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  • BIND master/slave does not respond for queries for its slave

    - by Savas
    Systems are all Centos 6.2 Lets say I have a masterdns with IP 10.2.1.2, authoritative for the 10.2.1.X subnet and let say it is domain example.com I have another two subnets, 10.2.2.X and 10.1.2.X Each one has its own DNS server, dns2 and dns1 respectively and let say these are domains dom2.example.com and dom2.example.com respectively. The masterdns server has slave zones for dns1, dns2 and respond to requests OK. The dns1, dns2 have the masterdns zones as slaves two, and respond to requests OK. So, the masterdns has as slave zones all the subordinate domains of example.com Each of dns1 and dns2 use masterdns as a forwards (which uses another dns cache/proxy server) for dns resolution of internet public domain names. It works OK that too. The problem is, and I cannot figure it out. Why queries for example at dns1 for hostnames of dom2.example.com do not resolve? If i use nslookup - masterdns at dns1 server, resolve (i use directly the dns facility of masterdns). If I use nslookup locally, meaning queries are sent to dns1, for hosts that are at dom2.example.com, they do not resolve. Everything other works OK.

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  • What to look for in a reliable backup hard disk?

    - by Senthil
    I want to buy an internal hard disk and use a docking station along with it for backing up important data. The size will be around 500GB to 1TB. I have a budget and several models fit into it. So far, they only seem to vary in size, speed and brand. These are the only things I can compare from the specs. I guess asking for which brand is best is completely subjective so I won't do that. I want my disk to have long life and be reliable. Doesn't matter if it is somewhat slow. Size: Should I go for the one with highest size within my budget? Will higher density cause problems? Or should I go for a moderately sized one? Does the number of platters have an impact? Speed: I do not want high performance. I want it to be reliable and last long. I am definitely not going to choose the expensive 10,000 rpm ones. Should I go for 5400 or 7200? Do these numbers affect longevity and reliability? Are there any other technical and objective factors that I should look for?

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  • How do I convert a video to GIF using ffmpeg, with reasonable quality?

    - by Kamil Hismatullin
    I'm converting .flv movie to .gif file with ffmpeg. ffmpeg -i input.flv -ss 00:00:00.000 -pix_fmt rgb24 -r 10 -s 320x240 -t 00:00:10.000 output.gif It works great, but output gif file has a very law quality. Any ideas how can I improve quality of converted gif? Output of command: $ ffmpeg -i input.flv -ss 00:00:00.000 -pix_fmt rgb24 -r 10 -s 320x240 -t 00:00:10.000 output.gif ffmpeg version 0.8.5-6:0.8.5-0ubuntu0.12.10.1, Copyright (c) 2000-2012 the Libav developers built on Jan 24 2013 14:52:53 with gcc 4.7.2 *** THIS PROGRAM IS DEPRECATED *** This program is only provided for compatibility and will be removed in a future release. Please use avconv instead. Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input.flv': Metadata: major_brand : mp42 minor_version : 0 compatible_brands: isommp42 creation_time : 2013-02-14 04:00:07 Duration: 00:00:18.85, start: 0.000000, bitrate: 3098 kb/s Stream #0.0(und): Video: h264 (High), yuv420p, 1280x720, 2905 kb/s, 25 fps, 25 tbr, 50 tbn, 50 tbc Metadata: creation_time : 1970-01-01 00:00:00 Stream #0.1(und): Audio: aac, 44100 Hz, stereo, s16, 192 kb/s Metadata: creation_time : 2013-02-14 04:00:07 [buffer @ 0x92a8ea0] w:1280 h:720 pixfmt:yuv420p [scale @ 0x9215100] w:1280 h:720 fmt:yuv420p -> w:320 h:240 fmt:rgb24 flags:0x4 Output #0, gif, to 'output.gif': Metadata: major_brand : mp42 minor_version : 0 compatible_brands: isommp42 creation_time : 2013-02-14 04:00:07 encoder : Lavf53.21.1 Stream #0.0(und): Video: rawvideo, rgb24, 320x240, q=2-31, 200 kb/s, 90k tbn, 10 tbc Metadata: creation_time : 1970-01-01 00:00:00 Stream mapping: Stream #0.0 -> #0.0 Press ctrl-c to stop encoding frame= 101 fps= 32 q=0.0 Lsize= 8686kB time=10.10 bitrate=7045.0kbits/s dup=0 drop=149 video:22725kB audio:0kB global headers:0kB muxing overhead -61.778676% Thanks.

