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  • how to go about scaling a web-application ?

    - by phoenix24
    for someone whoes been primarily a web-application developer, and know not much about scaling/scalability techniques. I'll start by stating my application is written in Python, using Django; a fairly standard setup. I currently use Apache 2.2 for my webserver, and MySql for my database server; both running on the same vps server. Up until now, it was basically a prototype and merely 15-30 concurrent users at any given time; so I had no issues, but now since we'll be adding more users we'll have severe performance issues. So my question is how do i go about scaling my web-application? and my plan is as follows. Now I have just one vps server running, apache + mysql. Next, I plan to add another vps server, to run only MySql; so i'll have one web-server and one db server. Next, I'll add Memcache to the webserver for caching data; and taking some load off mysql. Next, another web-server for serving all the static content; Next, a vps server for load-balancing (nginx/varnish) behind which would be my two web-servers and then db-server. Does that sound like a workable strategy, please guide me around here.

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  • In solaris, how monitor & auto-respond to critical events

    - by mamcx
    I have a website that randomly fail. Is running in open solaris on joyent. I have a monitoring service that alert me when the site is down, but, I want a way to put a "insider" tool that tell me why that happened. Is because the cpu is too high? Not memory? Which process fail? Is possible to have a backtrace of that? Everything is running on the Solaris Service Management Facility. The webserver is cherokee, the database is mysql and the language is python/django. I want the most simple setup to monitor that & auto-respond , ie: restart the webserver or the django process in case of failure. I prefer a low-overhead tool. I don't need the fancy monitoring that some tools have, no ned graphs or sms alert. Only know what fail, restart it if possible (maybe up to n times), and have a log somewhere when I will check it.

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  • Why does my exchange message filtering rule not work?

    - by Jon Cage
    I have two rules set up to sort incoming bug reports. The first is specific to a single device: Apply this rule after the message arrives sent to SMS Distribution and with <source_device_number>: in the body move it to the BugReports\<source_device_number> folder ..and the second is a catch-all for everything else: Apply this rule after the message arrives sent to SMS Distribution move it to the BugReports folder For some reason though, the first rule never seems to act even though it's higher in the list. So for some reason an email like the following doesn't seem to get caught by the first rule: From: <SourceDeviceUID> To: SMS Distributor Subject: Message from <SourceDeviceUID> Message: <source_device_number>: Device encountered a problem. Details below... ...where <source_device_number> is an integer. The second rule works fine. But for some high-priority devices, I want them automatically sorted. Why might that first rule fail?

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  • Radeon 6950 - Garbling of text and graphics in certain Windows only

    - by Greg
    This morning I noticed the text in Gmail (in Firefox 4) looked a little funny (kind of thin, maybe some color fringing). I went to work and thought it might be some ClearType issue or something with the way Direct way that FF4 draws to the screen. When I came back from work (I left the computer on), the problem was much worse - way beyond ClearType nit-picking. The text was barely readable. I opened Chrome and there was no such problem. It seems like only Windows that use hardware acceleration are garbled, and ones that use GDI are not. But, I fired up Dragon Age and didn't notice any problems (I only really looked at the main menu though). Here is a link to a screen shot that illustrates the problem. Notice how the Windows Live Mesh window is completely unreadable, the text in Firefox 4 (left) is pretty bad, while Chrome, the Windows Control Panel, and the task bar are perfectly fine. The fact that the problem shows up in screen shots and that it only happens in certain Windows makes me confident that the problem cannot be with the monitor or DVI cable. I am using the AMD Radeon drivers from 4/27/11. The card I have (MSI Frozr II) came with a slight overclock (810Mhz) out of the box, but it looks like when I'm on the Windows desktop it's not running at full clock (CCC reports 450Mhz). Still, I underclocked it to the stock reference clock (800Mhz) and it made no difference. The idle temperature according to Afterburner is 42-44 Celsius, which seems a tad high but not enough to cause a problem - it's cold to the touch if I open up the machine. What the heck could be causing this? The problem varies in intensity. As we speak I'm in Firefox and things look better than they did earlier - it'll probably get worse again soon. Radeon 6950 (MSI Frozr II), Seasonic X 560, Core i5 2500K at stock clockspeeds, 16GB RAM, Asus P8P67 M Pro

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  • All applications quit when printing on imac OS 10.5.8

