How to Use the Command 'sqfstar' (with examples)

The sqfstar command is a powerful utility designed to create squashfs filesystems from tar archives. Squashfs is a highly compressed read-only filesystem that is optimally used for limited storage environments and efficient data distribution. The sqfstar tool allows users to transform tar archives, which may be uncompressed or compressed using different algorithms, into this compact and accessible format. This command stands out for its flexibility in handling various compression methods and its ability to include or exclude specific files from the final filesystem.

Use Case 1: Creating a Squashfs Filesystem from an Uncompressed Tar Archive

Code:

sqfstar filesystem.squashfs < archive.tar

Motivation:

Creating a squashfs filesystem from an uncompressed tar archive is a common use case when working with applications or data sets that need to be encapsulated in a compact, immutable format. This can improve portability and deployment efficiency, particularly in constrained environments where storage space and bandwidth are limited.

Explanation:

• sqfstar: Invokes the command to create a squashfs filesystem.
• filesystem.squashfs: This is the output destination, the file that will store the created squashfs filesystem.
• < archive.tar: This syntax reads from the specified tar archive, archive.tar, which is uncompressed, meaning it isn’t wrapped with any compression like gzip or xz.

Example Output:

Upon successful execution, you’ll have a .squashfs file ready for mounting or distribution, containing the filesystem as compressed by Squashfs’ default algorithm (gzip).

Use Case 2: Creating a Squashfs Filesystem from a Gzip-compressed Tar Archive with a Specific Compression Algorithm

Code:

zcat archive.tar.gz | sqfstar -comp gzip|lzo|lz4|xz|zstd|lzma filesystem.squashfs

Motivation:

When dealing with gzip-compressed tar archives, it’s often desirable to retain compression efficiency while customizing the algorithm used for the squashfs filesystem. This flexibility allows for adjusting compression based on specific needs like decompression speed or maximum compression ratio, depending on later usage scenarios.

Explanation:

• zcat archive.tar.gz: This command decompresses a gzip-compressed tar archive on-the-fly, allowing sqfstar to process its output.
• sqfstar -comp: Specifies the execution of the sqfstar tool alongside the -comp option to define the compression algorithm applied to the resulting squashfs.
• gzip|lzo|lz4|xz|zstd|lzma: These represent the algorithms available for selection, each offering unique benefits like varying compression levels and speeds.
• filesystem.squashfs: The target destination file for the compressed filesystem.

Example Output:

The output will be a squashfs filesystem that is compressed using the specified algorithm. Its size and compression effectiveness will vary based on the chosen method.

Use Case 3: Excluding Specific Files When Creating a Squashfs Filesystem from an Xz-compressed Tar Archive

Code:

xzcat archive.tar.xz | sqfstar filesystem.squashfs file1 file2 ...

Motivation:

Sometimes not all files within an archive are required in the final squashfs filesystem. This use case is valuable when you need to exclude unnecessary or sensitive files, reducing the final size and ensuring critical data is protected or omitted from distribution.

Explanation:

• xzcat archive.tar.xz: Used to decompress an xz-compressed archive in a streaming manner to be processed by sqfstar.
• sqfstar filesystem.squashfs: Initiates the creation of the squashfs, targeting the specified output file.
• file1 file2 ...: A list of files or directories to include specifically in the squashfs, implying the exclusion of other files.

Example Output:

The result is a squashfs file containing only the files listed, optimizing storage by excluding unwanted data.

Use Case 4: Excluding Files with Specific Extensions When Using a Zstd-compressed Tar Archive

Code:

zstdcat archive.tar.zst | sqfstar filesystem.squashfs "*.gz"

Motivation:

When managing archives where certain file types are non-essential, like logs or temporary files ending in .gz, it becomes beneficial to exclude them to conserve space or simplify the filesystem structure.

Explanation:

• zstdcat archive.tar.zst: Decompresses a tar archive compressed with zstd, streaming it to sqfstar.
• sqfstar filesystem.squashfs: Execute the command to create a squashfs.
• "*.gz": A pattern that targets files ending with .gz, explicitly excluding them from the squashfs.

Example Output:

The final filesystem omits all files matching the specified pattern, thus streamlining the content and reducing size.

Use Case 5: Excluding Files Based on a Regular Expression from an Lz4-compressed Tar Archive

Code:

lz4cat archive.tar.lz4 | sqfstar filesystem.squashfs -regex "regular_expression"

Motivation:

This approach is particularly advantageous when you need to exclude a dynamic set of files matching a complex pattern. Using regular expressions allows sophisticated selection criteria, ensuring only pertinent data is included.

Explanation:

• lz4cat archive.tar.lz4: Decompresses the lz4-compressed tar archive, enabling real-time data processing for sqfstar.
• sqfstar filesystem.squashfs: Invokes the creation of a squashfs.
• -regex "regular_expression": A switch to use regular expressions for specifying which files to exclude from the filesystem.

Example Output:

The output squashfs will effectively exclude any files matching the given regular expression, allowing precise control over the contents.

Conclusion:

The sqfstar command provides versatile options for creating compact squashfs filesystems from various types of tar archives. By supporting different compression techniques and offering powerful exclusion capabilities, it accommodates a wide array of use cases, making it indispensable for optimizing storage and distribution workflows. Understanding and effectively applying these options ensures efficient data management and deployment across diverse environments.