How can I sync two local directories?

Question

I have two backup directories (dir1 and 2) on two different (local) HDDs and I want to create one of them. How can I really sync their contents so that both directories will have the same contents?

Solution

To sync the contents of dir1 to dir2 on the same system, type:

rsync -av --progress --delete dir1/ dir2

-a, --archive
        archive mode

--delete
        delete extraneous files from dest dirs

-v, --verbose
        Verbose mode (increase verbosity)

--progress
        show progress during transfer

                        ^{— from rsync(1)}

Note : The / after dir1 is necessary to mean "the contents of dir1".  Without the trailing slash, would place dir1, including the directory, within dir2. This would create a hierarchy that looks like:

…/dir2/dir1/[files]

Comments

[Kusalananda]

Do you want to do a one-way sync, or do you need to update the files both ways?

[roaima]

You seem to know one correct command (rsync). What have you tried so far?