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ZMODEM transfers (sz and rz)

ZMODEM moves files through the terminal session itself — no SFTP, no second connection. There is no button in SigilTTY; the remote side starts everything:

  • Run sz file … on the remote host and SigilTTY detects it and downloads the files.
  • Run rz and SigilTTY asks you to pick a file to send.

What works where

Section titled “What works where”
Transport Download (sz) Upload (rz)
SSH ✓ ✓
Telnet ✓ —
Serial (Mac) ✓ —

Uploading needs a raw binary input channel, which only SSH provides. On Telnet or serial, rz prints a notice in the terminal suggesting the SFTP file browser instead.

Where downloads land

Section titled “Where downloads land”
  • Mac — ~/Downloads.
  • iPhone and iPad — the app’s Documents folder, visible in the Files app (the same place as SFTP downloads).

Files are written as .part first and only renamed once the transfer verifies complete. A name clash auto-renames; an aborted or interrupted transfer deletes its .part — you never find a half-file posing as the real thing.

Progress and cancelling

Section titled “Progress and cancelling”

A compact overlay at the top of the terminal shows the direction, file name, a progress bar and byte counts — plus a Cancel button.

While a transfer runs, keystrokes are discarded: anything typed would corrupt the protocol’s reverse channel. The one exception is pressing Ctrl-X three or more times in a row, which aborts the transfer — the same muscle memory lrzsz users already have. Cancelling the upload file picker (or letting it sit for 60 seconds) tells the remote rz to exit cleanly instead of erroring out.

Limits

Section titled “Limits”
  • No resume — an interrupted transfer starts over (sz -r is not supported).
  • XMODEM, YMODEM and Kermit are not supported; they have no reliable in-stream signature to detect automatically.
  • ZCOMMAND is permanently refused, in both directions — it is the protocol channel that would let a remote host hand the app commands to execute.
  • On Telnet without binary mode, bytes can be mangled in transit. CRC checks catch it and retransmit, and if that keeps failing the transfer errors out — a silently corrupted file is never produced.
  • On iPhone and iPad, transfers are bounded by the roughly 30-second background keep-alive window: a long transfer won’t survive locking the screen.