Though we rarely defragment the filesystem on unix-like os, sometimes we still need it.

The demonstrate is on LinuxMint 17.1 Cinnamon 64-bit which is based on Ubuntu 14.04 LTS.

Okay, let’s check the fragmentation first!

Here is a very easy method to check the fragment on ext4 online:
$ sudo fsck -fn /dev/sdXY, replace XY for yourself, for example, $ sudo fsck -fn /dev/sda1

The output will look like this:

fsck from util-linux 2.20.1
e2fsck 1.42.5 (29-Jul-2012)
Warning! /dev/sda1 is mounted.
Warning: skipping journal recovery because doing a read-only filesystem check.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/sda1: 247/121920 files (0.4% non-contiguous), 66062/487424 blocks

(BTW, this method could also work on ext2, ext3)

and on xfs:
$ xfs_db -c frag -r /dev/sdXY, for example,$ xfs_db -c frag -r /dev/sda1

The output will look like this:

actual 297843, ideal 286076, fragmentation factor 3.95%

And defrag a partition now!

This is the command to defrag ext4 online:
$ sudo e4defrag -v /dev/sdXY, for example, $ sudo e4defrag -v /dev/sda1
(BTW, device /dev/sdXY can be replaced by a regular file or a directory, this is supported in e2fsprogs 1.42.9)

The output will look like this:

ext4 defragmentation for device(/dev/sda1)
[2/238]/boot/System.map-3.2.0-4-686-pae: 100% [ OK ]
[3/238]/boot/vmlinuz-3.16-0.bpo.2-686-pae: 100% [ OK ]
[5/238]/boot/grub/video_cirrus.mod: 100% [ OK ]
[6/238]/boot/grub/usb_keyboard.mod: 100% [ OK ]
[8/238]/boot/grub/locale/pl.mo: 100% [ OK ]
[9/238]/boot/grub/locale/nl.mo: 100% [ OK ]

.
.
.

[223/238]/boot/grub/password_pbkdf2.mod: 100% [ OK ]
[224/238]/boot/grub/videotest.mod: 100% [ OK ]
[225/238]/boot/grub/ntldr.mod: 100% [ OK ]
[226/238]/boot/grub/udf.mod: 100% [ OK ]
[227/238]/boot/grub/halt.mod: 100% [ OK ]
[228/238]/boot/grub/minix.mod: 100% [ OK ]
[229/238]/boot/grub/gfxterm.mod: 100% [ OK ]
[230/238]/boot/config-3.2.0-4-686-pae: 100% [ OK ]
[231/238]/boot/memtest86+_multiboot.bin: 100% [ OK ]
[232/238]/boot/memtest86+.bin: 100% [ OK ]
[233/238]/boot/System.map-3.16-0.bpo.2-686-pae: 100% [ OK ]
[234/238]/boot/initrd.img-3.2.0-4-686-pae: 100% [ OK ]
[235/238]/boot/initrd.img-3.16-0.bpo.2-686-pae: 100% [ OK ]
[237/238]/boot/config-3.16-0.bpo.2-686-pae: 100% [ OK ]
[238/238]/boot/vmlinuz-3.2.0-4-686-pae: 100% [ OK ]

Success: [ 234/238 ]
Failure: [ 4/238 ]

And here is the command to defrag xfs online:
$ sudo xfs_fsr -v /dev/sdXY, for example, $ sudo xfs_fsr -v /dev/sda1
(device /dev/sdXY by a file, but a directory is not supported yet in xfs_fsr version 3.1.9)

/ start inode=0
ino=1020
extents before:2 after:1 DONE ino=1020
ino=2000
extents before:3 after:1 DONE ino=2000
ino=2270
extents before:2 after:1 DONE ino=2270
ino=2272
extents before:2 after:1 DONE ino=2272
ino=2497
extents before:2 after:1 DONE ino=2497
ino=2498
extents before:2 after:1 DONE ino=2498
.
.
.

Not very hard, but useful, if the data on the target to defrag is important, I’ll respectfully suggest you to backup first, in case there is an accident like losing electrical power.