Atlantic Linux Blog

Java on Debian tip

The default Java environment installed by Debian is the GNU Compiler for Java, while GNU have made remarkable progress with this – anyone doing mainstream Java development will probably prefer to install the latest Sun Java environment on their system – even free software projects like Hadoop are primarily tested in this environment.

Most Linux distributions provide packages for Sun’s Java as well as GCJ and probably OpenJDK. When you install more than one package which provides similarly named commands, Debian’s Alternatives System comes into play – allowing you to select one command or another. When you install a different Java, you can of course manually update each Java command (java, javac, javadoc, jconsole, jmap,jps and so on) using the update-alternatives command, but if you want a quicker way, try the update-java-alternatives command from the java-common package.  It will automatically update the paths to all provided Java commands in one go once you tell it which installed Java environment you wish to use, for example,

update-java-alternatives -s java-6-sun

Tags: Debian 5.0, java, linux, sun java

Debian 5.0 (Lenny) install on Software RAID

As mentioned in previous posts, I’m a big fan of Linux Software RAID. Most of the Ubuntu servers I install these days are configured with two disks in a RAID1 configuration. Contrary to recommendations you’ll find elsewhere, I put all partitions on RAID1, not some (that includes swap, /boot and / – in fact I don’t normally create a separate /boot partition, leaving it on the same partition as /). I guess if you’re using RAID1, I think you should get the advantage of it for all of your data, not just the really, really important stuff on a single RAIDed partition.

When installing Ubuntu (certainly recent releases including 8.10 and 9.04) you can configure all of this through the standard installation process – creating your partitions first, flagged for use in RAID and then configuring software RAID and creating a number of software RAID volumes.

I was recently installing a Debian 5.0 server and wanted to go with a similar config to the following,

When I followed a standard install of Debian using the above configuration, when it came to installing GRUB, it failed with an error. The error seemed to be related to the use of Software RAID. Searching the web for possible solutions mostly turned up suggestions to create a non-RAIDed /boot partition but since this works on Ubuntu I figured it should also work on Debian (from which Ubuntu is largely derived).

First, a little background to GRUB and Linux Software RAID. It seems that GRUB cannot read Linux software RAID devices (which it needs to do to start the boot process). What it can do, is read standard Linux partitions. Given that Linux software RAID1 places a standard copy of a Linux partition on each RAID device, you can simply configure GRUB against the Linux partition and, at a GRUB level, ignore the software RAID volume. This seems to be how the Ubuntu GRUB installer works. A GRUB configuration stanza like the following should thus work without problems,

title           Debian GNU/Linux, kernel 2.6.26-2-amd64
root            (hd0,1)
kernel          /boot/vmlinuz-2.6.26-2-amd64 root=/dev/md1 ro
initrd          /boot/initrd.img-2.6.26-2-amd64

When I tried a configuration like this on my first install of Debian on the new server, it failed with the aforementioned error. Comparing a similarly configured Ubuntu server with the newly installed Debian server, the only obvious difference I could see is that the partition table on the Ubuntu server uses the old msdos format while the partition table on the Debian server seems to be in GPT format. I can’t find any documentation on when this change was made in Debian (or indeed whether it was something in my configuration that specifically triggered the use of GPT) but it seems like this was the source of the problems for GRUB.

To circumvent the creation of a GPT partition table on both disks, I restarted the Debian installer in Expert mode and installed the optional parted partitioning module when prompted. Before proceeding to the partitioning disks stage of the Debian installation, I moved to a second virtual console (Alt-F2) and started parted against each disk and ran the mklabel command to create a new partition table. When prompted for the partition table type, I input msdos.

I then returned to the Debian installer (Alt-F1) and continued the installation in the normal way – the partitioner picks up that the disks already have an partition table and uses that rather than recreating it.

This time, when it came to the GRUB bootloader installation step, it proceeded without any errors and I completed the installation of a fully RAIDed system.

