Clarification: "Jail" -vs- "Chroot"

Valentin Bud valentin.bud at
Wed Jul 14 07:27:26 UTC 2010

On Wed, Jul 14, 2010 at 2:30 AM, Aiza <aiza21 at> wrote:

> Ed Flecko wrote:
>> Hi folks,
>> I'm reading about "jails" and "chroot", and I'm not clear about the
>> differences so I'm hoping someone can clarify this for me.
>> Here's what I "think" is correct:
>> 1.) FreeBSD has both "chroot" capability as well as "jail" capability.
>> 2.) Only FreeBSD has true, "jail" functionality? Yes?...No?
>> 3.) When reading something (book, article, etc.), is there a way to
>> determine if the author is, in fact, talking about truly a "jail" or
>> are they really just referring to a "chroot" environment? For example,
>> I have a book ("Preventing web attacks with Apache") that says:
>> "Chroot is short for change root and essentially allows you to run
>> programs in a protected or jailed environment. The main benefit of a
>> chroot jail is that the jail will limit the portion of the file system
>> the daemon can see to the root directory of the jail. Additionally,
>> since the jail only needs to support Apache, the programs available in
>> the jail can be extremely limited."
>> 4.) Jail is the more secure of the two options?
>> 5.) When would you "typically" use a jail -vs- a chroot? The new, 2nd
>> edition of "Absolute FreeBSD" says:
>> "Chrooting is useful for web servers that have multiple clients on one
>> machine—that is, web servers with many virtual hosts."
>> Comments??? Suggestions???
>> Thank you!
>> Ed
> Well let me take a shot at this. First of all we are only talking about the
> FreeBSD operating system. The ability to chroot a directory tree has been
> available since RELEASES 2.0. The jail utility first appeared in RELEASE
> 4.0. The jail utility is just a basic effort to automate the building and
> administration of an chrooted directory tree which is pretty much useless
> unless it contains a complete copy of the Freebsd operating system binaries.
> The major short coming of the jail command jail system is each jail has it's
> own copy of the hosts running system binaries. Freebsd reserves a limited
> number of control structures for storing files and directories, called
> inodes. Creating a few jails consumes many of these valuable inodes,
> eventually preventing the creation of new jails and new files on the host.
> Worst yet is each jail loads it's own copy of it's running binaries into
> memory which causes thrashing on the swap device as memory pages are swapped
> in and out as the limited memory is shared between the host and jails.
> Besides consuming resources and creating performance degradation, this also
> causes a major administration headache when wanting to update the host
> running system, because the host and the jails all have to be running the
> same RELEASE version.
> Now with some considerable hand jobbing per the jail section of the
> handbook, a jail environment can be created where by a single copy of the
> jailed running binaries are shared among all the jails. But this still
> leaves you with an administration nightmare as the number of jails deployed
> grows past 5. Now there are some ports in the port system that are utility
> wrappers around the jail command that tries to address this administration
> nightmare. My experience with these are they are very poorly documented and
> you really need to have a good grasp on how jails work and network ip
> address usage before they are useful. Their easy of use quickly evaporates
> as the number of jails deployed reaches 10.
> The next generation of a jail utility for the deployment of a large number
> of jails is in project phase right now. Keep checking the ports system for
> qjail.
> Now about what to run in a jail. Well since each jail is like a complete
> stand-a-lone operating system, you can populate it with any application you
> want. The real limitation is how is that jail going to gain public internet
> access so the domain name of your apache website can be found and accessed.
> A static ip address is pretty much required, though with some creative ip
> address assignments this can be circumvented. Thats a whole other subject
> area.

Hello community,

 Aiza could you please tell us more about qjail. google isn't very helpful
and I am very interested in the subject.

thank you.

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