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Thread: LiveUsb / Casper: Mount error with live-media-path and persistence; other related ?'s

  1. #1
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    Question LiveUsb / Casper: Mount errors with persistence (/cow); other related ?'s

    I've been having pretty good success creating a bootable USB flash drive with the Ubuntu "live" environment (casper). I'm using the official release of Karmic Koala (9.10), x86, and have followed the notes at https://wiki.ubuntu.com/LiveUsbPendrivePersistent (method 3) and https://help.ubuntu.com/community/LiveCD/Persistence .

    The only real difference so far is that I plan on using Ext2 (or maybe even 3 or 4) instead of Fat16/32, and as such am using Grub2 (1.97) instead of SYSLINUX. I'm also testing everything using VirtualBox, and as such, am using a virtual hard disk instead of an actual USB drive, as VirtualBox currently doesn't support booting from USB.

    I had everything working great, including persistence. However, the root of my boot drive seemed very messy, with 5+ folders created for the contents of the live CD (casper, preseed, etc.), another 5+ folders for persistence (etc, home, var, etc.), and everything else I was hoping to share the partition with. Ideally, all of the contents of the live CD would be copied into a "ubuntu-live" directory, and all of the persistence data would be kept in a "ubuntu-persistence" directory.

    Here is the Grub2 entry that I had when everything was working as expected:

    Code:
    menuentry "Ubuntu 9.10 32-bit - Live" {
    	linux /casper/vmlinuz boot=casper persistent --
    	initrd /casper/initrd.lz
    }
    I then moved all of the live CD folders (casper, preseed, etc.) into /ubuntu-live, and updated the Grub2 entry with the "live-media-path" option as documented at http://manpages.ubuntu.com/manpages/...e-getty.7.html :

    Code:
    menuentry "Ubuntu 9.10 32-bit - Live" {
    	linux /ubuntu-live/casper/vmlinuz boot=casper live-media-path=/ubuntu-live/casper ignore_uuid persistent --
    	initrd /ubuntu-live/casper/initrd.lz
    }
    I had to add the "ignore_uuid" option to prevent the boot from hanging with infinite "stdin: error 0" outputs (after "Begin: Running /scripts/casper-premount ...", 2 "Done." lines, and a few EXT4-4s kernel debug outputs, apparently due to the hidden ".disk" directory missing from the root of the drive.

    However, I'm stuck with the following output: (OCR'd from VirtualBox print-screen using tesseract with manual edits)

    Code:
    [ 5.780380] device-mapper: dm-raid45: initialized v0.2594b
    Done.
    Begin: Running /scripts/init-premount ...
    Done.
    Begin: Mounting root file system... ...
    [ 6.937398] EXT4-fs (sda1): barriers enabled
    Begin: Running /scripts/casper-premount ...
    Done.
    Done.
    [ 6.939426] kjournald2 starting: pid 339, dev sda1:8, commit interval 5 seconds
    [ 6.940156] EXT4-fs (sda1): delayed allocation enabled
    [ 6.940575] EXT4-fs: file extents enabled
    [ 6.941079] EXT4-fs: mballoc enabled
    [ 6.941384] EXT4-fs (sda1): mounted filesystem with ordered data mode
    [ 6.996176] aufs 2-standalone.tree-30-20090727
    [ 7.167173] squashfs: version 4.0 (2009/01/31) Phillip Lougher
    BusyBox u1.13.3 (Ubuntu 1:1.13.3-lubuntu?) built-in shell (ash)
    Enter 'help’ for a list of built-in commands.
    (initramfs) mount: mounting /dev/sdal on /cow failed: Device or resource busy
    Can not mount /dev/sdal on /cow
    Hitting enter gives a "(initramfs)" BusyBox prompt.

    Removing the "persistent" option allows for a successful boot as a normal live CD, but without persistence.

    What does "cow" stand for in this context?

    After some digging, this appears to be coming from line 426 in /initrd/scripts/casper , shortly after calling the "find_cow_device" function that is defined in casper-helpers. Overall, it seems that something else already has /dev/sda1 locked, but I don't know what. Not knowing exactly what "/cow" is supposed to be or what it is used for doesn't help, either. I'm wondering if maybe this entire mount section is unnecessary, and if a symbolic link would suffice instead?

    I considered trying to edit the casper script to make this work, or at least to add some additional debugging. Is there an easier way to do this short of rebuilding it into a new casper/initrd.lz every time? (https://wiki.ubuntu.com/CustomizeLiveInitrd)

    Some additional references that I found:


    Finally, I also found http://manpages.ubuntu.com/manpages/...e-getty.7.html . It mentions that it is a fork of Casper, and most significantly, includes a "persistent-path" option in addition to "live-media-path" and other potentially useful options. Should I consider trying to switch over to this, instead, if even possible?

