Category Archives: Systems

Tips on Operating Systems mostly focus on Linux and Mac OS X
Trucs et astuces, tests autour des systèmes d’exploitation, principalement Linux et MacOsX

Installation of a piratebox on T-Link MR3040

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I just received the TL-MR3040 wifi portable access by T-link. This little box is really like the mr3020 i had for my piratebox with the main advantage of having and internal battery making the piratebox mobile for a small price ! For actually 38€ (but you may found it at lower price) it is an interesting and compact solution to bring you piratebox out.

I’ll try in the next part of this article to detail the installation process as friendly as possible. Never forget that this kind of operations are not always easy and may damage your device. Do it at your own risk.

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Nmon cpu_summ vs cpu_all in a SMT environment

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In a SMT CPU you have real primary core and SMT core, all can have process allocated to them but the performance of the primary logical processor compared to the SMT one are not equivalent. Usually the SMT power is about 20-30% of the primary one.

This impact the way the performance is measured

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Network performance measurement script

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I regularly have to test some network products like routers or homeplug devices and most of the time, I like to test the performance of that product. I’m doing it generally a couple of time and the result can vary test after test and I did not had a good, simple and basic tool to use to measure this variation.

So, after having think to it for long months, I finally started to write some bash lines to get this tool and start to get measures…

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FreeNas and OpenFiler experimentation

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/!\ Article in progress, not yet finish /!\

As I needed to create a iSCSI share for some VM on a private subnetwork, instead of using a simple NFS server configuration, I was looking to test a NAS distribution. I saw on Internet two different distributions, one based on OpenBSD named FreeNas (here in version 8), the other based on Linux OpenFiler (here in version 2.99). I will test both for creating this share.

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Oracle VM – experimentation

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/!\ Article in progress, not yet finish /!\

I was looking  to test Oracle Linux since Open World, mostly because I’m curious about OVM and the nice integration with Enterprise manager 12c as a global system to manage hardware, operating system, hypervisor, virtual machine on demand and middle-ware + software.

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Activate Masquerading (NAT) on Linux router

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To activate NAT on a Linux Box used as a router, just use the following line :

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

eth0 is the network interface able to access Internet directly

Then you can list the NAT entry in iptables with the following command

# iptables -t nat -L

You can get more details with:

# iptables -t nat -L -v

The conntrack tool also help to see what happen in the NAT

# conntrack -L --src-nat / --dst-nat

Latency impact on NFS link

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Interesting document about NFS and iSCSI performance over latency, even if it is new a new document, the study made is really complete and interesting. As I was mostly interested on the performance of NFS over a WAN access with a high latency, I would summarize it by concluding that the maximum performance of file transfer over NFS is not so far the following list:

Time to read 128MB / latency (read is the worst case)

  • 10 ms latency requires 200s, max bandwidth is about 640KB/s – 5.12Mbits/s
  • 20 ms latency requires 300s, max bandwidth is about 427KB/s – 3.41Mbits/s
  • 30 ms latency requires 500s, max bandwidth is about 256KB/s – 2.05Mbits/s
  • 50 ms latency requires 800s, max bandwisth is about 160KB/s – 1.28Mbits/s
  • 90 ms latency requires 1600s, max bandwidth is about 80KB/s – 640Kbits/s

For details and much more information, take a look to the source document : http://lass.cs.umass.edu/papers/pdf/FAST04.pdf

Acceder à une imprimante cups depuis Mac Os X

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Enigme résolue (en lisant un peu la doc…) pour acceder depuis un MAC à une imprimante partagée depuis un Linux au travers de IPP, il faut mettre la configuration suivante:
Dans le champ adresse : l’ip du serveur
Dans le champ nom de la file : /printers/nom de l’imprimante
Ensuite il faut choisir le driver correspondant à l’imprimante
Le tout etait donc de bien penser à ajouter /printers …