How to use the command `sqfstar` (with examples)

The command sqfstar is used to create a squashfs filesystem from a tar archive. Squashfs is a compressed read-only file system that is commonly used for creating live CDs, embedded systems, and other disk image applications. The sqfstar command allows users to convert tar archives into squashfs filesystems, giving them the ability to compress and exclude specific files as needed.

Use case 1: Creating a squashfs filesystem from an uncompressed tar archive

Code:

sqfstar filesystem.squashfs < archive.tar

Motivation: This use case is useful when you have an uncompressed tar archive and want to convert it into a squashfs filesystem. The resulting filesystem will be compressed using gzip by default.

Explanation:

• sqfstar is the name of the command.
• filesystem.squashfs is the name of the output squashfs filesystem file.
• < archive.tar is the input tar archive file.

Example output: The command will create a compressed squashfs filesystem named filesystem.squashfs from the uncompressed tar archive archive.tar.

Use case 2: Creating a squashfs filesystem from a gzip-compressed tar archive and compressing the filesystem using a specific algorithm

Code:

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

Motivation: This use case is helpful when you have a tar archive compressed with gzip but want to use a different compression algorithm for the resulting squashfs filesystem.

Explanation:

• zcat archive.tar.gz extracts the contents of the archive.tar.gz file.
• sqfstar -comp <algorithm> is used to specify the compression algorithm to be used for the squashfs filesystem. Choose one from the options gzip, lzo, lz4, xz, zstd, or lzma.
• filesystem.squashfs is the name of the output squashfs filesystem file.

Example output: The command will extract the contents of the archive.tar.gz file and create a squashfs filesystem named filesystem.squashfs using the specified compression algorithm.

Use case 3: Creating a squashfs filesystem from an xz-compressed tar archive and excluding certain files

Code:

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

Motivation: This use case is useful when you have a tar archive compressed with xz and want to exclude specific files from the resulting squashfs filesystem.

Explanation:

• xzcat archive.tar.xz extracts the contents of the archive.tar.xz file.
• sqfstar is the name of the command.
• filesystem.squashfs is the name of the output squashfs filesystem file.
• file1 file2 ... are the names of the files to be excluded from the squashfs filesystem.

Example output: The command will extract the contents of the archive.tar.xz file, excluding the specified files, and create a squashfs filesystem named filesystem.squashfs.

Use case 4: Creating a squashfs filesystem from a zstd-compressed tar archive and excluding files ending with .gz

Code:

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

Motivation: This use case is helpful when you have a tar archive compressed with zstd and want to exclude files that end with the .gz extension from the resulting squashfs filesystem.

Explanation:

• zstdcat archive.tar.zst extracts the contents of the archive.tar.zst file.
• sqfstar is the name of the command.
• filesystem.squashfs is the name of the output squashfs filesystem file.
• "*.gz" is a wildcard pattern specifying files ending with the .gz extension to be excluded from the squashfs filesystem.

Example output: The command will extract the contents of the archive.tar.zst file, excluding any files that end with .gz, and create a squashfs filesystem named filesystem.squashfs.

Use case 5: Creating a squashfs filesystem from a tar archive compressed with lz4 and excluding files matching a regular expression

Code:

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

Motivation: This use case is useful when you have a tar archive compressed with lz4 and want to exclude files that match a specific regular expression from the resulting squashfs filesystem.

Explanation:

• lz4cat archive.tar.lz4 extracts the contents of the archive.tar.lz4 file.
• sqfstar is the name of the command.
• filesystem.squashfs is the name of the output squashfs filesystem file.
• -regex "regular_expression" is an option that allows you to specify a regular expression pattern to exclude matching files from the squashfs filesystem.

Example output: The command will extract the contents of the archive.tar.lz4 file, excluding any files that match the specified regular expression, and create a squashfs filesystem named filesystem.squashfs.

Conclusion:

The command sqfstar provides users with the ability to create squashfs filesystems from tar archives, allowing for compression and exclusion of specific files. The provided use cases demonstrate different scenarios where the command can be applied, covering various compression algorithms and file exclusion patterns. By leveraging these use cases, users can effectively utilize the sqfstar command and leverage the capabilities of squashfs filesystems for their specific needs.