On Mon, 29 Jul 2019 13:47:34 -0300
Luciano ES <lucm...@gmail.com> wrote:

> I want to archive almost all of my email in MH mail boxes to an
> external disk. The idea is to free up space in the running disk. 
> I thought I could just move ~/Mail to external and start with a new
> empty Mail directory, but then I realized I want to do incremental
> backups in the future and I have no idea how to do that.

TL;DR man rsync

rsync is an intelligent wrapper that can do all sorts of incremental
copies. It's the SAK of backups. The man page is rather long and
complicated so I'll give two commonly-used recipes:

1. I've got a directory tree A that I want to copy to directory tree B.
I want to copy from A only what isn't already present on B, and I want
everything I ever copied on B to remain there

rsync -axvn /my/mh /backup

The "n" above in -axvn says "dry run." I've used rsync for more than a
decade and under deprivation of sleep and/or coffee I still make
mistakes. It's best to test any rsync recipe with the -n option, that
way it will show you what it would have done but not actually do
anything. When you are convinced it does what you want, recall the
command line and delete the n. All the examples I'm typing here are
going to include it so hopefully you won't make any mistakes!

The other thing about rsync is that ending / characters matter. Greatly!

Here I'm copying the mh directory (or file) to /backup

If I would have used

rsync -axvn /my/mh/ to /backup/

then rsync would have copied everything in the mh directory but not the
mh directory itself. Be careful with this, it's easy to make mistakes
and shell completion often causes problems by appending ending /

Simply, including a / in the path means "everything in the directory
but not the directory itself," while not including it means the
directory *and* everything in it.

The other common case is when you want to sync two directory trees such
that the source and destination both contain exactly the same files.
For example if you delete something from the source, you want the next
rsync to delete it from the destination also. This doesn't sound like
your case, but it's useful generally.

rsync -axvn --delete /my/mh /backup

does this.

There are many options and variations. The other great thing about
rsync is that the source and destination don't have to be on the same
machine. rsync will use scp or ssh to copy the files depending on your
command line, ssh config, etc.

For example I want to copy my mh directory on my desktop to a backup
directory on a backup server located on ip

rsync -axvn /my/mh

The source file can also be on a remote machine...

The -a flag says "preserve attributes" and it keeps the owner, group,
atime etc on the backup file

The -x flag says "don't span filesystems." This may or not be necessary
but when trying it out I like to use x as a default.

The -v flag says "be verbose." This way you see most of what rsync
would do / is doing. If you don't include it you will not see any
progress indication and it will just end and tell you how many bytes it


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