How to create a formatted partition image file from scratch?
If on Linux, when loading the loop
module, make sure you pass a max_part
option to the module so that the loop devices are partitionable.
Check the current value:
cat /sys/module/loop/parameters/max_part
If it's 0:
modprobe -r loop # unload the module
modprobe loop max_part=31
To make this setting persistent, add the following line to /etc/modprobe.conf
or to a file in /etc/modprobe.d
if that directory exists on your system:
options loop max_part=31
If modprobe -r loop
fails because “Module loop is builtin”, you'll need to add loop.max_part=31
to your kernel command line and reboot. If your bootloader is Grub2, add to it to the value of GRUB_CMDLINE_LINUX
in etc/default/grub
.
Now, you can create a partitionable loop device:
truncate -s64M file # no need to fill it with zeros, just make it sparse
fdisk file # create partitions
losetup /dev/loop0 file
mkfs.vfat /dev/loop0p1 # for the first partition.
mount /dev/loop0p1 /mnt/
(note that you need a relatively recent version of Linux).
losetup /dev/loop0 file -o 1048576 --sizelimit limit
Offset specified should be in bytes (1048576 = 2048 sectors * 512 bytes per sector).
mount -o loop,offset=1048576,sizelimit=limit
For more information see losetup and mount.
The following procedures allow you to mount the partitions of the image to modify them.
losetup 2.21 -P option
losetup -P -f --show my.img
Creates one /dev/loopXpY
per partition.
Advantage: executable pre-installed in many distros (util-linux package).
Disadvantage: quite recent option, not present in Ubuntu 14.04.
losetup -P
automation
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"
)
kpartx
sudo apt-get install kpartx
losetup -fs my.raw
sudo kpartx -a my.img
ls /dev/mapper
Output:
/dev/mapper/loop0
/dev/mapper/loop0p1
where loop0p1
is the first partition, so we can do:
mkdir -p d
sudo mount /dev/mapper/loop0p1 d
Advantage of this method: works on Ubuntu 14.04 without rebooting.