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FreeBSD: Xorg in jail

Attention! Current pages describe CBSD version 13.0.x. If you are using an older version, please update first.

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Traditionally, it is assumed that FreeBSD — decent choice as a server OS, but on the role as a modern workstation suitable weak. Apologists and just hotheads on both sides of this opinion give different pros and cons and this article is not about this stupid dispute. Instead, there will also attempt to relate and fantasize about seemingly completely different technologies, such as Xorg and Jail, and demonstrated one of the scenarios with FreeBSD as a workstation.

Not so rare on the Internet you can find information about what additional properties from the *nix system acquires user running Xorg-based application chroot(8).

There may be many reasons, one of them — you like to experiment with different numbers of environments and do not really want to convert the file system in the trash (and possibly receive conflicts between one or another application on the file system.)

Also, do not last role security. No one can guarantee that any installed software, whether skype, mc, screen, firefox and so, at the first update, due to an unfortunate typo in the code will scan randomly your home directory for id_rsa keys and known_hosts, .mysql_history, .bash_history and all your settings from an account ~/.local, ~/.config , ~/.kde4 and send them to the developer’s website as necessary for further development of software updates statistics. Thus, chroot allows in this case to keep your eggs in one basket, which in itself — perfect.

If chroot deal with it, one might ask — «what can give jail startup it Xorg». Chances are, if you know the differences between jail and chroot and since you are reading this article, the answer is found and you can proceed to the next chapter. If not, then:

The main difference in this respect from jail chroot, a grouping of processes by ID (jid), which may participate in certain activities as an audit only for these processes, the ability to gather statistics through RACCT, setting limits through rctl(8) (useful for profiling applications). And, of course, binding network addresses, the ability to stack isolated and separate routing tables for all jailed processes.

The remaining additional advantages can already provide specific jail management utility. So, what can you get from X-jail, depends on your knowledge and imagination, and FreeBSD as usual, playing only a tool for the task.

Bring their own particular cases that receives and uses the author.

In the case of CBSD/jail/FreeBSD, an opportunity to:

  • downloaded from the repository environment preconfigured with various embodiments of the popular Windows Manager: KDE4, Fluxbox, Gnome3, LXDE and so on;
  • convenient option to export and import the image;
  • repciation via zrep for incremental backup;
  • opportunity to apply file snapshots;
  • opportunity to using cpuset(1) to bind all X applications on a specific core or core group;
  • You can use different limits for the entire cell, whereas the chroot, you can apply through the limits limit(1) only user or PID, which is not so convenient.
  • In the case of chroot and having multiple IP alias-s in the system as a source ip for a connection, the application will always use the first IP. In the case of jail and having multiple IP, you can restrict the IP for applications to only those that you need. In this case you can use PF/IPFW to calculate the X-traffic applications emulate the «bad» network, adding delay or loss on the net this jail, playing with traffic bandwith, etc. to study the work of an application under different conditions.
  • If you have multiple workstations via jail you can make a «floating» environment in a simpler way: for any station you would not be, you are always in the same environment, all history, all received email, even if it was adopted with the work station to another — always with you. You do not need to update the software directly in 3 systems if you ispoluete 3 working system and a set of software changes.

What is required for X-jail

To Xorg worked successfully in jail, it is necessary to remove the restrictions jailed processes to access /dev/io and /dev/kmem devices. Already long time there are patches of Alexander Leidinger aka netchild, optionality that provide these settings. And now, as far as I know, Jammie Gritton gave a jolt to the discussion the possible inclusion of patches in one form or another in the base. You can apply the patch and recompile your kernel yourself, or you can use the command:

			% cbsd repo action=get sources=kernel

And get a kernel with patches applied from the repository CBSD.

Attention: Due to resource limitations, this patch is applied only for the FreeBSD kernel 11 aka HEAD (as of this writing) in the repository CBSD

Attention: allow_kmem option violates the concept of jail security and should be used for containerization ONLY YOUR X-jails. Do not enable this feature in the jail that have the potential attackers access.

In the presence of these patches, configuration CBSD jail will have the option allow_kmem, which can be set through cbsd jset or cbsd jconfig

In addition, you may need to add a separate rule for devfs.ruleset(5), appropriate devices to become visible in the /dev directory in jail. For example this content:

			add include $devfsrules_hide_all
			add include $devfsrules_unhide_basic
			add include $devfsrules_unhide_login
			add path agpgart unhide
			add path console unhide
			add path consolectl unhide
			add path dri unhide
			add path 'dri/*' unhide
			add path io unhide
			add path 'nvidia*' unhide
			add path sysmouse unhide
			add path mem unhide
			add path pci unhide
			add path tty unhide
			add path ttyv0 unhide
			add path ttyv1 unhide
			add path ttyv8 unhide

and specify the appropriate number 8 in devfs_ruleset parameter from jail config.

The configuration is completed and further work on the launch of Xorg in jail is no different from the usual steps:

  • Install software
  • Generate /etc/X11/xorg.conf (if necessary) and create ~/.xinitrc
  • Run X

Attention: allow_kmem option violates the concept of jail security and should be used for containerization ONLY YOUR X-jails. Do not enable this feature in the jail that have the potential attackers access.

Short demo of XJail from scratch.