    - by Tamany
    Hello and hoping someone might be able to help. Recently ran software update (not sure if problems are associated with this but pretty sure they are as i printed successfully before update. checked log at time of printing: any thoughts on how to fix this? THANKYOU!! 03/05/2010 22:03:15 Microsoft Word[697] * -[NSCFString _getValue:forType:]: unrecognized selector sent to instance 0x17a82b50 03/05/2010 22:03:15 [0x0-0x51051].com.microsoft.Word[697] Ignoring Quickdraw drawing between QDBeginCGContext and QDEndCGContext 03/05/2010 22:03:16 [0x0-0x51051].com.microsoft.Word[697] Ignoring Quickdraw drawing between QDBeginCGContext and QDEndCGContext 03/05/2010 22:03:16 [0x0-0x51051].com.microsoft.Word[697] Ignoring Quickdraw drawing between QDBeginCGContext and QDEndCGContext 03/05/2010 22:03:16 [0x0-0x51051].com.microsoft.Word[697] Ignoring Quickdraw drawing between QDBeginCGContext and QDEndCGContext 03/05/2010 22:03:16 [0x0-0x51051].com.microsoft.Word[697] Ignoring Quickdraw drawing between QDBeginCGContext and QDEndCGContext 03/05/2010 22:03:16 [0x0-0x51051].com.microsoft.Word[697] Ignoring Quickdraw drawing between QDBeginCGContext and QDEndCGContext 03/05/2010 22:03:17 [0x0-0x51051].com.microsoft.Word[697] Mon May 3 22:03:17 leopards-imac-2.local Word[697] : The function CGPDFDocumentGetMediaBox' is obsolete and will be removed in an upcoming update. Unfortunately, this application, or a library it uses, is using this obsolete function, and is thereby contributing to an overall degradation of system performance. Please useCGPDFPageGetBoxRect' instead. 03/05/2010 22:22:09 Microsoft Word[697] * -[NSCFString _getValue:forType:]: unrecognized selector sent to instance 0x1b036500

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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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  • Windows 7 BSOD when changing power plan

    - by dd5
    i have a strange problem. When i want to change the power plan on my laptop from High performance to Balanced, Windows freezes and i get bsod. The power plan settings are all default. Laptop specs: - Intel Core i3 330M/350M - Intel® HM55 Express Chipset - DDR3 1066 MHz SDRAM 8GB - ATI Mobility™ Radeon HD5730 1GB DDR3 VRAM - Intel SSD330 128gb - Windows 7 Home premium I've searched the internets but couldnt find a similar issue. BSOD first started when i installed this SSD and stopped when i've updated the chipset controller driver then started again yesterday when i wanted to change the power settings plan.Minidump file here. Any help with this weird issue appriciated, thanks. Edit: - i've ran Memory diagnostic tool, - Intel SSD diagnostics - and updated the firmware to 3.2.1. Non of these steps worked or shown signs of errors - but still got BSOD when changing power plan settings. After analizing the dump file via osronline.com here a first few lines: CRITICAL_OBJECT_TERMINATION (f4) A process or thread crucial to system operation has unexpectedly exited or been terminated. Several processes and threads are necessary for the operation of the system; when they are terminated (for any reason), the system can no longer function. Arguments: Arg1: 0000000000000003, Process Arg2: fffffa8008661b30, Terminating object Arg3: fffffa8008661e10, Process image file name Arg4: fffff800033de270, Explanatory message (ascii) -- Solution -- Provided by Vinayak: After installing the Intel Rapid storage Technology from MajorGeeks, i didn't experience a BSOD since, thank you :)

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  • Remote paging with Nagios when network is down and email won't work -- cellular modems and alternatives

    - by Quinten
    What is the best option for remote paging when network services are down? I'm looking for a solution that can let me know when network services are down during off-hours only, and especially when email/smtp services are out. Therefore, it needs to be redundant to our network and power supply. I'm imagining a cellular modem is one option. What's the price range for these? Is anybody using them and feel that they are worth the cost? I'm imagining that it's something we would end up sending an emergency page ~ 1x/month at most, so I'd like the pricing to reflect that--I don't mind a high per-page cost as long as it has a low recurring cost. Another option would be to expose at least one server to remote ping, and run a check script on a remote server. Are there paid options for this? Currently, we run Nagios on a Linux VM on a Windows 2008 Hyper-V host. It would be great if the solution would work in that environment, but I know it's tricky with external devices, and we could move Nagios to a standalone workstation if needed.

