pressure-vessel — tools to put Steam in containers
pressure-vessel is a bit like a simplified version of Flatpak for Steam games.
Use cases
$HOME
Protecting If we change the meaning of /home
for a game to be a fake
app-specific directory, then the game can't write random files in unknown
subdirectories of $HOME, and we can be reasonably sure that uninstalling
a game removes all of its files. (As a side benefit, this could make it
easier to be sure that all the necessary files have been selected for
Steam Cloud Sync, because we could prevent the game writing anywhere
that won't be synchronised, other than /tmp or similar.)
Using an alternative runtime
We can get a more predictable library stack than the
LD_LIBRARY_PATH
-based Steam Runtime by making an alternative runtime
available over /usr
, /lib*
, /bin
, /sbin
, analogous to Flatpak
runtimes, using some or all of the host system's graphics stack.
A future goal is to use libcapsule to avoid the library dependencies of the host system's graphics stack influencing the libraries loaded by games, particularly libstdc++. This is not yet implemented.
Building a relocatable install
To make the built version compatible with older systems, you will need an environment based on Ubuntu 12.04 'precise' or Debian 8 'jessie'. SteamRT 1 'scout' or SteamRT 1.5 'heavy' should be suitable. SteamOS 2 'brewmaster' is not suitable, because its amd64 and i386 linux-libc-dev packages are not currently co-installable.
The most straightforward method is to have a prebuilt version of libcapsule-tools-relocatable:amd64 and libcapsule-tools-relocatable:i386 in your build environment. For example, you could do the build in a SteamRT 1 'scout' or SteamRT 1.5 'heavy' Docker image that has those packages already. Then you can do:
meson --prefix=$(pwd)/_build/relocatable-install _build
ninja -C _build
meson test -v -C _build # optional
ninja -C _build install
For more convenient use on a development system, if you have a
SteamRT 1 'scout' SDK tarball or an unpacked sysroot, you can place a
tarball at _build/sysroot.tar.gz
or unpack a sysroot into
_build/sysroot
, and prefix those commands with
./sysroot/run-in-sysroot.py
:
./sysroot/run-in-sysroot.py meson ...
(Or put them in different locations and pass the --sysroot
and
--tarball
options to ./sysroot/run-in-sysroot.py
.)
If your build environment has libcapsule-tools-relocatable
available
but uninstalled, you can unpack them with dpkg-deb -x
and use something
like:
meson \
--prefix=$(pwd)/_build/relocatable-install \
-Drelocatabledir=./usr/lib/libcapsule/relocatable \
_build
ninja -C _build
meson test -v -C _build # optional
ninja -C _build install
Alternatively, build a Debian source package (.dsc
, .debian.tar.*
,
.orig.tar.*
for libcapsule 0.20190402.0 or later, which will require
autoconf-archive 20160916-1~bpo8+1 or later if you are building from git.
Put it in the top-level directory of pressure-vessel
, for example:
dcmd cp ../build-area/libcapsule_0.20190402.0-0co1.dsc .
There is experimental support in sysroot/
for building a container
for the build using debos, but it requires an unusual container
(Debian jessie or SteamRT 1.5 'heavy' with a backport of meson) and
so is not currently recommended.
The relocatable install ends up in _build/relocatable-install
.
Instructions for testing
-
Install Steam and some games. Convenient choices for a reasonably small free-to-play game on various engines include:
- Floating Point (game ID 302380)
- very small/quick to install, works OK on weak hardware
- UnityPlayer 4.3.4f1
- Life is Strange, episode 1 (319630)
- Unreal Engine 3
- Team Fortress 2 (440)
- Source engine
- Unturned (304930)
- UnityPlayer 5.5.3f1
- Floating Point (game ID 302380)
-
Unpack
pressure-vessel-
VERSION-bin.tar.gz
(or...-bin+src.tar.gz
) in some convenient place (I used/opt/pressure-vessel
, but a production deployment in Steam would more realistically use somewhere under~/.steam
or~/.local/share/Steam
):-
be a user who can sudo
$ cd /opt $ sudo mkdir pressure-vessel $ sudo chown $(id -nu) pressure-vessel $ tar --strip-components=1 -C pressure-vessel -xzvf ~/pressure-vessel-*-bin.tar.gz $ chmod -R a+rX pressure-vessel
-
-
Launch a game once without pressure-vessel
-
Configure the launch options for the chosen game:
-
be the Steam user, possibly via sudo -u steam -s
$ nano ~/.steam/steam/userdata/[0-9]*/config/localconfig.vdf
-
navigate to UserLocalConfigStore/Software/Valve/Steam/Apps/game ID
-
below LastPlayed, add:
"LaunchOptions" "/opt/pressure-vessel/bin/pressure-vessel-unruntime -- %command%"
-
restart Steam (on SteamOS use
sudo systemctl restart lightdm
)- TODO: Is there a scriptable way to make Steam edit
localconfig.vdf
itself, or to make it reload an editedlocalconfig.vdf
?
