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Accepted
George Udosen
Asked: 2018-09-09 12:39:07 +0800 CST

Are these processes basically the same " sudo mount -o loop imagefile mntpoint" vs " sudo losetup /dev/loop2 imagefile"

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I am trying understand what the difference is between two ways of creating a loop mount point. Now I can create this with:

  1. sudo mount -o loop /file_to_use /mntpoint, and

  2. sudo losetup /dev/loop1 /file_to_use and then mount sudo mount /dev/loop1 /mntpoint

Question:

Are these the two processes the same as I have tested them and there both result in the same mount points as seen here, but I could be wrong?

NAME   FSTYPE LABEL UUID                                 MOUNTPOINT
sda                                                      
├─sda1 ext4         7af461fe-8d2d-4499-a12a-72ff586ff5d6 /boot
├─sda2 swap         44744c25-8797-4cd2-b83e-f129e97efc85 [SWAP]
├─sda3 ext4         3d39068d-96da-4f90-be42-b0921fb7278e /
└─sda4 ext4         643c8738-9823-43cd-b2b2-efe0b81b7611 /home
sr0                                                      
loop0  ext4         ac7deda8-7f3b-4835-8308-e4020ffe5302 /mnt/vfs
loop1  ext4         68a0676b-ad59-4dff-9c50-eca5d972c1c7 /mnt/tempdir
mount loop-device

1 Answers

  1. Best Answer

    Yes, both are essentially doing the same thing. Refer to man page of mount: https://linux.die.net/man/8/mount

    The Loop Device

    One further possible type is a mount via the loop device. For example, the command

    mount /tmp/fdimage /mnt -t vfat -o loop=/dev/loop3

    will set up the loop device /dev/loop3 to correspond to the file /tmp/fdimage, and then mount this device on /mnt.

    This type of mount knows about four options, namely loop, offset, sizelimit and encryption, that are really options to losetup(8). (These options can be used in addition to those specific to the filesystem type.)

    If no explicit loop device is mentioned (but just an option '-o loop' is given), then mount will try to find some unused loop device and use that.

    Since Linux 2.6.25 is supported auto-destruction of loop devices and then any loop device allocated by mount will be freed by umount independently on /etc/mtab.

    You can also free a loop device by hand, using 'losetup -d' or 'umount -d'.

    Bonus: sudo mount /file_to_use /mntpoint will work too. mount will automatically setup a loop device for you!

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