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/homeexecon
data/system/usr_compatexecon
data/system/usr_compatsetu­idon
data/system/usr_localexecon
data/system/usr_localsetu­idon
data/system/usr_objexecon
data/system/usr_portsexecon
data/system/usr_portssetu­idon
data/system/usr_srcexecon
data/system/usr_supsec­ondarycachenone
data/system/var_portsexecon

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.

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