Full Example Step-by-Step: KDE4 in xjail with NVIDIA GL

For Radeon/Intel graphics user steps are the same, except for installation of nvidia-settings, nvidia-driver and /usr/src

Initial state - installed from scratch FreeBSD, without ports and source tree system

1) Install CBSD and init workdir:

% pkg install cbsd
% env workdir="/usr/jails" /usr/local/cbsd/sudoexec/initenv
% service cbsdd start

2) We need a mouse, turn the service moused:

% sysrc moused_enable="YES"

3) Create jail with kde4 name. In submenu pkglist choose MANUAL and write what software we need in a jail: x11/xorg x11/kde4:

The rest of the software and settings - at your discretion.

4) We need a kernel with patches. You can build your own for instructions FreeBSD maillist or receive from CBSD repository:

% cbsd repo action=get sources=kernel

5) Install new kernel into /boot/kernel:

% cbsd upgrade target=kernel

6) Reboot system to new kernel:

% shutdown -r now

7) In the settings jail solve allow_kmem and change devfs_ruleset any non-existent (for example 99). In this case, will be open all /dev. If you all to open inappropriately - use the information above to create your ruleset:

% cbsd jstop kde4
% cbsd jset jname=kde4 allow_kmem=1
% cbsd jset jname=kde4 devfs_ruleset=99
other than that (only for NVIDIA users) ask CBSD to mount /usr/src in jail. It is necessary to build nvidia-driver port (from which the need in environment)
% cbsd jset jname=kde4 mount_src=1

Instead jset You can use the TUI configurator: cbsd jconfig jname=kde4

8) Only for NVIDIA users: we need a source tree /usr/src to build x11/nvidia-drivers

To do this, fill /usr/src and /usr/ports relevant content. Or, you can ask it to do CBSD

For receive /usr/ports from SVN FreeBSD:

% cbsd portsup

For receive $workdir/src/src\* (which we will create a symlink to not keep two copies) from SVN FreeBSD:

% cbsd srcup
% rmdir /usr/src ( or, on ZFS installation, remove pseudo-fs: zfs destroy zroot/usr/src )
% ln -sf ~cbsd/src/src_10.1/src /usr/src

(If the version of FreeBSD does not 10.1, the path will be different)

9) Only for NVIDIA users: install dependencies nvidia-driver repository of the installation and removal nvidia-driver. In addition, we need glproto

% pkg install x11/glproto x11/nvidia-driver 
% pkg remove nvidia-driver

10) Only for NVIDIA users: Install the NVIDIA driver from ports:

	env BATCH=yes make -C /usr/ports/x11/nvidia-driver install

11) Only for NVIDIA users: prescribes module nvidia.ko in autoload, increase ipc.shmall as advised by the port:

% sysrc kld_list="nvidia"
% echo "kern.ipc.shmall=1310720" >> /etc/sysctl.conf

11) The same actions, but for users with Intel graphics: just add into /boot/loader.conf:


12) Restarting the server (or load modules manually), run and prepare jail:

% shutdown -r now
% cbsd jstart kde4
% cbsd jlogin kde4

13) Subsequent steps are performed in the environment. Inside the jail expose dbus to autostart

% sysrc dbus_enable="YES"
% service dbus start

14) Install nvidia-driver into jail by analogy with paragraph 9 and 10

% pkg install x11/glproto x11/nvidia-driver 
% pkg remove nvidia-driver
% env BATCH=yes make -C /usr/ports/x11/nvidia-driver install

15) If you do not know how to write still working xorg.conf from scrath, better to generate it via nvidia-xconfig:

% pkg install x11/nvidia-xconfig
% nvidia-xconfig

Users with Intel can take advantage with X staff:

% X -configure

And copy the generated /root/ in /etc/X11/xorg.conf

Append in the generated /etc/X11/xorg.conf the ServerFlags section:

Section "ServerFlags"
       Option         "AutoAddDevices" "off"
       Option         "AutoEnableDevices" "off"
       Option         "AllowEmptyInput" "off"

16) Create a user xuser, if you have not done so when creating jail:

% pw useradd xuser -m -s /bin/csh

17) Go to the user, write standard ~/.xinitrc and run KDE:

% su - xuser
% echo startkde >> ~/.xinitrc
% xinit

It may be useful to make additional settings

18) Mount Linux-specific FS, for normal Linux-applications in the jail. To do this, the master node to create a local fstab to jail with this content:

файл /usr/jails/jails-fstab/fstab.kde4.local

	linprocfs       /usr/compat/linux/proc  linprocfs       rw      0       0

19) If you plan to synchronize the jail to another server and periodically run on another node, and the configuration of the second node is different, it is best to save the xorg.conf in the master node and create a script that will copy it every once in to /etc/X11/ in the jail. The same must be done for the other node

Делается в мастер ноде

% cp /usr/jails/jails-data/kde4-data/etc/X11/xorg.conf /etc/X11

In /usr/jails/jails-system/kde4/master_poststart.d directory create new script with such content:

cp -a /etc/X11/xorg.conf ${data}/etc/X11/xorg.conf

Make script executable:

% chmod +x /usr/jails/jails-system/kde4/master_poststart.d/

You can also do with /etc/resolv.conf and /etc/hosts if necessary