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  • Linux per-process resource limits - a deep Red Hat Mystery

    - by BobBanana
    I have my own multithreaded C program which scales in speed smoothly with the number of CPU cores.. I can run it with 1, 2, 3, etc threads and get linear speedup.. up to about 5.5x speed on a 6-core CPU on a Ubuntu Linux box. I had an opportunity to run the program on a very high end Sunfire x4450 with 4 quad-core Xeon processors, running Red Hat Enterprise Linux. I was eagerly anticipating seeing how fast the 16 cores could run my program with 16 threads.. But it runs at the same speed as just TWO threads! Much hair-pulling and debugging later, I see that my program really is creating all the threads, they really are running simultaneously, but the threads themselves are slower than they should be. 2 threads runs about 1.7x faster than 1, but 3, 4, 8, 10, 16 threads all run at just net 1.9x! I can see all the threads are running (not stalled or sleeping), they're just slow. To check that the HARDWARE wasn't at fault, I ran SIXTEEN copies of my program independently, simultaneously. They all ran at full speed. There really are 16 cores and they really do run at full speed and there really is enough RAM (in fact this machine has 64GB, and I only use 1GB per process). So, my question is if there's some OPERATING SYSTEM explanation, perhaps some per-process resource limit which automatically scales back thread scheduling to keep one process from hogging the machine. Clues are: My program does not access the disk or network. It's CPU limited. Its speed scales linearly on a single CPU box in Ubuntu Linux with a hexacore i7 for 1-6 threads. 6 threads is effectively 6x speedup. My program never runs faster than 2x speedup on this 16 core Sunfire Xeon box, for any number of threads from 2-16. Running 16 copies of my program single threaded runs perfectly, all 16 running at once at full speed. top shows 1600% of CPUs allocated. /proc/cpuinfo shows all 16 cores running at full 2.9GHz speed (not low frequency idle speed of 1.6GHz) There's 48GB of RAM free, it is not swapping. What's happening? Is there some process CPU limit policy? How could I measure it if so? What else could explain this behavior? Thanks for your ideas to solve this, the Great Xeon Slowdown Mystery of 2010!

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  • Reliable Linux RAID Card

    - by Chris S
    Can anyone recommend an appropriate RAID card for use under Linux (Ubuntu)? I have three Western Digital SATA drives, and would like to setup either RAID-1 or RAID-5. Software RAID has been very flakey and unreliable for me (e.g. it doesn't seem to mirror the boot partition). Unfortunately, most RAID cards I've seen online don't mention any Linux driver support. Would most cards work in Linux, or do I have to look at a select few that explicitly support Linux?

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  • File creation time on Windows vs Linux

    - by Sergei
    We have following setup: mountserver - debian linux fileserver1 - Windows 2008 R2 Storage server fileserver2 - Celerra NS20 exporting CIFS share workstation - windows 7 with mapped drive to share on fileserver2 What we are doing: mounted share from fileserver1 on mountserver, e.g. /shared/fileserver1 mounted share from fileserver2 on mountserver, e.g. /shared/fileserver2 ran rsync on mountserver to sync data from fileserver1 to fileserver2.Used atime as parameter to sync data not older than X after a while tried to delete data older that Y on /shared/fileserver2. From what I see, linux stat command on mountserver returns following when quering file on /shared/fileserver2: At the same time when I open property for the same file using mapped drive connected to fileserver2,I see following for the same file: As you can see, Created date of 12 August shown in Windows Explorer is nowhere to be seen using stat command Am I missing something here?

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  • Logging with Resource Monitor?

    - by Jay White
    I am having sudden spikes in disk read activity, which can tie up my system for a few seconds at a time. I would like to figure out the cause of this before I set my machine to go live. With Performance Monitor I know I can log activity, but this does not show me individual processes that cause a spike. Resource Monitor allows me to see processes, but I have no way to keep logs. It seems unless I have Resource Monitor open at the time of a spike, I will not be able to identify the process causing the spike. Can someone suggest a way to log with Resource Monitor, or an alternative tool that can?

