Documentation/filesystems/squashfs.rst

1 .. SPDX-License-Identifier: GPL-2.0
7 Squashfs is a compressed read-only filesystem for Linux.
14 Squashfs is intended for general read-only filesystem use, for archival
19 Mailing list (kernel code): linux-fsdevel@vger.kernel.org
20 Web site: github.com/plougher/squashfs-tools
23 ----------------------
39 Tail-end packing (fragments)	yes			no
41 Hard link support		yes			no
44 32-bit uids/gids		yes			no
53 file type, i.e. regular file, directory, symbolic link, and block/char device
57 -----------------
59 As squashfs is a read-only filesystem, the mksquashfs program must be used to
61 are very likely packaged by your linux distribution (called squashfs-tools).
62 The source code can be obtained from github.com/plougher/squashfs-tools.
66 -----------------
68 errors=%s              Specify whether squashfs errors trigger a kernel panic
72                          continue  errors don't trigger a panic (default)
73                             panic  trigger a panic when errors are encountered,
86                            single  use single-threaded decompression (default)
104                                    decompression is load-balanced across the
126 -----------------------------
131 	 ---------------
133 	|---------------|
136 	|---------------|
139 	|---------------|
141 	|---------------|
144 	|---------------|
147 	|---------------|
150 	|---------------|
153 	|---------------|
156 	 ---------------
164 -----------------------
167 dictionary size).  If non-default compression options have been used, then
171 ----------
175 block is uncompressed.  A block will be uncompressed if the -noI option is set,
180 by a 48-bit number which encodes the location of the compressed metadata block
194 ---------------
197 in a directory table.  Directories are accessed using the start address of
204 compressed metadata block, and therefore, can share the start block.
206 header containing the shared start block value, and a sequence of directory
207 entries, each of which share the shared start block.  A new directory header
208 is written once/if the inode start block changes.  The directory
214 in each metadata block.  Directories are sorted in alphabetical order,
224 -------------
227 compressed fragment block (tail-end packed block).   The compressed size
236 retaining a simple and space-efficient block list on disk.  The cache
243 -------------------------
253 ------------------------
256 converted to 32-bit uids/gids using an id look up table.  This table is
262 ----------------
265 can optionally (disabled with the -no-exports Mksquashfs option) contain
276 ---------------
287 also allows values to be de-duplicated, the value being stored once, and
291 To reduce overhead in inodes, rather than storing the on-disk
292 location of the xattr list inside each inode, a 32-bit xattr id
297 -------------------------------
300 -------------
305 ---------------------------
311 the page-cache in the normal way.  The cache is used to temporarily cache
316 which have been packed with it, these because of locality-of-reference may be