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发表于 2012-07-26 07:49 |只看该作者 |倒序浏览

本帖最后由 ulovko 于 2012-07-26 07:51 编辑

FreeBSD jails are a great tool. Whether you are using them to virtualize some of your systems (like I am) or to isolate certain processes, they are flexible enough and reliable enough to use for production.

Recently, I had to retire some old jails and add some new jails. Instead of just deleting one and creating an new jail, I wanted to rename the existing jail. I figured this was easier than recompiling all the apps that my jail would require.

A few notes on this decision:

My jails are all very similar.
In this case, I was moving from one version of PostgreSQL to another
One jail is called pg74 (as in PostgreSQL 7.4)
I was going to retire pg74 (which does regression tests on Bacula against PostgreSQL 7.4) and create pg91

Also, I am using ezjail to administer my jails. This tool is used several times in this article. That said, you will still see what I'm doing, and if you're not using ezjail, you'll be able to do the same thing with your admin tool of choice.

Removing, but not deleting, the old jail
The first step: stop the old jail.

# /usr/local/etc/rc.d/ezjail stop pg74.example.org
Stopping jails: pg74.example.org.

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Now, let's remove the jail from ezjail's configuration. Note that I could have skipped the previous step by adding the -f flag to this step:

# ezjail-admin delete pg74_example_org

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At this point, the jail is no longer running. However, the files are still present on disk:

# ls /usr/jails/pg74.example.org/
.cshrc COPYRIGHT bin dev home libexec mnt rescue sbin tmp var
.profile basejail boot etc lib media proc root sys usr

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Modifying the DNS (optional)
In my case, I wanted to create a new hostname to go with the new jail. But I was going to use the same IP address. This is the patch to my DNS zone files.

$ cvs di example.org.db example.org.rev.db
Index: example.org.db
===================================================================
RCS file: /home/repositories/websites/dns-private/example.org.db,v
retrieving revision 1.101
diff -r1.101 example.org.db
5c5
< 2012011700 ; Serial
---
> 2012060800 ; Serial
157c157
< pg74 IN A 10.0.0.104
---
> pg91 IN A 10.0.0.104
Index: example.org.rev.db
===================================================================
RCS file: /home/repositories/websites/dns-private/example.org.rev.db,v
retrieving revision 1.32
diff -r1.32 example.org.rev.db
3c3
< 2011072600 ; Serial
---
> 2012060800 ; Serial
33c33
< 104 IN PTR pg74.example.org.
---
> 104 IN PTR pg91.example.org.

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Making these changes and updating your DNS is outside the scope of this article. I'm mentioning it here so I remember this step when I need to do this again.

'Creating' the 'new' jail
In this step, we rename the directory and create the new jail.

First, we rename the directory. Strictly speaking, this is optional. The name of the directory is not related to the hostname of the jail. But convention dictates that the jail directory name should reflect the hostname for that jail.

# cd /usr/jails/
# mv -i pg74.example.org pg91.example.org

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Now, let's start the new jail:

# ezjail-admin create -x pg91.example.org 10.0.0.104
Warning: Some services already seem to be listening on IP 10.0.0.104
This may cause some confusion, here they are:
root ntpd 1459 27 udp4 10.0.0.104:123 *:*
Warning: Some services already seem to be listening on all IP, (including 10.0.0.104)
This may cause some confusion, here they are:
root ntpd 1459 20 udp4 *:123 *:*
root ntpd 1459 21 udp6 *:123 *:*

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Starting the new jail
This was easier than I thought. Starting the new jail is simple: