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  • [FreeBSD kernel ]How to maintain a linked list on kernel lever?

    - by Andy Leman
    The situation is: I will implement sets of new system calls. Each of them need to access (read or write) a linked list. So, that means I will have several C programs. So, how can I maintain a linked list in memory and let several programs access it? Or,this is wrong....I should save it as a file? (but I hardly think this is a good idea).. A lot of confused questions here...Need help. Thank you indeed!

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  • Resources for writing kernel in C

    - by anon
    I don't want to write my own boot loader -- happy to use Grub. I just want to implement pre-emptive multi threading, a basic file system, and virtual memory. I want something that can run on top of qemu. What's a good resource (book / tutorial) for accomplishing this goal? Thanks!

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  • For kernel/OS is C still it

    - by Recursion
    I like operating systems and would eventually like to become a OS developer mostly working on kernels. In the future will C still be the language of choice and what else should I be trying to learn.

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  • Reducing video mode switching during Linux boot

    - by Zack
    When I boot up my desktop computer, which only has Linux on it, the video mode and/or console font gets switched four times: When GRUB starts, it switches from 80x25 text to a graphical mode so it can draw a pretty background behind its menu; GRUB then goes back to 80x25 text after I pick something from the menu; When the KMS driver for my video card loads, it switches to a much higher-resolution text mode (I don't know if this is a hardware text mode or not); Finally X starts and it goes graphics and stays that way. I think this last switch does not change the resolution of the video mode, only the graphicalness. I'd like to get rid of as many of these mode switches as possible. Ideally, when GRUB takes over from the BIOS it would go directly to the same high-resolution text mode that the KMS driver selects, and the display would stay in that mode till X starts and brings up graphics. I am under the impression that this is possible by mucking with the kernel command line and/or the GRUB console module load parameters, but I don't know the details. GRUB 1.98+20100706, kernel 2.6.32.15 using Nouveau video drivers. Distro is Debian unstable. Please no answers that involve recompiling anything or cobbling together bleeding-edge kernel/driver combinations, I don't care enough about this to go to that much trouble. EDIT: Tobu suggests setting GRUB_GFXMODE to the full pixel resolution of the monitor, and GRUB_GFXPAYLOAD_LINUX=keep to avoid the mode switch after the menu goes away. This does part of what I want, but winds up being worse overall. There's no mode switch after the menu, but there's still a painfully-slow screen repaint (I should probably just give up on GRUB's gfxmode, it's waaaay too slow at 1920x1200). More seriously, there's now a double mode switch when nouveaufb loads, along with fun-looking error messages in dmesg [ 5.923798] [drm] nouveau 0000:02:00.0: allocated 1920x1200 fb: 0x40250000, bo ffff8801ba5f4600 [ 5.923802] fb: conflicting fb hw usage nouveaufb vs EFI VGA - removing generic driver [ 5.923821] [drm] nouveau 0000:02:00.0: PFIFO_INTR 0x00000010 - Ch 1 ("PFIFO_INTR" message repeats 400+ times) [ 5.925609] Console: switching to colour dummy device 80x25 [ 5.925802] Console: switching to colour frame buffer device 240x75

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  • What does it mean when ARP shows <incomplete> on eth1

    - by Geoff Dalgas
    We have been using HAProxy along with heartbeat from the Linux-HA project. We are using two linux instances to provide a failover. Each server has with their own public IP and a single IP which is shared between the two using a virtual interface (eth1:1) at IP: 69.59.196.211 The virtual interface (eth1:1) IP 69.59.196.211 is configured as the gateway for the windows servers behind them and we use ip_forwarding to route traffic. We are experiencing an occasional network outage on one of our windows servers behind our linux gateways. HAProxy will detect the server is offline which we can verify by remoting to the failed server and attempting to ping the gateway: Pinging 69.59.196.211 with 32 bytes of data: Reply from 69.59.196.220: Destination host unreachable. Running arp -a on this failed server shows that there is no entry for the gateway address (69.59.196.211): Interface: 69.59.196.220 --- 0xa Internet Address Physical Address Type 69.59.196.161 00-26-88-63-c7-80 dynamic 69.59.196.210 00-15-5d-0a-3e-0e dynamic 69.59.196.212 00-21-5e-4d-45-c9 dynamic 69.59.196.213 00-15-5d-00-b2-0d dynamic 69.59.196.215 00-21-5e-4d-61-1a dynamic 69.59.196.217 00-21-5e-4d-2c-e8 dynamic 69.59.196.219 00-21-5e-4d-38-e5 dynamic 69.59.196.221 00-15-5d-00-b2-0d dynamic 69.59.196.222 00-15-5d-0a-3e-09 dynamic 69.59.196.223 ff-ff-ff-ff-ff-ff static 224.0.0.22 01-00-5e-00-00-16 static 224.0.0.252 01-00-5e-00-00-fc static 225.0.0.1 01-00-5e-00-00-01 static On our linux gateway instances arp -a shows: peak-colo-196-220.peak.org (69.59.196.220) at <incomplete> on eth1 stackoverflow.com (69.59.196.212) at 00:21:5e:4d:45:c9 [ether] on eth1 peak-colo-196-215.peak.org (69.59.196.215) at 00:21:5e:4d:61:1a [ether] on eth1 peak-colo-196-219.peak.org (69.59.196.219) at 00:21:5e:4d:38:e5 [ether] on eth1 peak-colo-196-222.peak.org (69.59.196.222) at 00:15:5d:0a:3e:09 [ether] on eth1 peak-colo-196-209.peak.org (69.59.196.209) at 00:26:88:63:c7:80 [ether] on eth1 peak-colo-196-217.peak.org (69.59.196.217) at 00:21:5e:4d:2c:e8 [ether] on eth1 Why would arp occasionally set the entry for this failed server as <incomplete>? Should we be defining our arp entries statically? I've always left arp alone since it works 99% of the time, but in this one instance it appears to be failing. Are there any additional troubleshooting steps we can take help resolve this issue? THINGS WE HAVE TRIED I added a static arp entry for testing on one of the linux gateways which still didn't help. root@haproxy2:~# arp -a peak-colo-196-215.peak.org (69.59.196.215) at 00:21:5e:4d:61:1a [ether] on eth1 peak-colo-196-221.peak.org (69.59.196.221) at 00:15:5d:00:b2:0d [ether] on eth1 stackoverflow.com (69.59.196.212) at 00:21:5e:4d:45:c9 [ether] on eth1 peak-colo-196-219.peak.org (69.59.196.219) at 00:21:5e:4d:38:e5 [ether] on eth1 peak-colo-196-209.peak.org (69.59.196.209) at 00:26:88:63:c7:80 [ether] on eth1 peak-colo-196-217.peak.org (69.59.196.217) at 00:21:5e:4d:2c:e8 [ether] on eth1 peak-colo-196-220.peak.org (69.59.196.220) at 00:21:5e:4d:30:8d [ether] PERM on eth1 root@haproxy2:~# arp -i eth1 -s 69.59.196.220 00:21:5e:4d:30:8d root@haproxy2:~# ping 69.59.196.220 PING 69.59.196.220 (69.59.196.220) 56(84) bytes of data. --- 69.59.196.220 ping statistics --- 7 packets transmitted, 0 received, 100% packet loss, time 6006ms Rebooting the windows web server solves this issue temporarily with no other changes to the network but our experience shows this issue will come back. Swapping network cards and switches I noticed the link light on the port of the switch for the failed windows server was running at 100Mb instead of 1Gb on the failed interface. I moved the cable to several other open ports and the link indicated 100Mb for each port that I tried. I also swapped the cable with the same result. I tried changing the properties of the network card in windows and the server locked up and required a hard reset after clicking apply. This windows server has two physical network interfaces so I have swapped the cables and network settings on the two interfaces to see if the problem follows the interface. If the public interface goes down again we will know that it is not an issue with the network card. (We also tried another switch we have on hand, no change) Changing network hardware driver versions We've had the same problem with the latest Broadcom driver, as well as the built-in driver that ships in Windows Server 2008 R2. Replacing network cables As a last ditch effort we remembered another change that occurred was the replacement of all of the patch cords between our servers / switch. We had purchased two sets, one green of lengths 1ft - 3ft for the private interfaces and another set of red cables for the public interfaces. We swapped out all of the public interface patch cables with a different brand and ran our servers without issue for a full week ... aaaaaand then the problem recurred. Disable checksum offload, remove TProxy We also tried disabling TCP/IP checksum offload in the driver, no change. We're now pulling out TProxy and moving to a more traditional x-forwarded-for network arrangement without any fancy IP address rewriting. We'll see if that helps.

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  • Announcing: Oracle Database 11g R2 Certification on Oracle Linux 6

    - by Monica Kumar
    Oracle Announces the Certification of the Oracle Database on Oracle Linux 6 and Red Hat Enterprise Linux 6 Yesterday we announced the certification of Oracle Database 11g R2 with Oracle Linux 6 and Unbreakable Enterprise Kernel. Here are the key highlights: Oracle Database 11g Release 2 (R2) and Oracle Fusion Middleware 11g Release 1 (R1) are immediately available on Oracle Linux 6 with the Unbreakable Enterprise Kernel. Oracle Database 11g R2 and Oracle Fusion Middleware 11g R1 will be available on Red Hat Enterprise Linux 6 (RHEL6) and Oracle Linux 6 with the Red Hat Compatible Kernel in 90 days. Oracle offers direct Linux support to customers running RHEL6, Oracle Linux 6, or a combination of both. Oracle Linux will continue to maintain compatibility with Red Hat Linux. Read the full press release. 

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  • Oracle E-Business Suite 12 Certified on Additional Linux Platforms

    - by John Abraham
    As a follow up to our original certification announcement regarding Oracle Linux 6, Oracle E-Business Suite Release 12 (12.1.1 and higher) is now certified on the following additional Linux x86/x86-64 operating systems: Oracle Linux 6 (32-bit) Red Hat Enterprise Linux 6 (32-bit) Red Hat Enterprise Linux 6 (64-bit) Novell SUSE Linux Enterprise Server (SLES) version 11 (64-bit) New installations of the E-Business Suite on these operating systems require version 12.1.1 of the Release 12 media.  Cloning of existing 12.1 Linux environments to this new OS is also certified using the standard Rapid Clone process. There are specific requirements to upgrade technology components such as the Oracle Database (to 11gR2) and Fusion Middleware as necessary. These and other requirements are noted in the Installation and Upgrade Notes (IUN) below. References Oracle E-Business Suite Installation and Upgrade Notes Release 12 (12.1.1) for Linux x86-64 (My Oracle Support Document 761566.1) Oracle E-Business Suite Installation and Upgrade Notes Release 12 (12.1.1) for Linux x86 (My Oracle Support Document 761564.1) Cloning Oracle Applications Release 12 with Rapid Clone (My Oracle Support Document 406982.1) Interoperability Notes Oracle E-Business Suite Release 12 with Oracle Database 11g Release 2 (11.2.0) (My Oracle Support Document 1058763.1) Oracle Linux website

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  • Why is the installation of certain programs always such a pain in Linux [closed]

    - by Saif Bechan
    I am new to Linux and I am trying to set up a server. For this I sometimes to need to install special software, but the installation of this is always such a pain. For example I wanted to try the htscanner to see if it did the job for me. When i got to the page there is NO INSTALLATION guide. I had to search for the right one on google. Even on google its a pain to find the right method. Just try it - google search.After a long search and tried different things I finally found out that I had te install some more software before it will work. The website says that the version I used did not had any dependencies. Thats a lie. Release0.8.1: No dependencies registered. You do need certain things for it to work. After managing to set it up it still didn't work I can't figure out why because there is no official guide on the website. So I wanted to just uninstall it and find a better solution. Uninstalling. Uninstalling something in Linux is a real mystery how this actually works. The best answer I got is to manually look for the files and delete them. Whats up with that! There is never something said about uninstalling on the websites. Even on the website of CentOS itself it tels you how to install something like rpmforge packages (it's a miracle they tell you and not have to google it) but there is no mention of what to do when you want to uninstall. Why not? The forums you get on when trying to solve your problem are most of the time in plain text, and you have to scroll trough huge error logs before you see somethings that vaguely resembles your question if you are lucky. The Question My question is if there are any recommended websites / forums that explain the basic concepts of installing and uninstalling software on Linux. And explain other useful operations. And not Wikipedia or the first hits of Google, I have been there already. I am looking for some easy to read trough guides on these operations on Linux. I have been on a lot of websites that explain some Linux operation, but I bet its easier to get a degree in rocket science than to read trough the website and understand what they try to say.

