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Re: Installer: GUIX_IMAGE as /dev/sda on some hardware?


From: Tobias Geerinckx-Rice
Subject: Re: Installer: GUIX_IMAGE as /dev/sda on some hardware?
Date: Sat, 25 May 2019 13:58:20 +0200

Giovanni Biscuolo wrote:
This is **very** important when installing grub, in fact grub
installation failed when instantiating my config.scm on the HP ProLiant
simply because it was on /dev/sda pointing to the USB media;

/dev/xdyN names have never been safe to use in this way, though. I guess they're fine (at your own risk…) as short identifiers during a single CLI session, but not across reboots. It just often *happens* to work on most machines, which as we all know, is the most dangerous kind of working.

3. how is the USB media "relocated" to the last /dev/sd? device by the
installer?

It's… not? Dev nodes & names are doled out by the kernel. As you've discovered, they aren't to be relied on, and you should use labels or UUIDs instead.

Even if we'd pretend differently in the installer, for example through artificially delayed probing for usb_storage devices, things would still break when that lie would be exposed by adding a new SATA drive, or when using a different (rescue) distro, or…

1. has anyone observed a similar issue?

2. what could have caused it?

I used to own a system that scanned drives in a different order depending on whether or not a USB keyboard was attached. It was intended as a headless system; great fun debugging that! I once corrupted a drive (luckily part of a RAID-1 array, but it was still stupid of me) because the rescue CD scanned drives in a different order than the distro I was used to.

My first SATA motherboard enumerated drives differently between cold and warm boots — but only sometimes. I think it had something to do with spin-up times.

I could go on.  I often do.  Sorry.

Hoping to have scared you into using UUIDs,

T G-R

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