Tags: Debian, Debian 5.0, grub, linux, Linux software raid, partitioning, Ubuntu, ubuntu 8.10, ubuntu 9.04

BIOS flash upgrades on Linux

To upgrade your system BIOS you normally need to run a piece of software from the system manufacturer which loads an updated copy of the BIOS into the EPROM chip on your system motherboard – a process known as flashing your BIOS. Most system manufacturers supply BIOS upgrades in a form that will run under DOS or, occasionally, Windows. It is rare to find a BIOS upgrade program that runs under Linux (I’d love to hear about one). Recognising that not all of their customers are necessarily running a 28 year old, 16-bit operating system – some system manufacturers supply their BIOS upgrades in the form of an image which you can burn to a CDROM and boot from (making the question of what OS you are running irrelevant).

I recently had to upgrade the BIOS on one of our Supermicro systems (an X7DVL-E system). Supermicro provide their BIOS upgrades as a ZIP file containing the actual BIOS and a DOS flash program. They also seem to provide some software which you can run on Windows to create a BIOS flash floppy disk (for the younger readers in the audience, that’s another wonderful technology from the 80s, and I’m talking about the super-modern 3.5″ floppy there). I’m not singling out Supermicro for particular criticism here, a lot of the system manufacturers seem to work on the assumption we’re still running PCs with Windows and a floppy drive (to be fair, if you have the optional IPMI management card installed, you can normally upload your firmware through that, but we don’t) – but for those of us running Linux servers, upgrading the BIOS can be a painful process.

There is a work-around for this problem. Thanks to the Linux boot-loader, GRUB – you can boot from a DOS disk image containing your BIOS upgrade program and run the program from within that booted image without ever actually installing DOS or a floppy drive in your system. The following procedure worked well for me on an Ubuntu 9.04 system (with thanks to this OpenSUSE page and and this Ubuntu forums posting for some assistance along the way) and the same approach should work on other distributions.

WARNING: Upgrading your system BIOS is an inherently risky process – with the primary risk being that if things go wrong you can brick your system. Things that can go wrong include flashing your system with a BIOS upgrade for a different system or the power getting interrupted while you are in the middle of a BIOS upgrade. In some cases, you may be able to reflash the BIOS using some emergency procedure but with most systems, you may be looking at a motherboard replacement. So proceed with caution and only upgrade your BIOS if you have a specific problem which the upgrade fixes.

1. Download a bootable DOS disk image from the FreeDOS distribution site (FreeDOS is an excellent open source version of DOS. It is widely used by hobbyists and companies including Dell, HP and Seagate).

   wget http://www.fdos.org/bootdisks/autogen/FDOEM.144.gz

2. Download your system manufacturers BIOS upgrade

   wget http://www.example.com/bios/version2.zip

3. Place the downloaded BIOS upgrade program and files into the downloaded bootable DOS image.

   gunzip FDOEM.144.gz
   sudo mount -o loop FDOEM.144 /mnt
   sudo mkdir /mnt/bios
   cd /mnt/bios
   unzip <path to download BIOS upgrade file>/version2.zip
   umount /mnt

4. Add the bootable DOS image (with the bios upgrade software) to your Linux bootloader (this requires a file from the syslinux package),

   sudo aptitude install syslinux
   sudo mkdir /boot/dos
   sudo cp /usr/lib/syslinux/memdisk /boot/dos
   sudo cp FDOEM.144 /boot/dos
   sudo vi /boot/grub/menu.lst

   and add the following section to the end of the file

   title DOS BIOS upgrade
   kernel /boot/dos/memdisk
   initrd /boot/dos/FDOEM.144

5. Reboot your system and choose the DOS BIOS upgrade boot option. If the boot is successful you should shortly be presented with the A:\ DOS boot prompt. At this point you can run the BIOS upgrade software, for example,

