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On 25/06/2016 20:33, Helmut Jarausch wrote: |
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> Hi, |
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> |
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> I'm a dino since I still use grub-1 but I prefer recent kernels |
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> (currently 4.70-rc4) |
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> |
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> I don't understand the 'root=' option on the boot line like |
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> kernel /boot/vmlinuz-4.7.0-rc4 root=/dev/sda1 |
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> |
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> Here my bad experience: |
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> |
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> Having booted by SystemRescueCD from the cdrom device, my root device is |
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> labelled /dev/sda1 |
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> BUT trying to use that on the kernel boot line fails (the kernel cannot |
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> find the root file system) |
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> |
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> By trial and error I've found that I have to use root=/dev/sdb1 |
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> |
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> but if I plug in an external drive (via USB) this doesn't work any more. |
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> |
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> So, I came up with root=UUID=uuid_number of the root file system. |
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> |
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> But to my surprise I now got a kernel panic |
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> syncing: VFS: unable to mount root fs on unknown block(0,0) |
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> |
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> So, please tell me what I'm missing? |
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> |
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> Many thanks!!! |
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> Helmut |
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> |
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> |
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I've run into this with my last 3 laptops. grub, systemrescue and most |
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other things that run before my kernel is booted usually find the SSD as |
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the first drive (what a running kernel would call sda), and the spinning |
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rust is sdb. |
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When the kernel eventually boots and does device discovery, it decides |
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the spinning rust is the primary drive (sdb) - the opposite way around. |
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So why does this happen? screwed if I know, BUT, the the kernel has |
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never guaranteed it will always find and enumerate devices the same way |
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every time always. This might account for why SystemRescueCD and your |
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installed system do opposite things[1]. We don't know *why* it's sdb, |
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but we know at grub time that it is. SO use whatever that software |
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thinks the thing is called :-) |
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[1] It's also one of the reasons persistent device naming came into |
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udev, to try guarantee the same device will always have the same name |
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-- |
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Alan McKinnon |
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alan.mckinnon@×××××.com |