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  • Using a Level 2 switch as a core switch

    - by imtech
    I have a small user base of about 20 people on at a time and spiking up to about 80 people during peak times. Most people (80+%) are connected over our Aruba managed wireless system. We have a Windows Domain. We have 3 24-Port switches all connecting back to a central 48-port switch where additional access ports, firewall, servers, and wireless controller all centrally connect back to. It's a flat network with dumb switches. I'm in the process of upgrading our infrastructure. Cisco pricing for switches is pretty high for us so I've been looking at HP Procurves which seem to be within our budget range. I want to eventually make use of 802.1x, SNMP, QoS for possible VOIP upgrades, VLAN to separate guest VLAN from authenticated users, and other more advanced features. PoE would be nice but that's probably too expensive for us. I was thinking of having our core switch be a Procurve 2610 and the rest of our switches that centrally connect to it be Procurve 2510s. A true and full blown level 3 switch is way out of our price range but a 2610 seems to be good enough for us. The 2610 does static routing which ought to be good enough for us but I'm in unfamiliar territory so I'm looking for any gotchas. Also, should all the switches be 2610s or just the core switch? Do I even need the 2610, can I just go with all 2510s? I'm new to VLANs as well so I'm not sure what it is I need but I would like an affordable infrastructure that won't need replacing 2-3 years down the line because I choose a product that was lacking.

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  • Install and enforce a scheduled task across a Windows domain

    - by Ricket
    We have a small domain of about 70 Windows computers (XP and 7). We want to schedule a command (an update mechanism) to run on all computers periodically, and we want the task to run regardless of the computer's connection to our network (i.e. the task should run even on a laptop that isn't connected to our VPN). We have a Microsoft System Center Essentials 2010 server so that might come in handy. The options I see are these: Do it completely manually. Install the scheduled task by hand or remotely using psexec (and the at command?) for each computer in our network. Enforce that newly imaged computers should have this task installed on them before deployed to the employee, or the task should be in the image. High initial cost (having to do this for each of 70 computers) but building it into the image might work... But there is some maintenance in making sure the task is added to everything. And I fear that a year or two down the road, we will have forgotten about it or gotten sloppy or had new IT employees who miss this step and some computers won't have the task. Having one of our servers run a script that loops through all computers and psexec's the command on each computer in the network -- it would only run on running, connected computers, so this solution wouldn't work. I suspect SCE could do something like this too, but again this is not a good solution. Neither of these are ideal, and I'm certain there is a better way to do it -- right? What is the best way to accomplish this task?

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  • NAT vs public IP (and blocked ports)

    - by user1646166
    I have a problem with my ISP. They say that they don't block any ports and I have public IP, while I think these both statements are false. Before I talk to them again (which is really tough when my understanding of these terms is different than theirs) I would like to make some things clear. It seems like my computer is behind NAT (is it possible to have public IP and be behind NAT at the same moment?). When I check my IP, through some external server, and type that IP into browser I get a home page of some router (not mine). Isn't that a proof that my IP isn't public? Also, I have problems with making connections via some ports. E.g. when I'm trying to connect through some high port ( 1023) via SSH, it doesn't work. Is it possible that certain range of outgoing ports from my computer are blocked? Or is it simply because that my ssh client (PuTTY) can't receive incoming packets because of blocked incoming ports? To avoid some questions: it's not a problem with my router, I tried connecting my PC directly and it also didn't work, while having connected by 3G using phone with USB tethering, it does work. Thanks!

