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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  de‐
       vice,  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  fragmenta‐
              tion 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 per‐
       formance 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 avail‐
       able, 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 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)