Shuron’s Letters

Personal blog of Alexander Holbreich

SSH tunnel without password

SSH (Secure Shell) allows simple establishment of encrypted and authenticated connection between computers. Today i describe how easy it is do establish such SSH tunnels without using a password. You may need such connections when they have to be opened by daemons (e.g. Cron) without user interaction.

Two words on theory. Password-less connections have to be authenticated at least so strong like the password enabled one, so asymmetric cryptography which enables certificates comes into play.  The clue is to have private and public keys and share your public key with domains which should be able identify you.

So therefore let’s start by generation a needed key-pair.

Generating Keys

It is possible to create key with pass-phrase and without (or empty pass-phrases). I prefer to not use pass phrase because it is asked every-time on later usage of a ssh. Even there are ways to gives the pass-phrase to ssh command, but it is more work, with no significant security benefits. So i do the following statement and do not enter any pass-phrase (just hit enter on question).

$ ssh-keygen -t rsa

This will create RSA key-pair as following files in ~/.ssh directory:

• id_rsa
• id_rsa.pub

Now public key need to be copied to remote host and has to be added to end of ~/.ssh/authorized_keys file.

Transfer Public keys

The best way to do it is to use ssh-copy-id program which is inside of many linux distributions.

$ ssh-copy-id -i ~/.ssh/id_rsa.pub remote-user@remote-server.org

In that case everything is done automatically and you are ready after that. But if ssh-copy-id is not available, you can copy keys manually e.g. like that.

$ cat ~/.ssh/*.pub | ssh remote-user@remote-server.org 'umask 077; cat >>.ssh/authorized_keys'

Attention! On some linux distrs SSH2 searches for keys in ~/.ssh/authorized_keys2 . Not so in actual Debian (Lenny), but seems to be so in SuSe linux.

Test

Now remote login, scp and sftp can be used without password. Test it:

# establish connection
$ ssh remote-user@remote-server.org
#or copy files secure and password-less.
$ scp /home/user/some-file remote-user@remote-server.org:/some-path/dir/

More information on SSH related man pages.

JBoss 5 GA on Debian linux

This short tutorial describes how to configure JBoss Application Server (Jboss GA 5.1.0) on a debian linux (Debian GNU/Linux 5.x “Lenny” ). Article starts with installation of java JDK and continues with JBoss installation and basic configuration according to standard  file system hierarchy. Also init.d. scripts configuration is given here.

Installing Java SDK

Nowadays  installing Java environment on Debian is an easy task. I used JDK 1.6. Don’t confound JDK with JRE, because bare Java Runtime Environment is not enough for running JBoss. Debian Wiki maintains (hope) a list of available java .deb packages, which are easily can be installed with your preferred way. I prefer aptitude, but apt-get of course works too.

$ aptitude install sun-java6-jdk
#or by good old apt-get.
$ apt-get install sun-java6-jdk

Installation is done after seconds. Now test your java installation with

$ java -version
# Here example result on my configuration:

java version "1.6.0_12"
Java(TM) SE Runtime Environment (build 1.6.0_12-b04)
Java HotSpot(TM) 64-Bit Server VM (build 11.2-b01, mixed mode)

If you get something like this, you’re done and your java should be already in the PATH.

Installing JBoss AS

Now let’s install  JBoss Application Server.

Preparing

Normally you are not willing  to start services (especially when they are accessed from outher machines) with root privileges. Therefore we have to define new user and group which will be used to manage JBoss.  So next line will create new group and new user with this group.

 $ groupadd jboss
 $ useradd -s /bin/bash -d /home/jboss -m -g jboss jboss

This jboss user has no password, so nobody can login with this username. If you consider to  login with jboss user,  password has to be set. Use passwd jboss command for that.

