation of the Kermit "kernel" was written in the C
language, and widely distributed in the Kermit Protocol Manual. This kernel
was intended merely to illustrate the protocol, and did not include a "user
interface", nor some of the fancy features like server support, 8-bit quoting,
file warning, timeouts, etc. Several sites have added the necessary trappings
to make this a production version of Kermit, usually under the UNIX operating
system. Limited server functions have also been added to the Os9 version.
The keyword style of user/program interaction favored by Kermit (program types
prompt, user types command followed by operands, program types another prompt,
etc) is contrary to the UNIX style, so UNIX implementations have a style more
familiar to UNIX users. The Os9 version has retained this style of command
interface. C versions of Kermit are running successfully on VAX and PDP-11
UNIX systems, IBM 370-compatible mainframes under Amdahl UTS, and the SUN
Microsystems MC68000-based and other workstations.
There is a new version of Kermit written in C called C-Kermit. (The current
version as of July 1985 is 4c.) It is recommended for Unix and adapting to
other operating systems if memory is adiquate. (It is being adapted to
Os9/68000, but is probably to large for Os9/6809.)
Os9 filespecs are of the form
dir1/dir2/dir3/ ... /filename
where the tokens delimited by slashes form a path name, and are each limited to
29 characters in length. The final token in a path is the actual file name.
By convention, it is of the form name.type, but there is nothing special about
the dot separating name and type; to Os9 it's just another character, and there
may be many dots in a filename.
In the tradition of UNIX, here's the Os9 KERMIT "man page".
NAME kermit - file transfer, virtual terminal over tty link
SYNOPSIS kermit cl[e] line [esc]
kermit r[ddifl] [line]
kermit s[ddifl] [line] file ...
kermit gl[ddif] line file ...
2
kermit ql[ddif] line
kermit h[ddifl] [line]
DESCRIPTION Kermit provides reliable file transfer and primitive virtual
terminal communication between machines. It has been
implemented on many different computers, including
microprocessors (see below). The files transferred may be
arbitrary ASCII data (7-bit characters) and may be of any
length. The file transfer protocol uses small (96 character)
check summed packets, with ACK/NACK responses and timeouts.
Os9 Kermit by defaults (changeable by compilation options) uses
a fifteen "second" timeout and ten retries.
The arguments to kermit are a set of flags (no spaces between
the flags), three optional args (which, if included, must be in
the same order as the flags which indicate their presence),
and, if this is a Send or Get operation a list of one or more
files.
Kermit has six modes, Connect, Send, Receive, Get, Quit, and
Host. Connect is for a virtual terminal connection, Send and
Receive may be used to transfer files in a non-server mode,
Send, Get, and Quit are used with a remote kermit server, and
Host is used to make the Os9 system a server itself. These
modes are specified by the first flag, which should be c, s, r,
g, q, or h respectively. Exactly one mode must be specified.
The d flag (debug) makes kermit a bit more verbose. The states
kermit goes through are printed along with other traces of its
operation. A second, third, and even fourth d flag will cause
kermit to give an even more detailed trace.
The i flag (image) allows slightly more efficient file transfer
between Os9 machines. Normally (on Kermits defined to run on
Os9 systems) return is mapped to CRLF on output, LF's are
discarded on input, and bytes are masked to 7 bits. If this is
set, no mapping is done on returns, and all eight bits of each
byte are sent or received.
The l flag (line) specifies the tty line that kermit should use
to communicate with the other machine. This is specified as a
regular filename, like "/t2". If no l option is specified,
standard input is used and kermit assumes it is running on the
remote host (i.e.. NOT the machine to which your terminal is
attached).
The e flag (escape) allows the user to set the first character
of the two character escape sequence for Connect mode. When
the escape character is typed, kermit will hold it and wait for
the next character. If the next character is c or C, kermit
will close the connection with the remote host. If the second
3
character is the same as the escape character, the escape
character itself is passed. An exclamation mark ('!') as the
second character will cause shell to be forked. (Use your EOF
character to return to the kermit connect mode.) Any character
other than these two results in a bell being sent to the user's
terminal and no characters passed to the remote host. All
other typed characters are passed through unchanged. The
default escape character is tilde ('~'). (Control-3 on the
standard Coco keyboard.)
The file arguments are only meaningful to a Send or Get kermit.
The Receiving kermit will attempt to store the file with the
same name that was used to send it. Os9 kermits normally
convert outgoing file names to uppercase and incoming ones to
lower case (see the f flag). If a filename contains a slash
(/) all outgoing kermits will strip off the leading part of the
name through the last slash. In the Get command, filenames
will be sent to the remote host as is and the filenames sent
back will be converted as usual for a receiving kermit.
(Wildcard characters may be expanded on the remote end.)
The Quit command will send a "Generic Finish" packet to the
remote kermit server.
The Host command has not been fully implemented and tested as
of this writing.
EXAMPLE For this example we will assume two Os9 machines. We are
logged onto "Os9a" (the local machine), and want to communicate
with "Os9b" (the remote machine). There is a modem on "/t2".
We want to connect to "Os9b", then transfer "file1" to that
machine.
We type:
kermit cl /t2
Kermit answers:
Kermit: connected...
Now we dial the remote machine and connect the modem. Anything
typed on the terminal will be sent to the remote machine and
any output from that machine will be displayed on our terminal.
We hit RETURN, get a "login:" prompt and login.
Now we need to start a kermit on the remote machine so that we
can send the file over. First we start up the remote, (in this
case receiving) kermit, then the local, (sending) one.
Remember that we are talking to Os9b right now.
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We type:
kermit r
(there is now a Receive kermit on Os9b)
We type ~ (the escape character) and then the letter c to kill
the local (Connecting) kermit: ~c
Kermit answers:
Kermit: disconnected.
We type:
kermit sl /t2 file1
Kermit answers:
Sending file1 as FILE1
When the transmission is finished, kermit will type either
"Send complete", or "Send failed.", depending on the success of
the transfer. If we now wanted to transfer a file from os9b
(remote) to os9a (local), we would use these commands:
kermit cl /t2
(connected to Os9b)
kermit s file9
~c (talking to Os9a again)
kermit rl /t2
After all the transfers were done, we should connect again, log
off of Os9b, kill the Connect kermit and hang up the phone.
FEATURES Kermit can interact strangely with the tty driver.
The KERMIT Protocol uses only printing ASCII characters,
Ctrl-A, and CRLF. Ctrl-S/Ctrl-Q flow control can be used
"underneath" the Kermit protocol, but is not currently
implemented in Os9 Kermit.
Since BREAK is not an ASCII character, kermit cannot send a
BREAK to the remote machine. On some systems, a BREAK will be
read as a NUL.
This kermit does have timeouts when run under Os9, so the
protocol is stable when communicating with "dumb" kermits (that
don't have timeouts).
DIAGNOSTICS cannot open device
The file named in the line argument did not exist or had the
5
wrong permissions.
Could not create file
A Receive kermit could not create the file being sent to it.
nothing to connect to
A Connect kermit was started without a line argument.