question about fstab in squeeze and uuid
in [Debian]
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From: Paul E Condon on 12 Mar 2010 13:30 I'm working on a computer that I am trying to make dual-boot into both Lenny and Squeeze. As some are already aware, squeeze rewrites /etc/fstab to replace devices like /dev/hda2 with a UUID for the device that is a long computer generated string. I know very little about UUIDs but I suppose they are intended to be 'unique'. But I suppose that they are required to be persistent, i.e. they don't change over time. I experienced non-persistence today. While running Squeeze I noticed that one of my partitions, in particular the one that contained the Lenny installation, which I had put in the /dev/hda3, had been re-identified with a different UUID on reboot of the compute so that the entry in /etc/fstab could not be used to mount that partition under Squeeze (which was installed in /dev/hda2). I edited /etc/fstab to contain the new, diffenent UUID that I found by looking in /dev/disk/by-uuid, and was able to mount the partition, but it was hardly 'automatic'. I'm looking for reliable information on how UUIDs are generated, and how their uses is intended within Squeeze, so that I can puzzle out what I might be doing wrong. I think I know already that they are suppose to overcome some difficulties in the traditional way SCSI devices are handled in the Linux kernel. The disks that I am working with are NOT SCSI. But the fix for SCSI seems to be stepping on the traditional solution for ATA that had been working nicely. Or, maybe I just did something stupid. I need to read some more. Please make suggestions. -- Paul E Condon pecondon(a)mesanetworks.net -- To UNSUBSCRIBE, email to debian-user-REQUEST(a)lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster(a)lists.debian.org Archive: http://lists.debian.org/20100312182755.GJ4159(a)big.lan.gnu
From: Javier Barroso on 12 Mar 2010 14:00 Hi, On Fri, Mar 12, 2010 at 7:27 PM, Paul E Condon <pecondon(a)mesanetworks.net> wrote: > I'm working on a computer that I am trying to make dual-boot into both > Lenny and Squeeze. As some are already aware, squeeze rewrites > /etc/fstab to replace devices like /dev/hda2 with a UUID for the > device that is a long computer generated string. I know very little > about UUIDs but I suppose they are intended to be 'unique'. But I > suppose that they are required to be persistent, i.e. they don't > change over time. > > I experienced non-persistence today. While running Squeeze I noticed > that one of my partitions, in particular the one that contained the > Lenny installation, which I had put in the /dev/hda3, had been > re-identified with a different UUID on reboot of the compute so that > the entry in /etc/fstab could not be used to mount that partition > under Squeeze (which was installed in /dev/hda2). I edited /etc/fstab > to contain the new, diffenent UUID that I found by looking in > /dev/disk/by-uuid, and was able to mount the partition, but it was > hardly 'automatic'. I can't imagine any case where an filesystem UUID change "by the face", I think this is not possible if you didn't execute any filesystem command to do it. I don't know how did you install both systems, but maybe /etc/mtab file is causing the fault or maybe a root wrong option in grub Regards, -- To UNSUBSCRIBE, email to debian-user-REQUEST(a)lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster(a)lists.debian.org Archive: http://lists.debian.org/81c921f31003121059l2fdae414o59259307ffe216b6(a)mail.gmail.com
From: Camaleón on 12 Mar 2010 14:10 On Fri, 12 Mar 2010 11:27:55 -0700, Paul E Condon wrote: (...) > I'm looking for reliable information on how UUIDs are generated, and how > their uses is intended within Squeeze, so that I can puzzle out what I > might be doing wrong. There a FAQ about UUID here. While focused on Linux Mint, I think pretty much fits for Debian, also: *** UUID - what is it and why is it a problem http://www.linuxmint.com/wiki/index.php/UUID_-what_is_it_and_why_is_it_a_problem *** In brief, it seems that chanching/resizing/formatting partitions can lead into UUID being modified. If that's true, it seems scaring :-/ There are other options we can use to identify/mount our devices, say "label, "id" and "path" (ls -l /dev/disk/*). For instance, last time I used openSUSE was using "by-id" method in /etc/fstab. Maybe there is a good comparison chart about all these methods that list their "pros" and "cons" :-? Greetings, -- Camaleón -- To UNSUBSCRIBE, email to debian-user-REQUEST(a)lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster(a)lists.debian.org Archive: http://lists.debian.org/pan.2010.03.12.19.00.24(a)gmail.com
