UMB(4)

💖 UMB(4) — the cellular modem driver glow-up 💖

okay bestie, so this one lives in the Kernel Interfaces Manual (yes, that's the UMB(4) vibe) and it's literally all about getting your lil USB cellular modem online. let's get into it 🫶

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✨ NAME ✨

umb — the USB Mobile Broadband Interface Model (MBIM) cellular modem driver. that's it, that's the whole name, no cap 💅

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🌸 SYNOPSIS 🌸

device usb
device umb

and in loader.conf(5):

umb_load="YES"

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🦋 DESCRIPTION 🦋

so umb is the driver that has your back for USB MBIM devices. and here's the cute part: if the right hardware gets detected, the driver literally loads itself automatically via devmatch(8) — main character energy, it shows up on its own 😌✨

but if you wanna load it manually (respect), you can do it in loader.conf(5) or right at the loader(8) prompt.

MBIM devices do their thing by establishing connections via cellular networks such as GPRS, UMTS, and LTE. they show up as a regular point-to-point network interface, just transporting raw IP frames. iconic behavior honestly.

now listen — required config parameters like PIN and APN have to be set with umbctl(8). lowkey important so don't skip it 🎀

once the SIM card has been unlocked with the correct PIN, it stays in that state until the MBIM device is power-cycled. and if your device happens to be plugged into an "always-on" USB port? it may be possible to connect to a provider without entering the PIN again — even if the system was rebooted. yes bestie, it remembers you 💜

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🔥 HARDWARE 🔥

the umb driver should support any USB device implementing MBIM, including these cellular modems (a whole lineup, slay):

• Ericsson H5321gw and N5321gw
• Fibocom L831-EAU
• Medion Mobile S4222 (MediaTek OEM)
• Sierra Wireless EM7345
• Sierra Wireless EM7455
• Sierra Wireless EM8805
• Sierra Wireless MC8305

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👑 SEE ALSO 👑

intro(4), netintro(4), usb(4), ifconfig(8), umbctl(8)

and also this absolute banger of a spec: Universal Serial Bus Communications Class Subclass Specification for Mobile Broadband Interface Model, at http://www.usb.org/developers/docs/devclass_docs/MBIM10Errata1_073013.zip.

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🌈 HISTORY 🌈

the umb device driver first appeared in OpenBSD 6.0, NetBSD 9.0, and FreeBSD 15.0. a true multi-platform queen 💅

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⭐ AUTHORS ⭐

the umb driver was written by Gerhard Roth <gerhard@openbsd.org> and ported from OpenBSD by Pierre Pronchery <khorben@defora.org>. give them their flowers 💐

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💀 CAVEATS 💀

okay so, real talk, two things:

• the umb driver does not support IPv6. yep. that's the whole bullet. 😭
• devices that fail to provide a conforming MBIM implementation will probably be attached as some other driver, such as u3g(4). so if yours is acting brand new, check who it actually attached to, iykyk 🙈

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🎀 sign-off 🎀

Deiban… wait no — Debian, September 3, 2025. that's the source/version and date, bestie, we been knew. catch you in the next man page 💖✨🌸