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• Ubuntu 12.04 open port 80 inside WLAN

  - by Eduard

  I have an nginx server running on ubuntu 12.04 that serves http through port 80 and https through port 443. Everything works fine if I access it from the same computer via localhost, 127.0.0.1 or the local IP 192.168.0.11. If I try to access the server from another computer in the same VLAN it does not work for http; it works for https. I have changed my nginx configuration to also listen to port 8000 for http; I can then access http from the other computer in the same VLAN via "http://192.168.0.11:8000". I also have a web server running on port 80 on a windows machine and can access it from another device in the same VLAN, therefore the router is not blocking incoming http traffic. The nginx process is run by root. I have used tcpdump and I see that packets are arriving to Ubuntu: 192.168.0.16.49735 192.168.0.11.80 and that some response is being given 192.168.0.11.80 192.168.0.16.49735 (I do not know what the response is though). There is no request arriving at the nginx web server (I have checked the access log). I have iptables empty. I have unsuccessfully tried to find a solution for a long time to this, it has now become a matter of happiness or bitterness :).

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• Scaling databases with cheap SSD hard drives

  - by Dennis Kashkin

  Hey guys! I hope that many of you are working with high traffic database-driven websites, and chances are that your main scalability issues are in the database. I noticed a couple of things lately: Most large databases require a team of DBAs in order to scale. They constantly struggle with limitations of hard drives and end up with very expensive solutions (SANs or large RAIDs, frequent maintenance windows for defragging and repartitioning, etc.) The actual annual cost of maintaining such databases is in $100K-$1M range which is too steep for me :) Finally, we got several companies like Intel, Samsung, FusionIO, etc. that just started selling extremely fast yet affordable SSD hard drives based on SLC Flash technology. These drives are 100 times faster in random read/writes than the best spinning hard drives on the market (up to 50,000 random writes per second). Their seek time is pretty much zero, so the cost of random I/O is the same as sequential I/O, which is awesome for databases. These SSD drives cost around $10-$20 per gigabyte, and they are relatively small (64GB). So, there seems to be an opportunity to avoid the HUGE costs of scaling databases the traditional way by simply building a big enough RAID 5 array of SSD drives (which would cost only a few thousand dollars). Then we don't care if the database file is fragmented, and we can afford 100 times more disk writes per second without having to spread the database across 100 spindles. . Is anybody else interested in this? I've been testing a few SSD drives and can share my results. If anybody on this site has already solved their I/O bottleneck with SSDs, I would love to hear your war stories! PS. I know that there are plenty of expensive solutions out there that help with scalability, for example the time proven RAM-based SANs. I want to be clear that even $50K is too expensive for my project. I have to find a solution that costs no more than $10K and does not take much time to implement.

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• Sql Server 2005 Connection Unstable When Sharing Connection

  - by intermension

  When connecting to a customers hosting service via Sql Server Management Studio on an internet connection that also has other activity on it, the Sql Server connection to the hosting service is often dropped. An obvious work around to this problem is to NOT have additional traffic on the connection but it still begs the question "Why the Sql Server connection is so unstable?". If there is, for arguments sake, 100kb of bandwidth and a couple of downloads running that are being serviced at 35kB each then there is 30kB bandwidth spare capacity. If a 3rd download is started, that can be serviced at 35kB by the server, it will top out at 30kB and leave zero spare capacity. This is fine and all downloads get along nicely. However it seems that with Sql Server connections it doesn't matter if there is spare bandwidth. Sql Server regularly times out if there is any additional activity on the connection even if i have 1024kB spare bandwidth capacity. This has been experienced across different customer hosting providers over the years and so the assumption is that it's Sql Server related. Why does Sql Server (apparently) require exclusive access to the internet connection in order to maintain a connection... even if that connection has plenty of spare capacity over and above any additional activity on the connection?

