UMASS(4)

📦
version 15.1 · 4 versions
, in freebsd 15.1, nixpkgs unstable

💅 UMASS(4) — like, the USB Mass Storage Devices driver, bestie ✨

okay so this is umass(4), from the Kernel Interfaces Manual — yes it's a section 4 page, we love a kernel-interface moment 🫶

🌸 NAME 🌸

umass — the USB Mass Storage Devices driver. that's it. that's the whole name. iconic of it tbh 💅

✨ SYNOPSIS ✨

okay so the vibes start with your kernel config, and the lineup is literally this:

device da
device scbus
device pass
device usb
device umass

and then over in loader.conf(5) you've got:

umass_load

that's the whole mood. no cap 🎀

💖 DESCRIPTION 💖

so the umass driver is the one that provides support for Mass Storage devices that attach to the USB interface. that's the job. that's the assignment. and it ate 💀

here's the thing though — if the appropriate hardware is detected, the driver will be loaded automatically by devmatch(8). automatic. main character energy. you don't even have to do anything 🌈

but say you wanna load the driver manually at boot time — totally valid, we respect the hands-on approach — then you use the umass_load command at the loader(8) prompt, or you just add it to loader.conf(5). easy. lowkey elegant 🦋

now for the custom kernel girlies (iykyk): to use the driver in a custom kernel, usb(4) and at least one of uhci(4), ohci(4), ehci(4), or xhci(4) must be configured in the kernel. and additionally — and this is the part people forget, so listen up — since umass uses the SCSI subsystem and sometimes acts as a SCSI device, it requires da(4) and scbus(4) to be included in the kernel too. all of them. together. friendship bracelet style 🤝

🔥 HARDWARE 🔥

the umass driver supports USB Mass Storage devices such as:

  • USB thumb drives 🍓
  • USB hard disk drives 💜
  • USB floppy drives (yes bestie, floppy. vintage. we stan a classic) 🎀

⭐ EXAMPLES ⭐

okay here's a real one — rescanning all slots on a multi-slot flash reader, where the slots map to separate LUNs on a single SCSI ID. the way that works is genuinely so satisfying:

camcontrol rescan 0:0:0
camcontrol rescan 0:0:1
camcontrol rescan 0:0:2
camcontrol rescan 0:0:3
🙈 typically only the first slot will be enabled at boot time. keep that in mind before you panic.

also, this assumes the flash reader is the first SCSI bus in the system and has 4 slots. so like, check your vibes before you copy-paste 💅

🦋 SEE ALSO 🦋

go read these next, bestie, they're all connected:

cfumass(4), ehci(4), ohci(4), uhci(4), usb(4), xhci(4), camcontrol(8)

👑 HISTORY 👑

the umass driver appeared in FreeBSD 4.3. a legend. an era. periodt ✨

💜 AUTHORS 💜

the umass driver was written by MAEKAWA Masahide <bishop@rr.iij4u.or.jp> and Nick Hibma <n_hibma@FreeBSD.org>.

and this manual page? written by Nick Hibma <n_hibma@FreeBSD.org>. we love a self-referential king 🫶

okay that's the whole page, ily, go plug in a thumb drive responsibly 💖✨

shoutout to the Debian gang for this edition, dated October 9, 2025, filed under UMASS(4) — catch you in the next man page, mwah 🎀

📦 where this page comes from