   A:\CD BIOS
   A:\FLASH V2BIOS.ROM

6. Once the upgrade finishes, reboot and enjoy your upgraded system.

Tags: BIOS, Boot loaders, Flash, FreeDOS, grub, linux, Linux startup process, syslinux, Ubuntu, ubuntu 9.04

Package repositories for old Ubuntu releases

While you shouldn’t run old, unsupported releases of any Linux distribution (and Ubuntu is no exception to this), if you have to for some good reason (like you have some server running some proprietary system which you haven’t gotten working on a current release yet, and you have put adequate security measures around this system) then may find http://old-releases.ubuntu.com useful.

To continue installing packages on your unsupported release of Ubuntu,

1. Edit /etc/apt/sources.list
2. Replace all occurrences of archive.ubuntu.com with old-releases.ubuntu.com
3. aptitude update
4. aptitude install <package name>

It is very much a band-aid, and shouldn’t be used to run old unsupported releases indefinitely (for the simple reason that you most likely have various unpatched security holes in that old release).

If you don’t like upgrading your distribution every few months, you should really be using an LTS release of Ubuntu (currently 8.04 with the next LTS expected to be 10.04 next year).

Tags: aptitude, linux, packages, ubuntu 7.10, ubuntu 8.04

Ubuntu 9.04 Fake RAID problems

So we have RAID – a technology that allowed computer users to achieve high levels of storage reliability from low-cost and less reliable PC-class disk-drive components, via the technique of arranging the devices into arrays for redundancy to quote the Wikipedia article.

In the beginning, manufacturers created dedicated hardware controllers to which disks were attached. These controllers include their own processor and memory and handle all the RAID functionality within the black box they present to the system (the good ones will even include a battery that lets the controller run for long enough in the event of a power failure so that any data stored in the RAID controller’s cache memory isn’t lost but can be written to the drives when the power comes back). As far as the system the controller is attached to is concerned – the RAID controller is one big disk. This is called hardware RAID.

As machines have gotten more powerful, most machines (certainly most desktop machines) are sitting idle most of the time, so it has become feasible to start using the system for operating system level tasks like providing RAID. All mainstream operating systems provide some form of this software RAID which performs exactly the same functionality as the hardware RAID controller above, but using the system’s processor and memory. There are advantages and disadvantages to both approaches (I’m increasingly leaning towards using software RAID on Linux – low end hardware RAID controllers aren’t very reliable and tend to be slow from an I/O perspective – most modern Linux servers tend to have multiple processor cores which are sitting idle most of the time and are perfectly suited to driving a RAID array) but they both work reasonably well.

In between these two comes something described as Firmware/driver-based RAID, HostRAID or Fake RAID. This is provided by cheap RAID controllers that do not implement all the RAID functionality (normally they are standard disk controllers with some special firmware) and utilise the main system processor for most of the heavy-lifting. They also rely on dedicated operating drivers to provide the RAID functionality, hence the name Fake RAID. I’m not a fan of Fake RAID controllers – apart from the fact that the manufacturers of these controllers rarely make it clear that they are not fully functional RAID controllers, their reliance on elaborate driver software makes them less reliable than hardware RAID but more complex to maintain than true software RAID. They are reasonably well supported under Linux these days using the Device-Mapper Software RAID Tool (aka dmraid) but personally, I prefer to use a Fake RAID controller as a standard SATA controller and if I require RAID on such a system, implement it using Linux’s excellent Software RAID support.

Up to recently, when people installed Ubuntu – if they did want to use their Fake RAID controller as a RAID controller, they ran into the problem of the installer not including dmraid support. Using Ubuntu 9.04 (Jaunty) – the installer detects at least some Fake RAID controllers and prompts you as to whether to use this controller via dmraid or not. If you choose not to, you will then be able to use it as a normal SATA controller.