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  • How to handle sh: fetch: command not found

    - by Tyler Johnson
    Okay, I'm a noobie. I know how to build and compose a website, but I have no idea what I'm doing when it comes to servers and server commands, etc. I've recently had a problem with all of my sites on our servers going down all at once and then I have to go in and reboot the server for them to come up again. At first this was annoying, but now it is becoming agonizing as it now takes 3-4 reboots for the websites to come back up. I contacted support for my hosting, but they are not being very helpful. They just keep telling me what the issue might be and basically telling me that I'm going to have to look into it and figure it out, which really isn't possible since I know nothing. Anyway, here are the things they said were possible reasons: They said I have "strange logs" in my Apache webserver log, error: sh: fetch: command not found. My php.ini memory limit is: 256M which is very high. It should be 32M or 64M. Server is reaching Max Clients, meaning we have more than 150 visitors at a time. (They supposedly "fixed" this, but the sites/server are still going down) I have some Wordpress sites with plugins getting errors like: PHP Warning: pack(): Type H: illegal hex digit G in... PHP Fatal error: Cannot use object of type stdClass as array in... PHP Fatal error: Maximum execution time of 30 seconds exceeded in... PHP Fatal error: Call to undefined function file_exists() in... PHP Parse error: syntax error, unexpected '<' I know that's a lot, but I really am at wits end and have no idea what to do now. If anyone could maybe give me some advice or point me in the right direction I would greatly appreciate it! Thanks! Oh, and here are the specs for my server: RAM: 2048MB CPU Shares: 40 Primary Disk: 50GB Data Transfer: 75GB Port Speed: 5Mbps

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  • TCP Server Memory management: #Connections Vs. #Requests

    - by Andrew
    Given that, there is no theoretical limit to number of concurrent TCP connections a Windows 2008 server can handle. Only thing will happen is, with each connection there will be memory consumption in server. Unfortunately, memory is not unlimited (and I want to utilize only physical memory). For example, lets say we've 2GB server memory. Now there are two extreme cases: Case 1: If we've allocated 64KB buffer for each connection (only to receive incoming request), then 32768 connections can consume all the 2GB of memory. This will not leave any memory to queue/process incoming requests from those connections. Case 2: On the other hand, lets say a single (or very few) connections continuously keeps sending request buffers (for example, video streaming from one connection to other) and server cannot process them within time, those buffers will get piled up in server and eventually will occupy most of the servers memory. And it will not leave any memory for new connection thereafter. This is the real dilemma in server design bugging me badly for last many days. If I can decide on max size of request buffer per connection and max number of requests to allow in queue per connection. Then, based on available server memory, it will then automatically set limit on max number of concurrent connections. How to decide on these limits to achieve best performance and throughput? I am just looking for perfect utilization of server resources. Are there any standard guidelines or empirical data available with someone who can share with me please.

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  • Nagios check_host_alive and check_ping not showing host as down

    - by Kyle
    I am using the check_host_alive command to send 5 packets every minute to all my routers at remote locations. I noticed today I received a notification from The AT&T Global Client Support Center that a router was down (which can take 5-30 minutes to send these notices out) and never received a notice from Nagios. I went onto Nagios and it is was showing the host as alive with a latency of 0ms. This tells me it is seeing the automated response from my router in the data center that, "TTL expired in transit" as a reply from the remote router. Is there anyway for me to tell nagios to check where the reply is comming from? I feel like other people have to of had this issue... I tested it with the check_ping command and it produced the same results. I have the command defined has %hostname% and the proper IP in the host definition, and it works fine for telling me the latency is high. Any ideas are welcome, I have already exercised my Google skills with no results. EDIT: root@IM-UBTU:/# /usr/local/nagios/libexec/check_ping -H 192.168.250.1 -w 100.0,10% -c 200.0,20% -vvv CMD: /bin/ping -n -U -w 10 -c 5 192.168.250.1 Output: PING 192.168.250.1 (192.168.250.1) 56(84) bytes of data. Output: From 10.69.10.2 icmp_seq=1 Time to live exceeded It knows something is wrong why doesn't it give me a warning?

