µOSv is lightweight edition of OSv, which uses mruby interpreter instead of Java VM for its system language.
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µOSv Build Status

µOSv is lightweight edition of OSv, which uses mruby interpreter instead of Java VM for its system language.
Here's a movie how µOSv looks like: http://www.youtube.com/watch?v=hSK_VZkwmxI

What's this?

It's cloud OS which specialized for running mruby script, works on both KVM and Xen, and some IaaS/VPS services.
Able to run very few memory amount(>90MB for now), very small disk image size(26MB for now), very fast boot-up speed(less than 2sec).
Original OSv is great OS to run Java application, but it's too huge in some usecases. µOSv offers much smaller / simpler enviroment for developers who loves scripting language.

Tested HostOS

KVM on Ubuntu 13.10/x86_64


There are prerequisite packages before start building.


sudo apt-get install openjdk-7-jdk autotools-dev libltdl-dev libtool autoconf autopoint libboost-all-dev \
genromfs zfs-fuse autoconf ant libffi-dev ruby bison gyp git build-essential qemu-utils qemu-system-x86 \
bridge-utils libvirt0 libvirt-bin

wget https://launchpad.net/ubuntu/+archive/primary/+files/libuv-dev_0.10.18-1_amd64.deb
wget https://launchpad.net/ubuntu/+archive/primary/+files/libuv0.10-dbg_0.10.18-1_amd64.deb
wget https://launchpad.net/ubuntu/+archive/primary/+files/libuv0.10_0.10.18-1_amd64.deb
sudo dpkg -i libuv*.deb

To start building, execute following command:

git clone https://github.com/syuu1228/uosv.git
cd uosv

Running µOSv

To run µOSv, execute following command:


You also can specify VM memory size like this:

./run.sh 90m

Updating µOSv filesystem

Add files under userdata/, then execute following command:



  • mruby-libuv is very unstable for now.
  • µOSv disables OSv's ZFS, so you only have ramfs for now.
    You can write files on ramfs, but you'll lost all you written data beyond shutdown/reboot.