If you have large number of files that you want to compare to find duplicate files or replace or update old files with latest ones then FreeFileSync is a great tool to perform that. FreeFileSync compares two folders and based on what you want it can add, update, mirror files of two folders. FreeFileSync recently released 8.2 which fixes couple of bugs.
What's New In FreeFileSync 8.2?
FreeFileSync 8.2 released with some bug fixes and improvements.
How To Use FreeFileSync In Ubuntu Or Other Derivatives Linux?
FreeFileSync is very simple to use. Instead of installing it permanently on your system, you can download .tar file and run it as a portable program each time you want to use it. Download FreeFileSync 8.2 from the link below -
When downloaded, simple extract the files from archive. Open terminal (ctrl + alt+ t) and move into the folder you just extracted.
Firstly, enter the folder you extracted and from there on run FreeFileSync using the second command mentioned above. It should run FreeFileSync.
Browse the folders that you want to compare. First click Compare and it will give you the comparison files. To sync the both folders, click "Synchronize". The default Synchronize will update both folders files, i.e. Both folders will be same after the Two way sync.
If you want, you can change the Synchronize option to mirror and update. Mirroring the two folders will make the mirror of the left folder to the right side folder and updating two folders will the copy all the new files from the left side folder to the right side folder. Other than these options you can also make your own custom rules of Synchronization.