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  • Membership in two domains

    - by imagodei
    Hello! I would your suggestions for an effective solution for a person, who needs to access resources in two Windows domains and wants to use one computer. It's about our CEO, who has accepted a second position in another company. Accessing files and folders isn't big problem. The greatest challenge I see is that he wants to conveniently access Exchange accounts in both companies; he would like to send and receive mail in single Outlook if possible (two profiles?) There is also a challenge with calendars: he would like to have one calendar for all activities from both Exchange accounts. Creating a POP3 account for accessing second Exchange server is a last resort, because obviously there is a problem with scheduling meetings and other calendar related tasks. Forwarding and receiving all mail/tasks on primary Exchange server is inconvenient because simple replying to original sender is disabled; and also when manually changing the recepient, he will receive mail from the wrong address. We were considering Virtualisation, that is setting up an instance of virtual machine inside existing installation and then joining this virtual computer to a second domain. Then installing another MS Outlook. This would of course mean two different Outlook accounts, two different calendars, but would at least enable our CEO to access all information from a single laptop. Does anyone have any other idea? I know setting up two domains on a single computer is a no-go (without much hacking at least), but effective workarounds are appreciate. The thing I am looking here is high usage/efficiency/productivity, but also as elegant solution from the administration point of view. Thank you very much (if you managed to read this through, this is a good sign ^_^ )

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  • Time-Machine backup over SSH tunnel to NFS mount

    - by BTZ
    I've recently started using a new NAS which runs CentOS 6.2. One of the purposes of the NAS would be to serve as a backup target. Whilst I have been using Apple's Time-Machine for a while and I am very satisfied with it, I'd like to continue using it. Backing up directly to an address in my network is no hassle; all works fine. For security reasons I'd like all my traffic to go through an ssh tunnel to the NAS. This way I can avoid needing to get a VPNserver (for personal reasons). As of NFSv4 the NFS deamon is bound to port 2049, which makes it easy for me to direct all traffic through a ssh tunnel. Tunnel: ssh -f admin@ms -L 2000:localhost:2049 -N Mount: mount -t nfs -o nfsvers=4,rw,proto=tcp,sync,intr,hard,timeo=600,retrans=10,wsize=32768,rsize=32768,port=2000 localhost:/mac_backup /Volumes/backup This works fine for Finder/terminal and throughput is almost equal to direct traffic. (CPU of the NAS does ride high when I reach max bandwidth though) Now the problem: With Time-Machine I can't use the NFS mount point mounted on localhost. TM seems to try to connect to it and then give me a "OSStatus error 65". I also tried using NFSv3 (I correctly forwarded all ports) with no luck. Can anyone shed a light on this and/or give a solution?

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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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  • IIS crashes with unhandled exception in ASP.NET

    - by SnowCrash
    We had an issue recently with an unhandled exception in an ASP.NET C# application bringing down IIS and all application pools that it was hosting. IIS Manager was unable to restart or stop/start the service and I was unable start IIS again after killing w3wp.exe in the task manager. A system reboot restored IIS to a running state; as a primarily Linux admin, I generally consider an unplanned system reboot to resolve a software error to be an act of high heresy. Is there a way to "harden" IIS so that a faulting application does not affect anything but the request that exposes the fault? Some details on the server and application fault. IIS: 7.5 .NET: 4.0 Windows Server 2008 R2 Faulted on call to System.Net.Dns.Resolve() with a url pointing to a non-existant domain as the argument. (I'm aware that this method is deprecated but the point that a page code issue shouldn't bring down the server still stands) The exception generated was SocketException. The faulting module according to event viewer was KERNELBASE.dll The issue was resolved by wrapping the call in a try-catch, logging the exception and displaying some generic content on the page. I'm hoping that I missed something in the IIS config that would switch it to "production" mode or something.

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  • Best video codec to store my own collection

    - by Jack
    Hello! I think this question has already been asked but with different flavours. My problem resised in the fact that my camera (Canon G9) creates video with almost raw codec (I think it's plain old MPEG) so a 10 minutes video is almost 900mb. I would like to convert them in a format that has a good trade-off between space and quality, but I would prefer having the quality as good as the original (of course this is not possible because of lossy compression) just saving as much space is possible with a minimal lose of quality. Which codec should I look for? H264? It seems to be the champion of the moment.. otherwise which other ones could I try? XviD? Which parameters should I use? I mean how many kbits/s is a fair good bitrate to keep high quality? And what about audio codec? video specs are 640x480 at 30fps or 1024x768 at 15fps.. thanks in advance!

