From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80]) by finch.gentoo.org (Postfix) with ESMTP id AC05D1382CD for ; Sat, 25 Jun 2016 19:52:13 +0000 (UTC) Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id CC254E0AEB; Sat, 25 Jun 2016 19:52:05 +0000 (UTC) Received: from mail-wm0-f68.google.com (mail-wm0-f68.google.com [74.125.82.68]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by pigeon.gentoo.org (Postfix) with ESMTPS id 7B4BEE0994 for ; Sat, 25 Jun 2016 19:52:04 +0000 (UTC) Received: by mail-wm0-f68.google.com with SMTP id 187so14178315wmz.1 for ; Sat, 25 Jun 2016 12:52:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-transfer-encoding; bh=1rm2tw1eo8o23RBWfpkxYIw/BZl7baBIba7UAcH3t4U=; b=syOscj2vyAd2J/tCut/9+MYIbfgm2H8nhMaDzDP0z/RwjT6ucKVWNhrzQlVpsf/ZTj tteYj38hPqotvI9E1e1+bJ2WgbVgpTDb/0hCNNGmx5RIg2Wb/zjTU646RcxxyHiyjTNi Kf7Xf+hgeYj7x32Zp0KVaEKfxHhIwsFPH32v2X6sOwM0i7Anb4bUZmClWyvjxk5wOdh3 uWFbxGna8xLsGNNgE29yFtgmrvDx7aG3eJsm/wn1wD69cpX5spgo7b3JvF03C8WA4IJ6 F8AZ/Bwbef1iurhoozGrIGqUcrpfoA/jS38wnVDvflOwnuWyv4tT4Yoae0EZsqYbWc4i yx5g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding; bh=1rm2tw1eo8o23RBWfpkxYIw/BZl7baBIba7UAcH3t4U=; b=EP/nMSXuiTNeNHamd+f3lfJP6qT4UPSJTYM3Y4qdsEJO3OtfwdIKPv5ZNJ/2nVRQPa 2dwgbS/y6W4Xbz0LpW1SXS8IlA/iSDShgIOxWDte1uOs5GXbWPwrNmczAEJKywXkGoss 7aChdbpBoVWxMH47020LasRd/8Fn2aB36ebUWsyYelH7GpgMIYP63IgghPqttff0B6mu z2SfAeiED7Q8TLFMK/n9y5kThFiSzfhd3Z7GZ/0NPNqrL+lbhevPZrzMAUgINZr68Zsg wBuKKbXNKFxa5bJk2SsF93AxMPkeRci2XvP6ZT7lq8GY+MLkFzcAfiE08duhaUqrMyjf Mr5Q== X-Gm-Message-State: ALyK8tJY8oU36vEIeSo6RdKJ/uWlBvTqjZc/lEmO4QzW1gcpDBge67Rf8RWQwboPM7xq7Q== X-Received: by 10.28.39.69 with SMTP id n66mr3850212wmn.3.1466884322837; Sat, 25 Jun 2016 12:52:02 -0700 (PDT) Received: from [172.20.0.40] ([196.212.62.210]) by smtp.googlemail.com with ESMTPSA id kc8sm3617530wjb.0.2016.06.25.12.52.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 25 Jun 2016 12:52:02 -0700 (PDT) Subject: Re: [gentoo-user] booting - I don't anystand how the (Linux) world works anymore To: gentoo-user@lists.gentoo.org References: From: Alan McKinnon Message-ID: <08789349-f812-e211-61b5-4159f8f13aae@gmail.com> Date: Sat, 25 Jun 2016 21:51:43 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Archives-Salt: 894cecef-784c-4830-94f8-8b5eaad04250 X-Archives-Hash: 24ad5d203fc82a82b4b10e79d37192d7 On 25/06/2016 20:33, Helmut Jarausch wrote: > Hi, > > I'm a dino since I still use grub-1 but I prefer recent kernels > (currently 4.70-rc4) > > I don't understand the 'root=' option on the boot line like > kernel /boot/vmlinuz-4.7.0-rc4 root=/dev/sda1 > > Here my bad experience: > > Having booted by SystemRescueCD from the cdrom device, my root device is > labelled /dev/sda1 > BUT trying to use that on the kernel boot line fails (the kernel cannot > find the root file system) > > By trial and error I've found that I have to use root=/dev/sdb1 > > but if I plug in an external drive (via USB) this doesn't work any more. > > So, I came up with root=UUID=uuid_number of the root file system. > > But to my surprise I now got a kernel panic > syncing: VFS: unable to mount root fs on unknown block(0,0) > > So, please tell me what I'm missing? > > Many thanks!!! > Helmut > > I've run into this with my last 3 laptops. grub, systemrescue and most other things that run before my kernel is booted usually find the SSD as the first drive (what a running kernel would call sda), and the spinning rust is sdb. When the kernel eventually boots and does device discovery, it decides the spinning rust is the primary drive (sdb) - the opposite way around. So why does this happen? screwed if I know, BUT, the the kernel has never guaranteed it will always find and enumerate devices the same way every time always. This might account for why SystemRescueCD and your installed system do opposite things[1]. We don't know *why* it's sdb, but we know at grub time that it is. SO use whatever that software thinks the thing is called :-) [1] It's also one of the reasons persistent device naming came into udev, to try guarantee the same device will always have the same name -- Alan McKinnon alan.mckinnon@gmail.com