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  • Oracle Linux 6.3 has been released

    - by Lenz Grimmer
    We're happy to announce the availability of Oracle Linux 6.3, the third update release for Oracle Linux 6. ISO images can now be obtained from the Oracle Software Delivery Cloud, the individual RPM packages have already been published from our public yum repository. This distribution now includes the Unbreakable Enterprise Kernel Release 2 (2.6.39-200), Oracle's recommended kernel version for Oracle Linux. For further details, please see the Oracle Linux 6.3 Release Notes. Remember, Oracle Linux can be downloaded, used and distributed free of charge, updates and errata are freely available. For support, you are free to decide for which of your systems you want to obtain a support subscription, and at which level each of  them should be supported. This makes Oracle Linux an ideal choice for both your development and production systems - you decide which support coverage is the best for each of your systems individually, while keeping all of them up-to-date and secure. Wim Coekaerts recently wrote several blog posts about the benefits of Oracle Linux, which are worth a read: Oracle Linux components More Oracle Linux options My own personal use of Oracle Linux

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  • How to get rid of multiple linux versions in grub boot menu

    - by Silver Light
    I've been using dual boot on my PC for some time now, to use Ubuntu along side with Windows 7. One very disturbing thing happens, when Ubuntu linux core gets updated (this happens once in a while). They are added as options to the grub menu so, my boot menu now looks like this: Ubuntu, with linux 2.6.35-27 generic Ubuntu, with linux 2.6.35-27 generic (recovery mode) Ubuntu, with linux 2.6.35-25 generic Ubuntu, with linux 2.6.35-25 generic (recovery mode) Ubuntu, with linux 2.6.35-24 generic Ubuntu, with linux 2.6.35-24 generic (recovery mode) Ubuntu, with linux 2.6.35-22 generic Ubuntu, with linux 2.6.35-22 generic (recovery mode) Memory test Windows 7 This gets very annoying, because I want to load windows by default, but after every update it shifts down and I have to go to grub config and change the default option. My question: How to get rid of older versions of linux in the grub menu and leave only the newest one?

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  • IBM HS23 Blade Server (7875) onboard NIC driver for linux

    - by Igor Spivak
    I work with IBM HS23 Blade Server (7875). It's onboard NIC adapter is: Emulex OCl11104-F-X Virtual Fabric Adapter 2-port 10GB and 2-port 1GB LOM . I'm tryed to the following Linux OS with the server: 2.6.32-22-generic-pae #36-Ubuntu SMP. and discovered my OS has not proper Network drive installed (for the NIC adapter described above). After investigation I made, I discovered that the driver I need is "be2net" placed in "net" directory of the linux under the folder "be2net". I managed to download this driver with the latest package for my kernel. Driver info ("modinfo be2net" result) is as follows: --------------------------------------------------------------------------------------- filename: /lib/modules/2.6.32-22-generic-pae/kernel/drivers/net/benet/be2net.ko license: GPL author: ServerEngines Corporation description: ServerEngines BladeEngine2 10Gbps NICDriver 2.101.205 version: 2.101.205 srcversion: 199ADD251CB874C3727CC47 alias: pci:v000019A2d00000710sv*sd*bc*sc*i* alias: pci:v000019A2d00000701sv*sd*bc*sc*i* alias: pci:v000019A2d00000700sv*sd*bc*sc*i* alias: pci:v000019A2d00000221sv*sd*bc*sc*i* alias: pci:v000019A2d00000211sv*sd*bc*sc*i* depends: vermagic: 2.6.32-22-generic-pae SMP mod_unload modversions 586TSC parm: rx_frag_size:Size of a fragment that holds rcvd data. (uint) --------------------------------------------------------------------------------------- After starting linux, I get the following error: be2net 0000:16:00.x: Emulex OneConnect 10Gbps NIC (be3) initilization failed. I checked the same server with another Linux version (Red-Had 5.5.1.0) and the NICs worked properly, so seems there is no problem in HW. Also, on IBM or Emulex offical sites I managed to find drivers only for Red-Had and SUSE versions.

