bionic (8) e4defrag.8.gz

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).