rsync

Was ist rsync?

“rsync” is a program which enables you to synchronize 2 folders. Basically it’s a better version of “cp”. rsync is built on the SSH protocol to fo example handle authorization and authentication.

Can’t I just use FTP or SFTP?

FTP => NO, SFTP => OK but not as good as rsync

A detailed description of the most common file transfer methods can be found HERE.

Why is rsync better than SFTP if both are based on SSH?

Requirement: Rsync is installed on both sides, client and server.

The main difference here is, that rsync only transfers the changed files from one system to another. Rsync uses a special “delta codec algorithm” and therefore saves a lot of time and traffic.

How do i use rsync?

First you have to check if rsync is installed on both client and server. Via the command “rsync --version” you can check which version you are currently running. Currently it should be (September 2019) at Version 3.

Let’s image the following example:

Your current computer (PC1) has a local folder, which should be synced to another external computer (PC2).

Command

rsync -aP <source> <destination>

So we are logged in to PC1 and have a folder called “wordpress” in our home directory which we want to sync to the external computer PC2 into the directory /var/www/html. For our external computer PC2 we use as an example the address devguide.at and as a user “admin“.

rsync -aP wordpress admin@devguide.at:/var/ww/html

What happens now? Depending on the SSH-Daemon settings of the external PC2 their could a password prompt or nothing happens.

But since we don’t want to enter the users password everytime we want to transfer something we can use the “Public-Key-Auth” so we don’t need to enter anything. See HERE for details.

So now we have configured our “Public-Key-Auth” and can login to the external PC without a password.

ssh admin@devguide.at

Now the following command should run through without any problems.

rsync -aP wordpress admin@devguide.at:/var/ww/html

What happens now?

The folder “wordpress” will be synced into the folder “/var/ww/html”. So now we have the folder structure “/var/ww/html/wordpress” on PC2.

But what if we just want to sync the content from the folder “wordpress” and not the whole folder?

rsync -aP wordpress/ admin@devguide.at:/var/ww/html

The difference here is the appended / at the end of the <source> part.
It wouldn’t make a difference on the <destination> part if you append a / or not.

But I just want to download something from PC2 to my local PC1!

Then just swap <source> and <destination>!

rsync -aP admin@devguide.at:/var/ww/html/ wordpress

I just want the files from <source> in <destination> and nothing else!

Per default rsync never deletes anything from <destination> even if they are not present in <source>.

But there are situations when you want to delete any unwanted files from the <destination> and therefore just want to have the state of <source> being present after the transfer is complete.

Thats what the option “–delete” does

Example

Therefore the following command

rsync -aP --delete html/ admin@devguide.at:/var/ww/html

all files from PC1 will be transferred to PC2 AND the nfo.php will be deleted since it is not present in PC1.

If you remove the “--delete” option the nfo.php won’t be deleted.

More options for rsync

• -a is the same as -rlptgoD. Basically recursive + permission + owner + group + times
  • -r: Copies folders recursively
  • -l: If Symlinks are present don’t remove them
  • -p: Show the process of the sync why syncing
  • -t: Also copy creation- and modification-date of the files and folders.
  • -g: If possible transfer the group of each filer and folder from <source> to <destination>
  • -o: If possible transfer the owner of each filer and folder from <source> to <destination>
  • -D: Also transfer “special files” and “devices” from <source> to <destination>
• -P is the same as --partial --progress
  • If a connection gets interrupted , keep partially transferred files in <destination> and show the progress
• –delete
  • remove files which are present in <destination> but are not present in <source>
• –exclude
  • exclude specific files and/or folders