[gentoo-user] Allow delay for booting from USB device?

[Thomas Mueller]

Is there a way to make Gentoo or other Linux allow extra time when root is on a USB device?  Any way to say "just a second" or more like 15 seconds before aborting with the message that root partition does not exist?

In this case it's an IDE hard drive in a USB enclosure.

FreeBSD seems to handle this situation better.  I would get a 
mountroot>
prompt, to which I would respond 
ufs:/dev/ada0p3
and be good.

I could avoid this situation with /boot/loader.conf

legal.realtek.license_ack=1
rsu-rtl8712fw_load="YES"
kern.cam.scsi_delay="13000"     # Delay (in ms) before probing SCSI
kern.cam.boot_delay="16000"    # Delay (in ms) of root mount for CAM bus
hint.re.0.disabled="1"

but don't know if Linux has anything like this.

Only lines 3 and 4 are relevant to this issue; other lines are for different issues.

Tom