Management Infrastructure

Since the Qubes R3.1 release we have included the Salt (also called SaltStack) management engine in dom0 as default (with some states already configured). Salt allows administrators to easily configure their systems. In this guide we will show how it is set up and how you can modify it for your own purpose.

In the current form the API is provisional and subject to change between minor releases.

Understanding Salt

This document is not meant to be comprehensive Salt documentation; however, before writing anything it is required you have at least some understanding of basic Salt-related vocabulary. For more exhaustive documentation, visit official site, though we must warn you that it is not easy to read if you just start working with Salt and know nothing.

The Salt Architecture

Salt is a client-server model, where the server (called master) manages its clients (called minions). In typical situations, it is intended that the administrator interacts only with the master and keeps the configurations there. In Qubes, we don’t have a master. Instead we have one minion which resides in dom0 and manages domains from there. This setup is also supported by Salt.

Salt is a management engine (similar to Ansible, Puppet, and Chef), that enforces a particular state of a minion system. A state is an end effect declaratively expressed by the administrator. This is the most important concept in the entire engine. All configurations (i.e., the states) are written in YAML.

A pillar is a data back-end declared by the administrator. When states become repetitive, instead of pure YAML they can be written using a template engine (preferably Jinja2); which can use data structures specified in pillars.

A formula is a ready to use, packaged solution that combines a state and a pillar (possibly with some file templates and other auxiliary files). There are many formulas made by helpful people all over the Internet.

A grain is some data that is also available in templates, but its value is not directly specified by administrator. For example, the distribution (e.g., "Debian" or "Gentoo") is a value of the grain "os". It also contains other information about the kernel, hardware, etc.

A module is a Python extension to Salt that is responsible for actually enforcing the state in a particular area. It exposes some imperative functions for the administrator. For example, there is a system module that has a system.halt function that, when issued, will immediately halt a domain. There is another function called state.highstate which will synchronize the state of the system with the administrator’s configuration/desires.

Configuration

States

The smallest unit of configuration is a state. A state is written in YAML and looks like this:

stateid:
  cmd.run:  #this is the execution module. in this case it will execute a command on the shell
  - name: echo 'hello world' #this is a parameter of the state. 

The stateid has to be unique throughout all states running for a minion and can be used to order the execution of the references state. cmd.run is an execution module. It executes a command on behalf of the administrator. name: echo 'hello world' is a parameter for the execution module cmd.run. The module used defines which parameters can be passed to it.

There is a list of officially available states. There are many very useful states:

With these three states you can define most of the configuration of a VM.

You can also order the execution of your states:

D:
  cmd.run:
  - name: echo 1
  - order: last
C:
  cmd.run:
  - name: echo 1
B:
  cmd.run:
  - name: echo 1
  - require:
    - cmd: A
  - require_in:
    - cmd:C
A:
  cmd.run:
  - name: echo 1
  - order: 1

The order of execution will be A, B, C, D. The official documentation has more details on the require and order arguments.

State Files

When configuring a system you will write one or more state files (*.sls) and put (or symlink) them into the main Salt directory /srv/salt/. Each state file contains multiple states and should describe some unit of configuration (e.g., a state file mail.sls could setup a VM for e-mail).

Top Files

After you have several state files, you need something to assign them to a VM. This is done by *.top files (official documentation). Their structure looks like this:

environment:
  target_matching_clause:
  - statefile1
  - folder2.statefile2

In most cases, the environment will be called base. The target_matching_clause will be used to select your minions (VMs). It can be either the name of a VM or a regular expression. If you are using a regular expressions, you need to give Salt a hint you are doing so:

environment:
  ^app-(work|(?!mail).*)$:
  - match: pcre
  - statefile

For each target you can write a list of state files. Each line is a path to a state file (without the .sls extension) relative to the main directory. Each / is exchanged with a ., so you can’t reference files or directories with a . in their name.

Enabling Top Files and Applying the States

Now, because we use custom extensions to manage top files (instead of just enabling them all), to enable a particular top file you should issue command:

$ qubesctl top.enable my-new-vm

To list all enabled top files:

$ qubesctl top.enabled

And to disable one:

$ qubesctl top.disable my-new-vm

To apply the states to dom0 and all VMs:

$ qubesctl --all state.highstate

(More information on the qubesctl command further down.)

Template Files

You will sometimes find yourself writing repetitive states. To solve this, there is the ability to template files or states. This is most commonly done with Jinja. Jinja is similar to Python and in many cases behaves in a similar fashion, but there are sometimes differences when, for example, you set some variable inside a loop: the variable outside will not get changed. Instead, to get this behavior, you would use a do statement. So you should take a look at the Jinja API documentation. Documentation about using Jinja to directly call Salt functions and get data about your system can be found in the official Salt documentation.

Salt Configuration, QubesOS layout

All Salt configuration files are in the /srv/ directory, as usual. The main directory is /srv/salt/ where all state files reside. States are contained in *.sls files. However, the states that are part of the standard Qubes distribution are mostly templates and the configuration is done in pillars from formulas.

The formulas are in /srv/formulas, including stock formulas for domains in /srv/formulas/dom0/virtual-machines-formula/qvm, which are used by firstboot.

Because we use some code that is not found in older versions of Salt, there is a tool called qubesctl that should be run instead of salt-call --local. It accepts all the same arguments of the vanilla tool.