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  • "Network Error - 53" while trying to mount NFS share in Windows Server 2008 client

    - by Mike B
    CentOS | Windows 2008 I've got a CentOS 5.5 server running nfsd. On the Windows side, I'm running Windows Server 2008 R2 Enterprise. I have the "Files Services" server role enabled and both Client for NFS and Server for NFS are on. I'm able to successfully connect/mount to the CentOS NFS share from other linux systems but am experiencing errors connecting to it from Windows. When I try to connect, I get the following: C:\Users\fooadmin>mount -o anon 10.10.10.10:/share/ z: Network Error - 53 Type 'NET HELPMSG 53' for more information. (IP and share name have been changed to protect the innocent :-) ) Additional information: I've verified low-level network connectivity between the Windows client and the NFS server with telnet (to the NFS on TCP/2049) so I know the port is open. I've further confirmed that inbound and outbound firewall ports are present and enabled. I came across a Microsoft tech note that suggested changing the "Provider Order" so "NFS Network" is above other items like Microsoft Windows Network. I changed this and restarted the NFS client - no luck. I've confirmed that the share folder on the NFS server is readable/writable by all (777) I've tried other variations of the mount command like: mount 10.10.10.10:/share/ z: and mount 10.10.10.10:/share z: and mount -o anon mtype=hard \\10.10.10.10:/share * No luck. As per the command output, I tried typing NET HELPMSG 53 but that doesn't tell me much. Just "The network path was not found". I'm lost on how to proceed with troubleshooting. Any ideas?

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  • repo sync "CyanogenMod/android_prebuilt" size and resume capability.?

    - by james
    I'm downloading CyanogenMod-10.1 source on a low speed broadband. About 4GB of source is downloaded . In that 4GB, there is a big project "CyanogenMod/android_frameworks_base" which alone took 1GB of download without any interruption. Ok now, after 4GB of download, my internet got disconnected and I had to stop (ctrl + z) repo sync while it was downloading the project "CyanogenMod/android_prebuilt". Before I stopped repo sync the android_prebuilt got downloaded till 250MB and is at 42percent. I checked the working folder and there is a file "tmp_pack_df5CKb" of size 250MB in the path "$WORKING_DIR/.repo/projects/prebuilt.git/objects/pack/" . Then I restarted repo sync and it was downloading the android_prebuilt project. But I'm not sure if it was downloading from start or resuming from 250MB. While downloading this time , the previous "tmp_pack_df5CKb" isn't deleted and the content is being downloaded to a new file "tmp_pack_HPfvFG". I heard repo sync cannot be resumed for a project. But here, since the previous file isn't deleted I want to ask if android_prebuilt is resuming or downloading from start again? Now that my high speed internet is over (current speed 256kbps), I'm not sure if I can download the remaining ~4GB if single project is in size 500 MB.

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  • How to connect a USB GDI printer to Linux over a D-Link print server?

    - by jpe
    The setup is the following: +------------+ +-----------------+ +---------+ | HP LJ P1005|--USB--| D-Link DPR-1020 |---LAN---| PC Linux| +------------+ +-----------------+ + +---------+ | +------------+ +--| PC Windows | +------------+ HP LJ P1005 is one of those GDI printers that requires the printer driver to do most of the work for it and therefore is a bit "special". D-Link DPR-1020 is a print server with an Ethernet and an USB port that actually supports printing to challenged (read GDI) printers using a utility called PS-Link. What the utility does is basically mirror a USB port over the network to the print server so that the printer driver and the printer both are happy to talk to each other. The PC-s are notebooks that come and go, i.e. are not there all the time. Is there an equivalent of the D-Link PS-Link utility for Linux that could mirror a USB port over the network for a Linux host? And can the solution be used with D-Link DPR-1020? If not then I basically wasted the money buying the print server because the goal was to share a small printer among a couple of users with diverse operating systems in an office. The print server specs say that it supports Linux and LJ P1005, but the Catch 22 appears to be the solution used for GDI printers... It should be noted that it is possible to print from Linux to LJ P1005 directly over USB. This far sharing involved reconnecting the USB cable to appropriate computer to print. Now one of the desks is separated, so the cable does not work. Searching the net did not yield anything useful. Please do not suggest solutions involving a Windows machine (either virtual or not), my question is whether a solution only involving a Linux machine exists.

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  • Drobo-like linux file server - how do I do it?

