Loopback Device: Difference between revisions
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A Loopback Device is a mechanism used to interpret files as real devices. The main advantage of this method is that all tools used on real disks can be used with a loopback device.
Note: This article only covers UNIX environments (including [[Cygwin]]). For information on how to use loopback devices on Windows, see [
== Loopback Device under Linux==
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setup (fd0)
NOTE: You must unmount /mnt/myfloppy before using a emulator to directly read /dev/loop0, such as
qemu -fda /dev/loop0
NOTE: When deleting the loop device, the original floppy.img file will be saved with the modified contents.
=== Floppy Disk Images With FAT16 ===
dd if=/dev/zero of=floppy.img bs=512 count=2880
losetup /dev/loop0 floppy.img
mkdosfs /dev/loop0
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For ext2fs, use:
mke2fs -b1024 /dev/loop0 #blocks
Explanation:
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For FAT32, use:
mkdosfs -F32 /dev/loop0 #blocks
Explanation:
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mount -text2 /dev/loop0 /mnt/wherever
or:
mount -tvfat /dev/loop0 /mnt/wherever
Explanation:
{| {{Wikitable}}
mount Linux command to mount a filesystem▼
|-
-text2/-tvfat Filesystem being used, Linux can usually figure this out on its own.▼
| mount
/dev/loop0 The device representing our PARTITION▼
|-
| -text2 / -tvfat
|-
| /dev/loop0
|-
| /mnt/wherever
| A directory to mount the partition on.
|}
This should leave you with a nicely mounted partition. If you run df -Th you should end up with a line similar to:
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/dev/loop0 vfat 492M 4.0K 492M 1% /mnt/wherever
...or for ext2fs
Filesystem Type Size Used Avail Use% Mounted on
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Explanation:
{| {{Wikitable}}
|-
/dev/loop0 The device that was mounted▼
| umount
|-
| /dev/loop0
|}
==== Making it Easier ====
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One final thing to do, which is to simplify mounting and unmounting that partition.
Mounting:
mount -text2 -oloop=/dev/loop0,offset=32256 /path/to/c.img /mnt/wherever
Unmounting:
umount /path/to/c.img
This is essentially a combination of the losetup and mount commands we used previously when formatting the partition. If used it also means we lose access to the raw 'disk' or 'partition' through /dev/loop0.
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See also http://www.pixelbeat.org/scripts/lomount.sh
Finally, if you have to mount and umount that image very frequently and you're too lazy to type the sudo password each time, just add to /etc/fstab:
/path/to/c.img /mnt/wherever ext2 user,loop 0 0
now you can just▼
▲now you can just call:
mount /mnt/wherever
umount /mnt/wherever
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Things to remember:
losetup type command will give you the equivalent of a raw disk device (Eg /dev/hda)▼
▲* losetup -o type command will give you the equivalent of a raw
== Loopback Device under FreeBSD ==
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