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  • Recommended motherboard with hardware raid for Linux

    - by luison
    Hi. We want to setup an internal office server for testing jobs (LAMP), email and samba. Only about 5-10 users. We are also considering starting to virtualize, initially by a base Ubuntu Server with Xen or VMWare Open Source server. Our current system runs with a Linux Raid which has worked great but it's always been complicated to recover the boot sector when one the drives fail and therefore I would prefer using now a hardware raid instead, but ideally with some kind of software monitoring. For this reason and considering we don't want to spend a fortune a I would appreciate any comments on the following options. Motherboard with RAID with linux support... which could you recommend. Motherboard + Hardware Raid card... Adaptec does not seem to have great Linux suppport. 3Ware seems to have a tc soft controller which we've used on a hosting company, but hard to find here in Spain. HP Proliant type basic server, which? Dell Small Servers... any good for Linux? Thanks in advance for any feedback.

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  • Advantages of Ubuntu LTS versions over regular Ubuntu?

    - by Adam Matan
    Do the LTS versions of Ubuntu have any advantages for the non-paying customers (who don't get any support?) From the tech spec only, these versions seem outdated in many aspects - mainly drivers and installed software versions. For instance, My previous (bounty!) problem regarding the AGN 5100 drivers would have been solved under Ubuntu 9.04.

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  • Install Linux Mint on PC without bootable CD

    - by crosenblum
    Unfortunately my PC's CD drive is not bootable; I have such a mixture of SATA and IDE drives, so until I have more money to redo my controller setup, I can't boot from any cd. Currently, I have a DVD burned with latest version of Linux Mint, and I have an USB drive with an old version of Mint. I have a partition ready to install Linx Mint into, but no idea how to install it, since I can only boot to my hard drive. I am totally unable to boot to CD, so that is definitely out. My main partition is WinXP Pro SP3. Is there software I can use to format my Linux partition, so that I can then just copy Mint over to that partition? Or is there a better way to install linux mint? I have to do it within Windows XP, since that's all that I can boot right now. I have considered Mint4Win, but that doesn't allow a full installation of Linux Mint. Any ideas?

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  • Ensuring a repeatable directory ordering in linux

    - by Paul Biggar
    I run a hosted continuous integration company, and we run our customers' code on Linux. Each time we run the code, we run it in a separate virtual machine. A frequent problem that arises is that a customer's tests will sometimes fail because of the directory ordering of their code checked out on the VM. Let me go into more detail. On OSX, the HFS+ file system ensures that directories are always traversed in the same order. Programmers who use OSX assume that if it works on their machine, it must work everywhere. But it often doesn't work on Linux, because linux file systems do not offer ordering guarantees when traversing directories. As an example, consider there are 2 files, a.rb, b.rb. a.rb defines MyObject, and b.rb uses MyObject. If a.rb is loaded first, everything will work. If b.rb is loaded first, it will try to access an undefined variable MyObject, and fail. But worse than this, is that it doesn't always just fail. Because the file system ordering on Linux is not ordered, it will be a different order on different machines. This is worse because sometimes the tests pass, and sometimes they fail. This is the worst possible result. So my question is, is there a way to make file system ordering repeatable. Some flag to ext4 perhaps, that says it will always traverse directories in some order? Or maybe a different file system that has this guarantee?

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  • How can I bridge a VM to a remote network?

    - by asciiphil
    I have a system running QEMU/KVM (via libvirt). One of its VMs needs to have a presence on a subnet that is not local to the VM host. I have a Linux system on the remote subnet. Is there a way to set up some sort of tunneled bridge to cause the VM to appear present on the remote system? This will be a temporary situation (hopefully just until the VM owner can configure their system) and network performance and long-term maintainability aren't really issues. To give some more concrete information: My VM host has IP address 192.168.54.155/24. The VM has IP address 192.168.65.71/24. I have a remote system at 192.168.65.254/24. Both the VM host and remote system are running Scientific Linux 6.5. I do not control the network or routing in between the VM host and remote system. I do not have access to the guest OS on the VM. I would like traffic to the VM's IP address to end up at the VM even though its host isn't directly connected to the appropriate network. I've tried using iproute2's tunnelling, but Linux won't let me add a tunnel to a bridge. I've considered using some sort of iptables mangling to route traffic over the tunnel and make the VM think it's on the right network, but I'm not sure whether there are better approaches. What's the best way to accomplish this hack?

