[Sorry: original sent before complete; ignore earlier message] I am trying to read some files off of a virtual disk without running the entire virtual machine. (Running a VM would involve at least using a later version of the VirtualBox, or a switch to KVM, and I already have enough complexity).
When I attempt to mount a logical volume from that virtual disk, I get the error: --------------------------------- root@barley:~/tempserver-check# date; mount /dev/stretch-vg/boot stretch_boot Mon 13 May 2019 11:42:15 PM PDT mount: /root/tempserver-check/stretch_boot: can't read superblock on /dev/mapper/stretch--vg-boot. --------------------------------------------- Same error if I add -t ext2, 3, or 4. The /dev/mapper entry is present. But when I check the block device, there don't seem to be any complaints: ================================ root@barley:~/tempserver-check# date; e2fsck -n /dev/stretch-vg/boot Mon 13 May 2019 11:45:49 PM PDT e2fsck 1.44.5 (15-Dec-2018) /dev/stretch-vg/boot: clean, 345/97536 files, 116077/389120 blocks ============================== I also tried e2fsck using the /dev/mapper/... path. It was happy with that too. See below for more info from dumpe2fs. The only thing that struck me as odd was the mount count of -1, but I'm no extN expert. I suspect this is some problem with my use of qemu-nbd. Running on buster. The virtual disks I'm trying to read were created under wheezy with VBox 4.3. Any ideas? The stack is pretty complex: /dev/stretch-vg/boot is an LVM logical volume from a volume group (stretch-vg) based on an LVM "physical volume" which is a partition (3) of a virtual disk served up by qemu-nbd which is based on a virtual disk file, stretch vdi which sits on a trivial RAID array (RAID1 with only one member) md/media5 whose only member is a partition sdf2 That partition was created by ddrescue from a disk that was failing; all but one 4k sector were recovered. The start and end sectors on the new disk are the same as the start and end sectors on the old one. FWIW this particular virtual machine seemed to be operating OK even after the disk error. File systems and devices were opened read only where possible. My real target is some logical volumes that are encrypted, and so involves one more layer. But I figure if I can't handle an unencrypted partition my chances of reading an encrypted one are slim. Thanks. Ross Boylan EVEN MORE DETAILED DETAILS Key commands and results, working from the bottom of the previous stack up. dumpe2fs just before the last command: mdadm -v --assemble --readonly /dev/md/media5 /dev/sdf2 Mon 13 May 2019 08:12:09 PM PDT mdadm: looking for devices for /dev/md/media5 mdadm: /dev/sdf2 is identified as a member of /dev/md/media5, slot 0. mdadm: added /dev/sdf2 to /dev/md/media5 as 0 mdadm: /dev/md/media5 has been started with 1 drive. root@barley:~/tempserver-check# mount -r -t ext4 /dev/md/media5 spare root@barley:~/tempserver-check# df spare Filesystem 1K-blocks Used Available Use% Mounted on /dev/md127 3905540432 3781174980 46211380 99% /root/tempserver-check/spare # hmm I don't think the original was that full. # failed initial attempt to use qemu-nbd omitted. I closed all devices and unloaded the nbd module # root@barley:~/tempserver-check# date; modprobe -v nbd Mon 13 May 2019 11:33:07 PM PDT insmod /lib/modules/4.19.0-4-amd64/kernel/drivers/block/nbd.ko root@barley:~/tempserver-check# date; qemu-nbd -v -r --fork -c /dev/nbd3 spare/stretch/stretch.vdi Mon 13 May 2019 11:36:36 PM PDT root@barley:~/tempserver-check# parted /dev/nbd3 p Model: Unknown (unknown) Disk /dev/nbd3: 21.5GB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: Number Start End Size File system Name Flags 1 1049kB 200MB 199MB bios_grub 2 200MB 1201MB 1000MB spare 3 1201MB 21.5GB 20.3GB big lvm # pvdisplay of /dev/ndb3p3 looks good, as do other lvm indicators # next command was probably unnecessary root@barley:~/tempserver-check# lvchange -ay stretch-vg/boot root@barley:~/tempserver-check# date; mount /dev/stretch-vg/boot stretch_boot Mon 13 May 2019 11:42:15 PM PDT mount: /root/tempserver-check/stretch_boot: can't read superblock on /dev/mapper/stretch--vg-boot. root@barley:~/tempserver-check# date; mount -t ext2 /dev/stretch-vg/boot stretch_boot Mon 13 May 2019 11:42:36 PM PDT mount: /root/tempserver-check/stretch_boot: wrong fs type, bad option, bad superblock on /dev/mapper/stretch--vg-boot, missing codepage or helper program, or other error. root@barley:~/tempserver-check# date; mount -t ext3 /dev/stretch-vg/boot stretch_boot Mon 13 May 2019 11:42:45 PM PDT mount: /root/tempserver-check/stretch_boot: wrong fs type, bad option, bad superblock on /dev/mapper/stretch--vg-boot, missing codepage or helper program, or other error. root@barley:~/tempserver-check# date; mount -t ext4 /dev/stretch-vg/boot stretch_boot Mon 13 May 2019 11:42:51 PM PDT mount: /root/tempserver-check/stretch_boot: can't read superblock on /dev/mapper/stretch--vg-boot. root@barley:~/tempserver-check# dumpe2fs -h /dev/stretch-vg/boot dumpe2fs 1.44.5 (15-Dec-2018) Filesystem volume name: <none> Last mounted on: /boot Filesystem UUID: e288f277-27a6-4500-9631-e17c3b661c68 Filesystem magic number: 0xEF53 Filesystem revision #: 1 (dynamic) Filesystem features: has_journal ext_attr resize_inode dir_index filetype extent 64bit flex_bg sparse_super large_file huge_file dir_nlink extra_isize metadata_csum Filesystem flags: signed_directory_hash Default mount options: user_xattr acl Filesystem state: clean Errors behavior: Continue Filesystem OS type: Linux Inode count: 97536 Block count: 389120 Reserved block count: 19456 Free blocks: 273043 Free inodes: 97191 First block: 1 Block size: 1024 Fragment size: 1024 Group descriptor size: 64 Reserved GDT blocks: 256 Blocks per group: 8192 Fragments per group: 8192 Inodes per group: 2032 Inode blocks per group: 254 Flex block group size: 16 Filesystem created: Tue May 8 12:50:24 2018 Last mount time: Tue May 7 08:42:06 2019 Last write time: Wed May 8 02:32:53 2019 Mount count: 17 Maximum mount count: -1 Last checked: Thu Feb 21 07:09:31 2019 Check interval: 0 (<none>) Lifetime writes: 802 MB Reserved blocks uid: 0 (user root) Reserved blocks gid: 0 (group root) First inode: 11 Inode size: 128 Journal inode: 8 Default directory hash: half_md4 Directory Hash Seed: 84ad0f32-1fe8-4b7a-8d1a-353028e247fa Journal backup: inode blocks Checksum type: crc32c Checksum: 0xd26b1d66 Journal features: journal_64bit journal_checksum_v3 Journal size: 8M Journal length: 8192 Journal sequence: 0x00000347 Journal start: 0 Journal checksum type: crc32c Journal checksum: 0xe13c80a9 root@barley:~/tempserver-check# date; e2fsck -n /dev/stretch-vg/boot Mon 13 May 2019 11:45:49 PM PDT e2fsck 1.44.5 (15-Dec-2018) /dev/stretch-vg/boot: clean, 345/97536 files, 116077/389120 blocks
