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GEOM_UZIP(4)	       FreeBSD Kernel Interfaces Manual		  GEOM_UZIP(4)

     geom_uzip -- GEOM based compressed	disk images and	partitions

     To	compile	this driver into the kernel, place the following line in your
     kernel configuration file:

	   device xz
	   options zstd
	   options GEOM_UZIP

     Alternatively, to load the	driver as a module at boot time, place the
     following line in loader.conf(5):


     The geom_uzip framework provides support for compressed read-only disk
     images.  This allows significant storage savings at the expense of	some
     CPU time on each read.  Data written in the GEOM label area allows
     geom_uzip to detect compressed images which have been created with
     mkuzip(8) and presented to	the kernel as a	logical	disk device via	md(4).
     geom_uzip creates a unique	md#.uzip device	for each image.

     geom_uzip is not limited to supporting only md(4) images.	The image can
     also reside on a block device.  (For example, a disk, USB flash drive,
     DVD-ROM, etc).  The appropriate device node will appear with the .uzip

	   # gpart show	da0
	   =>	   0  7833600  da0  BSD	 (3.7G)
		   0  2097152	 1  freebsd-ufs	 (1.0G)
	     2097152  5736448	    - free -  (2.7G)
	   # gpart add -t freebsd-ufs -s 1G da0
	   da0b	added
	   # dd	if=/tmp/20160217_dcomp_zcomp.uzip bs=256k of=/dev/da0b
	   3190+1 records in
	   3190+1 records out
	   836331008 bytes transferred in 111.021489 secs (7533055 bytes/sec)
	   # fsck -t ffs /dev/da0b.uzip
	   ** /dev/da0b.uzip (NO WRITE)
	   ** Last Mounted on /mnt
	   ** Phase 1 -	Check Blocks and Sizes
	   ** Phase 2 -	Check Pathnames
	   ** Phase 3 -	Check Connectivity
	   ** Phase 4 -	Check Reference	Counts
	   ** Phase 5 -	Check Cyl groups
	   97455 files,	604242 used, 184741 free (2349 frags, 22799 blocks,
	      0.3% fragmentation)
	   # mount -o ro /dev/da0b.uzip	/mnt
	   # df	/dev/da0b.uzip
	   Filesystem	  1K-blocks    Used  Avail Capacity  Mounted on
	   /dev/da0b.uzip   3155932 2416968 738964    77%    /mnt

     The geom_uzip device is subsequently used by FreeBSD kernel to access the
     uncompressed data.	 The geom_uzip driver does not allow write operations
     to	the underlying disk image.  To check which "providers" match a given
     geom_uzip device:

	   # geom uzip list
	   Geom	name: md1.uzip
	   1. Name: md1.uzip
	      Mediasize: 22003712 (21M)
	      Sectorsize: 512
	   1. Name: md1
	      Mediasize: 9563648 (9.1M)
	      Sectorsize: 512

	   Geom	name: da0b.uzip
	   1. Name: da0b.uzip
	      Mediasize: 3355443200 (3.1G)
	      Sectorsize: 512
	   1. Name: da0b
	      Mediasize: 1073741824 (1.0G)
	      Sectorsize: 512

     geom_uzip allows mounting the root	file system from a compressed disk
     partition by setting the vfs.root.mountfrom tunable.  See loader.conf(5)
     for details.

     Several flags are provided	for tracing geom_uzip I/O operations and TOC
     parsing via the following sysctls.

	     Log level.	 Zero disables logging.	 Higher	values enable more
	     verbose debug logging for geom_uzip.  Supported levels are	from 0
	     (no logging) to 4 (maximum	amount of logging).

	     Log operations involving compressed cluster number.

     GEOM(4), md(4), geom(8), mkuzip(8)

     Zstd support was added in FreeBSD 13.0.

     The geom_uzip driver was written by Max Khon <>.  The
     block de-duplication code as well as some geom_uzip driver	optimizations
     have been contributed by Maxim Sobolev <>.  The	LZMA
     decompression support and CLOOP 3.0 support have been added by Aleksandr
     Rybalko <>.

     This manual page was written by Ceri Davies <>.

FreeBSD	13.0			April 28, 2021			  FreeBSD 13.0


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