Creating a Slave DNS Server on Bind9

29 Nov 2009 — eric

I couldn’t find a quick and dirty list of commands for setting up a slave DNS server so I figured I would just throw it together.

Starting with a fully working primary name server, we are going to set up a slave name server. We are going to make the following assumptions:
primary – 1.2.3.4
slave – 4.5.6.7
* We want to have the domain example.com have a slave name server

On the primary (or master) name server, add the following lines to the options section.

options {
    allow-transfer { 4.5.6.7; };
    notify yes;
};

Ensure that you update the serial number in the SOA on the master. Then run:

# rndc reload

On the slave name server, add the following entry to the named.conf file (or whichever file houses your zone entries). Ensure that the path leading up to the zone file exists and that bind has write access to that directory.

 zone "example.com"  { type slave; file "/etc/bind9/zones/example.com.slave"; masters { 1.2.3.4; }; };

Then once you made the changes to the slave, you will need to reload the configuration. Do this the same way you did on the master:

# rndc reload

If you watch your DNS log, you should see the transfer happen as soon as you restart both named servers.

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SSH Over The Web With Web Shell

27 Nov 2009 — eric

After reading a Tweet from Matt Cutts about being able to SSH from the iPhone (and the web in general), I had to give it a try. I am always looking for better ways to be able to check on systems when necessary. I have iPhone apps for SSHing around if I need as well, but like with any “new” tool, I have to try it out to see if it serves a purpose or makes my admin life easier in any way.

First go check out the Google Code repository for Web Shell. Webshell is written in Python and is based on Ajaxterm. All that’s required is SSL And Python 2.3 or greater. It works on any browser that has Javascript and can make use of AJAX.

The way Web Shell works is you start it up on a server and then can use a web browser to access only that machine over SSH. The works best if you have a gateway server to a network and use a single point of entry to access the rest of the servers. Web Shell runs on HTTPS on port 8022. Reading the README will lead you through the same set of instructions I used below. Once installed, we connect by using a web browser: https://server.com:8022/
Read the rest of this entry »

Posted in System Administration. Tags: , . 3 Comments »

Quick Date Calculations With Date

21 Jul 2009 — eric

I frequently find myself needing to do quick date calculations in order to make scripts run when I want them to or how I want them to. Usually Date::Calc is just a bit too heavily, especially if it’s something as simple as a BASH script. As it happens, date is quite a powerful tool for some command line fu.

For example, to find the first and last day of last month:

FIRST_DOLM=`date -d "-1 month -$(($(date +%d)-1)) days" "+%Y-%m-%d"`
LAST_DOLM=`date -d "-$(date +%d) days" "+%Y-%m-%d"`

You can do the same thing using the date command on a mac with a slightly different set of switches:

FIRST_DOLM=`/bin/date -v1d -v-1m "+%Y-%m-%d"`
LAST_DOLM=`/bin/date -v31d -v-1m "+%Y-%m-%d"`

Both of these will produce the same results:

2009-06-01
2009-06-30
Posted in System Administration. Tags: . 1 Comment »

HOWTO Recreate /dev/null

27 May 2009 — eric

If something happens that requires you to recreate /dev/null on your *nix system. Don’t fret, it’s easy. The most recent issue I had was that a Capistrano recipe inadvertently clobbered /dev/null. The file looked like this:

[root@web1 ~]# ls -l /dev/null
-rw-r--r-- 1 capistrano engineering 0 May 26 04:02 /dev/null

Thankfully to bring it back to its original state, just run the following commands:

[root@web1 ~]# rm /dev/null
rm: remove regular empty file `/dev/null'? yes
[root@web1 ~]# mknod /dev/null c 1 3
[root@web1 ~]# chmod 666 /dev/null
[root@web1 ~]# ls -l /dev/null
crw-rw-rw- 1 root root 1, 3 May 26 15:09 /dev/null

Take note of the following things:

  • It is not a joke that the mode of /dev/null needs to be 666. It should be user, group, and world read and write.
  • The user and group ownership here is root.
  • There is no size in the ls like you see in the top one. All you should see are the major (1) and minor (3) device numbers (separated by a comma) prior to the date.
Posted in System Administration. Tags: . 2 Comments »
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