    - by John Hunt
    I've been pondering for a long time about how I can set up a server which operates much like the Drobo storage thing. The reasons I don't actually want a drobo is because I've heard scare stories, plus I'd like to do this on the cheap. So ideally I'm looking for something like lvm so I can create a logical volume that spans many hard disks of varying sizes... obviously that only offers redundancy if I put the LV on a raid array (as far as I know..) I have however been reading about technologies such as Microsoft's drive extender which duplicates files at the filesystem level and makes sure that the mirrored files are on a different phyiscal disk.. does anyone know or recommend a filesystem or method like this as it'll hopefully make much better use of the space available than raid ever could. Performance isn't an issue, I'd just really like to make the most of the hard disks I have lying around whilst having a bit of redundancy incase a disk dies. I understand full well that this is no replacement for a backup, but I'll only be storing files of medium importance and using the nas itself as a backup of my main pc and other systems. Thanks in advance! I'm hoping zfs or btrfs or something can do something clever for me :)

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  • Kickstart: Serve dynamic kickstart images via a CGI or PHP script?

    - by Stefan Lasiewski
    I'd like to kickstart a couple dozen RHEL6/SL6 servers. However, some of these servers are different and I don't want to create a new ks.cfg file for each class of server. Are there any products which can generate a Kickstart file dynamically on the fly, from a template? For example, if I append a line like this to the KERNEL: APPEND ks=http://192.168.1.100/cgi-bin/ks.cgi Then the script ks.cgi can determine what host this is (Via the MAC address), and print out Kickstart options which are appropriate for that host. I could optionally override some options by passing parameters to the script, like this: APPEND ks=http://192.168.1.100/cgi-bin/ks.cgi?NODETYPE=production&IP=192.168.2.80 After we kickstart the server, we activate Cfengine/Puppet on this system and manage the system using our favorite Configuration Management product. We're experimenting with xCAT but it is proving too cumbersome. I've looked into Cobbler, but I'm not sure it does this. Update: A roll-your-own solution is discussed in the O'Reilly book: Managing RPM-Based Systems with Kickstart and Yum, Chapter 3. Customizing Your Kickstart Install Dynamic ks.cfg, which echos some of the comments in this thread: To implement such a tool is beyond the scope of this Short Cut, but I can walk through the high-level design. Any such solution would mix a data store (the things that change) with a templating solution (the things that don’t change). The data store would hold the per-machine data, such as the IP address and hostname. You would also need a unique identifier, perhaps the hostname, such that you could pick up a given machine’s data. The data store could be a flat file, XML data, or a relational database such as PostgreSQL or MySQL. In turn, to invoke the system, you pass a machine’s unique identifier as a URL parameter. For example: boot: linux ks=http://your.kickstart.server/gen_config?host-server25 In this example, the CGI (or servlet, or whatever) generates a ks.cfg for the machine server25. But where, oh where, is the code for ks.cgi?

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  • Bad Mumble control channel performance in KVM guest

    - by aef
    I'm running a Mumble server (Murmur) on a Debian Wheezy Beta 4 KVM guest which runs on a Debian Wheezy Beta 4 KVM hypervisor. The guest machines are attached to a bridge device on the hypervisor system through Virtio network interfaces. The Hypervisor is attached to a 100Mbit/s uplink and does IP-routing between the guest machines and the remaining Internet. In this setup we're experiencing a clearly recognizable lag between double-clicking a channel in the client and the channel joining action happening. This happens with a lot of different clients between 1.2.3 and 1.2.4 on Linux and Windows systems. Voice quality and latency seems to be completely unaffected by this. Most of the times the client's information dialog states a 16ms latency for both the voice and control channel. The deviation for the control channels mostly is a lot higher than the one of the voice channels. In some situations the control channel is displayed with a 100ms ping and about 1000 deviation. It seems the TCP performance is a problem here. We had no problems on an earlier setup which was in principle quite like the new one. We used Debian Lenny based Xen hypervisor and a soft-virtualised guest machine instead and an earlier version of the Mumble 1.2.3 series. The current murmurd --version says: 1.2.3-349-g315b5f5-2.1

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  • gcc built by crosstool-ng gives undefined reference

