Good reference on Crontab

Got rusty on this good old utility crontab and found a very good article of crontab. Read Crontab – Quick Reference

SGI® Altix® UV Scales Microsoft® Windows Server® to Its Maximum

Interesting hardware achievement for SGI Altix UV which is able to scale Four Times the Scale of HP, 2.6 Times the Scale of IBM.

From the website, SGI® Altix® UV Scales Microsoft® Windows Server® to Its Maximum, this table summarise SGI Altix UV achievement......

Vendor	Platform	Architecture	Physical Cores
SGI	UV 1000	Intel x86	256
IBM*	X3950 M2	Intel x86	96
HP**	Proliant DL980 G7	Intel x86	64

Red Hat Summit 2010 Presentations slides

A good respository of latest technologies presentation slides that was presented at Boston 2010. See Red Hat Summit Presentations

Understanding the difference between .bash_profile, .bash_logout and .bashrc

Important Notes on bash file

1. These files in your home directories have special meaning to bash, providing a way to setup the account environment when you log in and when you invoke another bash command
2. If the files are not found in your home directory, you are using the default system on /etc/profile
3. Most important is the .bash_profile which is read and the command in it is executed by bash every time you logged on to the system.
4. .bashrc is invoked when you start a new shell or by typing bash on the command line.
5. If you just need to have the same command run regardless of  a subshell or a login shell, you can easily source .bashrc and hence execute .bashrc from within .bash_profile
6. .bash_logout is read and executed every time a login shell exits.

Locking and Unlocking user account on Linux

If you need to politely refuse a login for a user, you use the command

# usermod -s /sbin/nologin UserLoginName

To unlock the user account

# usermod -s /bin/bash UserLoginName

Alternatively, you can use the commands to lock the user account

# passwd -l UserLoginName

To unlock the user account

# passwd -u UserLoginName

Getting DUP! error when pinging a IP Address which uses trunked port

I have aggregated 2 ports for the external LAN and incoming LAN for my Big-IP F5 Load Balancer. Interestingly when I was pinging the IP which uses the aggregated ports of the switch, I got a

..............
64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=12.4.8 ms (DUP!)
64 bytes from 192.168.1.1: icmp_seq=2 ttl=64 time=0.216 ms
64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=12.4.8 ms (DUP!)
64 bytes from 192.168.1.1: icmp_seq=2 ttl=64 time=0.196 ms
.............

After a while, the DUP! disappeared. As usual I google around and notice the article which explain the phenenomen. In a nutshell, the (DUP!) is caused by

......it is a side effect of how many switches update their MAC forwarding tables. Initially, the switch does not associate the MAC address in the packet with a particular switch port, and so it may send the
traffic to all ports until its MAC forwarding table is updated.


Since the interfaces attached to the bond may occupy multiple ports on a single switch, when the switch (temporarily) floods the traffic to all ports, the bond device receives multiple copies of the same packet (one per slave device)..........

For more information, see Duplicate ping error with network bonding driver in Linux

Articles on Parallel NFS

A good series of articles for reading on pNFS which hold promises for those who like the user-friendly NFS protocols and need the Intensive I/O requirements bveyond what the traditional NFS can offer

1. Scale your file system with Parallel NFS (IBM DeveloperWorks)
2. pNFS.com (Information on Parallel NFS)
3. NFSv4 delivers seamless network access (IBM DeveloperWorks)

Blade hangs on boot and "FW/BIOS, firmware progress (ABR Status) FW/BIOS ROM corruption" message in AMM

If you see and encounter error

Blade hangs on boot and "FW/BIOS, firmware progress (ABR Status) FW/BIOS ROM corruption" message in AMM - IBM BladeCenter HS22, HS22V

Symptoms
When booting BladeCenter HS22 or HS22V with Integrated Management Module (IMM) build yuoo84c installed, the blade may hang at the "UEFI Platform Initializing" screen. The hang will be accompanied by the following event in the chassis Advanced Management Module (AMM) log:

FW/BIOS, firmware progress (ABR Status) FW/BIOS ROM corruption

Affected Systems:
The system may be any of the following IBM servers:

• BladeCenter HS22, type 1936, any model
• BladeCenter HS22, type 7870, any model
• BladeCenter HS22V, type 1949, any model
• BladeCenter HS22V, type 7871, any model 

Workaround
This failure may be reduced by disabling Internet Protocol Version 6 (IPv6) support for the IMM. This can be done via the following steps:

1. Boot the blade to the F1 Unified Extensible Firmware Interface (UEFI) setup screen.
2. Select "System Settings" and press Enter
3. Select "Integrated Management Module" and press Enter
4. Select "Network Configuration" and press Enter
5. Change "IP6" setting to "Disable"

Occasionally, the failure can be recovered by restarting the IMM. If this is not successful, then it is necessary to reseat the blade in the chassis to recover. After a reseat, the blade will boot normally.

Additional Information
This error only occurs at boot time so production servers that are up and running are not at risk.

For more information, see Blade hangs on boot and "FW/BIOS, firmware progress (ABR Status) FW/BIOS ROM corruption" message in AMM - IBM BladeCenter HS22, HS22V

Compiling ScaLAPACK

ScaLAPACK is a library of high-performance linear algebra routines for distributed-memory message-passing MIMD computers and networks of workstations supporting PVM [68] and/or MPI [64, 110]

There are 2 ways you can compile ScaLAPACK, you can download scalapack.tgz and manually compile. Do look at the excellent article ScaLAPACK, LAPACK, BLACS and ATLAS on OpenMPI Linux installation tutorial

One challenges you might face is that if scaLAPACK dependencies are compiled with different Fortran compilers, you will face quite a challenge to complete the compilation.

Alternatively you can use the scalapack installer from http://www.netlib.org/scalapack/. 
Do look at the README to see the flags you will need.

Listing all the environment variables set on a machine

This commands really help to list  all the environment variables set on a machine

# env

MANPATH=:/opt/xcat/share/man:
HOSTNAME=....................
.........
LD_LIBRARY_PATH=........
PATH=........................
............