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• Delayed internet access

  - by Joel Coel

  When I (and presumably my users) first start up or log in to my computer I can't get internet access until several minutes after logging in. Internet pages like serverfault.com will time out. During this time I can access internal web servers. Sometimes pinging the gateway seems to fix the problem. I'm using Windows 7 on this machine with wifi, and the problem seems limited to the wifi network, which is on a separate vlan. The wired network does not share the problem, but I know it's not the wifi connection itself because the internal sites work. The wifi access point is attached to a 3Com 4200 switch, with the port set for vlan 2 untagged, vlan 1 tagged. The 4200 has a fiber connection to a 3Com 4900SX fiber switch that acts almost as a router here. The fiber connection is vlan 1 untagged vlan 2 tagged at both ends. The gateway is then attached to a different 4200 (vlan 1 untagged, vlan 2 tagged) that has a similar fiber connection to the 4900SX. vlan 2 has 192.168.8.0/22 IPs, vlan 1 has 10.1.0.0/16 IPs. The 4900SX has an interface for both vlans (10.1.1.1/192.168.8.1), as does the gateway (10.1.1.5/192.168.8.5). There is one dchp server for both vlans on the same switch as the gateway. It chooses a dhcp scope based on the interface used by the 4900sx to forward the dhcp request. There is also a network access list on the 4900sx set to deny all vlan2 traffic to any 10.1.x.x host, with exceptions made for a few servers, including dhcp, 4900sx, and the gateway. I think that about covers it. Any ideas on why internet access would be delayed like this?

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• Isolating a computer in the network

  - by Karma Soone

  I've got a small network and want to isolate one of the computers from the whole network. My Network: <----> Trusted PC 1 ADSL Router --> Netgear dg834g <----> Trusted PC 2 <----> Untrusted PC I want to isolate this untrusted PC in the network. That means the network should be secure against : * ARP Poisoning * Sniffing * Untrusted PC should not see / reach any other computers within the network but can go out the internet. Static DHCP and switch usage solves the problem of sniffing/ARP poisoning. I can enable IPSec between computers but the real problem is sniffing the traffic between the router and one of the trusted computers. Against getting a new IP address (second IP address from the same computer) I need a firewall with port security (I think) or I don't think my ADSL router supports that. To summarise I'm looking for a hardware firewall/router which can isolate one port from the rest of the network. Could you recommend such a hardware or can I easily accomplish that with my current network?

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• Find slow network nodes between two data centers

  - by 2called-chaos

  I've got a problem with syncing big amount of data between two data centers. Both machines have got a gigabit connection and are not fully occupied but the fastest that I am able to get is something between 6 and 10 Mbit = not acceptable! Yesterday I made some traceroute which indicates huge load on a LEVEL3 router but the problem exists for weeks now and the high response time is gone (20ms instead of 300ms). How can I trace this to find the actual slow node? Thought about a traceroute with bigger packages but will this work? In addition this problem might not be related to one of our servers as there are much higher transmission rates to other servers or clients. Actually office = server is faster than server <= server! Any idea is appreciated ;) Update We actually use rsync over ssh to copy the files. As encryption tends to have more bottlenecks I tried a HTTP request but unfortunately it is just as slow. We have a SLA with one of the data centers. They said they already tried to change the routing because they say this is related to a cheap network where the traffic gets routed through. It is true that it will route through a "cheapnet" but only the other way around. Our direction goes through LEVEL3 and the other way goes through lambdanet (which they said is not a good network). If I got it right (I'm a network intermediate) they simulated a longer path to force routing through LEVEL3 and they announce LEVEL3 in the AS path. I basically want to know if they're right or they're just trying to abdicate their responsibility. The thing is that the problem exists in both directions (while different routes), so I think it is in the responsibility of our hoster. And honestly, I don't believe that there is a DC2DC connection which only can handle 600kb/s - 1,5 MB/s for weeks! The question is how to detect WHERE this bottleneck is

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• configuring lighttpd for large downloads

  - by ahmedre

  i run a web site that hosts pages that are just general scripts (php, etc) and mp3 downloads (some of which are fairly large - up to 200mb). i am running lighttpd on the servers on linux (ubuntu 64). everything is fine, but under high load, the server is not accessible (or very slow - even sshing in takes a while), and i am guessing this is due to a huge number of mp3 downloads at that time. consequently, dns sees the server as down and redirects all the traffic to the other servers, and after a while, it comes back up and things work again. so what's the best way to fix this? ideally, i want the server to continue running (and the web pages - php etc - to always work, but downloads don't always have to work). should i just have 2 web servers running (one for the downloads and one for the php pages), or is it perhaps something i can fix in my lighttpd configuration? here are the snippets from my configuration: server.max-worker = 4 server.max-fds = 2048 server.max-keep-alive-requests = 4 server.max-keep-alive-idle = 4 server.stat-cache-engine = "fam" fastcgi.server = ( ".php" => (( "bin-path" => "/usr/bin/php-cgi", "socket" => "/tmp/php.socket", "max-procs" => 1, "idle-timeout" => 20, "bin-environment" => ( "PHP_FCGI_CHILDREN" => "64", "PHP_FCGI_MAX_REQUESTS" => "1000" ), "bin-copy-environment" => ( "PATH", "SHELL", "USER" ), "broken-scriptfilename" => "enable" )) ) # normal php site $HTTP["host"] =~ "bar.com" { server.document-root = "/usr/local/www/sites/bar.com/" accesslog.filename = "|/usr/sbin/cronolog /var/log/lighttpd/%m/%d/%H/bar.log" } # download site $HTTP["host"] =~ "(download|stream).foo.com" { server.document-root = "/home/audio/" dir-listing.activate = "enable" dir-listing.hide-dotfiles = "enable" evasive.max-conns-per-ip = 1 evasive.silent = "enable" # connection.kbytes-per-second = 256 accesslog.filename = "|/usr/sbin/cronolog /var/log/lighttpd/%m/%d/%H/download.log" }

