Running Linux, Third Edition

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, ...