- TODO: Is there a scriptable way to make Steam edit
-
-
Run the game. If successful,
pstree -pa
will look something like this:|-SteamChildMonit,13109 -tenfoot -steamos -enableremotecontrol | `-sh,13110 -c... | `-pressure-vessel,13111 /opt/pressure-vessel/bin/pressure-vessel-wrap... | `-bwrap,13132 --new-session --setenv LD_LIBRARY_PATH... | `-Floating Point.,13133
-
To use a runtime instead of the host system, use:
/opt/pressure-vessel/bin/pressure-vessel-unruntime --runtime=$HOME/some-runtime -- %command%
The runtime can be either:
-
A merged
/usr
containingbin/bash
,lib/ld-linux.so.2
,bin/env
,share/locale
,lib/python2.7
and so on -
A Flatpak runtime such as
~/.local/share/flatpak/runtime/com.valvesoftware.SteamRuntime.Platform/x86_64/scout_beta/active/files
, for example produced by [flatdeb][] (this is a special case of a merged/usr
). For example, as the user that will run Steam:$ flatpak --user remote-add --no-gpg-verify smcv-flatdeb https://people.collabora.com/~smcv/flatdeb/repo $ flatpak --user install smcv-flatdeb com.valvesoftware.SteamRuntime.Platform/x86_64/scout_beta $ ln -fns ~/.local/share/flatpak/runtime/com.valvesoftware.SteamRuntime.Platform/x86_64/scout_beta/active/files \ ~/scout_beta-runtime
and then set the launch options to:
/opt/pressure-vessel/bin/pressure-vessel-unruntime --runtime=$HOME/scout_beta-runtime -- %command%
-
A sysroot containing
bin/bash
,lib/ld-linux.so.2
,usr/bin/env
,usr/share/locale
,usr/lib/python2.7
and so on, optionally withbin
,lib
etc. being symlinks intousr
In this mode, graphics drivers come from the host system, while their dependencies (notably glibc and libstdc++) come from either the host system or the runtime, whichever appears to be newer. This is currently hard-coded in
pressure-vessel-wrap
and cannot be configured.To see the filesystem in which the game is executing, get the process ID of some game process from
ps
and use:$ sudo ls -l /proc/$game_pid/root/
You'll see that the graphics drivers and possibly their dependencies are available in
/overrides
inside that filesystem, while selected files from the host are visible in/run/host
. -
-
To protect
$HOME
, add one of the following options before--
:-
--fake-home=/some/path
(automatically unshares the home directory) --freedesktop-app-id=com.example.Anything --unshare-home
-
--steam-app-id=70 --unshare-home
(when running from Steam you can use--steam-app-id=${SteamAppId}
)
-
-
To test something manually:
-
cd to the directory that you want to be the current working directory inside the container
-
Run:
/opt/pressure-vessel/bin/pressure-vessel-wrap -- ./whatever-game
Optionally add more options before the
--
.
-
-
For interactive testing, if your runtime (if used) or host system (if no runtime) contains an xterm binary, you can use something like:
/opt/pressure-vessel/bin/pressure-vessel-wrap --xterm -- %command%
to run an xterm containing an interactive shell. The interactive shell's current working directory matches the game's. Run
"$@"
in the interactive shell to run the game. -
For interactive testing, if you ran Steam from a shell (not normally valid on SteamOS!), you can use:
/opt/pressure-vessel/bin/pressure-vessel-wrap --interactive -- %command%
The interactive shell's current working directory matches the game's. Run
"$@"
in the interactive shell to run the game.
Use pressure-vessel-unruntime
if you are in a Steam Runtime environment
(the Steam Runtime's run.sh
or a Steam game), and pressure-vessel-wrap
if you are not ("Add non-Steam game" in Steam, or a non-Steam-related
interactive shell).
Steam integration
If a future version of Steam is modified to run certain games using
pressure-vessel, it should remove the Steam Runtime environment variables
from the environment with which it runs them (like it does for
"Add non-Steam game"), and use pressure-vessel-wrap
directly.
pressure-vessel-unruntime
is just a workaround for this not
being something that Steam supports yet.