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• Slackware - Assigning routes (IP address ranges) to one of many network adapters

  - by Dogbert

  I am using a Slackware 13.37 virtual machine within VirtualBox (current). I currently have a number of Ubuntu VMs on a single server, along with this Slackware VM. All VMs have been set up to use "Internal Network" mode, so they are all on a private LAN, and can see each other (ie: share files amongst themselves), but they remain private from the outside world. On on the these VMs (the Slackware one), I need to be able to grant it access to both this private network, and the internet at large. The first suggestion I found for handling this is to add another virtual network adapter to the VM, then set it to NAT. This results in the Slackware VM having the following network adapter setup: -NIC#1: Internal Network -NIC#2: NAT I want to set up the first network adapter (NIC#1) to handle all traffic on the following subnets: 10.10.0.0/255.255.0.0 192.168.1.0/255.255.255.0 And I want the second virtual network adapter (NIC#2) to handle everything else (ie: internet access). May I please have some assistance in setting this up on my Slackware VM? Additionally, I have searched for similar questions on SuperUser and Stackoverflow, but they all seem to pertain to my situation (ie: they all refer to OSX, or Ubuntu via the use of some UI-based tool). I'm trying to do this on Slack specifically via the command-line. Thanks!

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• Poor performance on IIS7, only on Windows Server 2008, fine on Windows 7?

  - by user32005

  Hi, I'm new to IIS7 but have experience with other versions. I've been working on an application that works great in a dev environment (as always) but when I push it to a windows server 2008/IIS7 box performance takes a noticeable hit. The dev environment is Windows7/IIS7. The configuration in IIS is the same on the dev box as the server. I've tried all sorts of things to try and find a reason for this but I cant come to any conclusion. I've ruled out database problems on the live box as all data is cached after the first request. I've confirmed this to be true and made sure there is no additional database traffic. I've ruled out network issues with a combination of monitoring requests with fiddler and local debugging on the server. Whenever the code runs on the server there seems to be a performance issue. The server: Intel Core 2 Quad CPU Q6600 @ 2.40ghz with 2gb RAM. I know this is not fantastic but I was expecting it to at least perform as well as my dev environment (which is running much more on a lower spec). The CPU using peaks at under 60%, and memory usage is less than half of the available. I've enabled failed request tracing and most of the time is spent in a custom HttpModule, this module works to handle every request, I cant get any more detail as to what within the module may be causing the problem. Any ideas, I've been pulling my hair out for days now. Thanks

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• SQL Server performance on VSphere 4.0

  - by Charles

  We are having a performance issue that we cannot explain with our VMWare environment and I am hoping someone here may be able to help. We have a web application that uses a databases backend. We have an SQL 2005 Cluster setup on Windows 2003 R2 between a physical node and a virtual node. Both physical servers are identical 2950's with 2x Xeaon x5460 Quad Core CPUs and 64GB of memory, 16GB allocated to the OS. We are utilizing an iSCSI San for all cluster disks. The problem is this, when utilizing the application under a repeated stress testing that adds CPUs to the cluster nodes, the Physical node scales from 1 pCPU to 8 pCPUs, meaning we see continued performance increases. When testing the node running Vsphere, we have the expected 12% performance hit for being virtual but we still scale from 1 vCPU to 4 vCPUs like the physical but beyond this performance drops off, by the time we get to 8 vCPUs we are seeing performance numbers worse than at 4 vCPUs. Again, both nodes are configured identically in terms of hardware, Guest OS, SQL Configurations etc and there is no traffic other than the testing on the system. There are no other VMs on the virtual server so there should be no competition for resources. We have contacted VMWare for help but they have not really been any suggesting things like setting SQL Processor Affinity which, while being helpful would have the same net effect on each box and should not change our results in the least. We have looked at all of VMWare's SQL Tuning guides with regards to VSphere with no benefit, please help!

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• Dynamically blocking excessive HTTP bandwidth use?

