Ubuntu – How to umount /dev/sda1 partition in ubuntu

diskmanagementfdiskUbuntuvirtual-machines

I have a Ubuntu VM which has an unmanaged OS disk associated with it.

I want to shrink my OS disk of size 50 GB to 40 GB.
However, when i try to unmount /dev/sda1 partition it tell me

umount: /mnt: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))

Therefore, i am unable to unmount it and then shrink it. Could anyone please help me with this?

Best Answer

Seems like your disk /dev/sda1 is mounted. So the best you can do is to boot from live CD and then do the operations you want to do. When boot from live CD /dev/sda1 will not be mounted.

Of course you can start to search for processes which keep open files in this filesystem. But this can take a lot of time.

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Linux – Ubuntu 6.06: Mounting /root/sda1 /root failed: No such device

Most of the time, e2fsck will not run unless it thinks it should. You can force it in a situation like this. Try adding the -f flag, like e2fsck -fp /dev/sda1.

Linux – How to decrease the size of a KVM virtual machine disk image

Thanks to those who posted, but your answers were way too vague to be of any help.

After hours of Googling, I finally found a guide(link redacted) providing step-by-step instructions on how to shrink my filesystem, logical volumes, and physical volumes. The trick that most guides miss is the need to actually delete the physical partitions, and recreate them with the correct size, because parted is unable to resize lvm partitions.

I then found this documentation on qemu-img, which explains how to shrink a raw-formatted virtual disk image by running:

sudo qemu-img resize /var/lib/libvirt/images/myvm.img 255G

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