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  • Live Screencast under Linux

    - by OmnipotentEntity
    I was having some difficulty with running a Live Screencast under Linux. I've found jtvlc and tried using that, but whenever I use it the stream comes out either blank or lagged with extremely high latency. I have a fast internet connection and a fast computer, but am I perhaps taxing it too much? Any ideas on what I could possibly be doing wrong? # 1. Get an account on http://www.justin.tv/ # 2. Copy streaming key from: http://www.justin.tv/broadcast/adv_other # 2. Install VLC: http://www.videolan.org/vlc/ # 3. Get Win/Mac/Lin Stream Client: \ # http://apiwiki.justin.tv/mediawiki/index.php/Linux_Broadcasting_API # 4. Adjust the vlc parameters to your liking and run VLC like this #!/bin/bash cvlc screen:// --input-slave=pulse:// \ --screen-width 1920 \ --screen-height 1080 \ --screen-fps 5 \ -v input_stream \ --sout='#duplicate{ dst="transcode{ scale=1, venc=x264{ keyint=60 }, vcodec=h264, vb=600, acodec=mp4a, ab=32, channels=2, samplerate=22050 } :rtp{dst=127.0.0.1,port=1234,sdp=file:///tmp/vlc.sdp} "}' \ --sout-transcode-threads=4 & sleep 2 # 5. Run JTVLC to stream like this: ./jtvlc/jtvlc omnipotententity censored /tmp/vlc.sdp # Notes: #- If you want to see what you're about to stream add 'dst=display, ' # before 'dst="transcode[' # More about the VLC parameters: http://wiki.videolan.org/Documentation:Modules/screen

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  • How to interrupt software raid resync?

    - by Adam5
    I want to interrupt a running resync operation on a debian squeeze software raid. (This is the regular scheduled compare resync. The raid array is still clean in such a case. Do not confuse this with a rebuild after a disk failed and was replaced.) How to stop this scheduled resync operation while it is running? Another raid array is "resync pending", because they all get checked on the same day (sunday night) one after another. I want a complete stop of this sunday night resyncing. [Edit: sudo kill -9 1010 doesn't stop it, 1010 is the PID of the md2_resync process] I would also like to know how I can control the intervals between resyncs and the remainig time till the next one. [Edit2: What I did now was to make the resync go very slow, so it does not disturb anymore: sudo sysctl -w dev.raid.speed_limit_max=1000 taken from http://www.cyberciti.biz/tips/linux-raid-increase-resync-rebuild-speed.html During the night I will set it back to a high value, so the resync can terminate. This workaround is fine for most situations, nonetheless it would be interesting to know if what I asked is possible. For example it does not seem to be possible to grow an array, while it is resyncing or resyncing "pending"]

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  • Apache directory authorization bug (clicking cancel gives acces to partial content)

    - by s4uadmin
    I got a minor problem (as the site is not high priority) but still a very interesting one. I have an apache root domain wherein other sites live "/var/www/" And I have foo.example.com forwarding to "/var/www/foo-example" (wordpress site) The problem here is that when you go to foo.example.com you are prompted to enter credentials. If you hit cancel it gives you the access denied page. But when you go to the servers' direct IP (this gives you the default index page) and hit cancel when prompted for credentials it just keeps giving you the login screen, and after pressing cancel a few times more it gives (a perhaps cached) bare html part of the page. How do I prevent this from happening? Perhaps this is a bug... Even if I would block access to the root directory when going to the ip/foo-example it would still do this. And I want to keep all the directories within the www directory or at least all in the same. Thanks PS: here is my configuration: <VirtualHost *:80> DocumentRoot /var/www/wp-xxxxxxx/ ServerName beta.xxxxxxxxx.nl <Directory "/var/www/wp-xxxxxxxxx/"> Options +Indexes AuthName "xxxxxxxx Beta Site" AuthType Basic require valid-user Satisfy all AuthBasicProvider file AuthUserFile /var/www/wp-xxxxxxx/.htxxxxxxxxx order deny,allow allow from all </Directory> ServerAdmin [email protected] ServerAlias beta.xxxxxxx.nl </VirtualHost>

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  • Is execution of sync(8) still required before shutting down linux?

