Date: Thu, 14 Feb 2002 06:59:57 -0600 From: Scott Bolte <listS+freebsd-questions@niss.com> To: BSD Freak <bsd-freak@mbox.com.au> Cc: FreeBSD Questions <freebsd-questions@FreeBSD.ORG> Subject: Re: File system layout with multiple jails Message-ID: <200202141259.g1ECxv067094@crag.niss.com>
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On Thu, 14 Feb 2002 17:44:14 +1100, BSD Freak wrote:
> Hi everyone,
>
> Does anyone have any bright ideas for good file system layouts when
> running multiple jails?
I won't say they are bright, but the ideas reflected in
this layout are working well for me:
/jails/ Home for most jail related material. Note I do not
backup /jails every night as I do other partitions.
(I do backup /data every night and you'll see below
how I make use of that in a jail.)
/jails is its own partition so if it fills, it will
not cause problems for the host system.
/jails/{jail_X}/
The root for one specific jail. Of course if you
have sets of jails, then /jails/jail_A/{cell_1,cell_2}
and /jails/jail_B/{cell_10,cell_11} where cell_#
is actually the root directory works well for
keeping them well organized.
/jails/etc/rc.d/
Startup scripts (e.g. jail_X.sh) for all jails.
If you augment $local_startup in /etc/rc.conf to
include /jails/etc/rc.d then all the jails will be
started automatically.
/jails/bin/
Jail management scripts.
.../bin/JAIL_CTL.sh A generic start, stop, enter, trace,
ps script. Each jail's startup
script sets a bunch of environment
variables and then calls JAIL_CTL.
.../bin/jail_clone duplicates a jail.
.../bin/jail_ps runs ps for all the processes in
a specific jail.
/jails/var/trace/
Home for kdump traces of jail execution.
/jails/template/
A reference jail that I can clone in a few minutes
time. Much easier then running (make world) every
time I need a new jail.
/data/jails/{jail_X}/
If there is a /data/jails/{jail_X} present, then
it is automatically mounted as /jails/{jail_X}/data
when the jail is started. That way the /data
directory in a jail can be treated separately then
from the rest of the jail.
One caveat if you do this. Multiple jails, each
with their own uid space, will rapidly overlap in
the host's uid space. To avoid this, my jail creation
script hashes the jail's IP address to create a
(relatively) unique starting point for that jail's
uids. That starting uid is placed in the jail's
/etc/adduser.conf as $uid_start. This minimizes the
chances that uids will collide.
/data/jails/{jail_X}/home/
Symlink to /data/home (in the jail of course). If
/data/jails/{jail_X} is mounted on the jail's /data,
then the home partition in the jail is actually
coming from /data of the host and therefore will
be backed up on a regular basis.
/data/jails/{jail_X}/proc/
If it is present, then /proc is mounted on this
directory when a jail is started and unmounted when
it is stopped.
> How do I stop /var/log in one the jails from filling up the whole drive
> and affecting the rest without giving each jail it's own partition?
>
> Is it possible to some how set a quota on how large a particular
> directory can get?
About all I can think of is to make a directory, and all its
subordinate directories, owned by a specific user. You can
then have per user quotas.
For the specific example of /var/log, you'd have to set the
user to be root_X. If you then set the user-ID-on-execution
bit (see chmod(1) or chmod(2)) for /var/log so all new files
and directories created under it would also be owned by root_X.
I suspect you'd have to pre-populate your /var/log directory
and chown everything to root_X. If you then change everything
there to have world write permissions then root in the jail
can update the files. Having world write access is a bad
idea, but it's your trade-off to consider.
Scott
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