Download, Installation,  filesystem layout

Now  download desired Jboss version. I started with JBoss 5.1.0 GA, which can be download with:

<pre>$ cd /tmp # swithch to temp dir
$ wget http://sourceforge.net/projects/jboss/files/JBoss/JBoss-5.1.0.GA/jboss-5.1.0.GA.zip/download

Check also the whole list of verisons if interested. As you may noticed JBoss binaries are packaged with ZIP. So it is comfortable to use unzip tool. Maybe you have to install it first. But before you extract  downloaded file, we have to decide, where exactly should JBoss files be placed on a  file-system. Unfortunately JBoss is not quite conform to Linux File System Hierarchy Standard per default, so there are many possibilities for a location configuration. Some of you may want to place JBoss  into /opt directory. But I prefer to split the installation a little bit and  want to start by putting  JBoss core files in /usr/local/, where local, unchangeable and read-only files usually placed. E.g. I use  /usr/local/jboss/510 as JBoss 5.1.0 GA root.  So let’s create that location and extract files into it.

mkdir /usr/local/jboss #create new jboss directroy
chown jboss:jboss /usr/local/jboss #now its belongs touser jboss and group jboss
su jboss
mkdir /usr/local/jboss/510
cd /usr/local/jboss/510
unzip /tmp/jboss-5.1.0.GA.zip

At this moment you should have new working JBoss. If you want, test it with

bin/run.sh -b 0.0.0.0

Where -b 0.0.0.0 means that JBoss is listening for every ip address of current machine. However at this stage the installed Jboss still brakes the  Linux Filesystem Hierarchy Standard, so let’s improve this situation.
Read the rest of this entry »

Software RAID on Debian Linux

Wow, my last post here is month ago. But don’t worry I did not forget about my blog. There are just many thing happened in my life, all of them are time consuming So there no reason to remove me from your RSS reader. Today i will share some thought on software RAID under linux with you. Sometimes you need to store data relative save and high available. That is where RAID solutions come in to play. Especially RAID 1 (mirroring) based solutions provide better availability of your data. But don’t forget to use backs anyway Some days ago i installed RAID 1 on Debian Lenny (amd64 arch) without any troubles for now. I just was following Jerry’s description which is enough detailed to make no mistakes except maybe one thing. The Partitions used in the RAID /dev/md0/ should both enable boot flag if you want to boot from RAID. This is worked for me.

Configuration

My configuration is the same as Jerry’s except partition sizes and chosed LVM. So boot is done form RAID partition /dev/md0. And SWAP is on RAID too, which is controversy solution but it the best one for me, of course availability of a system is primary goal. So how to check the state of raid after installation. The simplest is to look on /proc file-system with $cat /proc/mdstat. Here is my configuration.

$cat /proc/mdstat
Personalities : [raid1]
md1 : active raid1 sda2[0] sdb2[1]
476560128 blocks [2/2] [UU]

md0 : active raid1 sda1[0] sdb1[1]
497856 blocks [2/2] [UU]

unused devices: <none>

Here you see two RAID arrays md0 and md1. Also information about used devices and state are peresent. [UU] stand for “used” for every disc is used in a raid. On diskfailure you wold see something like [U_] and sdb2(F). Next example utilizes mdadm which is used by kernel in latest kernel versions. My is 2.6.26-2-amd64 (lenny default) Use of –detail or -D option with a device name gives more information. Here my example.

# mdadm --detail /dev/md1
/dev/md1:
Version : 00.90
Creation Time : Wed Jan  6 00:51:37 2010
Raid Level : raid1
Array Size : 476560128 (454.48 GiB 488.00 GB)
Used Dev Size : 476560128 (454.48 GiB 488.00 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 1
Persistence : Superblock is persistent

Update Time : Mon Jan 11 02:18:01 2010
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

UUID : fe3bbbfd:2c6963e7:9785a408:be715448
Events : 0.8

Number   Major   Minor   RaidDevice State
0       8        2        0      active sync   /dev/sda2
1       8       18        1      active sync   /dev/sdb2

Read the rest of this entry »

Eclipse Ganymede and WSCompile incompatibility?

