Archive for the 'docs' Category

Why and how to migrate to ext4

Date: May 6, 2008. Categories: docs, tips and linux. 0 Comments

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Ext4 is the latest in a long line of Linux file systems, and it’s likely to be as important and popular as its predecessors. As a Linux system administrator, you should be aware of the advantages, disadvantages, and basic steps for migrating to ext4. IBM DeveloperWorks article explains when to adopt ext4, how to adapt traditional file system maintenance tool usage to ext4, and how to get the most out of the file system:

The single most dramatic improvement in ext4 is in file and file system size. Thus, the users who are most likely to need ext4 are those who have more than a few terabytes of disk space. The list of features in Table 1, though, may present some other tempting improvements. For instance, you might want to try ext4 if you have directories with huge numbers of subdirectories or if you need timestamps accurate to less than a second. Read more >>

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OpenBSD: Secure Mail Server with Postfix, MySQL, ClamAV, SpamAssassin, Amavis-new

Date: April 17, 2008. Categories: howtos, docs, unix and tips. 0 Comments

openbsd logoFew days ago I started configuring corporate mail server that should be deployed on OpenBSD and comprise the following features:

  1. Easy to configure and powerful MTA (Postfix)
  2. Virtual domains and user accounts (this information is stored in MySQL database)
  3. Antispam and antivirus checking for all accounts (spamassassin and clamav via amavis-new)
  4. Secure access to mailboxes through POP3, IMAP and HTTP (squirellmail)
  5. Secure SMTP server
  6. Extremal Stability and Security

Actually OpenBSD 4.2 was chosen because of it’s "security by default". Thankfully Daniele Mazzocchio from friendly site www.kernel-panic.it wrote an excellent article about how to build such mail server on this operating system:

Offering a reliable and secure email service is probably one of the top priorities of most system administrators; therefore, in the next chapters, we will build a full-featured mail server, based on open-source software and focusing on security. Read more…

The only thing that is not covered by it is mail content filtering with maildrop and vacation messages that users often ask to set while they are out. Working on it! :)

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Nagios installation and configuration in SUSE Linux

Date: April 7, 2008. Categories: docs, suse and linux. 1 Comment

nagios logoAs we know Nagios is extremely popular open source network monitoring system. It watches hosts across the local area network (LAN) and/or across the Internet, services that you can specify, alerting you when things go bad. The following step-by-step guide written by Novel people (actually by Rainer Brunold) for sure would help if you plan to deploy Nagios monitoring system with Novel SUSE Linux. At least it helped me :)

I don't want to write here a full documentation about Nagios, I prefer to give you a basic installation guide so you can set it up very easy and play with it yourself. The installation guide will show you how to install Nagios as well as some interesting extensions and how they integrate into each other. During this installation you will make many modifications to the installation that will help to understand how it works, how you can integrate systems and different services. I will also provide some articles about monitoring special services where I describe what they do and what configuration changes are needed. All together should give you a very good overview and documentation on how you can enhance the Nagios installation yourself.

The rest of the article is here. Respect to the author!

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Microsoft tells how to recover data using Linux

Date: November 26, 2007. Categories: docs, sites and linux. 5 Comments

port 25 logoRecently I came across nice article published at Microsoft’s site Port 25 about how to recover crashed Windows using Linux. It’s rather helpful staff written by Chris Travers (who own Metatron Technology Consulting by the way). Here is an introduction quote from the document:

We have all run into cases where Windows refuses to load for one reason or another. The problem may be a hardware or a software failure, and the problem may seem to be irrecoverable. Yet often Linux can be used to help recover data that otherwise might be lost.

In writing this paper, we generally assume that either a Linux workstation is available to accept recovery information or that a USB drive of sufficient size is available to hold the data. Generally in either case, enough free space should be available to store the entire hard drive as a bit-for-bit file and still have at least 2GB of space free. However, if more space is available, the process of organizing the recovered data is a bit easier. If neither of these is available, the utility of Linux in data recovery will be limited.