    - by netvope
    I've successfully built a toolchain using crosstool-ng with the default configuration named x86_64-unknown-linux-gnu. The documentation says: Using the toolchain is as simple as adding the toolchain's bin directory in your PATH, such as: export PATH="${PATH}:/your/toolchain/path/bin" and then using the target tuple to tell the build systems to use your toolchain: ./configure --target=your-target-tuple or make CC=your-target-tuple-gcc or make CROSS_COMPILE=your-target-tuple- and so on... I followed the instructions and attempted to build GNU tar (tar-1.25.tar.bz2) with the toolchain. The commands ./configure --target=x86_64-unknown-linux-gnu and make CROSS_COMPILE=x86_64-unknown-linux-gnu- do not work (the build will succeed, but it uses the host system's gcc). The command make CC=x86_64-unknown-linux-gnu-gcc works, but in the very last step when it tries to link, it returns errors like this: compare.o: In function `openat': /dev/shm/x-tools/x86_64-unknown-linux-gnu/x86_64-unknown-linux-gnu/sys-root/usr/include/bits/fcntl2.h:134: undefined reference to `__openat_2' What could be the problem? Was the toolchain not properly setup? Perhaps x86_64-unknown-linux-gnu-gcc is using the header files from the host system but could not find the libraries in the target's sys-root?

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  • tod to avi mpg wmv, convert tod (.mpeg-2) to avi mpg wmv for Movie Maker.

    - by yearofhao
    Need to convert .tod (mpeg-2) to avi mpg wmv download from JVC Everio to PC with tod to avi mpg wmv converter convert tod to uncompressed/raw avi, mpg wmv Have a JVC Everio camcorder? Then you may encounter problems when saving the .tod files to your computer windows movie maker says it can't recognize and edit them to make videos. You may play them using media player but the problem is how to edit them? The bundled software Power cinema could be annoying, since you can only edit when the camera is plugged in to the PC - Power cinema can’t seem to edit from the saved clips alone. So, how do you save them to PC so that you can edit them without the camera and also using windows movie maker? JVC Everio Tod to avi mpg wmv converter costs you a penny to but help you perfectly convert tod file to AVI, MPG, WMV, YouTube FLV, MP4, DV, QuickTime.MOV or other common video formats with fast speed and while keeping the original HD quality. High definition TOD recordings from JVC Camcorders can playback fluidly, convert smoothly and edit professionally on with iOrgsoft TOD file converter iOrgsoft tod to avi mpg wmv Converter has been mostly used by Windows users who use Windows 7 or Vista, after the .tod (mpeg-2 the same codec) downloaded from JVC Everio to PC, it’s best to convert tod to avi, convert to xvid divx, convert tod to uncompressed avi or convert tod to raw avi, tod to mpg, tod to wmv, which are three Windows movie maker best formats to import. TOD to avi mpg wmv converter is a competent video-editing program that allows you to clip/cut TOD video clip, crop the video to encode, and help transfers video to devices like iPhone, iPod, to HDTV connected with Apple TV.

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  • Setting MSN or Yahoo! Messenger status to Invisible or Offline when idle for an hour

    - by Jian Lin
    Where, or how, do I set it up in MSN Messenger or Yahoo! Messenger to automatically switch my status to either "Invisible" or "Offline" when idle for a half hour, or an hour? I know how to set my status as "Away" or "Busy" after 10 minutes, but can't seem to find a way to set the offline status options without manual intervention. Back story As a software developer, I am very used to turning the computer on for the whole day and not turning it back off. (For example, checking email for urgent fixes, fix issue and push to web server). It's not even turned off when heading to sleep in case I might find it hard to fall asleep and come back to check on the computer. Or to have it there ready in the morning to check that everything is okay. If I'm seen as being online for 24 hours of a day, some people see me as weird. Their perception of my value decreases as I'm always there (hard to get = high value; always there = low value). Leaving it on makes everyone in my contacts list think I have nothing better to do all day than sit in front of the computer. Even though it's my job and I do admittedly spend more time online than other people. That's why I'd like to find a way to set my status as Invisible or Offline.

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  • Should I partition a 1TB Hard Disk whose primary use is media storage?

    - by Senthil
    I am going to get a 1TB hard disk. I will be storing 1080p or 720p movies, high-bitrate music and pictures in it. I use my PC 90% of the time only to play/listen/see those. I am running out of space in my current HD so I am getting another one. My specs are 2.7GHz Dual Core, 512MB GeForce 9400GT, 2GB DDR2 RAM and all the proper matroska codecs/players. I guess that is enough to play 1080p movies withough a glitch, given an ideal hard disk. I've read about proper partitioning giving performance improvement etc.. I don't want my hard disk to be the bottleneck. Can someone tell me whether I should partition my 1TB hard disk into many drives? If I should, what is the ideal size of each partition? Smooth playing of movies is very important to me. Once I start filling up the disk, there is no turning back. So I want to get it right before I start. Thanks.

