---
name: "geom_uncompress"
section: "4freebsd"
platform: "linux"
package: "freebsd-manpages"
version: "10.1~RC1-1"
release: "Debian 8 (Jessie)"
platforms: ["linux"]
url: "https://new.carta.tech/geom_uncompress"
---

# geom\_uncompress(4freebsd)

GEOM based compressed disk images

## NAME

**geom\_uncompress** – GEOM based compressed disk images

## SYNOPSIS

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

**options GEOM\_UNCOMPRESS**

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

```
geom_uncompress_load="YES"
```

## DESCRIPTION

The **geom\_uncompress** framework provides support for compressed read only disk images. This allows significant storage savings at the expense of a little CPU time on each read. Data written in the GEOM label area allows **geom\_uncompress** to detect compressed images which have been created with mkulzma(8) or [mkuzip(8)](/mkuzip/8.md) and presented to the kernel as a logical disk device via [md(4)](/md/4.md). **geom\_uncompress** creates a unique *md#.uncompress* device for each image.

The **geom\_uncompress** device is subsequently used by the FreeBSD kernel to access the disk images. The **geom\_uncompress** driver does not allow write operations to the underlying disk image. To check which [md(4)](/md/4.md) devices match a given **geom\_uncompress** device:

```
# geom uncompress list
Geom name: md0.uncompress
Providers:
1. Name: md0.uncompress
   Mediasize: 52428800 (50M)
   Sectorsize: 512
   Mode: r1w0e0
Consumers:
1. Name: md0
   Mediasize: 20864000 (20M)
   Sectorsize: 512
   Mode: r1w0e0
```

## SEE ALSO

[GEOM(4)](/GEOM/4.md), [md(4)](/md/4.md), [geom(8)](/geom/8.md), mkulzma(8), [mkuzip(8)](/mkuzip/8.md)

## AUTHORS

The **geom\_uncompress** driver was written by Maxim Sobolev ⟨sobomax@FreeBSD.org⟩ and Aleksandr Rybalko ⟨ray@FreeBSD.org⟩. This manual page was written by Luiz Otavio O Souza ⟨loos@FreeBSD.org⟩.