    - by Amos Shapira
    I still see people recommend use of "sync; sync; sync; sleep 30; halt" incantations when talking about shutting down or rebooting Linux. I've been running Linux since its inception and although this was the recommended procedure in the BSD 4.2/4.3 and SunOS 4 days, I can't recall that I had to do that for at least the last ten years, during which I probably went through shutdown/reboot of Linux maybe thousands of times. I suspect that this is an anachronism since the days that the kernel couldn't unmount and sync the root filesystem and other critical filesystems required even during single-user mode (e.g. /tmp), and therefore it was necessary to tell it explicitly to flush as much data as it can to disk. These days, without finding the relevant code in the kernel source yet (digging through http://lxr.linux.no and google), I suspect that the kernel is smart enough to cleanly unmount even the root filesystem and the filesystem is smart enough to effectively do a sync(2) before unmounting itself during a normal "shutdown"/"reboot"/"poweorff". The "sync; sync; sync" is only necessary in extreme cases where the filesystem won't unmount cleanly (e.g. physical disk failure) or the system is in a state that only forcing a direct reboot(8) will get it out of its freeze (e.g. the load is too high to let it schedule the shutdown command). I also never do the "sync" procedure before unmounting removable devices, and never hit a problem. Another example - Xen allows the DomU to be sent a "shutdown" command from the Dom0, this is considered a "clean shutdown" without anyone having to login and type the magical "sync; sync; sync" first. Am I right or was I lucky for a few thousands of system shutdowns?

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  • Connect to Nonencrypted Wireless Network Using Ubuntu Commands

    - by Tim
    I failed to connect to an open i.e. nonencrypted wireless network using Ubuntu command lines. Here is what I did: $ sudo /etc/init.d/NetworkManager stop * Stopping network connection manager NetworkManager [ OK ] $ sudo /sbin/ifconfig wlan0 up $ sudo iwconfig wlan0 essid "Cavalier High-Speed 866-4-CAVTEL" $ sudo dhclient wlan0 There is already a pid file /var/run/dhclient.pid with pid 10812 killed old client process, removed PID file Internet Systems Consortium DHCP Client V3.1.1 Copyright 2004-2008 Internet Systems Consortium. All rights reserved. For info, please visit http://www.isc.org/sw/dhcp/ wmaster0: unknown hardware address type 801 wmaster0: unknown hardware address type 801 Listening on LPF/wlan0/00:0e:9b:cd:4e:18 Sending on LPF/wlan0/00:0e:9b:cd:4e:18 Sending on Socket/fallback DHCPREQUEST of 192.168.1.67 on wlan0 to 255.255.255.255 port 67 DHCPREQUEST of 192.168.1.67 on wlan0 to 255.255.255.255 port 67 DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 7 DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 7 DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 8 DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 12 DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 21 DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 6 No DHCPOFFERS received. Trying recorded lease 192.168.1.67 PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data. --- 192.168.1.1 ping statistics --- 1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms Trying recorded lease 192.168.1.45 PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data. --- 192.168.1.1 ping statistics --- 1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms No working leases in persistent database - sleeping. $ sudo /sbin/iwconfig wlan0 wlan0 IEEE 802.11bg Mode:Managed Frequency:2.422 GHz Access Point: Not-Associated Tx-Power=27 dBm Retry min limit:7 RTS thr:off Fragment thr=2352 B Encryption key:off Power Management:off Link Quality:0 Signal level:0 Noise level:0 Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:0 Invalid misc:0 Missed beacon:0 I was wondering what the problem is and how I can do it right? Thanks and regards!

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  • Strange battery behavior on laptop

    - by EpsilonVector
    My laptop is behaving rather strangely lately, and I was hoping to get some idea as to what may be causing such symptoms. The problem: When charging, very minute or so it loses connectivity with the AC adapter for a split second, and regains it back immediately. When this happens the little light that indicates the computer is plugged in does flicker off and back on, but I checked the adapter by replacing the battery on my laptop, and this indeed solves the problem, so it is probably the battery which is at fault, not the adapter (I also tried to move the adapter's wire around just to make sure it had nothing to do with torn wires). I suppose that the obvious solution is to get a new battery, but as far as battery defects go- this is a rather strange one; it loses connection with the adapter, but still powers the computer, and changing the power setting to a balanced plan (was maximum performance) seem to have solved the problem too. Is there a chance this is not simply the battery, but some kind of other electronic defect? And if not, what can cause it to behave so strangely? PS I tried to recalibrate it- didn't help.