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  • APC fragmentation on EC2 Micro for Wordpress + W3TC

    - by Maarten Provo
    I'm trying to optimize APC for my Amazon EC2 Micro server running one Wordpress-site with W3TC. I've started with the settings advised by TechZilla in another topic but I keep getting high fragmentation with 50% of space being free. I've uploaded an image to http://www.maartenprovo.be/downloads/apc.jpg but I can't post it here since I need at least 10 reputation. What values can I optimize to prevent fragmentation? [apc] apc.enabled=1 apc.shm_segments=1 ;32M per WordPress install apc.shm_size=164M ;Leave at 2M or lower. WordPress does't have any file sizes close to 2M apc.max_file_size=2M ;Relative to the number of cached files apc.num_files_hint=1000 ;Relative to the size of WordPress apc.user_entries_hint=4096 ;The number of seconds a cache entry is allowed to idle in a slot before APC dumps the cache apc.ttl=7200 apc.user_ttl=7200 apc.gc_ttl=3600 ;Auto update chache files on change in WP-ADMIN or W3TC apc.stat=1 ;This MUST be 0, WP can have errors otherwise! apc.include_once_override=0 ;Only set to 1 while debugging apc.enable_cli=0 ;Allow 2 seconds after a file is created before it is cached to prevent users from seeing half-written/weird pages apc.file_update_protection=2 ;Ignore files apc.filters apc.slam_defense = 0 apc.write_lock = 1 apc.cache_by_default=1 apc.use_request_time=1 apc.mmap_file_mask=/var/tmp/apc.XXXXXX apc.stat_ctime=0 apc.canonicalize=1 apc.write_lock=1 apc.report_autofilter=0 apc.rfc1867=0 apc.rfc1867_prefix =upload_ apc.rfc1867_name=APC_UPLOAD_PROGRESS apc.rfc1867_freq=0 apc.rfc1867_ttl=3600 apc.lazy_classes=0 apc.lazy_functions=0

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  • All commands stopped working in centos 6.5

    - by Michael
    I have made a big mistake while removing some duplicate packages as it appears to be broken. yum 1036 rpm -e --nodeps glibc-2.12-1.132.el6_5.2.x86_64 1037 rpm -e --nodeps nscd-2.12-1.132.el6_5.2.x86_64 1038 rpm -e --nodeps glibc-common-2.12-1.132.el6_5.2.x86_64 1040 rpm -e --nodeps glibc-common-2.12-1.132.el6.x86_64 glibc-devel-2.12-1.132.el6.x86_64 glibc-headers-2.12-1.132.el6.x86_64 1041 rpm -e glibc.x86_64 1042 rpm -e --nodeps glibc.x86_64 The issue happened after doing 1042 step. None of commands work(including yum, rpm, ls, cp etc) and getting error /lib64/ld-linux-x86-64.so.2: bad ELF interpreter: No such file or directory I thought that installing glibc after removing all the current ones would help to resolve the duplicate package error :( Now I realised that it is used as the C library in the GNU system and most systems with the Linux kernel. It defines the "system calls" and other basic facilities such as open, malloc, printf, exit, etc. Is there any possible solutions other than reinstall? I have lost ssh access. Maybe anything can be done using rescue cd? Thanks

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  • What are the frequencies of current in computers' external peripheral cables and internal buses?

    - by Tim
    From Wikipedia, three different cases of current frequency are discussed along with the types of cables that are suitable for them: An Extra Ordinary electrical cables suffice to carry low frequency AC, such as mains power, which reverses direction 100 to 120 times per second (cycling 50 to 60 times per second). However, they cannot be used to carry currents in the radio frequency range or higher, which reverse direction millions to billions of times per second, because the energy tends to radiate off the cable as radio waves, causing power losses. Radio frequency currents also tend to reflect from discontinuities in the cable such as connectors, and travel back down the cable toward the source. These reflections act as bottlenecks, preventing the power from reaching the destination. Transmission lines use specialized construction such as precise conductor dimensions and spacing, and impedance matching, to carry electromagnetic signals with minimal reflections and power losses. Types of transmission line include ladder line, coaxial cable, dielectric slabs, stripline, optical fiber, and waveguides. The higher the frequency, the shorter are the waves in a transmission medium. Transmission lines must be used when the frequency is high enough that the wavelength of the waves begins to approach the length of the cable used. To conduct energy at frequencies above the radio range, such as millimeter waves, infrared, and light, the waves become much smaller than the dimensions of the structures used to guide them, so transmission line techniques become inadequate and the methods of optics are used. I wonder what the frequencies are for the currents in computers' external peripheral cables, such as Ethernet cable, USB cable, and in computers' internal buses? Are the cables also made specially for the frequencies? Thanks!

