# Gitian

Read about the project goals at the "project home page":https://gitian.org/ .

This package can do a deterministic build of a package inside a VM.

## Deterministic build inside a VM

This performs a build inside a VM, with deterministic inputs and outputs.  If the build script takes care of all sources of non-determinism (mostly caused by timestamps), the result will always be the same.  This allows multiple independent verifiers to sign a binary with the assurance that it really came from the source they reviewed.

## Synopsis:

Install prereqs:

    sudo apt-get install apt-cacher
    sudo service apt-cacher start

If you want to use kvm:
    sudo apt-get install python-vm-builder qemu-kvm

or alternatively, lxc (no need for hardware support):
    sudo apt-get install debootstrap lxc

Create the base VM for use in further builds (requires sudo, please review the script):

    bin/make-base-vm
    bin/make-base-vm --arch i386

or for lxc:

    bin/make-base-vm --lxc
    bin/make-base-vm --lxc --arch i386

Copy any additional build inputs into a directory named _inputs_.

Then execute the build using a YAML description file (can be run as non-root):

    export USE_LXC=1 # LXC only
    bin/gbuild <package>.yml

or if you need to specify a commit for one of the git remotes:

    bin/gbuild --commit <dir>=<hash> <package>.yml

The resulting report will appear in result/\<package\>-res.yml

To sign the result, perform:

    bin/gsign --signer <signer> --release <release-name> <package>.yml

Where <signer> is your signing PGP key ID and <release-name> is the name for the current release.  This will put the result and signature in the sigs/<package>/<release-name>.  The sigs/<package> directory can be managed through git to coordinate multiple signers.

After you've merged everybody's signatures, verify them:

    bin/gverify --release <release-name> <package>.yml

## Poking around

* Log files are captured to the _var_ directory
* You can run the utilities in libexec by running `PATH="libexec:$PATH"`
* To start the target VM run `start-target 32 lucid-i386` or `start-target 64 lucid-amd64`
* To ssh into the target run `on-target` or `on-target -u root`
* On the target, the _build_ directory contains the code as it is compiled and _install_ contains intermediate libraries
* By convention, the script in \<package\>.yml starts with any environment setup you would need to manually compile things on the target

TODO:
- disable sudo in target, just in case of a hypervisor exploit
- tar and other archive timestamp setter

## LXC tips

`bin/gbuild` runs `lxc-start`, which may require root.  If you are in the admin group, you can add the following sudoers line to prevent asking for the password every time:

    %admin ALL=NOPASSWD: /usr/bin/lxc-start

Recent distributions allow lxc-start to be run by non-priviledged users, so you might be able to rip-out the `sudo` calls in `libexec/*`.

If you have a runaway `lxc-start` command, just use `kill -9` on it.

The machine configuration requires access to br0 and assumes that the host address is 10.0.2.2:

    sudo brctl addbr br0
    sudo ifconfig br0 10.0.2.2/24 up