SZ

Section: User Commands (1)
Updated: OMEN
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NAME

sx, sb, sz - XMODEM, YMODEM, ZMODEM file transmission

SYNOPSIS

sz [-+1abdefkLlNnopqTtuvyY] file ...
sb [-1adfkqtuv] file ...
sx [-1akqtuv] file
sz [-1oqtv] -c COMMAND
sz [-1oqtv] -i COMMAND

DESCRIPTION

Sz uses the ZMODEM, YMODEM or XMODEM error correcting protocol to send one or more files over a serial port to a variety of programs running under PC-DOS, CP/M, Unix, VMS, and other operating systems.

The first form of sz sends one or more files with ZMODEM or YMODEM batch protocol. Normally, only the file name part of the pathname is transmitted. On Unix systems, additional information about the file is transmitted. If the receiving program uses this information, the transmitted file length controls the exact number of bytes written to the output dataset, and the modify time and file mode are set accordingly.

Output from another program may be piped to sz for transmission by denoting standard input with "-":

ps -ef | sz -
The program output is transmitted with the filename sPID.sz where PID is the process ID of the sz program. If the environment variable ONAME is set, that is used instead. In this case, the Unix command: ONAME=con ps -ef|sz -ay -
will send a "file" to the PC-DOS console display. The -y option instructs the receiver to open the file for writing unconditionally. The -a option causes the receiver to convert Unix newlines to PC-DOS carriage returns and linefeeds.

The second form is invoked as sb to send one or more files with YMODEM batch protocol. The initial ZMODEM initialization is not sent. When requested by the receiver, sb supports YMODEM-g with "cbreak" tty mode, XON/XOFF flow control, and interrupt character set to CAN (^X). YMODEM-g (Professional-YAM g option) increases throughput over error free channels (direct connection, X.PC, etc.) by not acknowledging each transmitted sector.

The third form of sz is invoked as sx to send a single file with XMODEM or XMODEM-1k protocol. The user must supply the file name to both sending and receiving programs.

Iff sz is invoked with $SHELL set and iff that variable contains the string rsh or rksh (restricted shell), sz operates in restricted mode. Restricted mode restricts pathnames to the current directory and PUBDIR (usually /usr/spool/uucppublic) and/or subdirectories thereof.

The fourth form sends a single COMMAND to the receiver for execution. Sz exits with the COMMAND return value. If COMMAND includes spaces or characters special to the shell, it must be quoted.

The fifth form sends a single COMMAND to the receiver for execution. Sz exits as soon as the receiver has correctly received the command, before it is executed.

If sz is invoked with stdout and stderr to different datasets, Verbose is set to 2, causing frame by frame progress reports to stderr. This may be disabled with the q option.

The meanings of the available options are:

+: Instruct the receiver to append transmitted data to an existing file (ZMODEM only).
1: Use file descriptor 1 for ioctls and reads (Unix only). By default, file descriptor 0 is used. This option allows sz to be used with the Professional-YAM $ command.
a: Convert NL characters in the transmitted file to CR/LF. This is done by the sender for XMODEM and YMODEM, by the receiver for ZMODEM.
b: (ZMODEM) Binary override: transfer file without any translation.
c COMMAND: Send COMMAND to the receiver for execution, return with COMMAND's exit status.
d: Change all instances of "." to "/" in the transmitted pathname. Thus, C.omenB0000 (which is unacceptable to MSDOS or CP/M) is transmitted as C/omenB0000. If the resultant filename has more than 8 characters in the stem, a "." is inserted to allow a total of eleven.
e: Escape all control characters; normally XON, XOFF, DLE, CR-@-CR, and Ctrl-X are escaped.
f: Send Full pathname. Normally directory prefixes are stripped from the transmitted filename.
i COMMAND: Send COMMAND to the receiver for execution, return Immediately upon the receiving program's successful recption of the command.
k: (XMODEM/YMODEM) Send files using 1024 byte blocks rather than the default 128 byte blocks. 1024 byte packets speed file transfers at high bit rates. (ZMODEM streams the data for the best possible throughput.)
L N: Use ZMODEM sub-packets of length N. A larger N (32 <= N <= 1024) gives slightly higher throughput, a smaller N speeds error recovery. The default is 128 below 300 baud, 256 above 300 baud, or 1024 above 2400 baud.
l N: Wait for the receiver to acknowledge correct data every N (32 <= N <= 1024) characters. This may be used to avoid network overrun when XOFF flow control is lacking.
n: (ZMODEM) Send each file if destination file does not exist. Overwrite destination file if source file is newer than the destination file.
N: (ZMODEM) Send each file if destination file does not exist. Overwrite destination file if source file is newer or longer than the destination file.
o: (ZMODEM) Disable automatic selection of 32 bit CRC.
p: (ZMODEM) Protect existing destination files by skipping transfer if the destination file exists.
q: Quiet suppresses verbosity.
r: (ZMODEM) Resume interrupted file transfer. If the source file is longer than the destination file, the transfer commences at the offset in the source file that equals the length of the destination file.
t tim: Change timeout to tim tenths of seconds.
u: Unlink the file after successful transmission.
v: Verbose causes a list of file names to be appended to /tmp/szlog . More v's generate more output.
y: Instruct a ZMODEM receiving program to overwrite any existing file with the same name.
Y: Instruct a ZMODEM receiving program to overwrite any existing file with the same name, and to skip any source files that do have a file with the same pathname on the destination system.

