How to install Debian within z/VM with just x3270

If you want to copy debian-installer for System z onto a z/VM user's CMS disk, you don't need access to FTP (and hence the host's TCP/IP stack). You can just use x3270 and transfer files with it. For odd reasons I forgot about this, so let's document it here:

• Figure out which CMS disk is actually writeable for you (most likely the A disk) by issuing Q DISK and looking for "R/W" in the STAT column.
• Select File, File Transfer.
• Tick "Send to host" and "Host is VM/CMS".
• Download the four installer files to your local machine: debian.exec (a startup script that punches the kernel, boot parameters and initrd onto cards and executes the card deck), kernel.debian, parmfile.debian (the boot parameters) and initrd.debian.
• Transfer debian.exec and parmfile.debian with "Transfer ASCII file" ticked and Record Format set to "Variable" ("Add/remove CR at end of line" and "Remap ASCII characters" should both be ticked by default; LRECL and BLKSIZE should both be empty.) The host filename is the CMS filename, so something like "DEBIAN EXEC A" (with the spaces, and A replaces with the letter of the writeable disk of your choice). Both files must be prefectly readable in XEDIT (i.e. properly converted to EBCDIC).
• Then transfer kernel.debian and initrd.debian with "Transfer binary file" ticked and Record Format set to "Fixed" with LRECL = 80. This may take a while.
• Boot up the installer by issuing DEBIAN to z/VM, starting the script. If you needed to rename the files above (the drive letter doesn't matter), you need to adjust DEBIAN EXEC first.
• You should see Linux kernel messages now. Profit.