Download this document in as pdf format here. You can read interesting comments on their site by clicking at this link.

By the way, Port 25 site is copyrighted by Microsoft under the Microsoft Permissive License that is available here.

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GNU GRUB Simplified for Newbies

Date: November 21, 2007. Categories: docs. 1 Comment

gnu grub logoGNU GRUB is a boot loader package from the GNU Project. GRUB is the reference implementation of the Multiboot Specification, which allows a user to have several different operating systems on their computer at once, and to choose which one to run when the computer starts. GRUB can be used to select from different kernel images available on a particular operating system’s partitions, as well as to pass boot-time parameters to such kernels.

Here is the Joydeep Bakshi’s GBUB guide that is distibuted under Open Content License and covers the following fields:

  • MBR, boot sector, boot loader
  • Backup & Restore boot loader
  • Grub stage1, stage2, stage3 and relation among them
  • Making Grub Floppy
  • Making Grub CD
  • Making Grub Pen drive
  • stage1 and stage2 on different media
  • Grub’s device and device.map file
  • Grub Rescue
  • Super Grub Disk
  • Grub’S GUI configuration
  • Manual booting with Grub shell
  • Disk investigation with Grub

Read full guide here…

More useful links:
GNU GRUB
GNU GRUB FAQ
GNU GRUB Manual 0.97
The list of command line and menu entry commands
GNU GRUB on Wikipedia

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Anatomy of the Linux file system

Date: October 31, 2007. Categories: docs. 0 Comments

ibmWhat I love IBM for is their DeveloperWorks :) Here is M. Tim Jones' latest publication exploring Linux filesystem. Respect to IBM and Tim!

When it comes to file systems, Linux is the Swiss Army knife of operating systems. Linux supports a large number of file systems, from journaling to clustering to cryptographic. Linux is a wonderful platform for using standard and more exotic file systems and also for developing file systems. This article explores the virtual file system (VFS)—sometimes called the virtual filesystem switch—in the Linux kernel and then reviews some of the major structures that tie file systems together.

Read more…

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Get uptime/loading/logins information remotely

Date: October 24, 2007. Categories: docs. 0 Comments

There are two utilities available in Linux and Unix that provide information about remote user logins. These are rusers and rwho, which are backed up by corresponding daemons, rusersd and rwhod. These daemons share login information over the network allowing sysadmins to monitor login activity on different hosts.

Once the daemons are installed and running (sudo apt-get install rwho rusers -y in Ubuntu, yum install rwho rusers in Fedora and etc.) at different hosts across the network, you can use several tools to get login information about all of these hosts. One of them is rwho that is the remote and network-enabled version of the well known who tool.

viper@viper-laptop:~$ rwho
tesadmin tes1000_v203_1322_tst0:pts/1 Oct 24 10:25
viper viper-laptop:pts/0 Oct 24 10:24
viper viper-laptop:pts/1 Oct 24 10:26 :01
viper viper-laptop:pts/2 Oct 24 10:25
viper viper-laptop:tty7 Oct 24 09:11

Another one is rusers tool that broadcasts over the network for the rusersd daemon on the other hosts to return the information about the users currently logged in:

viper@viper-laptop:~$ rusers
Sending broadcast for rusersd protocol version 3...
192.168.0.1 tesadmin
viper-laptop. viper viper viper viper

Another tool available when rwhod is running is ruptime that outputs the loading and uptime information for all servers running rwhod in the LAN.

viper@viper-laptop:~$ ruptime
tes1000_v203 up 14+19:00, 1 user, load 0.59, 0.47, 0.46
viper-laptop up 1:39, 4 users, load 0.40, 0.52, 0.45

This is really nice tool to monitor status of servers without need to log in to them.

You can read more information about these tools and related ones here (IBM’s doc).

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