I ran into an interesting problem on a recent reinstall of Ubuntu 9.04 onto a Supermicro X7DVL system which includes an Intel 631xESB/632xESB I/O controller which supports some sort of Fake RAID (Intel seems to call their Fake RAID Matrix Storage Technology). Given my stance on Fake RAID, I immediately disabled this in the BIOS by changing the controller to compatible mode (the datasheet above suggests this should disable RAID). When installing Ubuntu, the installer still detected the Fake RAID volumes and offered to configure dmraid for me. I declined the option and the native SATA disks (unRAIDed) were presented to me and fully partitioned and formatted.

I thought nothing more of this until I rebooted after completing the installation. The system booted as far as GRUB before dumping the message

No block devices found

It took me a while to figure out what was going on. Google turned up lots of people who had problems with Ubuntu and dmraid, but generally they were having the opposite problem of wanting to use dmraid but the installer not supporting it (like DMRAID on Ubuntu with SATA fakeraid,  dmraid missing from livecd and Need dmraid to support fakeraid). Presumably most of these problems have been fixed with the inclusion of dmraid in Jaunty.

This was the clue for me – I finally figured out (with some help from bug 392510 I must admit) that even though I had declined to use dmraid during the install, the newly installed operating system still contained dmraid and was loading the dmraid kernel modules at boot-time. This resulted in the kernel seeing some dmraid volumes rather than the partitions I had created during the OS install.

Once I figured that out, fixing the problem was relatively straightforward,

1. Reboot with the Ubuntu 9.04 install cd and select Rescue broken system.
2. When the rescue boot has been configured, select Execute shell and chroot into the installed environment.
3. aptitude purge dmraid (this removes the dmraid software and the dmraid kernel modules from the initramfs).
4. Reboot and enjoy your new OS.

Two things that I found misleading here are,

• I had declined to use dmraid during the Ubuntu install, but it still included this functionality during installation
• I had disabled SATA RAID in the BIOS but it was still visible to Ubuntu. I notice a newer version of the BIOS from Supermicro which may fix this problem but since Supermicro don’t include change log in their BIOS releases it’s hard to tell without going to the trouble of actually installing the update.

I should probably log a bug against the dmraid package in Ubuntu (if I get
around to it, it should appear against the dmraid package) – bug 392510 talks about supporting a nodmraid option to the kernel at boot time which would explicitly disable dmraid, I think this could be a good idea (Fedora apparently already does this).

Update 1: Bug 311637 already addresses this problem so I’ve added a comment to this.

Update 2: Upgrading the Supermicro system to the latest BIOS and disabling the Fake RAID controller through the BIOS seems to fix this problem also.

Tags: dmraid, fake raid, linux, raid, supermicro, ubuntu 9.04

Passing kernel module parameters in Ubuntu 8.10

Sorry for the mouthful of a title but I wanted to use something that would show up for the kind of queries I was firing into Google yesterday in a vain attempt to solve my problem.

A little background first: I’m working with some SuperMicro Twin systems (basically, two system boards in a single 1U chassis sharing a power supply – not as compact as a blade but not bad) which includes a nVidia MCP55V Pro Chipset Dual-port LAN / Ethernet Controller.  On Ubuntu 8.10 at least, this uses the forcedeth driver (originally a cleanroom implementation of a driver which competed with a proprietary offering from Nvidia – it now seems to have superceded that driver).

I noticed while doing large network transfers to or from one of these machines that the load on the machine seemed to spike. Running dmesg show a lot of these messages,

[1617484.523059] eth0: too many iterations (6) in nv_nic_irq.
[1617484.843113] eth0: too many iterations (6) in nv_nic_irq.
[1617484.869831] eth0: too many iterations (6) in nv_nic_irq.
[1617485.101377] eth0: too many iterations (6) in nv_nic_irq.
[1617485.855067] eth0: too many iterations (6) in nv_nic_irq.
[1617485.896692] eth0: too many iterations (6) in nv_nic_irq.

