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• Lots of dropped packages when tcpdumping on busy interface

  - by Frands Hansen

  My challenge I need to do tcpdumping of a lot of data - actually from 2 interfaces left in promiscuous mode that are able to see a lot of traffic. To sum it up Log all traffic in promiscuous mode from 2 interfaces Those interfaces are not assigned an IP address pcap files must be rotated per ~1G When 10 TB of files are stored, start truncating the oldest What I currently do Right now I use tcpdump like this: tcpdump -n -C 1000 -z /data/compress.sh -i any -w /data/livedump/capture.pcap $FILTER The $FILTER contains src/dst filters so that I can use -i any. The reason for this is, that I have two interfaces and I would like to run the dump in a single thread rather than two. compress.sh takes care of assigning tar to another CPU core, compress the data, give it a reasonable filename and move it to an archive location. I cannot specify two interfaces, thus I have chosen to use filters and dump from any interface. Right now, I do not do any housekeeping, but I plan on monitoring disk and when I have 100G left I will start wiping the oldest files - this should be fine. And now; my problem I see dropped packets. This is from a dump that has been running for a few hours and collected roughly 250 gigs of pcap files: 430083369 packets captured 430115470 packets received by filter 32057 packets dropped by kernel <-- This is my concern How can I avoid so many packets being dropped? These things I did already try or look at Changed the value of /proc/sys/net/core/rmem_max and /proc/sys/net/core/rmem_default which did indeed help - actually it took care of just around half of the dropped packets. I have also looked at gulp - the problem with gulp is, that it does not support multiple interfaces in one process and it gets angry if the interface does not have an IP address. Unfortunately, that is a deal breaker in my case. Next problem is, that when the traffic flows though a pipe, I cannot get the automatic rotation going. Getting one huge 10 TB file is not very efficient and I don't have a machine with 10TB+ RAM that I can run wireshark on, so that's out. Do you have any suggestions? Maybe even a better way of doing my traffic dump altogether.

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• Loss of wireless network connectivity when playing video via HDMI cable

  - by Jeff Fohl

  Hi Folks - New to Super User, so I hope this question fits in with the guidelines. Very strange problem I am having, and I am at a loss as to how to continue troubleshooting this one. The basic problem is that when I attempt to watch streamed video on a particular display device (an Optoma HD180 projector), my network connectivity drops like a stone to barely measurable levels. This is my setup: I have a Dell H2C 730x running Windows 7 64bit. This particular computer has two ATI Radeon HD 4800 video cards. I have two Samsung 22" monitors connected to one card, and an Optoma HD180 digital projector connected to the other card via an HDMI cable. My internet connection is normally a reliable 6Mbps. The problem I am having occurs when I stream video (or even just browse the web) on the Optoma Projector. When I do this, my internet connection drops to practically zero (just a few kilobits per second). When I move the browser away from the projector, and over to one of my Samsung monitors, the internet connection comes right back. Note that the Optoma projector is on and enabled as a third monitor all this time. I can move the mouse around on the projector without triggering the problem. I tried pinging my router when I was playing a movie on one of the monitors, and I get a 1 millisecond response. However, when I have the movie playing on the Optoma projecter, pinging the router gives me response times in the hundreds of milliseconds, or times out completely. So, it clearly is something local to my machine - and not some sort of throttling occurring down the line. I would think that it is possibly something to do with the HDMI driver conflicting somehow with my network driver (which is a USB-based wireless connection). This one has me really stumped. Anyone have any ideas? EDIT: I am now leaning towards the possibility that the HDMI cable is somehow interfering with the wireless network, when large amounts of data are being pushed through the cable. Is this possible?

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• Exchange-Server Query

  - by Rudi Kershaw

  First, a little background. I've recently been taken on as a web and software developer for a small company, who has no other in-house IT support. They've been asking my opinion on lots of IT subjects that are quite far out of my comfort zone. I'm definitely not a network admin. Their IT consultancy contractor is pushing them to upgrade their dedicated exchange server, even though it seems like the one they currently have has a lot of life left in it and is running problem free. They say it's "coming to the natural end of it's life". They want to install a monster with a Xeon E5-2420, 32GB RAM, 2x 1TB HDDs, Windows Server 2012 and Microsoft Exchange 2010. They want to charge a small fortune for it. Basically, this system seems massively over the top seeing as it won't be doing anything else other than running as an exchange server for a company with less than 25 email accounts. My employers also have a file server system in-house that hosts three web apps, an SQL server, their local domain, print server and shared folders. That machine is using the same specs as the proposed new one, and it is barely using any of it's potential. I asked if Microsoft Exchange 2010 could be installed on their file server, but they said that MS Exchange can't run on the same system as an SQL server because for some reason they will eat up each others resources (even though the SQL server isn't touching 1% of the current system's CPU or RAM). My question is really, are they trying to rip my employers off? Could MS Exchange be installed on their other server (on a virtual instance or not), or does the old one even need replacing at all? Going with their current suggestion will cost the company in excess of £6k, and it seems entirely unnecessary. I apologies, because I know this is probably a little thin on details, but if I carry on I could end up writing a massive essay that no-one will want to read. I've been doing my research, but I'm not knowledgeable enough make any hard decisions. Let me know if you need any more details. Thank you for any help you can offer. Further Details: The new exchange would need to support Outlook Web App, 25 users, a few public mailboxes, and email exchange with Blackberries.

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• How to disable or tune filesystem cache sharing for OpenVZ?

