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 merged into OSv. Please check upstream.
This repository is not maintained anymore.

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

Try Binary Image

Copy and paste following commands on your shell.

wget https://dl.dropboxusercontent.com/u/648670/uosv_20131219.img
sudo qemu-system-x86_64 -m 128m -drive file=uosv_20131219.img,if=virtio,cache=none \
-netdev user,id=un0,net=,host= \
-device virtio-net-pci,netdev=un0 -enable-kvm -cpu host,+x2apic \
-chardev stdio,mux=on,id=stdio -mon chardev=stdio,mode=readline,default \
-device isa-serial,chardev=stdio -nographic


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

If you want to enable GPL mrbgems, use


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:



OSv related products are almost under BSDL.
mruby related products are almost under MIT.
mruby-vedis is under Sleepycat License.

Product Dependencies License
OSv FreeBSD, ZFS, Prex, Musl BSDL
Prex MIT
mruby MIT
mruby-dir MIT
mruby-env MIT
mruby-errno MIT
mruby-ipaddr MIT
mruby-mock MIT
mruby-mtest MIT
mruby-pack MIT
mruby-process MIT
mruby-regexp-pcre MIT
mruby-require MIT
mruby-simple-random MIT
mruby-socket MIT
mruby-tempfile MIT
mruby-msgpack MIT
mruby-uv libuv MIT
libuv MIT
mruby-http mruby-uv MIT
mruby-json MIT
mruby-msgpack-rpc mruby-socket,mruby-msgpack MIT
mruby-yaml libyaml MIT
libyaml MIT
mruby-base64 MIT
mruby-md5 MIT
mruby-vedis Sleepycat License
mruby-sleep MIT
mruby-simplehttp MIT
mruby-httprequest MIT
mruby-aws-s3 mruby-uv, mruby-http, mruby-digest, mruby-pack, mruby-simplehttp, mruby-httprequest MIT
mruby-cfunc libffi MIT
libffi mruby-cfunc MIT
μOSv build scripts MIT
mruby-eshell mruby-io,mruby-dir,mruby-ipaddr MIT

These modules are lisenced under copyleft license, disabled by default.

Product Dependencies License
mruby-polarssl PolarSSL LGPLv3
PolarSSL GPL/Commercial(Dual)
mruby-sha1 GPL


  • libuv is ported, but 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.