    Are there any other ideas or fixes to get this working as expected?

    Thanks!
    Last edited by ziesemer; December 18th, 2009 at 10:35 PM.

  2. #2
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    Re: LiveUsb / Casper: Mount error with live-media-path and persistence; other related

    Now I'm getting the exact same error, even without trying to move directories around. I even tried re-creating everything from scratch, and am still getting the same "Can not mount /dev/sda1 on /cow" error.

    Any help would be appreciated - thanks!

  3. #3
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    Re: LiveUsb / Casper: Mount error with live-media-path and persistence; other related

    I thought that maybe this was an issue with Ext4. Repeated the setup with Ext2 instead, but still having the same issue with persistence. Can the Live files not share the same partition with persistence? (Both on a partition labeled "casper-rw"? Are 2 partitions required?)

  4. #4
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    Re: LiveUsb / Casper: Mount error with live-media-path and persistence; other related

    This is looking related to http://ubuntuforums.org/showthread.php?t=647844 "Live USB with persistence in a single FAT partition", which appears to be written for 7.10 (Gutsy Gibbon). Will have to see if the effort can be easily duplicated on Karmic.

  5. #5
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    Re: LiveUsb / Casper: Mount error with live-media-path and persistence; other related

    I finally found the answer to one of my questions, which seems so obvious now! COW: Copy-On-Write. ( http://en.wikipedia.org./wiki/Copy-on-write , http://wiki.debian.org/DebianLive/FA...s.2BAC8-cow.3F )

  6. #6
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    Re: LiveUsb / Casper: Mount error with live-media-path and persistence; other related

    Bump. Can anyone please help me with this? Thanks!

  7. #7
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    Re: LiveUsb / Casper: Mount error with live-media-path and persistence; other related

    This is a working USB Flash drive with that operates with full Ubuntu O.S.
    Has persistence for all 13 gig partition with boot in seperate partition done
    with gparted manually. It works I am using it now on Laptop.

    I have finally got a 16 gig Flash drive to work as independent system. A lot of trial and error.
    Used Live CD. 9.10 64 bit and the 16 gig flash drive.
    Booted Live CD and selected install.
    When it got to partitioning selected USB device of course.
    1st partition was 500 meg ext3 /boot as mounting point
    2nd partition was 13.5 gig ext3 / as mounting point
    3rd partition was 2 gig Swap

    IN THE 8TH PAGE YOU HAVE TO CLICK ADVANCED TAB AND SELECT BOOT AS THE SAME
    AS YOUR 1ST PARTITION THAT YOU SELECTED AS /BOOT AS MOUNTING POINT.

    Then add your repositories such as partners, medibuntu, backports, all the same ones as your normal install. You have over 12 gig left to work with so use what you want. Compiz works fine, the only thing in Karmic I have not gotten to work is sound and every install of 9.10 on my HP G71-34OUS has
    had sound issues, I will get it. WIFI came right in. Has been a normal install.

    Grub menu. When you upgrade it installs itself onto your systems grub with no partition
    number such as sba1 or any device. This works well it just installs a grub selection while
    plugged in to USB port with recovery selection.

    here is fdisk. I am running flash drive now.

    Device Boot Start End Blocks Id System
    /dev/sda1 * 1 26 203776 7 HPFS/NTFS
    Partition 1 does not end on cylinder boundary.
    /dev/sda2 26 26132 209696248 7 HPFS/NTFS
    /dev/sda3 26133 37330 89947935 5 Extended
    /dev/sda4 37331 38914 12709888 7 HPFS/NTFS
    /dev/sda5 32107 37111 40202631 83 Linux
    /dev/sda6 37112 37330 1759086 82 Linux swap / Solaris
    /dev/sda7 26133 31856 45977967 83 Linux
    /dev/sda8 31857 32106 2008093+ 82 Linux swap / Solaris

    Partition table entries are not in disk order

    Disk /dev/sdb: 16.7 GB, 16687038464 bytes
    64 heads, 32 sectors/track, 15914 cylinders
    Units = cylinders of 2048 * 512 = 1048576 bytes
    Disk identifier: 0x0008849e

    Device Boot Start End Blocks Id System
    /dev/sdb1 * 1 954 976880 83 Linux
    /dev/sdb2 3831 15914 12374016 83 Linux
    /dev/sdb3 956 3830 2944000 82 Linux swap / Solaris
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  8. #8
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    Re: LiveUsb / Casper: Mount error with live-media-path and persistence; other related

    garvinrick4 - thanks for the reply!

    However, it sounds like you're running the full Ubuntu OS, and not Casper? I'd like to still use Casper if at all possible, to use the enhanced persistence options, and help avoid unnecessary writes to my flash drive. This would also give me the option to run Casper with or without the persistent flag, just as 2 separate Grub entries.

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