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  • Should I switch to Linux for development?

    - by Alex
    Is there any advantage to use a Linux machine to develop instead of Windows? Everyone at work tells me to switch to Linux, since I'm developing hard-core on linux anyway. I manage 40 servers, and do everything from DB to data-backend to developing web services. I don't find anything wrong with Putty. I"m just too lazy to install another OS... What do you guys think?

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  • Is a ext3 Linux filesystem byte order independent

    - by Lothar
    I have a good old HP-C3700 Workstation with PA-RISC CPU here that I would like to use as a subversion server for a very large repository. I just worry what happens if the workstation dies (everybody who knows this computer knows that it is running like an Abrams tank and unlikely to happen in the next decade). I'm using Debian Linux on this system. If the mainboard dies can I just plug the SCSI drive into a PC and read the files from a normal Intel Linux PC? Which software RAID levels would be safe?

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  • Linux Security/Sysadmin Courses in London?

    - by mister k
    Hi, My employer has offered to send me on a couple of training courses and I'm just looking for some recommendations. I'm mainly looking to improve my security and general sysadmin skills. I would like to do something focused on UNIX as I mainly work with Linux boxes (but also a couple of FreeBSD boxes). I don't want to do a study-from-home course, so I would need to find somewhere based in London. It would be great to hear from anyone who has some experience with this kind of course. The courses I've found so far are: www.learningtree.co.uk/courses/uk433.htm www.city.ac.uk/cae/cfa/computing/systems_it/linux.html www.city.ac.uk/cae/cfa/computing/systems_it/unix_tools_ss.html I'm not sure the City University courses are advanced enough as I already have experience... Thanks!

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  • setting up a WGR614v7 behind a linux box

    - by commodore fancypants
    Here's the setup, I have an openSUSE box with 2 NICs, one goes to my home network router, the other has DHCP running and it attached to a wireless router. I'm trying to get this setup to work before I switch to the linux box as my home network router. My DHCP will offer the wireless router (a WGR614v7) an address, but anything that connects to the wireless router ends up with a APIPA address. I have all the firewalls on the wireless network turned off as well as the wireless router's own DHCP. The linux box isn't offering addresses to anything past the wireless router. Is this a problem with the router or my DHCP setup? For testing purposes, I have both NICs set in the internal zone and I've tried wireless and wired connections to the WGR614v7 both to no avail.

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  • Create NTFS symbolic links from within Linux

    - by rymo
    Is there a Linux utility that can create NTFS symbolic links? That is, a link on an NTFS partition that points to another NTFS folder - one that will work within Windows 7, specifically. I wish to relocate a folder that is normally in-use while Windows is running. This machine can already dual-boot into Ubuntu, so I'd like to leverage that. EDIT: To keep this from potentially turning into "which Windows Live CD is best", I will limit this question to "Is it possible with Linux, yes or no?"

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  • ls, rm, cd commands not working in SUSE LINUX

    - by Jak
    Hi All, Iam newbi to SUSE, I installed java in my SUSE linux Server edition, So i want to set the path in linux,So i created .bash_profile in in /root path using touch and added the path as "JAVA_PATH". When restart my linux the above command is not working and it show unknown command "JAVA_PATH", I can't able to boot in GUI mode, I can boot only in terminal mode, How to delete the file (.bash_profile in /root) ? And how to add java path in SUSE Note: Before all the commands are working fine Thanks in Advance, Jak...

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  • Linux servers seeing bad download performance behind Sonicwall firewall

    - by Joshua Penix
    I'm working with a pair of co-located CentOS Linux servers sitting behind a Sonicwall PRO 2040 Enhanced firewall running in transparent bridge mode. These servers are having a strange problem downloading files more than a few megabytes in size. For example, if I try to wget or FTP a copy of the Linux kernel from kernel.org, the first ~1-2MB will download at 600+K/s, and then throughput will drop off a cliff to 1K/s. I've reviewed all the firewall configuration settings for anything suspicious, but found nothing. More interestingly, I performed the same download with a Windows server sitting behind the same firewall, and it sailed right through at 600+K/s the whole way. Has anyone seen this? Where should I start looking to troubleshoot this problem?