  - by gertvdijk

  For OpenVZ, an example of container-based virtualization, it seems that host and all guests are sharing the filesystem cache. This sounds paradoxical when talking about virtualization, but this is actually a feature of OpenVZ. It makes sense too. Because only one kernel is running, it's possible to benefit from sharing the same pages of filesystem cache in memory. And while it sounds beneficial, I think a set up here actually suffers in performance from it. Here's why I think why: my machines aren't actually sharing any files on disk so I can't benefit from this feature in OpenVZ. Several OpenVZ machines are running MySQL with MyISAM tables. MyISAM relies on the system's filesystem cache for caching of data files, unlike InnoDB's buffer pool. Also some virtual machines are known to do heavy and large I/O operations on the same filesystem in the host. For example, when running cat *.MYD > /dev/null on some large database in one machine, I saw the filesystem cache lowering in another, monitored by htop. This essentially flushes all the useful filesystem cache in guests (FIFO) and so it flushes the MySQL caches in the guests. Now users are complaining that MySQL is very slow. And it is. Some simple SELECT queries take several seconds on times disk I/O is heavily used by other machines. So, simply put: Is there a way to avoid filesystem cache being wiped out by other virtual machines in container-based virtualization? Some thoughts: Choosing algorithm for flushing filesystem cache in the kernel. (possible? how?) Reserving a certain amount of pages for a single VM. (seems no option for filesystem cache type of pages that reading man vzctl) Will running MySQL on another filesystem get me anywhere? If not, I think my alternatives are: Use KVM for MySQL-MyISAM running VMs. KVM actually assigns memory to the VM and does not allow swapping out caches unless using a balloon driver. Move to InnoDB and tune the buffer pools, dirty pages, etc. This is now considered to be 'nice to have' on the long-term as not everyone responsible for administration of the system understands InnoDB. more suggestions welcome. System software: Proxmox (now 1.9, could be upgraded to 2.x). One big LV assigned for the VMs.

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• nginx + Jetty - thousands of connections stuck in LAST_ACK

  - by virulence

  I have a FreeBSD machine with jails -- two in particular, one that runs nginx and another that runs a Java program that accepts requests via Jetty (embedded mode) Jetty receives upwards of 500 requests/sec constantly and there has been an issue lately where I will constantly have over 60,000 connections in the LAST_ACK state between nginx and jetty. Distribution of all connections (includes some other services, particularly php-fpm) root@host:/root # netstat -an > conns.txt root@host:/root # cat conns.txt | awk '{print $6}' | sort | uniq -c | sort -n 18 LISTEN 112 CLOSING 485 ESTABLISHED 650 FIN_WAIT_2 1425 FIN_WAIT_1 3301 TIME_WAIT 64215 LAST_ACK Distribution of nginx - jetty connections root@host:/root # cat conns.txt | grep '10.10.1.57' | awk '{print $6}' | sort | uniq -c | sort -n 1 3 CLOSE_WAIT 3 LISTEN 18 FIN_WAIT_2 125 ESTABLISHED 64193 LAST_ACK I'd prefer every request to fully close the connection. Clients requests are about 10 minutes apart from each other so connections must be closed. Some of the connections, tcp4 0 0 10.10.1.50.46809 10.10.1.57.9050 LAST_ACK tcp4 0 0 10.10.1.50.46805 10.10.1.57.9050 LAST_ACK tcp4 0 0 10.10.1.50.46797 10.10.1.57.9050 LAST_ACK tcp4 0 0 10.10.1.50.46794 10.10.1.57.9050 LAST_ACK tcp4 0 0 10.10.1.50.46790 10.10.1.57.9050 LAST_ACK tcp4 0 0 10.10.1.50.46789 10.10.1.57.9050 LAST_ACK tcp4 0 0 10.10.1.50.46771 10.10.1.57.9050 LAST_ACK etc.. On Jetty's end I've set maxIdleTime to 2000 -- before this all connections were in ESTABLISHED but they are now LAST_ACK On Jetty's end I've set Connection: close (i.e response.setHeader(HttpHeaders.CONNECTION, HttpHeaderValues.CLOSE);) Jetty never reports a lot of open connections -- always very few. PF/IPFW is not currently being used nginx - reset_timedout_connection is on I cannot figure out how to get nginx or jetty to forcibly close the connection, is this simply something that needs to be fixed in Jetty so that it fully closes the socket after the request finishes? Thanks a lot in advance EDIT: forgot my nginx config for the proxy setup- proxy_pass http://10.10.1.57:9050; proxy_set_header HTTP_X_GEOIP $http_x_geoip; proxy_set_header GEOIP_COUNTRY_CODE $geoip_country_code; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_set_header Host $http_host; proxy_set_header Connection ""; proxy_http_version 1.1; EDIT2: Forcing Jetty to close the connection via request.getConnection().getEndPoint().close() does nothing -- it's obvious the connection IS being closed (as it's in LAST_ACK) but why isn't it getting past this? Is Nginx keeping the connection open to the backend for some reason?

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• How to setup GIT repo on server with need for working dir (non- bare)

  - by OrangeTux

  I want to have configurate a GIT repo for a website. Multiple users will have a clone of the repo on their local machine and on the end of each day they push their work to the server. I can setup a bare repo, but I want a working dir/non-bare repository. The idea is that the working dir of the repository will the root folder for the website. At the end of each day all changes will be visible directly. But I can't find a way to do this. Initializing the server repo with git init gives the following error when a client is trying to push some files: git push origin master [email protected]'s password: Counting objects: 3, done. Writing objects: 100% (3/3), 227 bytes, done. Total 3 (delta 0), reused 0 (delta 0) remote: error: refusing to update checked out branch: refs/heads/master remote: error: By default, updating the current branch in a non-bare repository remote: error: is denied, because it will make the index and work tree inconsistent remote: error: with what you pushed, and will require 'git reset --hard' to match remote: error: the work tree to HEAD. remote: error: remote: error: You can set 'receive.denyCurrentBranch' configuration variable to remote: error: 'ignore' or 'warn' in the remote repository to allow pushing into remote: error: its current branch; however, this is not recommended unless you remote: error: arranged to update its work tree to match what you pushed in some remote: error: other way. remote: error: remote: error: To squelch this message and still keep the default behaviour, set remote: error: 'receive.denyCurrentBranch' configuration variable to 'refuse'. To ssh://[email protected]/home/orangetux/www/ ! [remote rejected] master -> master (branch is currently checked out) error: failed to push some refs to 'ssh://[email protected]/home/orangetux/www/' So I'm wondering if this the right way to setup a GIT repo for a website? If so, how do I have to do this? If not, what is a better way to setup a GIT repo for the development of a website? EDIT you can't push to a non-bare repository Oke, clear. But whats the way to solve my problem? Create a bare repository on the server and have a clone of this repo on the same server in the htdocs folder? This looks a bit clumsy to me. To see the result of a commit I've to clone the repository each time.

