Monthly Archives: November 2012

Easy IPv4+IPv6 Nagios monitoring using check_v46

Not feeling ready to give up on IPv4 quite yet? In that case you most likely want your Nagios to probe your services on both their IPv4- as well as their IPv6 addresses.

Looking into how how to handle that duplication in a sane manner I stumbled over the rather convenient check_v46 plugin wrapper. Assuming the actual check being run provides the -4/-6 options check_v46 can automatically, based on a hostname lookup, test using IPv4 and/or IPv6, and then return the worst result. See below for a trivial example, as well a matching example response.

define command{
       command_name    dual_check_http
       command_line    /usr/local/nagios/check_v46 -H '$HOSTNAME$' /usr/lib/nagios/plugins/check_http

Do note that there is also the option of manually feeding check_v46 IPv4 and IPv6 addresses. See the plugin –help for the actual details. Also note that the check_v46 wrapper does not appear to work with the Nagios embedded Perl.

Of course, a more perfect solution probably requires Nagios itself to be more IPv4 vs IPv6 aware. For example, in the case that a host (or a datacenter) temporarily becomes unavailable over IPv6, it might then be more helpful if the service checks focused primarily on the IPv4 results, instead of either going full ballistic or completely silent. Yet, as long as good enough is good enough, the check_v46 wrapper is definitely an easy win.

Fully using apt-get download

Occasionally I need to download a Debian package or two. While I could find a download link using / I really do prefer using apt-get download. In addition to the general pleasantness of using a command line tool the main benefit really is that apt automatically will verify checksums and gpg signatures.

For me the most typical usage scenario is that I want to download a Debian package from a different release than the one I happen to run on my workstation. Instead of putting additional entries in /etc/apt/sources.list, and hence having to deal with apt pinning as well as it making my regular apt-get update runs slower, I find it much more convenient to setup a separate apt environment.

First there is the basic directory structure.

$ mkdir -p ~/.cache/apt/{cache,lists}
$ mkdir -p ~/.config/apt/{apt.conf.d,preferences.d,trusted.gpg.d}
$ touch ~/.cache/apt/status
$ ln -s /usr/share/keyrings/debian-archive-keyring.gpg ~/.config/apt/trusted.gpg.d/
$ ln -s /usr/share/keyrings/ubuntu-archive-keyring.gpg ~/.config/apt/trusted.gpg.d/

(For an Ubuntu system the /usr/share/keyrings/debian-archive-keyring.gpg keyring is provided by the debian-archive-keyring package.)

Then there is the creation of the files ~/.config/apt/downloader.conf and ~/.config/apt/sources.list. They should contain something like the following.

## ~/.config/apt/downloader.conf
Dir::Cache "/home/USERNAME/.cache/apt/cache";
Dir::Etc "/home/USERNAME/.config/apt";
Dir::State::Lists "/home/USERNAME/.cache/apt/lists";
Dir::State::status "/home/USERNAME/.cache/apt/status";
## ~/.config/apt/sources.list
# Debian 6.0 (Squeeze)
deb squeeze main contrib non-free
deb squeeze-updates main non-free
deb squeeze/updates main contrib non-free

# Debian 6.0 (Squeeze) Backports
deb squeeze-backports main contrib non-free

# Debian 7.0 (Wheezy)
deb wheezy main
deb wheezy/updates main

# Debian Unstable (Sid)
deb sid main

# Ubuntu 12.04 (Precise)
deb precise main restricted universe multiverse
deb precise-updates main restricted universe multiverse
deb precise-security main restricted universe multiverse

# Ubuntu 12.10 (Quantal)
deb quantal main restricted universe multiverse
deb quantal-updates main restricted universe multiverse
deb quantal-security main restricted universe multiverse

Given the just described setup, apt-get download can now download packages from any release/codename defined in ~/.config/apt/sources.list.

$ APT_CONFIG=~/.config/apt/downloader.conf apt-get update
$ APT_CONFIG=~/.config/apt/downloader.conf apt-get download git/squeeze-backports
Get:1 Downloading git 1: [6557 kB]
Fetched 6557 kB in 2s (2512 kB/s)
$ APT_CONFIG=~/.config/apt/downloader.conf apt-get download git/precise
Get:1 Downloading git 1: [6087 kB]
Fetched 6087 kB in 3s (1525 kB/s)

Do note that apt-get download was introduced in apt 0.8.11. For Debian that translates into Wheezy (7.0) and for Ubuntu that would be as of Natty (11.04). The main difference between apt-get download and apt-get –download-only install is that the later also does dependency resolution.