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what is the difference between available and free disk space? see image below: http://alvarberglind.se/disk.png

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available = free - reserved filesystem blocks(for root)

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On an EXT file system, a proportion of the free space is reserved for root usage, as the system needs some of this free space to run properly. The available space is the Free space, less this reserved amount.

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The ext filesystems (ext2, ext3, ext4) all, by default, reserve 5% of the space on a filesystem for use only by the root user. This is to ensure that the root user can perform necessary maintenance in the event that users fill up the filesystem.

You can change the amount of reserved space when you create the filesystem with the -m flag to mkfs:

mkfs -t ext4 -m 0 /dev/sda1

You can change the reservation on an existing filesystem using tune2fs:

tune2fs -m 0 /dev/sda1

In both cases, the argument to -m is a percentage.

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