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• Monitoring the status of accounts with IT Service providers (ISP, Domain Registrar etc.)

  - by Sholom

  Hi All, Short version: You have software that tells you when your servers power-outlet is down. It monitors multiple servers from one management console, alerts you when something is wrong etc. Does anyone know of software that will let me take the same approach to monitor if the money-outlet (the bill!) is down (not paid) to my IT Services providers (ISP, Domain Registrar, MX Backup service etc). I need a top down, centrally managed service that is capable of sending out alerts. Just like the one that monitors my own exchange server etc. I don't mind if i have to manually enter every payment. Long version: Our very likable but absent minded bookkeeper keeps neglecting to pay our IT vendors on time. Just this past week our internet service was disconnected. Same could happen to many other mission critical accounts (domain registrar, backup MX, anti-virus license, HackerSafe (McAfee secure) service and even an 800 number to name a few). As the sysadmin, i monitor my severs to make sure they are plugged into the power-outlet. I believe i should also monitor my services to make sure they are plugged in to their money-outlet. To compound the problem, when the power goes out someone else will likely notice and notify me. But if a bill is not payed, no one will ever notice until service is lost. Lost as in losing our domain name which would cause a lot more damage then the power failing on our server. [Solution] = [Doesn't work because]: Retrain the bookkeeper = Wishful thinking. Notify my manager = Already have (via email). Protects me, does not solve problem. Fire bookkeeper = What makes you so sure the next one will never forget? Bottom line: Humans are humans and sooner or later something critical will be royally messed up. We need to partner with a machine to help us out here. Anybody have the same problem? What software/solution do you use? I would like software that emails me when a bill is passed due just like i get an email when the power outlet fails. Anyone hear of anything like that? Thanks

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• Event ID 17890 (A significant part... paged out.) with SQL Server 2008

  - by Godeke

  I have a machine that has SQL Server 2008 Standard installed. Periodically (about once an hour) I am getting Event ID 17890 several times in a row. An example: 6:28:54 "A significant part of sql server process memory has been paged out. This may result in a performance degradation. Duration: 0 seconds. Working set (KB): 10652, committed (KB): 628428, memory utilization: 1%%. 6:34:27 "A significant part of sql server process memory has been paged out. This may result in a performance degradation. Duration: 332 seconds. Working set (KB): 169780, committed (KB): 546124, memory utilization: 31%%." 6:38:55 "A significant part of sql server process memory has been paged out. This may result in a performance degradation. Duration: 600 seconds. Working set (KB): 245068, committed (KB): 546124, memory utilization: 44%%." This pattern repeated at 7:26 - 7:37, 8:26 - 8:36, 9:24 - 9:35 and so with the same increasing working set and memory utilization pattern. I don't have any (known) background tasks running at this time. Backups run at 2:00 This subsided from 11:00 at night until it resumed at 4:00 in the morning and has been continuing the intermittent 10 minute glitch periods. As this server has plenty of RAM (the commit charge has peaked at 2,871,564 of 4,194,012 physical) I disabled the paging files after reading several items I dug up searching Google and not finding any of them changing the situation. This pattern I am documented is after removing the paging files, so I'm not even sure where we are paging the SQL process could be going. I also changed the SQL process memory to have a minimum of 500MB and a maximum of 2GB of RAM (as this is a light duty database server serving only a small workgroup). Has anyone encountered this? Prior to disabling the page files this error would cause 5 minutes of disk thrashing that disabled access to the databases, files, IIS webs and so on. Since disabling the page files it just logs strange things, but I'm not seeing a performance drop at least. Any suggestions would be welcome.

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• freebsd-update from 8.3-RELEASE to 9.0-RELEASE: How to deal with dozens of diffs?

  - by Stefan Lasiewski

  I am upgrading a FreeBSD 8.3-RELEASE system to FreeBSD 9.0-RELEASE using freebsd-update. This is my first time performing a major version upgrade in FreeBSD. At one point in the process, freebsd-update performs a diff on files which are different then what is expected for the 9.0-RELEASE. It compares the current version on the system with the new changes added from 9.0-RELEASE. There are dozens of files in the list. Thus, I am presented with dozens and dozens of diffs which open in a vi window and look like this: The following file could not be merged automatically: /etc/ntp.conf Press Enter to edit this file in vi and resolve the conflicts manually... ### vi window opens <<<<<<< current version driftfile /etc/ntp/drift ======= # # $FreeBSD: release/9.0.0/etc/ntp.conf 195652 2009-07-13 05:51:33Z dwmalone $ # # Default NTP servers for the FreeBSD operating system. # # Don't forget to enable ntpd in /etc/rc.conf with: # ntpd_enable="YES" # # The driftfile is by default /var/db/ntpd.drift, check # /etc/defaults/rc.conf on how to change the location. # >>>>>>> 9.0-RELEASE restrict default notrust nomodify ignore And so on. This requires that I manually edit each file and remove the strings like <<<<<<< current version >>>>>>> 9.0-RELEASE and =======. As I discovered afterwards, if I don't remove these strings, they end up in the file afterwards. There are dozens of files which differ between 8.3 and 9.0, and I have a dozen local modifications myself. It appears that freebsd-update is using a diff, sdiff or mergemaster function of some sort, but I can't tell what it is doing exactly. Processing these files is tedious. Is there a way that I can just say "Accept new version" or "keep old version" or "Your merge is correct"? There has got to be an easier way to deal with these files. I must be missing something. This isn't a huge problem for one machine, but eventually I'll be doing this dozens of times and I want to find an easier way.

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• Vista stuck at "Shutting down..." screen. Any way to get verbose logging?