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  • What are the most important aspects to consider when choosing a SAN for a small office virtualizatio

    - by Prof. Moriarty
    I am in the process of consolidating 6 physical servers running 6 different operating system flavors (don't ask) into two identical physical servers (Dell PowerEdge 2900), using the free VMware ESXi 4.0 platform. We will install an iSCSI SAN over a 1GbE network, and store all virtual machine images on the SAN. Each physical server would run 3 VMs, and in the case of a physical server failure, we would manually switch over the other 3. These are all internal servers, while important, they can tolerate some amount of downtime (say <1h) to keep cost and complexity associated with HA down. I now need to choose the SAN to be used for the setup, on a low budget. We currently have about 2TB of data, but of course I want to able to grow, do backups of VM snapshots on other drives and remove them to a different location, etc. So what I would like to know is: Which are the must have features for this setup, without which using a SAN is not worth it? We are mostly a Dell shop, so I have been looking at the EqualLogic PS4000E High Availability model. Any opinions, anecdotes, bad experiences with this model? (This is one of the few models which could accomodate our existing disks from the physical servers.) If you can recommend something that is not Dell, but it has better value, I would most definitely consider it. Caveats, things to look out for?

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  • SQL Server Database In Single User Mode after Failover

    - by jlichauc
    Here is a weird situation we experienced with a SQL Server 2008 Database Mirroring Failover. We have a pair of mirrored databases running in high-availability mode and both the principal and mirror showed as synchronized. As part of some maintenance I triggered a manual failover of the principal to the mirror. However after the failover the principal was now in single-user mode instead of the expected "Principal/Synchronized" state we usually get. The database had been in multi-user mode on the previous principal before this had happened. We ended up stopping all applications, restarting the SQL Server instances, and executing "ALTER DATABASE ... SET MULTI_USER" to bring the database back to the expected "Principal/Synchronized" state in a multi-user mode. Question. Does anyone know where SQL Server stores information about whether a database should be in single-user mode or not? I'm wondering if there is some system database or table that has this setting recorded somewhere. In particular we had an incident once with the database on the original principal (the one I was failing over to) where when trying to detach the database it was put into single-user mode. I'm wondering if that setting is cached somewhere and is the reason that SQL Server put it back into single-user mode after a failover.

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  • Keeping Xv Overlay configuration throughout an X session.

    - by kriss
    After upgrading my Linux system from Ubuntu 9.04 to Ubuntu 10.10, I suceeded correcting most problems (all related to Intel 82865G Integrated Graphics Adapter support and compiz is still not working but that's another matter) but for one I only have a partial solution. Whenever I play a video the colors are much too saturated. This is really a problem for tones of skins that appears reddish (everyone seems to be coming back from a ski vacation with deep sun burns). As this effect only occurs with videos, not with pictures, I finally figured out it was related to Video Overlays configuration and I can correct it typing: xvattr -a XV_SATURATION -v 120 This change the default saturation value, which is 500 and much too high in my case, at eye sight the correct value seems to be between 100 and 150. Now my problem is that I have to type the above command each time I run a video. If I type it before running the video it has no effect, if I close the video and open a new one, I have to type it again, etc. I tried to put it in Xsession and (logically) it has no effect either. How could I do to get the correct setting whenever I run a video without typing the above command every time ?