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  • mirroring linux server to external usb harddrive

    - by DuPie
    My google-fu must be sucking. i havent been able to find a good solution for the following: numerous Linux server on commodity hardware Trying to do a recovery mirror copy to external harddrives External harddrives are smaller than source harddrives, but larger than data External drives are connected via usb2 (slow) Servers range from 20GB of data to 400GB of data Servers are remote, so hands on access is a pain need to copy boot files. empty external drives currently Basicly, looking for a way to do use a ghosting solution from INSIDE a running linux server to an external harddrive, without booting a cd etc. the rsync/cpio solutions i've looked at dont work great with grub/dev/proc etc. I understand that since the system isnt offline, it wont be a "mirror" image as files change, but thats ok. Are there any free/commercial products that would work?

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  • mounting vsphere 4.0 file system in ubuntu linux

    - by sravan
    hi all, I am using VSpere 4.0 for my project work. I needed 4-5 servers my project work which is based on Database. I felt the virtualisation is very good to get the 5 servers running good at the same time. It was running good until few days back. Yesterday, it suddenly crashed and i had no idea of the reason.Today, it did not even boot up. Now, i need to take the data backup from that system. In order to do the same, i got the hard drive from the machine and tried to mount it on local linux machine.But, i was not successful. The disk was not even recognized by the linux machine. Can some one please tell me how to mount it and get the required data? Thank you all

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  • Linux (non-transparent) per-process hugepage accounting

    - by Dan Pritts
    I've recently converted some java apps to run with linux manually-configured hugepages. I've got about 10 tomcats running on a system and I am interested in knowing how much memory each one is using. I can get summary information out of /proc/meminfo as described in Linux Huge Pages Usage Accounting. But I can't find any tools that tell me about the actual per-process hugepage usage. I poked around in /proc/pid/numa_stat and found some interesting information that led me to this grossity: function pshugepage () { HUGEPAGECOUNT=0 for num in `grep 'anon_hugepage.*dirty=' /proc/$@/numa_maps | awk '{print $6}' | sed 's/dirty=//'` ; do HUGEPAGECOUNT=$((HUGEPAGECOUNT+num)) done echo process $@ using $HUGEPAGECOUNT huge pages } The numbers it gives me are plausible, but i'm far from confident this method is correct. Environment is a quad-CPU dell, 64GB ram, RHEL6.3, oracle jdk 1.7.x (current as of 20130728)

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  • Ubuntu Linux Utilities

    - by Wayne
    I've never used Ubuntu Linux before, but I am researching about the main system tools that are included, e.g. Windows has Disk Cleanup, Disk Defrag... but what does Ubuntu Linux have. I need to know what the main five utilities that are included on Ubuntu Linux and what do they do.

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  • Using Samba to share a folder from a Linux guest with a Windows host in VirtualBox

    - by AmV
    I would like to share a folder from a Linux Guest with a Windows host (with read and write access if possible) in VirtualBox. I read in these two links: here and here that it's possible to do this using Samba, but I am a little bit lost and I need more information on how to proceed. So far, I managed to set up two network adapters (one NAT and one host-only) and install Samba on the Linux guest, but now I have the following questions: What do I need to type in samba.conf to share a folder from the Linux guest? (the tutorial provided in one of the links above only explains how to share home directories) Are there any Samba commands that need to be executed on the guest to enable sharing? How do I make sure that these folders are only available to the host OS and not on the Internet? Once the Linux guest is setup, how do I access each of the individual shared folders from the Windows host? I read that I need to mount a drive on Windows to do this, but do I use Samba logins, or Linux logins, also do I use localhost? or do I need to set up an IP for this? Thanks!