I found strange problem with WSCompile-1.6 task in Ganymede release of Eclipse (Version 3.4.1). The problem lies in WSCompile-Ant-Task. Buildscript execution freezes on the wscompile task. I describe that problem more detailed on techjava.de Please feel free to comment here or there if you know what died changed in Ganymede in ant scripts handling since Europe release and how to fix it.

Extracting tar, gzip, bzip2, z

Sometimes you need to extract some files on Linux console. Here  some examples how to do that.

tar

Tar archives are the most common way of distributing bundles of files under Linux or UNIX. A .tar file is simply a bundle of files packaged with GNU tar program. To extract such files use following:

tar xf somearchive.tar
tar xvf somearchive.tar

• Provide option f if you want to extract content of files. Tar (from tape archive) has long history and was intended to work with tape media, so when you omit f tar tries to work with tape device.
• v- stands for verbose. List all the files by extract process.
• x- Extract command

Before extracting you may be interested in Looking inside of tar. Do it with option “t” :

tar tf archive.tar

For more tar parameters see Man pages.

gzip

Often tar-files are also compressed. One of the most known compressed formats is GNU Zip (gzip).  Tar bundeld and zipped file would  normally  have extension .tar.gz. To extract such files you can use tar with  “z” option, which causes tar to automatically invoke gzip. Modify abow example  and you get able to extract tar.gz  files too.

tar -xzf somearchive.tar.gz

In old tar version the “z” option is may be not available. In that case just use UNIX pipes:

gzip -dc target.tar.gz | tar xf -

Meaning of gzip options

• d – Do decompress!
• c – write to console (So that tar can take it from there )
• t – Tests file integrity
• l – lists archive file information

You will find more on Man pages.

bzip2

Sometimes you can find files ending with .tar.bz2. That are files packaged with bzip (a block-sorting file compressor). Use it like gzip

bzip2 -dc target.tar.gz | tar xf -

Options d,c,t have the same meaning. More on Man pages.

zcat

Some files have .tar.Z endings. They can be extracted by

zcat somearchive.tar.Z | tar xf -

Look in Man pages for more. Any questions? You are welcome to comment!

How to duplicate magento installation

In this article I explain how to create a copy of running Magento online shop . One of purposes of having duplicates  is e.g.  the need of developing or test environment. Test are very inmportant in magento. Many people do official Magento upgrades on productive environments and suffer form it.   You don’t need to do so, use always test environment first! However the copy procces of  Magento shop has following main steps

• duplication of database schema
• duplication of core sources
• duplication of downloader sources

Database

First, let me say say, that it is good idea to not install two Magento instances to the same database. Magento in  version 1.1.8 s has 198 database tables. Most of them are of type  InnoDB and they are  related with each other by checked foreign key constraints. That is background information. So new database for every  Magento instance save you from having headaches  and this not only because having just two magento installation i one DB leads too approx. 400 tables in one database but more to avoid possible problems or side effects with constraints and Co. (e.g. ) .  . The easiest way to export the database is to use phpMyAdmin. Go to export dialog of original database, select “zipped” option, select tabbles, let other options on their defaults (See screen 1) and get zipped download. Switch to new database and  upload the downloaded  there in the import dialog. Sound as a piece of cake, but sometimes the import of the SQL files will not work. I have already seen many different exceptions bu trying. Beginning with “SQL Syntax..” and ending with “constraint violation…”.  In my opinion the purpose of problems is size of some tables and therefore of whole backup. There are few MyISAM tables that are full with (useless) log data. And the amount of this data makes problems to the import routine. Don’t export them first at time! they don’t have any constraint to other tables so you can import them on second or third turn. Alternative  you can export only the DDL-Statement of this table not the data itself. Here are tables you can  omit in first step:

• log_url
• log_url_info
• log_visitor
• log_visitor_info

Don’t forget to change configured URL of origin shop to the  URLs of new shop in the table core_config_data. You can also use Search-Tool of phpMyAdmin and identify every record where old URL is used – but outside of core_config_data table  they are not so important and could be changed later in the Shop interface.

