3. The mksquashfs tool, exposed

3.1. Using mksquashfs

mksquashfs is the tool for creating new squashed file systems, and for appending new data to existing squashed file systems. The general command-line format for mksquashfs is:

	bash# mksquashfs source1 source2 ... destination [options]

Notes for default mksquashfs behavior:

See the next section for more details about all possible options.

3.2. Command-line options

All possible options for mksquashfs are shown in the table below.

Table 1. Command-line options of the mksquashfs tool

-all-root or -root-ownedmake all files in the target file system owned by root (UID=0, GID=0)
-always-use-fragmentsdivide all files greater than block size into fragments (2.x only, will result in greater compression ratios)
-b [block size]use [block size] filesystem block size (32 Kbytes default) - this can be either 512, 1024, 2048, 4096, 8192, 16384 or 32768
-be or -leforce a big or little endian file system, respectively
-check-dataenable additional file system checks
-e [file1] ( [file2] ... )specify which files and/or directories to omit from the new file system that is to be created
-ef [file]specify a file which contains the list of files/directories to exclude
-force-gid [GID]set all group IDs in target file system to [GID] (can be specified as a name or a number)
-force-uid [UID]set all user IDs in target file system to [UID] (can be specified as a name or a number)
-infoprint files, their original size and compression ratio, as they are added to the file system
-keep-as-directoryif the source is a single directory, force this directory to be a subdirectory of the root in the created file system
-noappendif the destination file/device already contains a squashed file system, overwrite it, rather than append the new data to an existing file system
-no-duplicatesdo not detect/remove duplicate file names
-noD or -noDataCompressiondo not compress the data
-noF or -noFragmentCompressiondo not compress the fragments (2.x only)
-no-fragmentsdo not generate fragment blocks (2.x only, this will produce almost the same filesystem as 1.x did)
-noI or -noInodeCompressiondo not compress the inode table
-nopaddo not pad the resulting file system to a multiple of 4 KBytes
-root-becomes [name]can be used while appending to a pre-existing squashed file system: it will make a new root, and [name] directory will contain all pre-existing files/directories
-versionprint the version, copyright and license message

In most cases, you should leave all compression/block options by default, as they allow mksquashfs to achieve the best possible compression ratios.