E4DEFRAG(8)		    System Manager's Manual		   E4DEFRAG(8)

NAME
       e4defrag - online defragmenter for ext4 file system

SYNOPSIS
       e4defrag [ -c ] [ -v ] target ...

DESCRIPTION
       e4defrag reduces fragmentation of extent based file. The file targeted
       by e4defrag is created on ext4 file system made with "-O extent" option
       (see mke2fs(8)).	 The targeted file gets more contiguous blocks and
       improves the file access speed.

       target is a regular file, a directory, or a device that is mounted as
       ext4 file system.  If target is a directory, e4defrag reduces
       fragmentation of all files in it. If target is a device, e4defrag gets
       the mount point of it and reduces fragmentation of all files in this
       mount point.

OPTIONS
       -c     Get a current fragmentation count and an ideal fragmentation
	      count, and calculate fragmentation score based on them. By
	      seeing this score, we can determine whether we should execute
	      e4defrag to target.  When used with -v option, the current
	      fragmentation count and the ideal fragmentation count are
	      printed for each file.

	      Also this option outputs the average data size in one extent. If
	      you see it, you'll find the file has ideal extents or not. Note
	      that the maximum extent size is 131072KB in ext4 file system (if
	      block size is 4KB).

	      If this option is specified, target is never defragmented.

       -v     Print error messages and the fragmentation count before and
	      after defrag for each file.

NOTES
       e4defrag does not support swap file, files in lost+found directory, and
       files allocated in indirect blocks. When target is a device or a mount
       point, e4defrag doesn't defragment files in mount point of other
       device.

       It is safe to run e4defrag on a file while it is actively in use by
       another application.  Since the contents of file blocks are copied
       using the page cache, this can result in a performance slowdown to both
       e4defrag and the application due to contention over the system's memory
       and disk bandwidth.

       If the file system's free space is fragmented, or if there is
       insufficient free space available, e4defrag may not be able to improve
       the file's fragmentation.

       Non-privileged users can execute e4defrag to their own file, but the
       score is not printed if -c option is specified. Therefore, it is
       desirable to be executed by root user.

AUTHOR
       Written by Akira Fujita <a-fujita@rs.jp.nec.com> and Takashi Sato <t-
       sato@yk.jp.nec.com>.

SEE ALSO
       mke2fs(8), mount(8).


e4defrag version 2.0		   May 2009			   E4DEFRAG(8)