How I setup a Jail-​Host

Everyone has his own way of setting up a machine to serve as a host of multiple jails. Here is my way, YMMV.

Initial FreeBSD install

I use several harddisks in a Software-RAID setup. It does not matter much if you set them up with one big partition or with several partitions, feel free to follow your preferences here. My way of partitioning the harddisks is described in a previous post. That post only shows the commands to split the harddisks into two partitions and use ZFS for the rootfs. The commands to initialize the ZFS data partition are not described, but you should be able to figure it out yourself (and you can decide on your own what kind of RAID level you want to use). For this FS I set atime, exec and setuid to off in the ZFS options.

On the ZFS data partition I create a new dataset for the system. For this dataset I set atime, exec and setuid to off in the ZFS options. Inside this dataset I create datasets for /home, /usr/compat, /usr/local, /usr/obj, /usr/ports/, /usr/src, /usr/sup and /var/ports. There are two ways of doing this. One way is to set the ZFS mountpoint. The way I prefer is to set relative symlinks to it, e.g. "cd /usr; ln -s ../data/system/usr_obj obj". I do this because this way I can temporary import the pool on another machine (e.g. my desktop, if the need arises) without fear to interfere with the system. The ZFS options are set as follows:

ZFS options for data/system/*

Dataset

Option

Value
data/system/home exec on
data/system/usr_compat exec on
data/system/usr_compat setuid on
data/system/usr_local exec on
data/system/usr_local setuid on
data/system/usr_obj exec on
data/system/usr_ports exec on
data/system/usr_ports setuid on
data/system/usr_src exec on
data/system/usr_sup secondarycache none
data/system/var_ports exec on

The exec option for home is not necessary if you keep separate datasets for each user. Normally I keep separate datasets for home directories, but Jail-Hosts should not have users (except the admins, but they should not keep data in their homes), so I just create a single home dataset. The setuid option for the usr_ports should not be necessary if you redirect the build directory of the ports to a different place (WRKDIRPREFIX in /etc/make.conf).

Installing ports

The ports I install by default are net/rsync, ports-mgmt/portaudit, ports-mgmt/portmaster, shells/zsh, sysutils/bsdstats, sysutils/ezjail, sysutils/smartmontools and sysutils/tmux.

Basic setup

In the crontab of root I setup a job to do a portsnap update once a day (I pick a random number between 0 and 59 for the minute, but keep a fixed hour). I also have http_proxy specified in /etc/profile, so that all machines in this network do not download everything from far away again and again, but can get the data from the local caching proxy. As a little watchdog I have a little @reboot rule in the crontab, which notifies me when a machine reboots:

@reboot grep "kernel boot file is" /var/log/messages | mail -s "`hostname` rebooted" root >/dev/null 2>&1

This does not replace a real monitoring solution, but in cases where real monitoring is overkill it provides a nice HEADS-UP (and shows you directly which kernel is loaded in case a non-default one is used).

Some default aliases I use everywhere are:

alias portmlist="portmaster -L | egrep -B1 '(ew|ort) version|Aborting|installed|dependencies|IGNORE|marked|Reason:|MOVED|deleted|exist|update' | grep -v '^--'"
alias portmclean="portmaster -t --clean-distfiles --clean-packages"
alias portmcheck="portmaster -y --check-depends"

Additional devfs rules for Jails

I have the need to give access to some specific devices in some jails. For this I need to setup a custom /etc/devfs.rules file. The files contains some ID numbers which need to be unique in the system. On a 9-current system the numbers one to four are already used (see /etc/defaults/devfs.rules). The next available number is obviously five then. First I present my devfs.rules entries, then I explain them:

[devfsrules_unhide_audio=5]
add path 'audio*' unhide
add path 'dsp*' unhide
add path midistat unhide
add path 'mixer*' unhide
add path 'music*' unhide
add path 'sequencer*' unhide
add path sndstat unhide
add path speaker unhide

[devfsrules_unhide_printers=6] add path 'lpt*' unhide add path 'ulpt*' unhide user 193 group 193 add path 'unlpt*' unhide user 193 group 193