Google returns lots of results for this message – some people seem to have experienced complete lockups while others noted slowdowns. The proposed solution seems to be to pass the max_interrupt_work option to the forcedeth kernel module to increase the maximum events handled per interrupt. The driver seems to default to running in throughput mode where each packet received or transmitted generates an interrupt (which would presumably ensure the fastest possible transfer of the data) but can also be configured to operate in CPU mode (aka poll mode) where the interrupts are controlled by a timer (I’m assuming this makes for higher latency of transfers but smoother before for high network loads – the documentation on this is a little thin). This behaviour is controlled by the optimization_mode option. You can investigate the options which can be passed to any kernel module by running,

modinfo <module name>

for example,

modinfo forcedeth

So, as an initial pass at tuning the behaviour on the server, I decided to pass the following options to the forcedeth driver.

max_interrupt_work=20 optimization_mode=1

The standard way on Ubuntu 8.10 to set kernel module parameters is to add a line to /etc/modprobe.d/options like the following

options forcedeth max_interrupt_work=20 optimization_mode=1

I tried this and then tried rebooting my system but found it didn’t have any effect (I started seeing the same error messages after running a large network transfer and the max iterations were still referenced as 6 rather than the 20 I should be seeing if my options were parsed).

After trying a few things and brainstorming with the good people on #ubuntu-uk I figured out that you need to run the following command, after modifying /etc/modprobe.d/options

sudo update-initramfs -u

This presumably updates the initramfs image to include the specified options. It is possible this is only needed for modules that are loaded early on in the boot process (such as the network driver) – I haven’t had the need to modify other kernel modules recently (and this stuff seems to change subtly between distributions and even versions).

Following another reboot and a large network transfer, the error messages suggesting that the options are now being parsed (some kernel modules allow you to review the parameters currently being used by looking in the file /sys/modules/<module name>/parameters but forcedeth doesn’t seem to support this).

I figured the trick with update-initramfs was worth publishing for the next person who runs into this problem. I’d also love to hear from others using the forcedeth driver as to what options they find useful to tune the throughput.

Tags: forcedeth, kernel module, linux, nvidia, tuning, ubuntu 8.10

Marketing 102 – Your business card

So, your business card. Should you bother? I mean, we’re all on the internet now, right? Yes, we mostly are and depending on your audience – the venerable business card may not be as important as it once was but I think it’s still important. At the very least, it’s all your contact details on a small, easy to carry piece of paper. At best, it’s a distinctive piece of marketing material which conveys to customers and potential customers that you are the right person to fix their problem (or prevent their problem from ever happening).

If you’re going to traditional networking events – if you’re not passing out business cards you’re wasting your time – unless you have a really impressive pitch, amazing presence and a really easy to remember web address, no one is going to remember how to contact you the following day, never mind in a few weeks or months (I know I’ve certainly dug through my collection of business cards on a few occasions, knowing I met someone that provided a useful service in the past but whose contact details escaped me).

So we’ve established that you need a business card. Now, what to put on it? At a minimum, you want your name, title, address, email and phone. After that, space permitting, the sky is the limit – most people will include their company logo (although traditional businesses like solicitors and doctors usually don’t), their website address, maybe their blog address, their skype username, maybe their twitter address and depending on their audience – maybe one or more of the social networking site address (linkedin, facebook, and so on). For a business audience, linkedin is probably the most useful – but certainly if you’re audience is web 2.0 then you may want to consider one or more of the others. Remember, there is a fine line between too much info and too little. Personally I like a minimalist, uncluttered business card but each to their own.

Once you’ve figured out what to put on your card – the next step is to design your card. If you have the budget, of course you can get someone to design your card. Assuming you’re an SME startup, I’m not sure it’s the best use of your marketing budget. It’s hard to make a mess of designing a business card. For inspiration, take a look at some business cards you’ve received from others. There are a few standard patterns. If you don’t have any (cmon, get out there and get networking!) – Wikipedia’s page on business cards will give you some examples. Depending on who you use to print your card, they may also provide some basic design tools and templates which you can use. As with all things marketing, you can tweak this over time so don’t agonise over it too much.