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  • Loads of memory in "standby" on Windows Server 2008 R2

    - by Jaap
    In our SharePoint farm, our Web Front End servers all have loads of memory in "standby" mode, meaning very little is available for our IIS worker process. We have 32 GB of RAM in each of the boxes, and standby memory will creep up to about 28 GB, whereas the IIS worker process only seems to be using about 2 GB. Also, we've seen the machine use the swap file extensively while this memory was in standby, so I am starting to think that this memory in standby mode is stopping IIS from using it, forcing it to swap to disk, causing more performance problems. I used SysInternals RamMap to indentify what is being kept in memory, and it was able to tell me that almost everything in standby memory is of type "Mapped File". When I sort the files listed under the file summary tab in RamMap by file size, the largest files (around a few hundred meg each) are IIS log files and SharePoint log files. I would like to understand which process is loading these files into standby memory and why they are not being released. When I do an iisreset, it does not release the memory. Any ideas? Thanks!

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  • EMC VNX iSCSI setup - unsure about SP/port assignment

    - by pauska
    We have a new VNX5300 waiting to get configured, and I need to plan out the network infrastructure before the EMC tech arrives. It has 4x1gbit iSCSI per SP (8 ports in total), and I'd like to get the most out of the performance until we jump over to 10gig iSCSI. From what I can read from the docs - the recommendation is to use only two ports per SP, with 1 active and 1 passive. Why is this? It seems kind of pointless to have quad-port i/o-modules and then recommend to not use more than two of them? Also - I'm a bit unsure about the zoning. The best practices guide state that you should separate each port on each SP from each other on different logical networks. Does this mean that I have to create 4 logical networks to be able to use all 8 ports? It also gives the following example: Does this mean that A0 and B0 should sit on the same physical switch aswell? Won't this make all traffic go on one switch (if both A1 and B1 are passive)? Edit: Another brainpuzzle I don't get it - each host (as in server) should not have more iSCSI bandwidth available than the storage processor. What on earth does this matter? If serverA have 1gbit and serverB have 100mbit, then the resulting bandwith between them is 100mbit. How can this result in some kind of oversubscription? Edit4: Wait, what. Active and passive ports? The VNX runs in a ALUA configuration with asymmetrical active/active.. there shouldn't be any passive ports, only preferred ones..

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  • Is Cherokee (probably) the best static content server for beginner sysadmins?

    - by Bad Learner
    I have read the pros and cons of most of the popular web servers and have come to a conclusion that Apache would (probably) be the best web server for serving dynamic content - - no wonder YouTube, Flickr and Facbook, among many others, use it. I do not know if that C10K problem applies to Apache even when serving dynamic content only, but I think any web server used to serve dynamic content needs some good tweaking for optimized performance, and the fact that nothing beats Apache when it comes to documentation, resources and support on the web, I think should will go with Apache for dynamic content. That apart, the confusion begins when it comes to choosing web servers for static content (including streaming videos). I see that Nginx, Cherokee and Lighttpd are among the best (I am not considering non-open source or non-linux stuff here). So, which too choose? I know one cannot go wrong with any of the three (Nginx, Cherokee, Lighttpd). Lighttpd's development has evidently gotten slower than it was a good time ago. The documentation is pretty good for all the three, and hopefully, so are the resources (knowledge of these among the users of Stackoverflow/Serverfault sites, the web etc). Precisely, and noting point [2] and [3], if I am not wrong, I should either go with Nginx or Cherokee. I would love to see someone clarify these... is Cherokee just as fast (mb/s), performant (connections/s), and reliable (think downtime/restarting server) as Nginx for serving static content and load balancing, for small, medium to large (and really large) websites and applications? (Think, the size of YouTube, Apache or Facebook.) if the answer for the Q above is a big "hell, yes!" then, I should probably prefer Cherokee, right? Because, since I am a beginner, it would a lot easier to setup Cherokee as it has a graphical admin user interface + really good documentation. Yes? I could be wrong, I could be right. I put down what I know so that you can offer most relevant advise. Pardon if anything I've said is offensive.

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