From: Stephen Powell on 12 Mar 2010 14:20 On Fri, 12 Mar 2010 13:27:55 -0500 (EST), Paul E Condon wrote: > > I'm working on a computer that I am trying to make dual-boot into both > Lenny and Squeeze. As some are already aware, squeeze rewrites > /etc/fstab to replace devices like /dev/hda2 with a UUID for the > device that is a long computer generated string. I know very little > about UUIDs but I suppose they are intended to be 'unique'. But I > suppose that they are required to be persistent, i.e. they don't > change over time. > > I experienced non-persistence today. While running Squeeze I noticed > that one of my partitions, in particular the one that contained the > Lenny installation, which I had put in the /dev/hda3, had been > re-identified with a different UUID on reboot of the compute so that > the entry in /etc/fstab could not be used to mount that partition > under Squeeze (which was installed in /dev/hda2). I edited /etc/fstab > to contain the new, diffenent UUID that I found by looking in > /dev/disk/by-uuid, and was able to mount the partition, but it was > hardly 'automatic'. > > I'm looking for reliable information on how UUIDs are generated, and > how their uses is intended within Squeeze, so that I can puzzle out > what I might be doing wrong. > > I think I know already that they are suppose to overcome some > difficulties in the traditional way SCSI devices are handled in the > Linux kernel. The disks that I am working with are NOT SCSI. But the > fix for SCSI seems to be stepping on the traditional solution for ATA > that had been working nicely. Or, maybe I just did something stupid. > > I need to read some more. Please make suggestions. Paul, I believe a UUID is generated when the partition is "formatted", either with mkfs or mkswap. If you asked for the partition to be formatted during the install of Lenny, which would be typical, the UUID will change. I believe that the installer's recent penchant for using UUIDs is the result of the sometimes-capricious device naming conventions chosen by udev. This has been made worse recently by the latest kernels using SCSI emulation for traditional ATA IDE hard disks. If SCSI emulation is not used, the partitions are called /dev/hda1, /dev/hda2, etc. If SCSI emulation is used, the partitions may be called /dev/sda1, /dev/sda2, etc. I personally don't like the use of UUIDS by the installer and I change them back to their traditional names. I guess I'll deal with the SCSI emulation issue when it gets here. Suit yourself. -- .''`. Stephen Powell <zlinuxman(a)wowway.com> : :' : `. `'` `- -- To UNSUBSCRIBE, email to debian-user-REQUEST(a)lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster(a)lists.debian.org Archive: http://lists.debian.org/1774076184.18698991268421047591.JavaMail.root(a)md01.wow.synacor.com
From: Javier Barroso on 12 Mar 2010 14:30 Hi, On Fri, Mar 12, 2010 at 8:00 PM, Camaleón <noelamac(a)gmail.com> wrote: > On Fri, 12 Mar 2010 11:27:55 -0700, Paul E Condon wrote: > > (...) > >> I'm looking for reliable information on how UUIDs are generated, and how >> their uses is intended within Squeeze, so that I can puzzle out what I >> might be doing wrong. > > There a FAQ about UUID here. While focused on Linux Mint, I think pretty > much fits for Debian, also: > > *** > UUID - what is it and why is it a problem > http://www.linuxmint.com/wiki/index.php/UUID_-what_is_it_and_why_is_it_a_problem > *** > > In brief, it seems that chanching/resizing/formatting partitions can lead > into UUID being modified. If that's true, it seems scaring :-/ > > There are other options we can use to identify/mount our devices, say > "label, "id" and "path" (ls -l /dev/disk/*). For instance, last time I > used openSUSE was using "by-id" method in /etc/fstab. > > Maybe there is a good comparison chart about all these methods that list > their "pros" and "cons" :-? Not a chart, but yes references to why uuid ... : https://bugzilla.redhat.com/show_bug.cgi?id=364441 http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=572376 Regards, -- To UNSUBSCRIBE, email to debian-user-REQUEST(a)lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmaster(a)lists.debian.org Archive: http://lists.debian.org/81c921f31003121121h6b491c0es8d346792e80d8a76(a)mail.gmail.com
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