The last question relating to design is what to put on the back of your card. Some people choose to leave this blank and there is nothing wrong with this. Others put an image (maybe a bigger version of their logo) and either their company tagline or the website url again. Of course the sky is the limit here and you can do all sorts of unique and visually striking things with your card. The problem with some of these is that they will dramatically increase your costs. So if you’re in the business of graphic design, it may make sense to spend here, otherwise something less expensive is probably the right choice. For Atlantic Linux, I decided to put a QR Code (a type of two-dimensional bar code that some mobile phones can read) including the company website URL on the back – it’s a little bit different and compliments our overall technology theme.

As an company that works extensively with open source software – where it makes business sense I prefer to use open source tools. Designing our business cards was no exception. We use the Scribus Open Source Desktop Publishing tool to create our cards. It is extremely powerful and allows fine-grained layout of our cards. It also allows us to export the final business card in a wide range of different formats suitable for consumption by whatever company you decide to use to print your cards. As with any software tool, there is a learning curve but overall I found Scribus to be reasonably intuitive and very powerful. A new release (1.3.5) is available now so it is a good time to check it out. You can of course use a graphics package or a word processor (such as OpenOffice) and they will work fine – but subsequently editing the design or moving items around may prove more difficult (word processors aren’t really designed for fine-grained layout of various elements).

So you have your card designed and developed and you’re ready to print it. In Ireland at least, this is more expensive than it should be especially for low volumes of cards. You can go to a traditional printers but they’re normally geared up to printing a few hundred or thousand cards in a run and price accordingly. If you have a need for that many cards and shop around for a few quotes you’ll get an ok price. The problem is, for a small business, unless you’re doing lots and lots of networking, you probably won’t use a few thousand cards in a year or two. In practice, you’ll want to change your card before then – either because you’re business has changed in some way (maybe moved to bigger offices!) or because you want to modify your design in some way.

I took to the Internet to see if there were any alternatives. I was looking for a company that would be willing to produce lower volumes of cards, accepting that the costs per card would be higher (we’re not talking hundreds of euros here but if you’re a startup, you should be aggressively focusing on all costs). I found two suitable companies, Smileprint and Moo.com. After looking at both sites, I eventually decided to go with Moo.com – they provide more options for the kind of card and layout you want and work out cheaper on smaller volumes of cards (I decided to only go with a very small amount of cards so I have the option of changing them more frequently).

The end result -

business card (front)

and

business card (back)

One other thing to note – for printing purposes, make sure you use a large DPI when you are creating your business card files, DTP packages usually offer better control of this than word processors (whose output is normally intended for screens, not printers). Also, printers usually prefer documents that use a CMYK colour model rather than RGB.  I might revisit these in a future posting if there is interest (although Google should turn up lots of info on these and your chosen printer will probably provide specific guidelines also).

Tags: marketing

Parallel ssh

I’m increasingly working on clusters of systems – be they traditional HPC clusters running some MPI based software or less traditional clusters running software such as Hadoop’s HDFS and MapReduce.

In both cases, the underlying operating systems are largely the same – pretty standard Linux systems running one of the main Linux distributions (Debian, Ubuntu, Red Hat Enterprise Linux, CentOS, SuSE Linux Enterprise Server or OpenSUSE).

There are various tools for creating standard system images and pushing those to each of the cluster nodes – and I use those (more in a future post), but often, you need to perform the same task on a bunch of the cluster nodes or maybe all of them. This task is best achieved by simply ssh’ing into each of the nodes and running some command (be it a status command such as uptime, or ps or a command to install a new piece of software).

