3. The SquashFS tools 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

-2.0 force mksquashfs version 2.1 to create a version 2.0 filesystem
-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 (by the version 2.x). It will result in greater compression ratios
-b [block size]use [block size] filesystem block size (32 Kbytes default for 2.x, 128 kbytes for 3.x) - this can be either 4096, 8192, 16384, 32768, 65536 or 131072
-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 (avaliable by 2.x)
-no-fragmentsdo not generate fragment blocks (avaliable by 2.x, 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
-recover [name]recover filesystem data using recovery file [name] (3.3)
-no-recoverydon't create a recovery file (3.3).
-no-exportsdon't make avaliable file system to export via NFS (3.x)
-no-sparsedon't check for sparse files (3.x)
-processors [number]set the number of CPU to create file system. By default it will be used all avaliable processors (3.x)
--read-queue [size]set input queue to [size] Mb. (Default is 64 Mb)(3.x)
-write-queue [size]set output queue to [size] Mb (3.x)
-sort [sort_file]sort files relating to priorities in [sort_file] (3.x)
-wildcardsenable the extended shell wildcards to exclude directories/files (to be used with -e)
-regexenable to use POSIX regular expressions (3.3)

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

3.3. Using unsquashfs

unsquashfs is the tool for extracting data from squashed file systems. The general command-line format for unsquashfs is:

unsquashfs [options] target [files/directories to extract]

Notes for unsquashfs behavior:

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

Table 2. Command-line options of the unsquashfs tool

-v[ersion] print the version, licence and copyright message
-i[nfo]print the files as they are extracted from the file system
-l[ist]list the squashed file system without extracting files
-lilist files with theyr attributes as they are unsquashed (3.3)
-lllist the squashed file system files with attributes without any extraction (3.3)
-d[estination] pathspecify a destination path for unsquashed items
-f[orce]if files exist overwrite them
-s[tat]display file system's superblock informations (it can discover the file system version and the options used to compress it) (3.3)
-e[f] [extract file]list of directories or files to extract (entries given one per line) (3.3)
-r[egex]treat extract names as POSIX regular expressions (3.3)

Note that by 3.x release you can extract 1.x and 2.x squashed file system too.