Run the same command on many Linux servers at once

 Guides, Pills  5 Responses »
May 212014
 

Original article by Linux Brigade

Ever have to check a list of Linux servers for various things like what version of CentOS they’re running, maybe how long each has been running to get an uptime report? You can and it’s very easy to get going with it with the command gsh

Group Shell (also called gsh) is a remote shell multiplexor. It lets you control many remote shells at once in a single shell. Unlike other commands dispatchers, it is interactive, so shells spawned on the remote hosts are persistent.
It requires only a SSH server on the remote hosts, or some other way to open a remote shell.
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How to convince apt-get NOT to use IPv6

 Guides, Pills  4 Responses »
Aug 252013
 

Recently I installed a Debian 7 VPS on Linode and as first thing I wanted to do an update of the system, but I found a small problem in doing this :

# apt-get update
0% [Connecting to ftp.us.debian.org (2610:148:1f10:3::89)] [Connecting to security.debian.org (2607:ea00:101:3c0b:207:e9ff:fe00:e595)]
Get:1 http://ftp.us.debian.org wheezy Release.gpg [1,672 B]                                                                           
...
Get:15 http://security.debian.org wheezy/updates/main Translation-en [56.6 kB]
Fetched 16.3 MB in <strong>4min 0s</strong> (67.5 kB/s)                                                                                                                                     
Reading package lists... Done

So 4 minutes to just update my repositories (and I had just the default for a Debian 7 just installed), this is due to the fact that linode VPS are IPV6 ready and so the servers of this company try to connect to security.debian.org via its IPv6 address by default when running apt-get update, and that results in having to wait for a lengthy timeout whenever you try to download updates of any sort.

But luckily change the system so apt-get will use IPV4 it’s not so hard.
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Using OpenDKIM to Sign Postfix Mails on Debian

 Guides  13 Responses »
May 142013
 

dkim-process

Article By Chris Pentago

Goal of this how-to: Step to step guide on how to setup  OpenDKIM with postfix on Debian GNU/Linux to send signed email from your VPS.

There are numerous methods or techniques that you can use to achieve email message signing. Good examples are DomainKey as well as DKIM which is an abbreviation for DomainKeys Identified Mail.

DomainKeys Identified Mail (DKIM) lets an organization take responsibility for a message that is in transit.  The organization is a handler of the message, either as its originator or as an intermediary. Their reputation is the basis for evaluating whether to trust the message for further handling, such as delivery. Technically DKIM provides a method for validating a domain name identity that is associated with a message through cryptographic authentication.

These two techniques will not use symmetric encryption but rather will employ asymmetric encryption. (more info: http://support.microsoft.com/kb/246071) In both methods, the common algorithm used is RSA. This algorithm is also the default for these methods of achieving email message signing.

For those wondering about what asymmetric means, the following is a detailed explanation. It is a technique that utilizes a key to sign the email message. Other methods will not require a key. One can have two types of keys: a private key and a public key. These keys will come into play to verify the message as well. The two methods of creating email message signing as highlighted above are filters for SMTP server. DomainKey works with a dk-filter although this filter has been discontinued in the market. OpenDKIM has become the preferred replacement where filters are concerned.

A mail server must be enabled with a filter to set up the server properly. In light of this, Postfix can be used because it is enabled accordingly. Another requirement is the freedom to add or change the DNS records as you desire. With the above in mind, the following is a step by step guide on how to set up Postfix email server with DomainKey Indentified Mail on Debian.

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How to setup postfix to forward email to another email account on Debian/Ubuntu

Since its initial introduction into the business world in 2005, Google Apps has been available to small business users for free. Even when the premium version was launched in 2007, Google still maintained a free standard version for individuals and small organizations, this was great for small website, they could have their emails managed by […]

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How to properly use ‘dd’ on Linux to benchmark the write speed of your disk?

Original article published on http://romanrm.ru This article is written to address sometimes incorrect usage of the “dd” program to measure disk write performance on a VPS by some visitors of the lowendbox.com website, and is originally based on this question and my answer to it.

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