  - by CapBBeard

  Hi all, My home machine has been running fine for about 3 years, no problems at all. Within the last couple of weeks it's had real trouble trying to shut down. It'll get so far and then just sit there at the "Shutting down..." screen for hours. I've left it overnight, I've tried in safe mode, all to no avail. These days, I just wait for the disk activity to finish up and then hold the power button to turn it off. Feels dirty as, especially because there's a RAID involved! The hardware itself is in pretty good shape and of decent spec; Core 2 Quad, 4GB RAM, 1TB RAID 1+0, so it's not quite like a 7 year old PC coming to end of life! In the last month, hardware hasn't changed except for a new monitor. Admittedly I haven't tried unplugging the monitor but I've never heard of that preventing a shutdown. I might give it a whirl later I guess, as a last resort. I've uninstalled old apps, done updates, checked the event log, looked in device manager, uninstalled all non-present devices, disabled various non-critical devices (imaging, audio etc), unplugged peripherals, stopped non-essential services, unplugged the network, disabled the network adapter entirely, ran chkdsk, verified my RAID, the list goes on. But not a single lead. I'm pretty stumped. It could be hardware, but I have no other evidence to suggest so; when the PC is running, it runs fine. Temperatures are good, gaming is smooth as always, disk performance is fine. Event log even makes it look like the shutdown was completed (gets to the point where the event log service stops). In fact, the PC doesn't appear to realise that I cut the power to it. So my question is, does anyone know if there is a way I can get some verbose output (or a log) from shutdown to give me some idea of what is causing the issue? I'm guessing it's stuck unloading some app/driver but it would be good to get some specifics! Unless anyone has any other ideas? I suspect a reinstall would resolve the issue, however I'm looking to get a new PC built in the next month or so, and the reinstall is going to be quite a big job so I'd rather just wait until then if it comes to that. Would still be nice to get this sorted in the mean time though. Cheers!

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• Lighttpd with FastCGI configuration running ViewVC - rewrite problems

  - by 0xC0000022L

  At the moment I am struggling with the configuration of lighttpd together with ViewVC. The configuration was ported from Apache 2.2.x, which is still running on the machine, serving the WebDAV/SVN stuff, being proxied through. Now, the problem I am having appears to be with the rewrite rules and I'm not really sure what I am missing here. Here's my configuration (slightly condensed to keep it concise): var.hgwebfcgi = "/var/www/vcs/bin/hgweb.fcgi" var.viewvcfcgi = "/var/www/vcs/bin/wsgi/viewvc.fcgi" var.viewvcstatic = "/var/www/vcs/templates/docroot" var.vcs_errorlog = "/var/log/lighttpd/error.log" var.vcs_accesslog = "/var/log/lighttpd/access.log" $HTTP["host"] =~ "domain.tld" { $SERVER["socket"] == ":443" { protocol = "https://" ssl.engine = "enable" ssl.pemfile = "/etc/lighttpd/ssl/..." ssl.ca-file = "/etc/lighttpd/ssl/..." ssl.use-sslv2 = "disable" setenv.add-environment = ( "HTTPS" => "on" ) url.rewrite-once += ("^/mercurial$" => "/mercurial/" ) url.rewrite-once += ("^/$" => "/viewvc.fcgi" ) alias.url += ( "/viewvc-static" => var.viewvcstatic ) alias.url += ( "/robots.txt" => var.robots ) alias.url += ( "/favicon.ico" => var.favicon ) alias.url += ( "/mercurial" => var.hgwebfcgi ) alias.url += ( "/viewvc.fcgi" => var.viewvcfcgi ) $HTTP["url"] =~ "^/mercurial" { fastcgi.server += ( ".fcgi" => ( ( "bin-path" => var.hgwebfcgi, "socket" => "/tmp/hgwebdir.sock", "min-procs" => 1, "max-procs" => 5 ) ) ) } else $HTTP["url"] =~ "^/viewvc\.fcgi" { fastcgi.server += ( ".fcgi" => ( ( "bin-path" => var.viewvcfcgi, "socket" => "/tmp/viewvc.sock", "min-procs" => 1, "max-procs" => 5 ) ) ) } expire.url = ( "/viewvc-static" => "access plus 60 days" ) server.errorlog = var.vcs_errorlog accesslog.filename = var.vcs_accesslog } } Now, when I access the domain.tld, I correctly see the index of the repositories. However, when I look at the links for each respective repository (or click them, for that matter), it's of the form https://domain.tld/viewvc.fcgi/reponame instead of the intended https://domain.tld/reponame. What do I have to change/add to achieve this? Do I have to "abuse" the index file mechanism somehow? Goal is to keep the /mercurial alias functional. So far I've tried sifting through the lighttpd book from Packt again, also through the lighttpd documentation, but found nothing that seemed to match the problem.

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• Is Samba Server what I'm looking for, and if so, what do I need? (currently on DD-WRT Micro)

  - by Anthony

  I am really confused as to what Samba actually does and how it works. Here's what I'm hoping it does: I set up a Samba server on my LAN, and everyone will be able to see each other's shared files and swap them. But some of the documentation makes it sound like it will just allow Mac/Linux computers to see Windows computers. Other bits of the documentation make it sound more like a local server, where a Linux machine would install Samba and they would see everyone and be visible to everyone, but that won't change if anybody else can see each other. While still other things I've read make it seem more like a file-server, where everyone sees each other but file transfers are not peer-to-peer but instead need a host disk for files to act as go between. So, assuming I'm even in the right ballpark of what Samba does in terms of my goal of total cross-visibility on the network, I am left with needing to know what I'd need to set up the server and whether it can be done and is worth it... DD-WRT's article on Samba is a bit ambiguous. One second it sounds as if I can run the server on micro as long as it's set up on a usb drive, but then it also sounds like micro can't run it at all, etc. If I can run it from a usb-connected drive, I still need to know if the files are actually stored on that drive. The dd-wrt article mentions: You can run a Samba server on your main computer and run a client on your router (thus gaining writable storage for the router) or you can use Samba to share a drive connected (typically by USB) to the router among all the computers connected to your network. That one part "to share a drive...among all the computers" makes it sound like the only benefit I get from Samba is a share drive that any OS on the network can see, but they still won't see each other. But I'm very hopeful I'm misreading this. If the computers can see each other but still need the disk, how much space is generally a good idea? I'm basing this on the idea that the drive is a temporary store point. Obviously I'd have to get a drive big enough to store everything people wanted to share if the drive is a full-on file server. If I do have this all wrong, is there any software that achieves what I have in mind? Something that connects to the main router to bridge all clients?