Core Sources

That is most easiest part. Just copy the source of magento to the new location, but don’t copy the following:

• downloader dir
• any content of dirs inside of var but .htacces file.
• media/tmp dir

If you use another DB for new Magento installation don’t forget to change DB setting in app/etc/local.xml file. Var directory hold any temporary content like sessions, caches and error-logs. Downloader is used by Magento connect module, before copy must do some preparations.

Magento Downloader

Warning! do not copy unchanged downloader to new location on the same server it may break your origin magento installation! Now I got your attention The problem is that downloder stores serverpath in many many configuration files. And if you don’t change the serverpath  and  starts updates on  new shop copy, you will update the origin shop and not the new copy of it! The server path of origin magento shop is stored in many many files in the downloader directory, you can’t change all of them manually. But you can do it automatically. If you have SSH access to your web-space  following command will help you:

//shows all files with OLD_PATH element

find  . -type f -exec grep -q "OLD_PATH" '{}' \; -print

//Replaces OLD_PATH string in all occurrences in every file to NEW_PATH

find . -type f -print | xargs sed -i -e ’s/OLD_PATH/NEW_PATH/g’

If you have only ftp access, then you can use [Alt+F7]-search in Total Commander. Then open each file with Notepad++ and then use “Search and Replace” functionality of Notepad++ on each file. Whole replacement willtake you max. 5 minutes. After replacing old path you can upload downloader to the new instance of Magento. Now everything including “Magento Connect” should work properly and independent form each othen on thow instances. The last thing my be useful   is to clear all caches in admin back-end of new instance. Good luck!

Open Question

This article describes how to double the Magento instance once. The next question which i didn’t answered for me yet is how to make permanent  mirroring of data from production environment to the test installation. Maybe someone has cool ideas?

Disclaimer

Please consider that I can’t guarantee that everything described here will work in your environment as it worked for me. Please use this tutorial as incitement and adopt my methods to your own situation. Be sure that you don’t peril origin Magento installation or other data. Do regular backup befor you begin!

Best related post plugin

Today I found very cool related post Plug-in which I want to share with you – dear Wordpress Blogger! The  name of that plug-in is  Microkid’s Related posts and I already like it much! It differs from other “Related posts”-plug-ins, which are based on automatic content analysis. What ever the content analysis algorithms are and how ever the configuration options used,  resulting related post lists are mostly just a bullsh$%.  That’s is understandably, then these plug-ins have same problem like search engines and other content analysis tools . In the reality of our age (It is 2009 A.D.) – computers cannnot understand any semantic of human written articles. So what is the solution for an good Related Post Plugin? Of cause simple to do it manually! You say it much work?  No!, with Micrkid’s Related posts Plugin, which  provides very comfortable AJAX driven interface, it becomes fun! It’s becomes so easy and quick as providing tags. You decide what is related to the actual post by creating meaningful related post list.  Try it out!

About Russians

If you live somewhere in the “West”, you may often hear or read something bad about Russians. What you hear and read is mostly “something like truth”.  Mostly these “news” are presented in a way, so that they cause bad opinnion about Russia. I personally don’t like it. Therefore I found the following citation interesting, funny and truth. Vyacheslav Nikonov, a prominent Russian commentator, has quoted his Canadian friend, who came up with the following explanation of Russophobia: The main problem is that these Russians have white skin. If they had been green, or pink, or came from Mars…or had flowers sticking out of their ears, then everybody would have said – well, these people are different, like Turks, or Chinese, or Japanese. We have no questions about the Japanese. They are different, their civilisation is different. But these Russians … they are white but they have totally different brains … which is thoroughly suspicious.

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