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Can I boot My Linux Server from iSCSI or SAN or NAS network attached storage?

My previous article related to iSCSI storage and NAS storage brought a couple of questions. An interesting question from my mail bag:

I've 5 Debian Linux servers with HP SAN box. Should I boot from SAN?

No, use centralized network storage for shared data or high availability configuration only. Technically you can boot and configure system. However I don't recommend booting from SAN or any other central server until and unless you need diskless nodes:

[a] Use local storage - Always use local storage for /boot and / (root) filesystem

[b] Keep it simply - Booting from SAN volumes is complicated procedure. Most operating systems are not designed for this kind of configuration. You need to modify scripts and booting procedure.

[c] SAN booting support - Your SAN vendor must support platform booting a Linux server. You need to configure HBA and SAN according to vendor specification. You must totally depend upon SAN vendor for drivers and firmware (HBA Bios) to get thing work properly. General principle - don't put all your eggs in one basket err one vendor ;)

[d] Other factors - Proper fiber channel topology must be used. Make sure Multipathing and redundant SAN links are used. The boot disk LUN is dedicated to a single host. etc

As you can see, complications started to increases, hence I don't recommend booting from SAN.

Linux tip: Save Power With Gigabit Ethernet By Using Lower Speed

This is a reader contributed article.

These days almost all server / laptop / desktop system has a gigabit Ethernet card (NIC) pre installed. Most servers are directly connected to internet using 100Mbps connections. You can save real power on your Linux server or desktop by operating at 100Mbps Ethernet speed. For example 1 gigabit link is going to consume more power than the power used at 100Mbps speed. Also note that not all systems actually use gigabit speed. For example my desktop system only used for browsing or chatting purpose or Linux web server used to display just static web pages. Now just calculate power consumption for 100 servers or 1000 desktop systems. Bottom line use Gigabit Ethernet speeds only when needed. Did you know - you can save 2 watts or more per Linux/UNIX/Windows server/desktop by just setting a correct speed :)

See current Ethernet card speed

Use ethtool comment to display current speed:
ethtool eth0 | grep -i speed

Set new speed and save power

Following command will set card speed to 100Mbps:
ethtool -s eth0 autoneg off speed 100

=> For more information see ethtool command and network interface speed, duplex . auto negotiate settings on Linux

About the author: Rocky Jr., is an engineer with VSNL - a leading ISP / global telecom company in India and a good friend of nixCraft.

How scriptkiddies turns Linux box into a Zombie

This is a good analysis and sort of demonstration for all new Linux admin. It does shows how to do forensic kind of analysis on a cracked box. A good read for everyone ~ if you want to know how Linux server is cracked and turned into a zombie ;)

Installing VMWARE server on CentOS 5 or Red hat enterprise Linux 64 bit version

VMware virtualization software is an excllent choice for x86-compatible computers. They have both commercial and free version. I received few email regarding VMWARE on 64 bit Linux. Installing VMWARE server on CentOS 5 or Red hat enterprise Linux 64 bit version is a tricky business. In this small howto I will explain vmware installation on 64 bit Linux server without facing any dependencies problem.

Following instructions are tested on both RHEL 5 and CentOS 5 running 64 bit Intel / AMD hardware and software. My kernel:
$ uname -mrs

Linux 2.6.18-8.1.6.el5 x86_64

My RHEL 5 release (same kernel for CentOS):
$ cat /etc/redhat-release

Red Hat Enterprise Linux Server release 5 (Tikanga)

Make sure you have following software installed:

  • Full gcc compiler and development environment
  • Kernel headers and devel packages for current kernel (i.e. kernel-headers and kernel-devel)

[click to continue…]

How do you disconnect inactive user sessions?

One of our regular reader hall sends an interesting question:

I work for a small company and most user login to centralized Linux server. I’d like to
automatically log out all inactive users from server for various reasons. How do I disconnect inactive user sessions?

To be frank, I don’t have any clear cut answer to question. There are at least 4-5 shells installed on a typical Linux installation. Also most user have has control over their own environment and user can switch to a different shell.

I hope our reader or seasoned UNIX admin can help to answer this question. Please share the experiences and advice in the comments.

Update: Checkout answer below in comments!

nixCraft FAQ Roundup June 19, 2007

Recently updated/posted Linux and UNIX FAQ (mostly useful to Linux/UNIX new administrators or users) :

nixCraft FAQ Roundup – Dec 8, 2008

Recently updated/posted Linux and UNIX FAQ:

=> Boot Ubuntu Linux into Rescue mode to fix system - How do I boot my Ubuntu Linux server into Rescue mode to fix system?

=> Unable to create installation source - Add directories into YaST as an installation source - I have created my own patch files on the hard drive. How do I add all those directories into Suse Linux YaST as an installation source?

=> How to uninstall GRUB - How do I uninstall GRUB using old good MS-DOS fdisk or Linux/UNIX dd command?

=> Can I run fsck or e2fsck when Linux file system is mounted? Can I run run fsck/e2fsc on a live Linux file system?

=> Configure Sendmail SSL encryption for sending and receiving email - Configure Sendmail MTA to use SSL encryption for sending/receiving email using valid SSL certificate.

=> Linux configure Network Address Translation or NAT - Old good Linux NAT!

=> Use sudo or sudoers to start, stop & restart Apache - Sudo to stop and/or restart Apache web server!

=> How to install firefox-2.0.tar.gz in Linux - I have downloaded firefox file from mozilla web site to my Linux desktop system. The name of file is firefox-2.0.tar.gz. How do I install firefox-2.0.tar.gz in Fedora Core Linux?