[devfsrules_unhide_zfs=7] add path zfs unhide

[devfsrules_jail_printserver=8] add include $devfsrules_hide_all add include $devfsrules_unhide_basic add include $devfsrules_unhide_login add include $devfsrules_unhide_printers add include $devfsrules_unhide_zfs

[devfsrules_jail_withzfs=9] add include $devfsrules_hide_all add include $devfsrules_unhide_basic add include $devfsrules_unhide_login add include $devfsrules_unhide_zfs

The devfs_rules_unhide_XXX ones give access to specific devices, e.g. all the sound related devices or to local printers. The devfsrules_jail_XXX ones combine all the unhide rules for specific jail setups. Unfortunately the include directive is not recursive, so that we can not include the default devfsrules_jail profile and need to replicate its contents. The first three includes of each devfsrules_jail_XXX accomplish this. The unhide_zfs rule gives access to /dev/zfs, which is needed if you attach one or more ZFS datasets to a jail. I will explain how to use those profiles with ezjail in a follow-up post.

Jails setup

I use ezjail to manage jails, it is more comfortable than doing it by hand while at the same time allows me to do something by hand. My jails normally reside inside ZFS datasets, for this reason I have setup a special area (ZFS dataset data/jails) which is handled by ezjail.The corresponding ezjail.conf settings are:

ezjail_jaildir=/data/jails
ezjail_use_zfs="YES"
ezjail_jailzfs="data/jails"

I also disabled procfs and fdescfs in jails (but they can be enabled later for specific jails if necessary).

Unfortunately ezjail (as of v3.1) sets the mountpoint of a newly created dataset even if it is not necessary. For this reason I always issue a "zfs inherit mountpoint " after creating a jail. This simplifies the case where you want to move/rename a dataset and want to have the mountpoint automcatically follow the change.

The access flags of  /data/jails directory are 700, this prevents local users (there should be none, but better safe than sorry) to get access to files from users in jails with the same UID.

After the first create/update of the ezjail basejail the ZFS options of basejail (data/jails/basejail) and newjail (data/jails/newjail) need to be changed. For both exec and setuid should be changed to "on" The same needs to be done after creating a new jail for the new jail (before starting it).

The default ezjail flavour

In my default ezjail flavour I create some default user(s) with a basesystem-shell (via /data/jails/flavours/mydef/ezjail.flavour) before the package install, and change the shell to my preferred zsh afterwards (this is only valid if the jails are used only by in-house people, if you want to offer lightweight virtual machines to (unknown) customers, the default user(s) and shell(s) are obviously up to discussion). At the end I also run a "/usr/local/sbin/portmaster -y --check-depends" to make sure everything is in a sane state.

For the packages (/data/jails/flavours/mydef/pkg/) I add symlinks to the unversioned packages I want to install. I have the packages in a common (think about setting PACKAGES in make.conf and using PACKAGES/Latest/XYZ.tbz) directory (if they can be shared over various flavours), and they are unversioned so that I do not have to update the version number each time there is an update. The packages I install by default are bsdstats, portaudit, portmaster, zsh, tmux and all their dependencies.

In case you use jails to virtualize services and consolidate servers (e.g. DNS, HTTP, MySQL each in a separate jail) instead of providing lightweight virtual machines to (unknown) customers, there is also a benefit of sharing the distfiles and packages between jails on the same machine. To do this I create /data/jails/flavours/mydef/shared/ports/{distfiles,packages} which are then mounted via nullfs or NFS into all the jails from a common directory. This requires the following variables in /data/jails/flavours/mydef/etc/make.conf (I also keep the packages for different CPU types and compilers in the same subtree, if you do not care, just remove the "/${CC}/${CPUTYPE}" from the PACAKGES line):

DISTDIR=  /shared/ports/distfiles
PACKAGES= /shared/ports/packages/${CC}/${CPUTYPE}

New jails

A future post will cover how I setup new jails in such a setup and how I customize the start order of jails or use some non-default settings for the jail-startup.

Leave a Reply

Your email address will not be published. Required fields are marked *