EXAMPLES

ZMODEM File Transfer
$ sz -a *.c
This single command transfers all .c files in the current Unix directory with conversion (-a) to end of line conventions appropriate to the receiving environment. With ZMODEM AutoDownload enabled, Professional-YAM and ZCOMM will automatically recieve the files after performing a security check.

$ sz -Yan *.c *.h
Send only the .c and .h files that exist on both systems, and are newer on the sending system than the corresponding version on the receiving system, converting Unix to DOS text format.

ZMODEM Command Download

cpszall:all
    sz -c "c:;cd /yam/dist"
    sz -ya $(YD)/*.me
    sz -yqb y*.exe
    sz -c "cd /yam"
    sz -i "!insms"
This Makefile fragment uses sz to issue commands to Professional-YAM to change current disk and directory. Next, sz transfers the .me files from the $YD directory, commanding the receiver to overwrite the old files and to convert from Unix end of line conventions to PC-DOS conventions. The third line transfers some .exe files. The fourth and fifth lines command Pro-YAM to change directory and execute a PC-DOS batch file insms . Since the batch file takes considerable time, the -i form is used to allow sz to exit immediately.

XMODEM File Transfer (To Crosstalk)
$ sx -a foo.c
ESC
rx foo.c
The above three commands transfer a single file from Unix to a PC and Crosstalk XVI 3.6, translating Unix newlines to DOS CR/LF.

VMS VERSION

The VMS version does not transmit the file date. The VMS version calculates the file length by reading the file and counting the bytes.

The VMS version does not support YMODEM-g or ZMODEM.

When VMS is lightly loaded, the response time may be too quick for MODEM7 unless the MODEM7 q modifier is used.

The VMS C standard i/o package and RMS sometimes interact to modify file contents unexpectedly.

FILES

32 bit CRC code courtesy Gary S. Brown.

sz.c, rbsb.c, zm.c, zmodem.h source files

/tmp/szlog stores debugging output (sz -vv)

TESTING FEATURE

The command "sz -T file" exercises the Attn sequence error recovery by commanding errors with unterminated packets. The receiving program should complain five times about binary data packets being too long. Each time sz is interrupted, it should send a ZDATA header followed by another defective packet. If the receiver does not detect five long data packets, the Attn sequence is not interrupting the sender, and the Myattn string in sz.c must be modified.

After 5 packets, sz stops the "transfer" and prints the total number of characters "sent" (Tcount). The difference between Tcount and 5120 represents the number of characters stored in various buffers when the Attn sequence is generated.

BUGS

Many programs claiming to support YMODEM only support XMODEM with 1k blocks, and they often don't get that quite right.

XMODEM transfers add up to 127 garbage bytes per file (1023 bytes with XMODEM-k). Most YMODEM programs use the file length transmitted at the beginning of the transfer to prune the file to the correct length; this may cause problems with source files that grow during the course of the transfer. This problem does not pertain to ZMODEM transfers, which preserve the exact file length unconditionally.

Most ZMODEM options are merely passed to the receiving program; some do not implement all these options.

Circular buffering and a ZMODEM sliding window should be used when input is from pipes instead of acknowledging frames each 1024 bytes. If no files can be opened, sz sends a ZMODEM command to echo a suitable complaint; perhaps it should check for the presence of at least one accessible file before getting hot and bothered. The test mode leaves a zero length file on the receiving system.

Some high speed modems have a firmware bug that drops characters when the direction of high speed transmissson is reversed. The environment variable ZNULLS may be used to specify the number of nulls to send before a ZDATA frame. Values of 101 for a 4.77 mHz PC and 124 for an AT are typical.

This document was created by man2html, using the manual pages.
Time: 21:21:13 GMT, January 24, 2023

SZ