Normally, one or more users on the cluster will have been configured to use password-less logins with ssh so a first-pass at running ssh commands on multiple systems would be to script the ssh calls from a management cluster node.  The following is an example script for checking the uptime on each node of our example cluster (which has nodes from cluster02 to cluster20, I’m assuming we’re running on cluster01).

#!/bin/bash
#
for addr in {2..20}
do
 num=`printf "%02d" $addr`
 echo -n "cluster${num}:" && ssh cluster${num} uptime
done

The script works, the downside is you have to create a new script each time you have a new command to run, or a slightly different sequence of actions you want to perform (you could improve the above by passing the command to be run as an argument to the script but even then the approach is limited).

What you really need at this stage is a parallel ssh, an ssh command which can be instructed to run the same command against multiple nodes. Ideally, the ssh command can merge the output from multiple systems if the output is the same – making it easier for the person running the parallel ssh command to understand which cluster nodes share the same status.

A quick search through Debian’s packages and a Google for parallel ssh turns up a few candidates,

• pssh
• dish
• taktuk
• clusterssh
• pdsh

This linux.com article reviews a number of these shells.

After looking at a few of these, I’ve settled on using pdsh. Each of the tools listed above use slightly different approaches – some provide multiple xterms in which to run commands – some provide a lot of flexibility in how the output is combined. What I like about pdsh is that it provides a pretty straightforward syntax to invoke commands and, most importantly for me, it cleanly merges the output from multiple hosts – allowing me to very quickly see the differences in a command’s output from different hosts.

You will need to configure your password-less ssh operation as normal. Once you have done that, on Debian or Ubuntu,  edit /etc/pdsh/rcmd_default and change the contents of this file to a single line containing the following,

ssh

(create the file it it doesn’t exist).

Now you can run a command, such as date (to verify if NTP is working correctly) on multiple hosts with the following,

pdsh -w cluster[01-05] date

This runs date on cluster01,cluster02,cluster03,cluster04 and cluster05 and returns the output. To consolidate the output from multiple nodes into a compact display format, pdsh comes with a second tool called dshbak, used as follows,

pdsh -w cluster[01-05] date | dshbak -c

Personally, I find this output most readable. On Debian and Ubuntu systems, to invoke dshbak by default, edit /usr/bin/pdsh (which is a shell script wrapper) and change the invocation line from

exec -a pdsh /usr/bin/pdsh.bin "$@"

to

exec -a pdsh /usr/bin/pdsh.bin "$@" | /usr/bin/dshbak -c

Now when you invoke pdsh by default, it’s output will be piped through dshbak.

Tags: hpc, linux, ssh

sudo via ssh

By default, if you attempt to run sudo through ssh, when you respond to the password prompt from sudo – it will echo the password back on your console. To avoid this, provide the -t option to ssh which forces the remote session to behave as if run through a normal tty (and thus masks the password), for example,

ssh -t foo.example.com sudo shutdown -r now

Tags: linux, ssh, sudo

The top 10 supercomputers in the world run Linux

Pingdom (a Swedish uptime monitoring company) took the results of the latest Top500.org list (Top500 is a site that publishes a list, usually twice a year, of the top-performing supercomputers in the world where the performance is ranked against the LINPACK benchmark) and published a study of what operating systems the top 20 supercomputers in world are running. It turns out that 19 of the top 20 are running some form of Linux (with the top 10 all running Linux).

While most of you reading this probably don’t plan on purchasing a supercomputer on the scale of Roadrunner or Jaguar in the near future (if you do, we’d love to assist you in the process) our own experience with deploying smaller HPC clusters for organisations is that Linux is equally suitable for smaller clusters for a variety of reasons including the cost of deployment, the flexibility of Linux as a server OS, the wide range of HPC software that is developed on or targetted at the Linux operating system and the excellent support provided by the Linux community for new hardware (see the recent announcement of Linux being the first operating to support USB 3.0 devices as a good example).

Tags: clusters, hpc, linux, supercomputer