Design constraints
-
Steam games assume that they are executed with the current working directory equal to the game's base directory, typically something like
SteamApps/common/Half-Life
. -
Steam games are delivered via existing code to use the Steam CDN, not as Flatpak packages.
-
Each game is assumed to have one subdirectory of
SteamApps
(for exampleSteamApps/common/Half-Life
) and one AppID (for example 70 for Half-Life). These are not correlated in any obvious way. -
Some games have distinct app IDs but share data: for example, X3: Terran Conflict (ID 2820) and X3: Albion Prelude (ID 201310) share
SteamApps/common/X3 Terran Conflict
. -
The Steam client and client library need to be able to communicate via shared memory and SysV semaphores.
- ⇒ We must share
/dev/shm
- ⇒ We must not unshare the IPC namespace
- ⇒ We must share
Assumptions
-
Games may write to their own subdirectories of
SteamApps/common
. -
Games should not see each other's saved games and other private data in
XDG_CONFIG_HOME
etc. -
X11, Wayland, PulseAudio, D-Bus etc. are assumed to use sockets in
/run
(including$XDG_RUNTIME_DIR
),/var
or/tmp
.- X11 uses
/tmp
: OK - Wayland uses
$XDG_RUNTIME_DIR
: OK - The D-Bus system bus always uses
/var/run
: OK - The D-Bus session bus uses
$XDG_RUNTIME_DIR/bus
on systems with systemd, systemd-logind and the user bus: OK - The D-Bus session bus uses abstract Unix sockets on other systems: OK
- PulseAudio uses
$XDG_RUNTIME_DIR
on modern systems with systemd: OK - PulseAudio uses
/var/run
on SteamOS: OK - PulseAudio might not work on non-systemd non-SteamOS machines?
- X11 uses
-
Games can't see
~/.local/share/fonts
,~/.fonts
,~/Music
,~/Desktop
, etc. and this is assumed to be OK.
TODO
-
Games can currently read each other's static data via
~/.steam/steam
and~/.steam/root
. This could be prevented, if we can define which parts of~/.steam
are considered to be API and which are to be masked. -
What paths did PulseAudio historically use? It might not work on non-systemd non-SteamOS machines.
-
Games like AudioSurf that want to read
~/Music
aren't going to work. They'll need some new special-case option analogous to Flatpak's--filesystem=xdg-music:ro
.
Design
Each game gets a private home directory in ~/.var/app
, the same as
Flatpak apps do. The name of the private home directory follows the
naming recommendations from the freedesktop.org Desktop Entry
Specification.
For Steam apps, unless a better name has been specified, the app's
freedesktop.org app ID is based on its Steam AppID, for example
com.steampowered.App70
for Half-Life.
For the game, XDG_CONFIG_HOME
, XDG_DATA_HOME
and XDG_CACHE_HOME
are set to the ./.config
, ./.local/share
and ./.cache
directories
inside its private home directory, so that well-behaved freedesktop-style
apps will write there, and badly-behaved freedesktop-style apps that
ignore the environment variables and hard-code their default values will
also write there.
- Example: X3: Terran Conflict writes to
$XDG_CONFIG_HOME/EgoSoft/X3TC
- Example: Mesa writes to
$XDG_CACHE_HOME/mesa
(assuming$MESA_GLSL_CACHE_DIR
is unset)
./config
, ./data
and ./cache
in the private home directory are symbolic
links to .config
, .local/share
and .cache
respectively, for better
discoverability and compatibility with Flatpak (which uses those directories in
~/.var/app
as its usual values for XDG_CONFIG_HOME
, XDG_DATA_HOME
and
XDG_CACHE_HOME
).
Anything that hard-codes a path relative to $HOME
(including .config
,
.local/share
or .cache
) will write to the corresponding directory in
~/.var/app
. This is the same as the behaviour of a Flatpak app with
--persist=.
.
- Example: Avorion writes to
~/.avorion/
in the container, which is~/.var/app/com.steampowered.App445220/.avorion/
in the real home directory
If more than one game is meant to share a private home directory, then
they need to be run with --freedesktop-app-id=
or --steam-app-id=
to set that up.
- For example, if X3: Terran Conflict and X3: Albion Prelude
are to share data, they would have to both be run with for example
--freedesktop-app-id=com.egosoft.X3TC
or--steam-app-id=2820
.
The app is not currently made available read-only on /app
(as it
would be in Flatpak). It could be, if desired.