I downloaded an raw SD card image that has two partitions.
It caused some file system errors when I tried to dd it directly into an SD card. I am not sure if the card is defective or the image.
Is there a way to examine this image without writing it to a physical card? Like trying to mount the partitions separately or checking the tables?
You can use kpartx or partx to create loop devices for the partitions on the image, and then mount them. So either:
$ sudo kpartx -v -a file.iso
add map loop0p1 (253:17): 0 8382464 linear 7:1 2048
$ mount /dev/mapper/loop0p1 ./mnt_point
... do something with the partition ...
$ umount ./mnt_point
$ kpartx -d -v file.iso
del devmap : loop0p1
loop deleted : /dev/loop0
or:
$ sudo partx -a -v file.iso
partition: none, disk: file.iso, lower: 0, upper: 0
Trying to use '/dev/loop0' for the loop device
/dev/loop0: partition table type 'dos' detected
range recount: max partno=1, lower=0, upper=0
/dev/loop0: partition #1 added
$ mount /dev/loop0p1 ./mnt_point
... do something with the partition ...
$ umount /dev/loop0p1 ./mnt_point
$ sudo partx -d -v /dev/loop0
partition: none, disk: /dev/loop0, lower: 0, upper: 0
/dev/loop0: partition #1 removed
See also How can I mount a disk image?
losetup -Pf in util-linux >= 2.21 (Ubuntu 16.04)
sudo losetup -Pf disk.img
sudo mkdir /mnt/loop0p1
sudo mount /dev/loop0p1 /mnt/loop0p1
See the losetup(8) man page and also https://askubuntu.com/questions/69363/mount-single-partition-from-image-of-entire-disk-device/673257#673257
losetup -P automation
Here are functions to automate if further. Usage:
$ los my.img
/dev/loop0
/mnt/loop0p1
/mnt/loop0p2
$ ls /mnt/loop0p1
/whatever
/files
/youhave
/there
$ sudo losetup -l
NAME SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE DIO
/dev/loop1 0 0 0 0 /full/path/to/my.img
$ # Cleanup.
$ losd 0
$ ls /mnt/loop0p1
$ ls /dev | grep loop0
loop0
Source:
los() (
img="$1"
dev="$(sudo losetup --show -f -P "$img")"
echo "$dev"
for part in "$dev"?*; do
if [ "$part" = "${dev}p*" ]; then
part="${dev}"
fi
dst="/mnt/$(basename "$part")"
echo "$dst"
sudo mkdir -p "$dst"
sudo mount "$part" "$dst"
done
)
losd() (
dev="/dev/loop$1"
for part in "$dev"?*; do
if [ "$part" = "${dev}p*" ]; then
part="${dev}"
fi
dst="/mnt/$(basename "$part")"
sudo umount "$dst"
done
sudo losetup -d "$dev"
)
The answer by @Catskul and @Cristian Ciupitu is perfectly fine, but it misses the loop unmount command. So if you have to do a second image, you will end up with using loop1, loop2 etc.
you can check which loop devices are connected to which images by calling losetup:
pk:~# partx -v -a /home/pkolmann/img/Test.img
partition: none, disk: /home/pkolmann/img/Test.img, lower: 0, upper: 0
Trying to use '/dev/loop1' for the loop device
/dev/loop1: partition table type 'dos' detected
range recount: max partno=2, lower=0, upper=0
/dev/loop1: partition #1 added
/dev/loop1: partition #2 added
pk:~# losetup
NAME SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE DIO LOG-SEC
/dev/loop1 0 0 0 0 /home/pkolmann/img/Test.img 0 512
/dev/loop0 0 0 0 0 /home/pkolmann/img/Test.img 0 512
after unmounting the partitions with
pk:~# partx -v -d /dev/loop0
partition: none, disk: /dev/loop0, lower: 0, upper: 0
/dev/loop0: partition #1 removed
/dev/loop0: partition #2 removed
pk:~# partx -v -d /dev/loop1
partition: none, disk: /dev/loop1, lower: 0, upper: 0
/dev/loop1: partition #1 removed
/dev/loop1: partition #2 removed
the loop devices are still used:
pk:~# losetup
NAME SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE DIO LOG-SEC
/dev/loop1 0 0 0 0 /home/pkolmann/img/Test.img 0 512
/dev/loop0 0 0 0 0 /home/pkolmann/img/Test.img 0 512
These need to be removed extra:
wspk:~# losetup -d /dev/loop0
wspk:~# losetup -d /dev/loop1
wspk:~# losetup
You can use guestfish, a command-line wrapper for libguestfs:
libguestfs is a set of tools for accessing and modifying virtual machine (VM) disk images. You can use this for viewing and editing files inside guests, scripting changes to VMs, monitoring disk used/free statistics, creating guests, P2V, V2V, performing backups, cloning VMs, building VMs, formatting disks, resizing disks, and much more
All this functionality is available through a scriptable shell called guestfish, or an interactive rescue shell virt-rescue.
Get a shell to interact with the disk image (use -r to make the volumes read-only, -w if you want to be able to edit files on the image):
$ sudo guestfish -r -a DiskImage.img
Welcome to guestfish, the guest filesystem shell for
editing virtual machine filesystems and disk images.
Type: ‘help’ for help on commands
‘man’ to read the manual
‘quit’ to quit the shell
><fs> run
><fs> list_filesystems
/dev/sda1: vfat
/dev/sda2: ext4
First volume is my boot volume, second is my root. To interact with the files on either of them, mount them first:
><fs> mount /dev/sda2 /
><fs> ls /
bin
boot
dev
etc
home
...
To edit a file directly:
><fs> edit /home/pi/.bashrc
You can do lots of other things as well, like copy files to/from the image from/to your local machine or change the partitions. You can also script all these commands together from your local shell as such:
sudo guestfish add DiskImage.img : run : list_filesystems : mount /dev/sda2 / : ls / : edit /home/pi/.bashrc
And when you are done, the disk image itself will have changed. Burn your new image to a new SD card and voilà!
This answer on ServerFault suggests:
use losetup to get a /dev/loop? device, then use kpartx on it to create dev mappings for the partitions in the image file.
First display the partition table to get the start of the partitions:
$ fdisk -l ./sdcard-20250422
Disk ./sdcard-20250422: 59.63 GiB, 64021856256 bytes, 125042688 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xd5c79402
Device Boot Start End Sectors Size Id Type
./sdcard-20250422p1 8192 532479 524288 256M c W95 FAT32 (LBA)
./sdcard-20250422p2 532480 125042687 124510208 59.4G 83 Linux
Then mount with the loop offset option (convert the start in Kilobytes):
$ sudo mkdir /mnt/rootfs
$ sudo mount -o loop,offset=$((532480/2))K ./sdcard-20250422 /mnt/rootfs/
No need to tinker with losetup as /dev/loop* devices are managed anyway
You could try:
mount -t type -o loop ./image /mnt
where "type" = fs type and "image" is the name of your downloaded file
