---
name: schunix-ramdisk-root-sizing
description: "Why `make iso` was failing with \"disk full\" — DOOM WADs in the ramdisk, not FSSIZE — and the three Makefile knobs that actually control that image."
metadata: 
  node_type: memory
  type: project
  originSessionId: 9d8a2aef-bcf0-47a0-96c6-f706efab4a95
  modified: 2026-08-08T12:04:27.952Z
---

Fixed 2026-08-08. `make iso` died with `mkfs: disk full -- used 6000 of 6000
blocks` and the advice "Increase FSSIZE in param.h". **`FSSIZE` was 150000 and
entirely innocent.** The ramdisk root's size is `RAMDISK_BLOCKS` in the Makefile.
The error message has been rewritten to name the right knob per image and print
the metadata breakdown; don't trust the old advice if it resurfaces anywhere.

**The actual cause: `make doom` stages 33 MB of WADs into `sysroot/`**
(`freedoom1.wad` 28.8 MB, `doom1.wad` 4.2 MB) and the ramdisk was trying to
swallow them into 6 MB. Real userland is only ~1.9 MB — the 244 `/bin` entries
are *hardlinks* to one 822 KB toybox, which is why `du` says 35 MB while the
file sizes sum to 229 MB.

**This is a licensing rule, not just a size one, and that is the reason it is
enforced in the build rather than by remembering to run `make doom-uninstall`.**
The ramdisk is linked *into the kernel binary*; `doom1.wad` is
non-redistributable shareware, so a kernel containing it could not be
distributed. See [[schunix-doom-acceptance-test]] and [[schunix-licensing]].

Three Makefile knobs, none of them FSSIZE:
- `RAMDISK_BLOCKS` (6000) — image size, BSIZE is 1024.
- `RAMDISK_NINODES` (2000) — **the inode table is preallocated.** mkfs's default
  12000 inodes cost 1501 of 6000 blocks, a quarter of the image, for ~260 files.
  Metadata went 1596 → 345 blocks.
- `RAMDISK_EXCLUDE` (`usr/share/doom bin/doom`) — `mkfs --exclude <relpath>`,
  repeatable, drops a whole subtree and prints what it skipped.

`mkfs` gained `--ninodes` and `--exclude`. Its option parser used to handle
exactly one flag then `break`, silently ignoring a second — now it compacts argv
properly, but both modes still identify themselves *positionally* (argv[2] is
`--sysroot` or the first file), so keep that contract if adding options.

**Verified:** ramroot boots with no disk attached at all, and the ISO boots from
optical media only (`ide: no drive on the primary channel`) to a full shell with
243 commands — 243 not 244 because `doom` is correctly excluded.

**`make iso` needs `mkisofs`, not xorriso, on this host.** There is no xorriso
package in scoop; cdrtools provides `mkisofs.exe` and was already installed.
`tools/mkiso.sh` now takes either — the El Torito flags are argument-compatible.
This also finally verified `-boot-load-size 49` (see
[[schunix-boot-splash-logo]]), which was untestable while xorriso was missing.

**Trap:** `make iso` builds the ramroot variant and does `rm -rf build/kernel`
first, so a failed run leaves objects compiled with `-DRAMDISK_ROOT` and the next
plain `make` dies on `_binary_ramdisk_size`. Recover with
`rm -rf build/kernel build/lib build/cmd`.