Puttygen's Public Key Problem with Linux Server

A need comes up to set up password authentication between my notebook and Linux server. I have to use puttygen to generate public/private key on my notebook because it is running Windows 7. Then I uploaded public key(example.pub) to Linux server and run the the following command to add it into ssh's authorized_keys file.

#cat example.pub >> ~/.ssh/authorized_keys

But passwordless authentication with putty failed with message saying "Server Refused Our Key". Then I googled the error and found below link.
http://www.walkernews.net/2009/03/22/how-to-fix-server-refused-our-key-error-that-caused-by-putty-generated-rsa-public-key/

To make long story short, you have to modify the public key so that it will work on Linux server. Below are the steps extracted from above link. Pardon me for being lazy..

Hope it useful for somebody.

GFS2 & CLVM

GFS needs to go together with CLVM according to the following Red Hat KB. Otherwise Red Hat won't support any problem for GFS.

https://access.redhat.com/site/solutions/46637

Rocks Cluster Installation Problems

Yes, I am damn stupid enough to screw up Rocks Cluster Installation that is as easy as ABC. Here is culprits giving me headache for 2 days -

1. Never ever try LVM during installation. Or your installation will fail with some python error. But you can use LVM on other harddisks after installation. 
2. Don't use ".local" as domain suffix for frontend node. I used "headnode.local" for my frontend hostname. Installation went through well without complaining anything. However, server came up without public network/interface after installation finished. I had been barking the wrong tree for 1 and half day checking switch, using lower version of Rocks and using different IP schema. Finally, I used other FQDN like ".netlynker.net" and it solved the issue.

Really hope this post helpful for somebody out there. :D

Experience With Oracle Virtualization

Here is some of my experience with OVM (Up to Version 3.1.1)

1) Docs says that 3 x mode are supported for NIC bonding.
- Active/Backup
- Adaptive Load Balancing
- Dynamic Link Aggregation (LACP)
But only A/B and Link Aggregation can be used for VM network. If you hook VM to ALB-bonded interface, VM will get extremely unstable connection.
Like you guess, we have to approach our network guys to configure LACP on their switches to get Redundancy+Performance.

2) Max. 2 x physical NIC ports per each bonded interface. You want more? Upgrade to 3.2.1 and you will get 4 ports at Max. for each bond. That sucks. Doesn't it? Especially for VMware guys...

3) It supports Live-Migration!!! Hold on a sec! You can live-migrate only one VM at a time. Sorry pals, you get a long way to go if you have many VMs to migrate live.

4) NO SNAPSHOT! Don't waste time finding how to take snapshot of VMs in OVM. Oracle gives you a work-around method close enough to taking snapshot:"Thin Cloning".
Yes. Thin Cloning is a neat thing that makes use of OCFS2's Reflinking feature. You can do "Thin Cloning" live. You can read more about Reflinking here.

To be continued.....

Let's Guess Which RHEL Version Will Boot From This Installation DVD

Mount RHEL DVD on any machine. And check a hidden file named ".discinfo" in it.  You can find OS version (including minor version) and architecture there.

Hope useful for someone like me who never carry CD marker around. ;)

Do We Really Need To Turn Off NetworkManager?

As a Linux user, I bet most of us had suffered from NetworkManager at least once in a lifetime. As legend goes, we disabled NetworkManager to solve the problem. We never thought, "That very NetworkManager will be useful for us one day".

Now we are using various kind of devices for network communication. Wifi adapters, 3G/4G modem adapters. Configuring your Linux box to get connected without NetworkManager become a daunting task. Have you tried using 3G modem on your Linux box? It is almost impossible to set it up without NetworkManager.

Well. We have to run NetworkManager now for those special purposes but we still want to keep some devices not to be managed by it. How??

For RHEL/CentOS, add a parameter in desired network config file.(e.g /etc/sysconfig/network-scripts/ifcfg-eth0) -

NM_CONTROLLED=no

service network restart

For Ubuntu, add a section in network manager config file.(i.e  /etc/NetworkManager/NetworkManager.conf)

[keyfile]
unmanaged-devices=mac:<MAC address>, mac:<MAC address>

/etc/init.d/network-manager restart

Now NetworkManager won't manage those devices anymore.

Remarks: I experience some bugs from RHEL/Fedora - Even though you add "NM_CONTROLLED=no", NetworkManager is still messing up with interfaces. Put in "service NetworkManager stop" in your troubleshooting checklist. :)

Happy Linuxing!

Using Serial-To-USB adapter on Linux

As and when, I need to manage some network devices(Switch, router, firewall and etc...) with serial console. I bought serial-to-usb adapter since my notebook doesn't come with serial port.


I am using Linux as on my notebook. I use "screen" utility to connect serial device.

sudo screen /dev/ttyUSB0

After I finish my job, I will kill screen session.

Ctrl+a+k

Press "k" to kill the session

Hope someone find it useful.