[SOLVED] Kernel panics during boot when USB is attached

NP_complete · Tux's lil' helper Joined: 21 Mar 2009 Posts: 137

My goal is to keep my portable USB drive plugged in semi-permanently. I don't want to have to plug and unplug it on each boot. But that's what I'm facing, or the kernel becomes hysterical:

totony · n00b Joined: 03 Dec 2014 Posts: 40

toralf

szatox · Advocate Joined: 27 Aug 2013 Posts: 3493

Point kernel to the root filesystem with it's UUID or LABEL instead of (hd....)
Those things leave less room for mistakes.

NeddySeagoon · Posted: Mon Feb 29, 2016 5:39 pm Post subject:

szatox,

LABEL= or UUID= are filesystem features. An initrd is required to use those features to mount root.
PARTUUID= works without an initrd.

NP_complete,

If things are moving around, you will need to write fstab in terms of filesystem UUIDs. That works because mount is available once root is mounted.

s4e8 · Guru Joined: 29 Jul 2006 Posts: 311

another method is add "usb_storage.delay_use=10" to kernel parameter, delay 10 seconds to initialize usb mass-storage devices, through UASP devices has not delay params.

NP_complete · Tux's lil' helper Joined: 21 Mar 2009 Posts: 137

Thank y'all for help!

NeddySeagoon,

You didn't say this explicitly, but it sounds like I need initramfs (which supercedes initrd) to be able to mount USB drives on boot. Am I correct?

I've re-done fstab in terms of UUIDs and updated grub.cfg via grub2-mkconfig, but nothing changed. The kernel looks to /dev/sda4, instead of UUID=<something>, for a root partition.

I just noticed that the kernel prints this before failing:

NeddySeagoon · Posted: Tue Mar 01, 2016 6:12 pm Post subject:

NP_complete,

I use the the terms initrd and initramfs interchangably.
No, that's not right, initramfs is more typing, so I probably don't use it at all.
The difference is really one of internal structure. Traditionally, an initrd was a compressed ext2 filesystem in a file and a initramfs is a compressed cpio archive of cpio archives. Both work.

You don't need initrd/initramfs to boot from USB or to mount USB partitions at boot.
You do need usb storage support built into your kernel.
You need rootdelay= or rootwait on your kernel command line. This overcomes the problem of root being mounted before the USB subsystem is started, which is the normal course of events. Its a verybadthing for root on USB.

See /usr/src/linux/Documentation/kernel-parameters.txt to learn what rootdelay= and rootwait do.

You do need an initrd/initramfs to use root=UUID= or root=LABLE= as they both depend on the user space mount command.
root=PARTUUID= and root=/dev/sd.. are both handled by the kernel.

Maybe grub is being too clever for its own good and translating whatever you pass the setup to /dev/sd...
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

NP_complete · Tux's lil' helper Joined: 21 Mar 2009 Posts: 137

I won! And the takeaway is:

1. Do the fstab in terms of UUIDs.

2. In /etc/default/grub, make GRUB_CMDLINE_LINUX contain root=PARTUUID=<the root partition's PARTUUID>.

3. Right or wrong, I never ended up needing rootdelay/rootwait.

My GRUB still inexplicably prepends root=/dev/sda-<something> to the command line at boot, so now I have two "root=" entries in there. Perhaps there is a way to get rid of the first "root=", but it's probably not essential.

Thanks much, NeddySeagoon!