Using Rsync To Copy Only Files That Have Changed, Not Files That Are New

Introduction

Rsync is a powerful command-line utility that allows you to efficiently copy and synchronize files and directories between two locations. One of its key features is its ability to copy only files that have changed, rather than transferring all files every time. This makes it an ideal tool for backing up data, synchronizing files between multiple machines, and mirroring directories. In this article, we will explore how to use rsync to copy only files that have changed, not files that are new.

Understanding Rsync

Before we dive into the specifics of using rsync to copy only files that have changed, it's essential to understand the basics of how rsync works. Rsync uses a combination of algorithms and techniques to determine which files have changed and need to be transferred. Here are some key concepts to keep in mind:

• Checksums: Rsync uses checksums to identify files and determine if they have changed. A checksum is a unique numerical value that represents the contents of a file.
• File metadata: Rsync also considers file metadata, such as permissions, ownership, and timestamps, when determining if a file has changed.
• Delta encoding: Rsync uses delta encoding to compress the differences between files, making it more efficient to transfer only the changes.

Using Rsync to Copy Only Files that Have Changed

Now that we have a basic understanding of how rsync works, let's explore how to use it to copy only files that have changed. The basic syntax for rsync is as follows:

rsync -avz source/ dest/

Here's a breakdown of the options used:

• -a: This option enables archive mode, which preserves file metadata, such as permissions and ownership.
• -v: This option enables verbose mode, which provides more detailed output about the transfer process.
• -z: This option enables compression, which can help reduce the amount of data transferred.

However, to copy only files that have changed, we need to use the --update option, which is also known as the -u option. Here's the updated syntax:

rsync -avuz source/ dest/

The --update option tells rsync to only copy files that have changed since the last transfer. If a file has been deleted, rsync will also remove the corresponding file in the destination directory.

Example Use Case

Let's say we have two directories, source and dest, that contain some files in common. We want to copy only the files that have changed since the last transfer. Here's an example of how we can use rsync to achieve this:

# Create the source and destination directories
mkdir source
mkdir dest
echo "Hello, world!" > source/file1.txt
echo "This is a test file." > source/file2.txt

echo "Hello, world!" > dest/file1.txt
echo "This is a test file." > dest/file2.txt

rsync -avuz source/ dest/

In this example, since both file1.txt and file2.txt are identical in both directories, rsync will not transfer any files. However, if we modify one of the files, rsync will copy the updated file to the destination directory.

Tips and Tricks

Here are some additional tips and tricks to keep in mind when using rsync to copy only files that have changed:

• Use the --delete option: This option tells rsync to remove files in the destination directory that no longer exist in the source directory.
• Use the --exclude option: This option allows you to exclude specific files or directories from the transfer.
• Use the --include option: This option allows you to include specific files or directories in the transfer, even if they are excluded by default.
• Use the --progress option: This option displays a progress bar during the transfer process.

Conclusion

Introduction

Rsync is a powerful command-line utility that allows you to efficiently copy and synchronize files and directories between two locations. In our previous article, we explored how to use rsync to copy only files that have changed, not files that are new. In this article, we will answer some of the most frequently asked questions about rsync.

Q: What is rsync?

A: Rsync is a command-line utility that allows you to efficiently copy and synchronize files and directories between two locations. It uses a combination of algorithms and techniques to determine which files have changed and need to be transferred.

Q: What are the benefits of using rsync?

A: The benefits of using rsync include:

• Efficient data transfer: Rsync uses delta encoding to compress the differences between files, making it more efficient to transfer only the changes.
• Preserves file metadata: Rsync preserves file metadata, such as permissions and ownership, when transferring files.
• Flexible options: Rsync has a wide range of options that allow you to customize the transfer process to suit your needs.

Q: How do I use rsync to copy files?

A: To use rsync to copy files, you can use the following basic syntax:

rsync -avz source/ dest/

Here's a breakdown of the options used:

• -a: This option enables archive mode, which preserves file metadata, such as permissions and ownership.
• -v: This option enables verbose mode, which provides more detailed output about the transfer process.
• -z: This option enables compression, which can help reduce the amount of data transferred.

Q: How do I use rsync to synchronize directories?

A: To use rsync to synchronize directories, you can use the following basic syntax:

rsync -avz source/ dest/

However, to synchronize directories, you need to use the --update option, which is also known as the -u option. Here's the updated syntax:

rsync -avuz source/ dest/

The --update option tells rsync to only copy files that have changed since the last transfer. If a file has been deleted, rsync will also remove the corresponding file in the destination directory.

Q: How do I exclude specific files or directories from the transfer?

A: To exclude specific files or directories from the transfer, you can use the --exclude option. Here's an example:

rsync -avuz --exclude 'file1.txt' source/ dest/

This will exclude the file1.txt file from the transfer.

Q: How do I include specific files or directories in the transfer?

A: To include specific files or directories in the transfer, you can use the --include option. Here's an example:

rsync -avuz --include 'file1.txt' source/ dest/

This will include the file1.txt file in the transfer.

Q: How do I remove files in the destination directory that no longer exist in the source directory?

A: To remove files in the destination directory that no longer exist in the source directory, you can use the --delete option. Here's an example:

rsync -avuz --delete source/ dest/

This will remove files in the destination directory that no longer exist in the source directory.

Q: How do I display a progress bar during the transfer process?

A: To display a progress bar during the transfer process, you can use the --progress option. Here's an example:

rsync -avuz --progress source/ dest/

This will display a progress bar during the transfer process.

Conclusion

In conclusion, rsync is a powerful tool for copying and synchronizing files and directories. By understanding how to use rsync, you can efficiently transfer data between two locations and preserve file metadata. With its flexible options and ability to compress data, rsync is a must-have tool for any system administrator or developer.