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  • Understanding tcptraceroute versus http response

    - by kojiro
    I'm debugging a web server that has a very high wait time before responding. The server itself is quite fast and has no load, so I strongly suspect a network problem. Basically, I make a web request: wget -O/dev/null http://hostname/ --2013-10-18 11:03:08-- http://hostname/ Resolving hostname... 10.9.211.129 Connecting to hostname|10.9.211.129|:80... connected. HTTP request sent, awaiting response... 200 OK Length: unspecified [text/html] Saving to: ‘/dev/null’ 2013-10-18 11:04:11 (88.0 KB/s) - ‘/dev/null’ saved [13641] So you see it took about a minute to give me the page, but it does give it to me with a 200 response. So I try a tcptraceroute to see what's up: $ sudo tcptraceroute hostname 80 Password: Selected device en2, address 192.168.113.74, port 54699 for outgoing packets Tracing the path to hostname (10.9.211.129) on TCP port 80 (http), 30 hops max 1 192.168.113.1 0.842 ms 2.216 ms 2.130 ms 2 10.141.12.77 0.707 ms 0.767 ms 0.738 ms 3 10.141.12.33 1.227 ms 1.012 ms 1.120 ms 4 10.141.3.107 0.372 ms 0.305 ms 0.368 ms 5 12.112.4.41 6.688 ms 6.514 ms 6.467 ms 6 cr84.phlpa.ip.att.net (12.122.107.214) 19.892 ms 18.814 ms 15.804 ms 7 cr2.phlpa.ip.att.net (12.122.107.117) 17.554 ms 15.693 ms 16.122 ms 8 cr1.wswdc.ip.att.net (12.122.4.54) 15.838 ms 15.353 ms 15.511 ms 9 cr83.wswdc.ip.att.net (12.123.10.110) 17.451 ms 15.183 ms 16.198 ms 10 12.84.5.93 9.982 ms 9.817 ms 9.784 ms 11 12.84.5.94 14.587 ms 14.301 ms 14.238 ms 12 10.141.3.209 13.870 ms 13.845 ms 13.696 ms 13 * * * … 30 * * * I tried it again with 100 hops, just to be sure – the packets never get there. So how is it that the server does respond to requests via http, even after a minute? Shouldn't all requests just die? I'm not sure how to proceed debugging why this server is slow (as opposed to why it responds at all).

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  • python reports socket in use, netstat and others claim its not

    - by captainmish
    We have a strange socket issue with a RHES3 box: Python 2.4.1 (#1, Jul 5 2005, 19:17:11) [GCC 3.2.3 20030502 (Red Hat Linux 3.2.3-52)] Type "help", "copyright", "credits" or "license" for more information. >>> import socket >>> s = socket.socket() >>> s.bind(('localhost',12351)) Traceback (most recent call last): File "<stdin>", line 1, in ? File "<string>", line 1, in bind socket.error: (98, 'Address already in use') This seems normal, lets see what has that socket: # netstat -untap | grep 12351 {no output} # grep 12351 /proc/net/tcp {no output} # lsof | grep 12351 {no output} # fuser -n tcp 12351 {no output, repeating the python test fails again} # nc localhost 12351 {no output} # nmap localhost 12351 {shows port closed} Other high ports work fine (eg 12352 works) Is there something magic about this port? Is there somewhere else I can look? Where does python find out that socket is in use that netstat doesnt know about? Any other way I can find out what/if that socket is?

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  • How many reverse proxies (nginx, haproxy) is too many?

    - by Alysum
    I'm setting up a HA (high availability) cluster using nginx, haproxy & apache. I've been reading great things about nginx and haproxy. People tend to choose one or the other but I like both. Haproxy is more flexible for load balancing than nginx's simple round robin (even with the upstream-fair patch). But I'd like to keep nginx for redirecting non-https to https among other things right at the point of entry to the cluster. On the other hand, nginx is a lot faster for serving static contents and would reduce the load on the powerful apache which loves to eat a lot of RAM! Here is my planned setup: Load balancer: nginx listens on port 80/443 and proxy_forwards to haproxy on 8080 on the same server to load balance between the multiple nodes. Nodes: nginx on the node listens to requests coming from haproxy on 8080, if the content is static, serve it. But if it's a backend script (in my case PHP), proxy forward to apache2 on the same node server listenning on a different port number. Technically this setup works but my concerns are whether having the requests going through several proxies is going to slow down requests? Most of the requests will be PHP requests as the backends are services (which means groing from nginx - haproxy - nginx - apache). Thoughts? Cheers

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