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  • Picking a linux compatible motherboard

    - by Chris
    Last time I bought a new computer (I build them myself) I got a motherboard that had really poor linux support for a long time. Specifically the audio. I had to wait months before the kernel supported the on board audio chipset. That is exactly the situation I'm trying to avoid this time around. I have some specific questions about "server motherboards" actually. I looked at a few models of server motherboards by intel, and some random models on newegg. I wasn't able to see much of a difference from regular desktop motherboard other than most had two sockets, and support for much more ram. These boards seem more popular with Linux users. Why? AMD and Intel both have server CPUs as well. Some question, what's the difference? To make this question more concrete, I was looking at this this motherboard. The main questions about it that I can't answer are: Can I get a motherboard without on board raid and audio? I wanted to get a hardware raid controller and a PCI audio card. I thought a server motherboard would be cheaper and not have these "extras", since who wants an audio card on a server? Where can I found out about Linux support for the components on this board? "Intel ICH10R", "Realtek ALC889", "Marvell 88E8056" I'm buying this computer to work as a Linux desktop for a lot of compiling, coding and audio/video work, but I don't want to rule out the possibility of installing windows and playing some games at one point. (even if the last game I got has been sitting in its box unopened for almost a year). Is it a good idea to buy a "server motherboard" and play games on it, or are desktop boards better value for this? The ultimate solution for me would be a motherboard that had GPL divers for onboard LAN, a single CPU socket, lots of PCI express and PCI. USB 3.0, and no fancy hard disk controllers since I'll be getting a separate one.

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  • Maximum number of files in one ext3 directory while still getting acceptable performance?

    - by knorv
    I have an application writing to an ext3 directory which over time has grown to roughly three million files. Needless to say, reading the file listing of this directory is unbearably slow. I don't blame ext3. The proper solution would have been to let the application code write to sub-directories such as ./a/b/c/abc.ext rather than using only ./abc.ext. I'm changing to such a sub-directory structure and my question is simply: roughly how many files should I expect to store in one ext3 directory while still getting acceptable performance? What's your experience? Or in other words; assuming that I need to store three million files in the structure, how many levels deep should the ./a/b/c/abc.ext structure be? Obviously this is a question that cannot be answered exactly, but I'm looking for a ball park estimate.

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  • Find out which task is generating a lot of context switches on linux

    - by Gaks
    According to vmstat, my Linux server (2xCore2 Duo 2.5 GHz) is constantly doing around 20k context switches per second. # vmstat 3 procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 2 0 7292 249472 82340 2291972 0 0 0 0 0 0 7 13 79 0 0 0 7292 251808 82344 2291968 0 0 0 184 24 20090 1 1 99 0 0 0 7292 251876 82344 2291968 0 0 0 83 17 20157 1 0 99 0 0 0 7292 251876 82344 2291968 0 0 0 73 12 20116 1 0 99 0 ... but uptime shows small load: load average: 0.01, 0.02, 0.01 and top doesn't show any process with high %CPU usage. How do I find out what exactly is generating those context switches? Which process/thread? I tried to analyze pidstat output: # pidstat -w 10 1 12:39:13 PID cswch/s nvcswch/s Command 12:39:23 1 0.20 0.00 init 12:39:23 4 0.20 0.00 ksoftirqd/0 12:39:23 7 1.60 0.00 events/0 12:39:23 8 1.50 0.00 events/1 12:39:23 89 0.50 0.00 kblockd/0 12:39:23 90 0.30 0.00 kblockd/1 12:39:23 995 0.40 0.00 kirqd 12:39:23 997 0.60 0.00 kjournald 12:39:23 1146 0.20 0.00 svscan 12:39:23 2162 5.00 0.00 kjournald 12:39:23 2526 0.20 2.00 postgres 12:39:23 2530 1.00 0.30 postgres 12:39:23 2534 5.00 3.20 postgres 12:39:23 2536 1.40 1.70 postgres 12:39:23 12061 10.59 0.90 postgres 12:39:23 14442 1.50 2.20 postgres 12:39:23 15416 0.20 0.00 monitor 12:39:23 17289 0.10 0.00 syslogd 12:39:23 21776 0.40 0.30 postgres 12:39:23 23638 0.10 0.00 screen 12:39:23 25153 1.00 0.00 sshd 12:39:23 25185 86.61 0.00 daemon1 12:39:23 25190 12.19 35.86 postgres 12:39:23 25295 2.00 0.00 screen 12:39:23 25743 9.99 0.00 daemon2 12:39:23 25747 1.10 3.00 postgres 12:39:23 26968 5.09 0.80 postgres 12:39:23 26969 5.00 0.00 postgres 12:39:23 26970 1.10 0.20 postgres 12:39:23 26971 17.98 1.80 postgres 12:39:23 27607 0.90 0.40 postgres 12:39:23 29338 4.30 0.00 screen 12:39:23 31247 4.10 23.58 postgres 12:39:23 31249 82.92 34.77 postgres 12:39:23 31484 0.20 0.00 pdflush 12:39:23 32097 0.10 0.00 pidstat Looks like some postgresql tasks are doing 10 context swiches per second, but it doesn't all sum up to 20k anyway. Any idea how to dig a little deeper for an answer?

