How to Use Rsync to Sync New or Changed/Modified Files in Linux

As a system administrator or Linux power user, you may have probably come across or even on several occasions, used the versatile Linux Rsync tool, which enables users to expeditiously copy or synchronise files locally and remotely. It is as well a great tool popularly used for backup operations and mirroring.

Some of its eminent features and advantages include; it is exceptionally versatile in that, it can copy locally, to/from a remote shell or remote rsync, it is also remarkably flexible, allowing users to specify any number of files to copy.

Furthermore, it permits copying of links, devices, file or directory owner, groups and the permissions. It also supports usage without root privileges coupled with many more.

One imperative differential of rsync in comparison to other file-copying commands in Linux is its use of the remote-update protocol, to transfer only the difference between files or directory content.

Therefore, in this article, we shall examine how rsync can help us only sync new or changed files or directory content while making backups and beyond in Linux.

To start with, you need remember that the conventional and simplest form of using rsync is as follows:

# rsync options source destination 

That said, let us dive into some examples to uncover how the concept above actually works.

Syncing Files Locally Using Rsync

Using the command below, am able to copy files from my Documents directory to /tmp/documentsdirectory locally:

$ rsync -av Documents/* /tmp/documents

In the command above, the option:

1. -a – means archive mode
2. -v – means verbose,

By default, rsync only copies new or changed files from a source to destination, when I add a new file into my Documents directory, this is what happens after running the same command second time:

$ rsync -av Documents/* /tmp/documents

As you can observe and notice from the output of the command, only the new file is copied to the destination directory.

The --update or -u option allows rsync to skip files that are still new in the destination directory, and one important option, --dry-run or -n enables us to execute a test operation without making any changes. It shows us what files are to be copied.

$ rsync -aunv Documents/* /tmp/documents

After executing a test run, we can then do away with the -n and perform a real operation:

$ rsync -auv Documents/* /tmp/documents

Syncing Files From Local to Remote Linux

In the example below, I am copying files from my local machine to a remote sever with the IP address – 10.42.1.5. So as to only sync new files on the local machine, that do not exist on the remote machine, we can include the --ignore-existing option:

$ rsync -av --ignore-existing Documents/* abcd@10.42.1.5:~/all/

Subsequently, to sync only updated or modified files on the remote machine that have changed on the local machine, we can perform a dry run before copying files as below:

$ rsync -av --dry-run --update Documents/* aaronkilik@10.42.1.5:~/all/
$ rsync -av --update Documents/* aaronkilik@10.42.1.5:~/all/

To update existing files and prevent creation of new files in the destination, we utilize the --existingoption.

You can run through the rsync man page to discover additionally useful options for advanced usage, as I had mentioned earlier on, rsync is a very powerful and versatile Linux tool and many System Administrator and Linux power users know just how advantageous it is.