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E4DEFRAG(8)                 System Manager's Manual                E4DEFRAG(8)
NAME
       e4defrag - online defragmenter for ext4 filesystem
SYNOPSIS
       e4defrag [ -c ] [ -v ] target ...
DESCRIPTION
       e4defrag  reduces fragmentation of extent based file. The file targeted
       by e4defrag is created on ext4 filesystem 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 filesystem.  If target is a directory, e4defrag reduces fragmenta-
       tion 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  see-
              ing  this  score,  we  can  determine  whether we should execute
              e4defrag to target.  When used with -v option, the current frag-
              mentation  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 filesystem  (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 insuffi-
       cient 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 desir-
       able to be executed by root user.
AUTHOR
       Written  by  Akira Fujita <a-fujita AT rs.com> and Takashi Sato <t-
       sato AT yk.com>.
SEE ALSO
       mke2fs(8), mount(8).
e4defrag version 2.0               May 2009                        E4DEFRAG(8)