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• How to rate-limit concurrent sessions with nginx or haproxy?

  - by bantic

  I'm currently using nginx to reverse-proxy requests from web clients that are doing long-polling to an upstream. Since we're doing long polling (as opposed to websockets), when a client connects it will make multiple http connections to the server in serial, re-establishing a connection every time the server sends it some data (or timing out and re-establishing if the server has nothing to say for 10 seconds). What I'd like to do is limit the number of concurrent web clients. Since the clients are constantly making new HTTP requests instead of keeping a single request open, it's a little tricky to count the total number of web clients (because it's not the same as total number of concurrently connected http clients). The method I've come up with is to track http requests by the originating IP address, and store the IP address somewhere with a TTL of 20 seconds. If a request comes in whose IP isn't recognized, then we check the total number of unexpired stored IP addresses; if that's less than the maximum then we allow this request through. And if a request comes in with an IP address that we can find in the look-up table that hasn't yet expired, then it is allowed through as well. All requests that are allowed through have their IPs added to the table (if not there before) and the TTL refreshed to 20 seconds again. I had actually whipped something together that worked correctly this way using nginx along with the Redis 2.0 Nginx Module (and the nginx lua module to simplify the conditional branching), using redis to store my IP addresses with a TTL (the SETEX command), and checking the table size with the DBSIZE command. This worked but the performance was horrible. nginx and redis ended up using lots of cpu and the machine could only handle a very small number of concurrent requests. The new stick-table and tracking counters that were added to Haproxy in version 1.5 (via a commission from serverfault) seem like they might be ideal to implement exactly this sort of rate limiting, because the stick-table can track IP addresses and automatically expire entries. However, I don't see an easy way to get a total count of the unexpired entries in the stick table, which would be necessary to know the number of connected web clients. I'm curious if anyone has any suggestions, for nginx or haproxy or even for something else not mentioned here that I haven't thought of yet.

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• Echo 404 directly from nginx to improve performance

  - by user64204

  I am in charge of production servers serving static content for a website. Those servers are constantly being crawled by bots looking for potential exploits (which isn't that much of a problem security-wise because no application can be reached behind the web server) but generates thousands of 404 per day, sometimes per hour. I am looking into ways of blocking those requests but it's tricky (you want to make sure you don't block legitimate traffic and these bots are becoming more and more clever at looking like they're legit) and is going to take me a while to find an acceptable solution. In the meantime I would like to reduce the performance impact of serving those 404 pages. Indeed we're using nginx which by default is configured to serve it's 404 page from the disk (This can be changed using the error_page directive but in the end the 404 will either have to be served from disk or from another external source (e.g. upstream application which would be worst)) which isn't ideal. I ran a test with ab on my local machine with a basic configuration: in one case I echo a message directly from nginx so the disk isn't touched at all, in the other case I hit a missing page and nginx serves its 404 from disk. server { # [...] the default nginx stuff location / { } location /this_page_exists { echo "this page was found"; } } Here are the test results (my laptop has Intel(R) Core(TM) i7-2670QM + SSD in case you're wondering why they are so high): $ ab -n 500000 -c 1000 http://localhost/this_page_exists Requests per second: 25609.16 [#/sec] (mean) $ ab -n 500000 -c 1000 http://localhost/this_page_doesnt_exists Requests per second: 22905.72 [#/sec] (mean) As you can see, returning a value with echo is 11% ((25609-22905)÷22905×100) faster than serving the 404 page from disk. Accordingly I would like to echo a simple 404 Page not Found string from nginx. I tried many things so far but they all failed, essentially the idea was this: location / { try_files $uri @not_found; } location @not_found { echo "404 - Page not found"; } The problem is that as soon as the echo directive is used, the http response code is set to 200. I tried changing that by doing error_page 200 = 400 but that breaks the configuration. How can I serve a 404 page directly from nginx? (without hacking the source which may be might next step)

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• Failed to start up after upgrading software in ubuntu 10.10

  - by Landy

  I've been running Ubuntu 10.10 in a physical x86-64 machine. Today Update Manager reminded me that there are some updates to install and I confirmed the action. I should had read the update list but I didn't. I can only remember there is an update about cups. After the upgrading, Update Manager requires a restart and I confirmed too. But after the restart, the computer can't start up. There are errors in the console. Begin: Running /scripts/init-premount ... done. Begin: Mounting root file system ... Begin: Running /scripts/local-top ... done. [xxx]usb 1-8: new high speed USB device using ehci_hcd and address 3 [xxx]usb 2-1: new full speed USB device using ohci_hcd and address 2 [xxx]hub 2-1:1.0: USB hub found [xxx]hub 2-1:1.0: 4 ports detected [xxx]usb 2-1.1: new low speed USB device using ohci_hcd and address 3 Gave up waiting for root device. Common probles: - Boot args (cat /proc/cmdline) - Check rootdelay=(did the system wait long enough) - Check root= (did the system wait for the right device?) - Missing modules (cat /proc/modules; ls /dev) FATAL: Could not load /lib/modules/2.6.35-22-generic/modules.dep: No such file or directory FATAL: Could not load /lib/modules/2.6.35-22-generic/modules.dep: No such file or directory ALERT! /dev/sda1 does not exist. Dropping to a shell! BusyBox v1.15.3 (Ubuntu 1:1.15.3-1ubuntu5) built-in shell(ash) Enter 'help' for a list of built-in commands. (initramfs)[cursor is here] At the moment, I can't input anything in the console. The keyboard doesn't work at all. What's wrong? How can I check boot args or "root=" as suggested? How can I fix this issue? Thanks. =============== PS1: the /dev/sda1 is type ext4 (rw,nosuid,nodev) PS2: the /dev/sda1 can be mounted and accessed successfully under SUSE 11 SP1 x64.

