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Since I updated to Ubuntu 14.04, I continually received an error, but ignored it. Now the system has become very slow, and it has become impossible to even format a hard disk. When I try to format, this is written to the console:

error unmounting/dev/sda1:
command-line 'umount "/dev/sda1"' exited with nonzero exit status 1:
umount: device is busy.
(in some cases useful info about processes that use the device is found by Isof(8) or fuser(1))
(udiskss-error-quar,14)
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  • It looks like something is wrong with your partition. Have you tried opening GParted? A lot of times it will tell you if a partition is unstable, sometimes it will offer fixes. Although Id be wary of some of those as sometimes they just make things worse. – Msquared Jun 18 '15 at 12:06
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    You can't unmount a partition that contains the currently-running system: that would be like sawing off the branch of the tree that you're sitting on. Any changes to the system partition will need to be made using another bootable medium such as a live CD or USB. – steeldriver Jun 18 '15 at 12:23
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The slowness and the error message don't appear to be related.

Rather, it seems you are trying to format your system partition (typically /dev/sda1). In most cases, this isn't what you want, unless you are aiming for a complete system reinstall, in which case you should boot from an installation CD or USB drive anyway.

If you're very sure you want to format this partition, you'll have to boot from another device, such as a live CD or USB drive. The reason is that you can never unmount the partition running the system, since the system can't unmount itself. For the same reason, simply booting in recovery mode isn't enough.

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