Fedora Loop Devices – Add More /dev/loop* Devices

Take a look and see if there are any mounts using any of the above loopback devices. You can use the mount command to see this:

$ mount

If they are mounted, they you'll likely need to unmount (umount) them prior to getting losetup -d <loopdevice> to detaching them.

$ umount /dev/some/mount

As to if it's safe or not, that really depends on what these are being used for. I'd probably hold off till I had a better grasp of what these loop devices are for, before I started unmounting them. Just a guess but they might have something to do with an encrypted drive.

Therefore I'd create another one just to be safe.

making another loop device

Here are the steps:

$ sudo mknod -m640 /dev/loop8 b 7 8

• -m640 define the permission of the device
• /dev/loop8 define the name of the device
• b for the creation of the special block device
• 7 8 the number 7 AND 8 define the MAJOR AND the MINOR

Check if the loop is created:

$ ls -l /dev/loop8
brw-r----- 1 root root 7, 8 Oct 3 14:54 /dev/loop8

Now set ownership on the device:

$ sudo chown root:disk /dev/loop8

References

• Howto create Loop Device on Linux

You need to use losetup -P for creating a -Partitioned loop device, or else you need to partition the original loop device then partx -update the kernel's partition table afterward. The /dev/loop0p devices will appear after the kernel recognizes that the partition has actually been partitioned. Probably this is partly what the intent behind the sleep 5 is - but that should almost definitely be a sync - or both - instead.

Anyway, to demonstrate:

sudo sh -s <<\IN
    losetup -D                          
    fallocate "-l$((1024*1024*1024))" loop        
    printf %s\\n n '' '' '' ''  w y | gdisk loop
    sync; losetup -f loop
    lsblk /dev/loop*
IN

So the above sequence first -Detaches all current loop devices (if any) fallocates a 1GB tmp file, writes a GPT partition table to it and does a single partition on it, then syncs the filesystem and assigns it to the -first available loop device before trying to list with lsblk all available loop devices. It prints:

NAME  MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0   7:0    0   1G  0 loop 

But if I alter the losetup line to read:

losetup -fP loop

...it instead prints:

NAME      MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
loop0       7:0    0    1G  0 loop 
├─loop0p1 259:0    0 1023M  0 loop 
└─loop0p2 259:1    0 1007K  0 loop 

...because losetup first scans the backing file for a partition table. As you can see, it's not very good at it - rather than noting the extra 1M (which is almost definitely the last iteration's partition table, actually) as unallocated space it interprets it as a separate partition, but that's probably because I'm writing to a tmpfs (twice in a row) at the top of a 1GB file hole - working w/ actual data will be much more precise (and zeroing the backing file as your script does w/ dd would handle that anyway). In any case - I can freely mkfs.whatever on the real partition there and afterwards mount it. partx -u on the /dev/loop0 would achieve the same results.