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• Too many Tunnel Adapter Interfaces

  - by Tomas Lycken

  If I open a command prompt on my machine and type ipconfig /all, I see lots of Tunnel adapter Local Area Connection* 9: Media state . . . . . . . . . . . . . : Media disconnected Connection-specific DNS Sufficx . . . : Description . . . . . . . . . . . . . : Microsoft 6to4 Adapter #5 Physical address. . . . . . . . . . . : 00-00-00-00-00-00-00-E0 DHCP Enabled. . . . . . . . . . . . . : No Autoconfiguration Enabled . . . . . . : Yes In fact, they're so many that my "real" adapters are pushed out of the stack, and can't be seen anymore. Is there any flag I can use on ipconfig to hide all virtual interfaces? Or is there some other way around this problem? Since they always say "Media disconnected" I suppose disabling could be an option, but if possible I'd rather not turn any functionality off. I just want to control what output I get from ipconfig. Also, I know these are related to IPv6 stuff. However, most of what I find on google merely states what these are, and that they're harmless - nothing about hiding/removing them.

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• dig @my-server-ip mydomain.com works from inside, not from outside?

  - by x4954

  My server has 2 ips: x.x.x.73 and x.x.x.248. I can access my site via these ips, using Web browser. {Now, from a CentOS machine (not my server), using terminal} If I: dig @x.x.x.73 mydomain.com dig @x.x.x.248 mydomain.com I get the result: Connection timed out; no server could be reached. Could somebody please tell me how to fix it? Thank you. More information: If I log in to my server using ssh and do: dig @x.x.x.73 mydomain.com dig @x.x.x.248 mydomain.com I can see my zone shown as expected: ; <<>> DiG 9.3.6-P1-RedHat-9.3.6-16.P1.el5_7.1 <<>> @x.x.x.73 mydomain.com ; (1 server found) ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12757 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 2 ;; QUESTION SECTION: ;mydomain.com. IN A ;; ANSWER SECTION: mydomain.com. 38400 IN A x.x.x.73 mydomain.com. 38400 IN A x.x.x.248 ;; AUTHORITY SECTION: mydomain.com. 38400 IN NS ns2.mydomain.com. mydomain.com. 38400 IN NS ns1.mydomain.com. ;; ADDITIONAL SECTION: ns1.mydomain.com. 38400 IN A x.x.x.73 ns2.mydomain.com. 38400 IN A x.x.x.248 ;; Query time: 20 msec ;; SERVER: x.x.x.73#53(x.x.x.73) ;; WHEN: Sun Jan 15 11:46:30 2012 ;; MSG SIZE rcvd: 129 BIND version 9.3.6, Centos 5. Logging to my server using ssh, do inga "dig google.com" also shows expected results.

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• Which hardware to VM ratio for Build-Server virtualization?

  - by Martin

  Let's start with saying that I'm a total noob wrt. to server virtualization. That is, I use VMs often during development, but they're simple desktop machine things for me. Now to my problem: We have two (physical) build servers, one master, one slave running Jenkins to do daily tasks and build (Visual C++ Builds) our release packages for our software. As such these machines are critical to our company, because we do lot's releases and without a controlled environment to create them, we can't ship fixes. (And currently there's no proper backup of these machines in place, because they do not hold any data as such - it just would be a major pain to setup them again should they go bust. (But setting up backup that I'd know would work in case of HW failure would even be more pain, so we have skipped that until now.)) Therefore (and for scaling purposes) we would like to go virtual with these machines. Outsourcing to the cloud is not an option, not at all, so we'll have to use on-premises hardware and VM hosts. Each Build-Server (master or slave) is a fully configured (installs, licenses, shares in case of the master, ...) Windows Server box. I would now ideally like to just convert the (two) existing physical nodes to VM images and run them. Later add more VM slave instances as clones of the existing ones. And here begin my questions: Should I go for one VM per one hardware-box or should I go for something where a single hardware runs multiple VMs? That would mean a single point of failure hardware wise and doesn't seem like a good idea ... or?? Since we're doing C++ compilation with Visual Studio, I assume that during a build the hardware (processor cores + disk) will be fully utilized, so going with more than one build-node per hardware doesn't seem to make much sense?? Wrt. to hardware options, does it make any difference which VM software we use (VMWare, MS, Virtualbox, ... ?) (We're using Windows exclusively for our builds.) Regarding budget: We have a normal small company (20 developers) budget for this. ;-) That is, if it's going to cost a few k$ it's going to cost. If it's free - the better. I strongly prefer solutions where there's no multi-k$ maintenance costs per year.

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• One user sometimes gets an unknown certificate error opening Outlook

  - by Chris

  Let me clarify a little. This isn't an unknown certificate error it's an unknown certificate error in so much as I can't figure out where the certificate comes from. This happens on a Win 7 Enterprise machine connecting to Exchange 2010 with Outlook 2010. The error he gets is that the root is not trusted because it's a self-signed cert. Take a look at this screenshot because even if I had generated this myself I wouldn't have put "SomeOrganizationalUnit" or "SomeCity" or "SomeState", etc. (Red block covers our domain name.) I'm a little concerned this is a symptom of a security breach. Exchange 2010 has three certificates installed but none of them are this certificate. They all have different expiration dates (one is expired) and different meta-data. edit: There are two scenarios that I see the certificate warning and one of them I can reliably repeat. When the user leaves his computer on over night Outlook pops the Security Warning window. I don't know what time this happens. Using Outlook Anywhere if I connect to Exchange externally via a cellular USB modem the Security Warning window will appear every time I close and reopen Outlook. Whether I say Yes or No does not make a difference on whether or not I can connect to Exchange and send/receive email. In other words, I can always connect to Exchange. I've checked my two Exchange servers and my Cisco router for a certificate that matches this one and I can't find it. edit 2: Here is a screenshot of the Security Alert window. (I've been calling it Security Warning... My mistake.) edit 3: I stopped seeing this error several weeks ago but I can't tie it to any single event (because I just sort of realized that warning had stopped showing up) but I think I found the source of the certificate. Last week I found out that the certificate on our website DomainA.com was invalid. I knew that our web admin had installed a valid certificate so when I look into the problem I found out I was being presented with the invalid certificate that this posting is in regards to. The Exchange server's domain is mail.DomainA.com so I can only guess that Outlook was passing this invalid certificate through as it did some kind of check on DomainA.com. This issue is still a mystery because the certificate warning stopped appearing several weeks ago whereas the invalid certificate issue on the website was only fixed last week. It ended up being a problem with the website control panel. The valid certificate was installed but not being served for some reason and instead the self-signed cert was being served.

