Appendix H. Zmodem File Transfer
The Zmodem protocol is a robust and fast data-transfer protocol. It
includes 32-bit cyclic redundancy checking (CRC) to
ensure error-free data transfer. On Unix
platforms, the RZSZ package provides the dominant
tools for implementing Zmodem protocols. Related protocols, such as
Xmodem and Ymodem, are also supported by commands that are part of the
RZSZ package.
These commands are available in the current RZSZ
package:
- rz
Receives files using the Zmodem batch protocol. If the sending
program doesn't send Zmodem protocol files within 50 seconds,
rz switches to rb mode. - rb
Receives files using the Ymodem or Ymodem-g protocol. rb is an alternative invocation for the
rz command. - rx
Receives a file using the Xmodem protocol. - sz
Sends files using the Zmodem batch protocol. - sb
Sends files using either the Ymodem or Ymodem-g protocol. sb is an alternative invocation for the
sz command. - sx
Sends a file using the Xmodem protocol.
sz provides automatic downloading in response to an
incoming rz request, and rz
automatically processes incoming Ymodem or Zmodem files.
sz can also be used as a filter to send standard
input to the receiving host.
The RZSZ tools
display information about the file transfers, including projections of
transmission time, incremental crash recovery, recognition of wildcard
file-selection arguments, and user notification on completion of
transfer. Because most popular PC terminal-emulation packages
(Professional-YAM, ZCOMM,
ProComm, Telix, and a host of others) support Zmodem transfer, the
RZSZ package makes it simple to transfer files
between Linux systems, MS-DOS, Macintosh,
VMS, and other operating systems.
Interestingly, although some Linux distributions include the
sz and rz commands, they may
omit portions of the RZSZ package (including the
manual pages). So we'll give you some FTP sites to
get the whole package in the next section.
Most of the time, you won't need to use Xmodem or Ymodem, so we will
restrict our discussion to the sz and
rz features.
H.1. Getting RZSZ
The
RZSZ package isn't acknowledged as such in the
Linux tools, which may mean that you won't find the whole package
collected and compiled for Linux. However, we have found a number of
FTP sites that carry the source, such as a
subdirectory of NetBSD packages called lrzsz at
ftp://ftp.cs.umn.edu.
The primary source for state-of-the-art RZSZ is
ftp://ftp.cs.pdx.edu, maintained in
directory /pub/zmodem by Chuck Forsberg of Omen
Technology, Inc.
Omen Technology (http://www.omen.com) offers a hardcopy
manual for its RZ/SZ package (as well as detailed
documentation for the PC terminal-emulation package
Professional-YAM) that you can buy if the manual
pages seem insufficient. You can download these packages on a
shareware basis (meaning you are expected to pay a small fee) from the
web site.
Technical support is offered for registered RZ/SZ
users. Omen Technology reports that almost all technical support
problems with RZ/SZ are caused by the network, OS
kernel bugs, or problems with third-party programs, not the
RZ/SZ code itself.
 |  |  | | G.4. lilo Command Options |  | H.2. Sending and Receiving Files |
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