---
name: schunix-verify-by-driving-shell
description: "Boots to a prompt" is not a passing test for Schunix — drive real commands over the serial console
metadata:
  type: feedback
---

Reaching `init: ready (pid 1)` and a `#` prompt proves almost nothing about
Schunix. A filesystem change shipped looking "verified" that way and the user
found the breakage by typing one command.

**Why:** nothing in the boot path opens a file from `/bin` or reads a
non-root inode. An image with corrupt inodes boots to a perfectly healthy
prompt and dies on the first `ls`.

**How to apply:** after any change to `tools/mkfs.c`, the on-disk format, or
`kernel/fs/*`, drive actual commands and read the output. QEMU's serial line is
an input console, but it has no flow control — a burst of piped input loses
about half its characters, and input sent before the shell is up is discarded
entirely. Both problems go away with: wait ~20s for boot, then send one
character every ~0.12s.

```sh
send() { s="$1"; i=0
  while [ $i -lt ${#s} ]; do
    printf '%s' "$(expr substr "$s" $((i+1)) 1)"; sleep 0.12; i=$((i+1)); done
  printf '\n'; sleep 7; }
sleep 20; send "ls"; send "ls /bin"; send "cat /etc/motd"
```

Pipe that into `qemu ... -serial stdio -display none` and read the log. `ls`,
`ls /bin` and `cat` on a real file are the minimum bar.

See [[schfs-v2-and-ramdisk]], [[schunix-build-environment]].