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• VPN Connection Causes Internal LAN Connection Loss with Server

  - by sleepisfortheweak

  I've tried configuring basic PPTP VPN at my small business using a number of different tutorials. As far as I can tell, the actual VPN connection worked fine, but upon connecting a client, the Server 'disappears' from the internal LAN. The RRAS service must be stopped before the connection is restored. My Setup: The network is simply a DSL Gateway/Router to the outside functioning as NAT/Firewall/DHCP. The server is a Win Server 2008 machine at fixed IP 192.168.1.200. The server has 1 NIC, so I used the 'custom' option when configuring RRAS. The RRAS settings should be default except that I've disabled ports for connection types I'm not using and reduced PPTP ports to 10. I've also created an address pool and disabled DHCP packet forwarding. The server only functions as a File Share and now a VPN Server. Local LAN computers all have mapped network shares to the server authenticated based on Local User/Group setup on the server. The Problem: The moment a client connects through VPN, the server 'disappears' from the local network. All mapped drives disconnect and there is no response to a ping 192.168.1.200. Even if the client disconnects, the server does not re-appear at that address until the RRAS service is stopped. I've Tried: Using an Address Pool inside and outside the local subnet. Using DCHP Relay Checking Inbound/Outbound filters (none enabled) The fact that nothing I've tried has had any effect, and that I can connect and successfully obtain an IP tells me that it's something more fundamental I'm missing. My gut tells me that it's something to do with the second IP address added by the VPN client somehow taking over the interface or traffic from the local LAN accidently getting routed to the VPN client instead of handled at the server once RRAS has become 'active' when a client connects. Hopefully this may be obvious to someone with real IT experience. I've been doing this a while and almost never been stumped. I'm starting to think it might actually be something tricky since my setup is pretty basic yet refuses to work. I'll be happy to include more info if this doesn't ring any bells right away for anyone. Thanks

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• Primary/secondary ethernet interfaces via NetworkManager in Ubuntu 9.10

  - by Josh

  I have an Ubuntu 9.10 machine with three ethernet interfaces, eth0, eth1 and eth2. eth2 is connected to a private network. eth0 and eth2 are connected to two different LANs. Either one will provide access to the internet. All three networks have DHCP servers. Using Ubuntu's the default settings (And Gnome), when I boot up all the interfaces are active and my system gets three IP addresses. However any attempt to access the internet results in connection timeouts and other weirdness. I suspect that traffic is going out on one NIC (like eth0) and coming back in on another (like eth1). I'm not sure what's going on. The only way I can access the internet at the moment is to bring two of the devices down with ifdown. How can I configure eth0 as my primary interface so all trafic goes out by default on that interface, while keeping the other two active? Also, I want to make sure Avahi broadcasts properly on all three IPs so that the computers on the LAN of eth1 can still connect to myHostname.local... EDIT: Here's my routing table: Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 172.16.151.0 0.0.0.0 255.255.255.0 U 0 0 0 eth2 172.16.30.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 10.1.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1 0.0.0.0 172.16.30.2 0.0.0.0 UG 0 0 0 eth0 0.0.0.0 10.1.0.1 0.0.0.0 UG 0 0 0 eth1 I want the 172.16.30.2 network to be the primary one and the 10.1.0.0 network to be the secondary one. EDIT2: My nameservers are also incorrect. It seems like Ubuntu is bringing the networks up in order, eth0, then 1, then 2, and the DHCP information from eth1 is overriding eth0, and eth2 is overriding eth1. How can I reverse this so the DHCP information from eth0 is the "master"? EDIT3: This seems to be an issue with Gnome's NetworkManager.

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• Does 64bit Windows 8 have the same 75% memory-usage limitation for applications as Windows 7?

  - by Barleyman

  64bit Windows 7 (and Windows Vista) have a built-in limit of not being able to use the last 25% of RAM. You will get a low memory warning when you get close to the limit. Even if you disable that warning, applications will run out of memory and crash since the OS will refuse to allocate memory from that last 25%. That was fine when Vista was designed, when machines had 1 GB of total memory, but is pretty daft for today's 8 GB machines. Yes, the system will run cache, etc. on that extra 2 GB, but running out of memory when you have "merely" 2 GB left.... NB: this has nothing to do with the page file. If you limit the page file to a sensible size like 2 GB, you will still see this behavior. The system will cram the page file to the last byte while refusing to touch that 1/4th of the RAM. Does Windows 8 change this behavior? Is there now some fixed minimum free RAM requirement, like 512 MB, or is it still 25%? Can you actually adjust the low memory limit? EDIT: Here is another older post here which discusses this same behavior on Windows 7. There is fixed 25% limit in Windows 7 and I'd like to know if it's still in Windows 8. Windows 7 / Page File Disabled / 12 GB RAM / 2+ GB RAM free and "your computer is running low on memory" Edit2: Here is another link discussing the low memory warning and how to disable it. Note he claims the limit for RAM usage is 80%, not 75%. It would seem to be correct as you can in fact allocate 6.4GB of RAM with 8GB machine. Anything above and beyond that goes to the pagefile, though. http://halflight.com.au/2011/04/06/how-to-disable-low-memory-warnings-and-the-advantages-of-removing-the-page-file/ Edit3: a Here's couple of process explorer screenshots that demonstrate how it goes down. Exhibit1: https://dl.dropbox.com/u/42068601/sysinfo.jpg Exhibit2: https://dl.dropbox.com/u/42068601/sysint2.jpg You can see that Windows 7 will use the memory 6.4GB as the very last resort. I have low memory warning switched off here so programs crashed at the last screenshot allocation. With low memory warning turned on, it starts nagging before you can push OS to use that remaining 1.6GB. The question is not "Is it OK windows does not want to allocate last 20% of RAM because X", it's "Does Windows 8 still behave this way". With 16GB this really becomes dumb.