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  • server will not reply (syn -ack)

    - by Brent
    I like to use the following commands to manage 'TIME_WAIT', in the hope to free up resources. echo 20 > /proc/sys/net/ipv4/tcp_fin_timeout sysctl -w net.ipv4.tcp_tw_reuse=1 sysctl -w net.ipv4.tcp_tw_recycle=1 I found something interesting while doing a tcpdump. Sometimes if a client makes a connection (syn), the server will not reply (syn -ack). My question is, could it be because of the top three commands.

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  • Iptables Forwarding problem

    - by ankit
    Hi all, I had initally asked question about sertting up my linux box for natting for my home network and was given suggestions in the thread here. Did not want to clutter the old question so starting a new one here. based on the earlier suggestions, i have come up with the following rules ... :PREROUTING ACCEPT [1:48] :OUTPUT ACCEPT [12:860] :POSTROUTING ACCEPT [3:228] -A POSTROUTING -o eth0 -j MASQUERADE COMMIT *filter :INPUT DROP [3:228] :FORWARD DROP [0:0] :OUTPUT DROP [0:0] -A INPUT -i lo -j ACCEPT -A INPUT -i eth0 -p icmp -j ACCEPT -A INPUT -i eth0 -p tcp -m tcp --dport 80 -j ACCEPT -A INPUT -i eth0 -p tcp -m tcp --dport 443 -j ACCEPT -A INPUT -i eth0 -p tcp -m tcp --dport 22 -j ACCEPT -A FORWARD -i eth1 -p icmp -j ACCEPT -A FORWARD -i eth1 -p tcp -m tcp --dport 80 -j ACCEPT -A FORWARD -i eth1 -p tcp -m tcp --dport 443 -j ACCEPT -A OUTPUT -p icmp -j ACCEPT -A OUTPUT -j ACCEPT COMMIT If you notice, i do have the proper MASQURADING rule and the proper FORWARD filter rule as well. However i am facing 2 problems On the linux box itself DNS resolving is not working the lan clients connected to the linux box, are still not able to get to internet. when i ping something from them, i see the DROP count in iptables INPUT rule increasing. now my question is, when i am pinging something from the lan client, how come it is being matched by the input chain ?! should it be in the forward chain ? Chain INPUT (policy DROP 20 packets, 2314 bytes) pkts bytes target prot opt in out source destination 99 9891 ACCEPT all -- lo any anywhere anywhere 0 0 ACCEPT icmp -- eth0 any anywhere anywhere 0 0 ACCEPT tcp -- eth0 any anywhere anywhere tcp dpt:http 0 0 ACCEPT tcp -- eth0 any anywhere anywhere tcp dpt:https 122 9092 ACCEPT tcp -- eth0 any anywhere anywhere tcp dpt:ssh Thanks ankit

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  • Performance monitoring on Linux/Unix

    - by ervingsb
    I run a few Windows servers and (Debian and Ubuntu) Linux and AIX servers. I would like to continously monitor performance on these systems in order to easily identify bottlenecks as well as to have an overview of the general activity on the servers. On Windows, I use Windows Performance Monitor (perfmon) for this. I set up these counters: For bottlenecks: Processor utilization : System\Processor Queue Length Memory utilization : Memory\Pages Input/Sec Disk Utilization : PhysicalDisk\Current Disk Queue Length\driveletter Network problems: Network Interface\Output Queue Length\nic name For general activity: Processor utilization : Processor\% Processor Time_Total Memory utilization : Process\Working Set_Total (or per specific process) Memory utilization : Memory\Available MBytes Disk Utilization : PhysicalDisk\Bytes/sec_Total (or per process) Network Utilization : Network Interface\Bytes Total/Sec\nic name (More information on the choice of these counters on: http://itcookbook.net/blog/windows-perfmon-top-ten-counters ) This works really well. It allows me to look in one place and identify most common bottlenecks. So my question is, how can I do something equivalent (or just very similar) on Linux servers? I have looked a bit on nmon (http://www.ibm.com/developerworks/aix/library/au-analyze_aix/) which is a free performance monitoring tool developed for AIX but also availble for Linux. However, I am not sure if nmon allows me to set up the above counters. Maybe it is because Linux and AIX does not allow monitoring these exact same measures. Is so, which ones should I choose and why? If nmon is not the tool to use for this, then what do you recommend?

