man > e4defrag(8)

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)