3. The mksquashfs tool, exposed3.1. 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]
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- source1, source2, etc.: files and directories to be
added to the resulting filke system, given with relative and/or absolute paths
- destination: a regular file (filesystem
image file), or a block device (such as /dev/fd0or /dev/hda3)
where you want to have your squashed file system
Notes for default mksquashfs behavior:
- When the new files are added to the new file system or appended to an existing one,
mksquashfswill automatically rename files with duplicate names:
if two or more files named textwill appear in the same
resulting directory, the second file will be renamed to
text_1, third one to text_2and so on.
- Duplicate files will be removed, so there will be only one physical instance
(with SquashFS 2.x, you can disable the detection/rtemoval of the duplicates
with the -no-duplicatesoption).
- If destinationhas a pre-existing SquashFS
file system on it, by default, the new sourceitems will be appended to
the existing root directory. Examine the options table below to force mksquashfsto overwrite the whole destination
and/or change the way new source items are added. Please note that it is not possible to
append to a file system created with mksquashfs1.x using
mksquashfs2.x. You will need to mount the SquashFS-1.x file system
and copy the files to some location, and then join them with other needed files
to create a SquashFS-2.x file system.
- If a single source file or directory is given, it becomes the root in a newly created file system. If two
or more source files and/or directories are given, they will all become sub-items in the root of
the new file system.
- The resulting filesystem will be padded to a multiple of 4 Kb: this
is required for filesystems to be used on block devices. If you are very sure
you don't ned this, use the -nopadoption to disable this
operation.
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 | Option | Description |
|---|
| -2.0 | force mksquashfs version 2.1 to create a version 2.0
filesystem | | -all-root or -root-owned | make all files in the target file system owned by root (UID=0, GID=0) | | -always-use-fragments | divide 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 -le | force a big or little endian file system, respectively | | -check-data | enable 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) | | -info | print files, their original size and compression ratio, as they are added to
the file system | | -keep-as-directory | if the source is a single directory, force this directory to be a subdirectory
of the root in the created file system | | -noappend | if the destination file/device already contains a squashed file system,
overwrite it, rather than append the new data to an existing file system | | -no-duplicates | do not detect/remove duplicate file names | | -noD or -noDataCompression | do not compress the data | | -noF or -noFragmentCompression | do not compress the fragments (2.x only) | | -no-fragments | do not generate fragment blocks (2.x only, this will
produce almost the same filesystem as 1.x did) | | -noI or -noInodeCompression | do not compress the inode table | | -nopad | do 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
| | -version | print 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.
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