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• Why did Intel drop the Itanium?

  - by Cole Johnson

  I was reading up on the history of the computer and I came along the IA-64 (Itanium) processors. They sounded really interesting and I was confused as to why Intel would decide to drop them. The ability to choose explicitly what 2 instructions you wanted to run in that cycle is a great idea, especially when writing your program in assembly, for example, a faster bootloader. The hundreds of registers should be convincing for any assembly programmer. You could essentially store all the functions variables in the registers if it doesn't call any other ones. The ability to do instructions like this: (qp) xor r1 = r2, r3 ; r1 = r2 XOR r3 (qp) xor r1 = (imm8), r3 ; r1 = (imm8) XOR r3 versus having to do: ; eax = r1 ; ebx = r2 ; ecx = r3 mov eax, ebx ; first put r2 into r1 xor eax, ecx ; then set r1 equivalent to r2 XOR r3 or ; SAME mov eax, (imm32) ; first put (imm32) into r1 xor eax, ecx ; then set r1 equivalent to (imm32) XOR r3 I heard it was because of no backwards x86 comparability, but couldn't thy be fixed by just adding the Pentium circuitry to it and just add a processor flag that would switch it to Itanium mode (like switching to Protected or Long mode) All the great things about it would have surly put them a giant leap ahead of AMD. Any ideas? Sadly this means you will need a very advanced compiler to do this. Or even one per specific model of the CPU. (E.g. a newer version of the Itanium with an extra feature would require different compiler). When I was working on a WinForms (target only had .NET 2.0) project in Visual Studio 2010, I had a compile target of IA-64. That means that there is a .NET runtime that was able to be compiled for IA-64 and a .NET runtime means Windows. Plus, Hamilton's answer mentions Windows NT. Having a full blown OS like Windows NT means that there is a compiler capable of generating IA-64 machine code.

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• PHP `virtual()` with Apache MultiViews not working after upgrade to Ubuntu 12.04

  - by Izzy

  I use PHP's virtual() directive quite a lot on one of my sites, including central elements. This worked fine for the last ~10 years -- but after upgrading (or rather moving, as it is on a new machine) to Ubuntu 12.04 it somehow got broken. Example setup (simplified) To make it easier to understand, I simplify some things (contents). So say I need a HTML fragment like <P>For further instructions, please look <A HREF='foobar'>here</P> in multiple pages. 10 years ago, I used SSI for that, so it is put into a file in a central place -- so if e.g. the targeted URL changes, I only need to update it in one place. To serve multiple languages, I have Apache's MultiViews enabled -- and at $DOCUMENT_ROOT/central/ there are the files: foobar.html (English variant, and the default) foobar.html.de (German variant). Now in the PHP code, I simply placed: <? virtual("/central/foobar"); ?> and let Apache take care to deliver the correct language variant. The problem As said, this worked fine for about 10 years: German visitors got the German variant, all others the English (depending on their preferred language). But after upgrading to Ubuntu 12.04, it no longer worked: Either nothing was delivered from the virtual() command, or (in connection with framesets) it even ended up in binary gibberish. Trying to figure out what happens, I played with a lot of things. I first thought MultiViews was (somehow) not available anymore -- but calling http://<server>/central/foobar showed the right variant, depending on the configured language preferences. This also proved there was nothing wrong with file permissions. The error.log gave no clues either (no error message thrown). Finally, just as a "last ressort", I changed the PHP command to <? virtual("central/foobar.html"); ?> -- and that very same file was in fact included. So PHP's virtual() function basically worked -- but the language dependend stuff obviously did no longer work together with it as it did before. Of course I tried to find some change (most likely in PHP's virtual() command), using Google a lot, and also searching the questions here -- unfortunately to no avail. Finally: The question Putting "design questions" aside (surely today I would design things differently -- but at least currently I miss the time to change that for a quite huge amount of pages): What can be done to make it work again? I surely missed something -- but I cannot figure out what...

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• Unable to boot from LiveCD/USB and even Super Grub Disk!

  - by Reuben L.

  Hi all, I'm in a fix. Basically this morning, I decided to format my Win7 as it was getting really slow and I did so with no problems. I also have a Linux Mint OS on dual boot. Since I was springcleaning my windows partition, I decided it was a good idea to do the same to my linux partition. I downloaded the latest version of Linux Mint (Julia) and burned the LiveCD. Now here is where the problem lies, when I restarted Windows and chose to boot from the LiveCD, it didn't work. No joke. There was just a little underscore blinking for a long time before it went back to GRUB which prompted me to select an OS to boot. However, when I went into my old Linux Mint OS and restarted the machine, the LiveCD worked... to a certain extent. It would load and look as though it was ready to install Linux Mint 10 but the moment it got to the option screen, the whole screen turned into a checkered and jumbled mess. At this point I thought it was the LiveCD or the .iso file. I had an Ubuntu LiveUSB for recovery purposes and I tried that. The exact same thing happened. Can't boot the LiveUSB if I restarted from Windows, but works when I reboot from Linux. BUT still the same checkered screen that doesnt respond. Did a bit of googling and reckoned it might be something wrong with my GRUB. Did some updating and didnt make a difference. Then I tried the Super Grub Disk and STUPIDLY uninstalled GRUB. (Note that booting to SGD had the exact same problem - can't be done if I rebooted from Windows). Now I can't access my Linux Mint 9 cos the the bootup screen (mbr) only has Windows 7 as an option. Remember me mentioning that I can't boot from any CD/USB/recovery CD when I reboot from Windows? And now that I can't access Linux, there's no way for me to do any form of recovery! I've tried using the command prompt utility at startup recovery but to no avail. Anyone can help me with this?

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