BOOT.CONFIG(5)

💾 boot.config(5) — the legacy boot blocks' little config bestie 🎀

okay so real talk: this is the manual page for boot.config, aka section 5 of the File Formats Manual, and it's all about the config file for the legacy boot blocks. it's giving "old but iconic" fr fr 💅

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✨ NAME ✨

boot.config — Configuration file for the legacy boot blocks 🫶

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🌸 DESCRIPTION 🌸

the boot.config file contains options for the FreeBSD boot block code. like, that's its whole job. main character energy honestly 👑

so here's the vibe: when the first- and second-stage FreeBSD boot loaders run, they search the "a" slice of the boot partition for a boot.config file. yep, that's right — they're out here looking for their bestie 🧚

⚠️ heads up bestie: as a result, slices which are missing an "a" partition require user intervention during the boot process. no "a" slice, no auto-magic — you're gonna have to step in yourself 😭

if the boot.config file is found, its contents are used as the default configuration options for the boot block code and are echoed to the system console. loud and proud, periodt 🔊

a valid format of this file is to put BIOS drive number, a controller type, a unit number, a partition, a kernel file name, and any other valid boot(8) option on a single line, as it is done at the "boot:" prompt. one line, all the deets, exactly like you'd type it at the prompt. slay ✨

the options related to the boot image selection described below and all the other options available for boot.config are documented in detail in the boot(8) manual page. so if you want the full lore, that's where it lives 📖

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🦋 FILES 🦋

• /boot.config — parameters for the boot blocks (optional)
• /boot/config — alternate location for boot config information

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🌈 EXAMPLES 🌈

okay the examples are lowkey the best part, let's go 💖

example one — the command:

# echo "-P" > /boot.config

will activate the serial console of FreeBSD if no keyboard is present, otherwise video console will be used. so it's like, "no keyboard? no problem, serial console it is" 🎀

example two — the command:

# echo "1:ad(1,a)/boot/loader" > /boot.config

will instruct the second stage of boot(8) on the first disk to boot with the third boot(8) stage from the second disk. very "collab across disks" of it 🤝

example three — the command:

# echo "1:ad(1,a)/boot/loader -P" > /boot.config

will do both of the above. combo move, ate 🔥

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⭐ SEE ALSO ⭐

• boot(8)
• loader(8)

go read those too, iykyk 💜

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👑 AUTHORS 👑

This manual page was written by Daniel Gerzo <danger@FreeBSD.org>. absolute legend, we stan 🫶

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and that's the whole page bestie!! this one's from the Debian crew, dated November 14, 2025 — bookmark it, screenshot it, whatever you gotta do. mwah 💋🌸