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  • Ubuntu server; Should I add a new user or not?

    - by Camran
    On my Ubuntu server, when I do everything now I do it as "root" user. So for example, logging into ftp filezilla, I enter "root" as username... Is this the way to do it, or should I create a users group and add priveliges to the users in that group? Don't know if I should create a new user or not, it works with root just fine, but I don't want any security flaws... Thanks

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  • Linux software Raid 10 no superblock

    - by Shoshomiga
    I have a software raid 10 with 6 x 2tb hard drives (raid 1 for /boot), ubuntu 10.04 is the os. I had a raid controller failure that put 2 drives out of sync, crashed the system and initially the os didnt boot up and went into initramfs instead, saying that drives were busy but I eventually managed to bring the raid up by stopping and assembling the drives. The os booted up and said that there were filesystem errors, I chose to ignore because it would remount the fs in read-only mode if there was a problem. Everything seemed to be working fine and the 2 drives started to rebuild, I was sure that it was a sata controller failure because I had dma errors in my log files. The os crashed soon after that with ext errors. Now its not bringing up the raid, it says that there is no superblock on /dev/sda2. I tried to reassemble manually with all the device names but it still would not bring up the raid 10 complaining about the missing superblock on sda2, and sda1 was also dropped from the raid 1. When I did examine on the raid10 it says that 1 of the initially failed drives is a spare, the other is spare rebuilding and sda2 is removed. It seems that sda decided to fail right when the system was vulnerable to it because when I boot up a live cd it spews out sda unrecoverable read failures. I have been trying to fix this all week but I'm not sure where to go with this now, I ordered more hard drives because I didn't have a complete backup, but its too late for that now and the only thing I could do is mirror all the hard drives onto the new ones (I'm not sure whether sda was mirrored without errors). On the internet I read that you can recover from this by recreating the array with the same options as when it was made, however because sda is failing I cant use it and I don't want to risk using its mirror instead, so I'm waiting to get another hard drive. I'm also not sure whether to include the out of sync drives or if I can actually use those instead to recover the array. Sorry if this is a mess to read but I've been trying to fix this all day and its late at night now, any thoughts on this would be greatly appreciated. I also did a memtest and changed the motherboard in addition to everything else. EDIT: This is my partition layout Disk /dev/sdb: 2000.4 GB, 2000398934016 bytes 255 heads, 63 sectors/track, 243201 cylinders, total 3907029168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0x0009c34a Device Boot Start End Blocks Id System /dev/sdb1 * 2048 511999 254976 83 Linux /dev/sdb2 512000 3904980991 1952234496 83 Linux /dev/sdb3 3904980992 3907028991 1024000 82 Linux swap / Solaris

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  • Linux compatible touchscreen monitor

    - by jrtokarz
    Can anybody recommend a linux compatible touchscreen monitor, the criteria are: 19inch or greater 1920x1080 or better only single touch required be able to operate in portait mode We currently have some IIyama Prolite MTS2250MS monitors but these do not natively support portait mode and we have had little success getting the touch functionality working in Linux (although they do report themselves as HID devices when plugged in). So an alternative to suggesting a monitor would be pointers to information on how we could get the IIyama monitor working in Linux.

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  • Install Rails on linux [migrated]

    - by Jseb
    I am trying to install Ruby on Rails. and i have followed the following link for the install https://www.digitalocean.com/community/articles/how-to-install-ruby-on-rails-on-ubuntu-12-04-lts-precise-pangolin-with-rvm. This link was helpful i was able to run it, and everything, however as soon has i restarted the computer i then go into my apps and run it again with rails s and this message occurs. The program 'rails' is currently not installed. You can install it by typing: sudo apt-get install rails But work before, what should i do, do i need to set the path of somesort?? I am not that great in linux so bear with me. I am using linux ubuntu 12.04 desktop and my user is john Thanks in advance

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