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  • "Possible SYN flooding" in log despite low number of SYN_RECV connections

    - by al4
    Recently we had an apache server which was responding very slowly due to SYN flooding. The workaround for this was to enable tcp_syncookies (net.ipv4.tcp_syncookies=1 in /etc/sysctl.conf). I posted a question about this here if you want more background. After enabling syncookies we started seeing the following message in /var/log/messages approximately every 60 seconds: [84440.731929] possible SYN flooding on port 80. Sending cookies. Vinko Vrsalovic informed me that this means the syn backlog is getting full, so I raised tcp_max_syn_backlog to 4096. At some point I also lowered tcp_synack_retries to 3 (down from the default of 5) by issuing sysctl -w net.ipv4.tcp_synack_retries=3. After doing this, the frequency seemed to drop, with the interval of the messages varying between roughly 60 and 180 seconds. Next I issued sysctl -w net.ipv4.tcp_max_syn_backlog=65536, but am still getting the message in the log. Throughout all this I've been watching the number of connections in SYN_RECV state (by running watch --interval=5 'netstat -tuna |grep "SYN_RECV"|wc -l'), and it never goes higher than about 240, much much lower than the size of the backlog. Yet I have a Red Hat server which hovers around 512 (limit on this server is the default of 1024). Are there any other tcp settings which would limit the size of the backlog or am I barking up the wrong tree? Should the number of SYN_RECV connections in netstat -tuna correlate to the size of the backlog? Update As best I can tell I'm dealing with legitimate connections here, netstat -tuna|wc -l hovers around 5000. I've been researching this today and found this post from a last.fm employee, which has been rather useful. I've also discovered that the tcp_max_syn_backlog has no effect when syncookies are enabled (as per this link) So as a next step I set the following in sysctl.conf: net.ipv4.tcp_syn_retries = 3 # default=5 net.ipv4.tcp_synack_retries = 3 # default=5 net.ipv4.tcp_max_syn_backlog = 65536 # default=1024 net.core.wmem_max = 8388608 # default=124928 net.core.rmem_max = 8388608 # default=131071 net.core.somaxconn = 512 # default = 128 net.core.optmem_max = 81920 # default = 20480 I then setup my response time test, ran sysctl -p and disabled syncookies by sysctl -w net.ipv4.tcp_syncookies=0. After doing this the number of connections in the SYN_RECV state still remained around 220-250, but connections were starting to delay again. Once I noticed these delays I re-enabled syncookies and the delays stopped. I believe what I was seeing was still an improvement from the initial state, however some requests were still delayed which is much worse than having syncookies enabled. So it looks like I'm stuck with them enabled until we can get some more servers online to cope with the load. Even then, I'm not sure I see a valid reason to disable them again as they're only sent (apparently) when the server's buffers get full. But the syn backlog doesn't appear to be full with only ~250 connections in the SYN_RECV state! Is it possible that the SYN flooding message is a red herring and it's something other than the syn_backlog that's filling up? If anyone has any other tuning options I haven't tried yet I'd be more than happy to try them out, but I'm starting to wonder if the syn_backlog setting isn't being applied properly for some reason.

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  • Journaled filesystems and power failure

    - by Yoga
    I heard that even a journaled filesystems such as EXT3/EXT4 might corrupted during power failure, e.g. from wikipedia [1]: In the event of a system crash or power failure, such file systems are quicker to bring back online and less likely to become corrupted. Can anyone provide more detail by giving examples such that when corruption can occur corruption is avoided by journaled filesystems [1] http://en.wikipedia.org/wiki/Journaling_file_system

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