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 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 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 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).