Configuring a VM’s System from Dom0

Starting with Qubes R3.2, Salt in Qubes can be used to configure VMs from dom0. Simply set the VM name as the target minion name in the top file. You can also use the qubes pillar module to select VMs with a particular property (see below). If you do so, then you need to pass additional arguments to the qubesctl tool:

usage: qubesctl [-h] [--show-output] [--force-color] [--skip-dom0]
                [--targets TARGETS | --templates | --app | --all]
                ...

positional arguments:
  command            Salt command to execute (e.g., state.highstate)

optional arguments:
  -h, --help         show this help message and exit
  --show-output      Show output of management commands
  --force-color      Force color output, allow control characters from VM,
                     UNSAFE
  --skip-dom0        Skip dom0 configuration (VM creation etc)
  --targets TARGETS  Coma separated list of VMs to target
  --templates        Target all templates
  --app              Target all AppVMs
  --all              Target all non-disposable VMs (TemplateVMs and AppVMs)

To apply a state to all templates, call qubesctl --templates state.highstate.

The actual configuration is applied using salt-ssh (running over qrexec instead of ssh). Which means you don’t need to install anything special in a VM you want to manage. Additionally, for each target VM, salt-ssh is started from a temporary VM. This way dom0 doesn’t directly interact with potentially malicious target VMs; and in the case of a compromised Salt VM, because they are temporary, the compromise cannot spread from one VM to another.

Writing Your Own Configurations

Let’s start with quick a example:

my new and shiny VM:
  qvm.present:
    - name: salt-test # can be omitted when same as ID
    - template: fedora-21
    - label: yellow
    - mem: 2000
    - vcpus: 4
    - flags:
      - proxy

It uses the Qubes-specific qvm.present state, which ensures that the domain is present (if not, it creates it).

  • The name flag informs Salt that the domain should be named salt-test (not my new and shiny VM).
  • The template flag informs Salt which template should be used for the domain.
  • The label flag informs Salt what color the domain should be.
  • The mem flag informs Salt how much RAM should be allocated to the domain.
  • The vcpus flag informs Salt how many Virtual CPUs should be allocated to the domain
  • The proxy flag informs Salt that the domain should be a ProxyVM.

As you will notice, the options are the same (or very similar) to those used in qvm-prefs.

This should be put in /srv/salt/my-new-vm.sls or another .sls file. A separate *.top file should be also written:

base:
  dom0:
    - my-new-vm

Note The third line should contain the name of the previous state file, without the .sls extension.

To enable the particular top file you should issue the command:

$ qubesctl top.enable my-new-vm

To apply the state:

$ qubesctl state.highstate

Example of Configuring a VM’s System from Dom0

Lets make sure that the mc package is installed in all templates. Similar to the previous example, you need to create a state file (/srv/salt/mc-everywhere.sls):

mc:
  pkg.installed: []

Then the appropriate top file (/srv/salt/mc-everywhere.top):

base:
 qubes:type:template:
    - match: pillar
    - mc-everywhere

Now you need to enable the top file:

$ qubesctl top.enable mc-everywhere

And apply the configuration:

$ qubesctl --all state.highstate

All Qubes-specific States

qvm.present

As in the example above, it creates a domain and sets its properties.

qvm.prefs

You can set properties of an existing domain:

my preferences:
  qvm.prefs:
    - name: salt-test2
    - netvm: sys-firewall

Note The name: option will not change the name of a domain, it will only be used to match a domain to apply the configurations to it.

qvm.service

services in my domain:
  qvm.service:
    - name: salt-test3
    - enable:
      - service1
      - service2
    - disable:
      - service3
      - service4
    - default:
      - service5

This enables, disables, or sets to default, services as in qvm-service.

qvm.running

Ensures the specified domain is running:

domain is running:
  qvm.running:
    - name: salt-test4

The qubes Pillar Module

Additional pillar data is available to ease targeting configurations (for example all templates). Note List here may be subject to changes in future releases.

qubes:type

VM type. Possible values:

  • admin - Administration domain (dom0)
  • template - Template VM
  • standalone - Standalone VM
  • app - Template based AppVM

qubes:template

Template name on which a given VM is based (if any).

qubes:netvm

VM which provides network to the given VM

Debugging

The output for each VM is logged in /var/log/qubes/mgmt-VM_NAME.log.

If the log does not contain useful information:

  1. Run sudo qubesctl --skip-dom0 --target=VM_NAME state.highstate
  2. When your VM is being started (yellow) press Ctrl-z on qubesctl.
  3. Open terminal in disp-mgmt-VM_NAME.
  4. Look at /etc/qubes-rpc/qubes.SaltLinuxVM - this is what is executed in the management VM.
  5. Get the last two lines:

    $ export PATH=”/usr/lib/qubes-vm-connector/ssh-wrapper:$PATH” $ salt-ssh “$target_vm” $salt_command

Adjust $target_vm (VM_NAME) and $salt_command (state.highstate).

  1. Execute them, fix problems, repeat.

Known Pitfalls

Using fedora-24-minimal

The fedora-24-minimal package is missing the sudo package. You can install it via:

$ qvm-run -p -u root fedora-24-minimal-template 'dnf install -y sudo'

The -p will cause the execution to wait until the package is installed. Having the -p flag is important when using a state with cmd.run.

Disk Quota Exceeded (When Installing Templates)

If you install multiple templates you may encounter this error. The solution is to shut down the updateVM between each install:

install template and shutdown updateVM:
  cmd.run:
  - name: sudo qubes-dom0-update -y fedora-24; qvm-shutdown {{ salt.cmd.run(qubes-prefs updateVM) }}

Further Reading