  - by Jeff Atwood

  We were a little surprised to see this on our Cacti graphs for June 4 web traffic: We ran Log Parser on our IIS logs and it turns out this was a perfect storm of Yahoo and Google bots indexing us.. in that 3 hour period, we saw 287k hits from 3 different google ips, plus 104k from yahoo. Ouch? While we don't want to block Google or Yahoo, this has come up before. We have access to a Cisco PIX 515E, and we're thinking about putting that in front so we can dynamically deal with bandwidth offenders without touching our web servers directly. But is that the best solution? I'm wondering if there is any software or hardware that can help us identify and block excessive bandwidth use, ideally in real time? Perhaps some bit of hardware or open-source software we can put in front of our web servers? We are mostly a windows shop but we have some linux skills as well; we're also open to buying hardware if the PIX 515E isn't sufficient. What would you recommend?

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• plesk: how to configure reverse proxy rules properly?

  - by rvdb

  I'm trying to configure reverse proxy rules in vhost.conf. I have Apache-2.2.8 on Ubuntu-8.04, monitored by Plesk-10.4.4. What I'm trying to achieve is defining a reverse proxy rule that defers all traffic to -say- http://mydomain/tomcat/ to the Tomcat server running on port 8080. I have mod_rewrite and mod_proxy loaded in Apache. As far as I understand mod_proxy docs, entering following rules in /var/www/vhosts/mydomain/conf/vhost.conf should work: <Proxy *> Order deny,allow Allow from all </Proxy> ProxyRequests off RewriteRule ^/tomcat/(.*)$ http://mydomain:8080/$1 [P] Yet, I am getting a HTTP 500: internal server error when requesting above URL. (Note: I decided to use a rewrite rule in order to at least get some information logged.) I have made mod_rewrite log extensively, and find following entries in the logs [note: due to a limitation of max. 2 URLs in posts of new users, I have modified all following URLs so that they only contain 1 slash after http:. In case you're suspecting typos: this was done on purpose): 81.241.230.23 - - [19/Mar/2012:16:42:59 +0100] [mydomain/sid#b06ab8][rid#1024af8/initial] (2) init rewrite engine with requested uri /tomcat/testApp/ 81.241.230.23 - - [19/Mar/2012:16:42:59 +0100] [mydomain/sid#b06ab8][rid#1024af8/initial] (3) applying pattern '^/tomcat/(.*)$' to uri '/tomcat/testApp/' 81.241.230.23 - - [19/Mar/2012:16:42:59 +0100] [mydomain/sid#b06ab8][rid#1024af8/initial] (2) rewrite '/tomcat/testApp/' - 'http:/mydomain:8080/testApp/' 81.241.230.23 - - [19/Mar/2012:16:42:59 +0100] [mydomain/sid#b06ab8][rid#1024af8/initial] (2) forcing proxy-throughput with http:/mydomain:8080/testApp/ 81.241.230.23 - - [19/Mar/2012:16:42:59 +0100] [mydomain/sid#b06ab8][rid#1024af8/initial] (1) go-ahead with proxy request proxy:http:/mydomain:8080/testApp/ [OK] This suggests that the rewrite and proxy part is processed ok; still the proxied request produces a 500 error. Yet: Addressing the testApp directly via http:/mydomain:8080/testApp does work. The same setup does work on my local computer. Is there something else (Plesk-related, perhaps?) I should configure? Many thanks for any pointers! Ron

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• Site Goes Offline Every Day At Midnight - No One Knows Why

  - by HollerTrain

  0 down vote favorite Seems today a website I manage has been going online and offline between 12a and 12:25a. I have no idea what is causing the issue so I am seeking guidance on where to start. It is a Wordpress based site. So here is what I DO know: I have a pingdom account which alerts me when the site goes offline so we can see every day, like clockwork, the site goes on/off. At the time of the ups/downs I see a lot of strain on the memory usage. Look at the load average when the site is going online/offline (http://screencast.com/t/BRlfXkqrbJII). Then I ran this command to restart http (http://screencast.com/t/usVtYWZ2Qi) and the memory usage then goes down to this (http://screencast.com/t/VdTIy3bgZiQB). An hour after I restarted http, the site then went offline/online so restarting the http didn't do much help. When the site is going offline/online, I ran the top command and get this (http://screencast.com/t/zEwr7YQj3). Here is a top command when the site is at it's lowest (http://screencast.com/t/eaMfha9lbT - so this would be dubbged "normal"). Here is a bandwidth report (http://screencast.com/t/AS0h2CH1Gypq). The traffic doesn't seem to be that much (http://screencast.com/t/s7hrWNNic1K), but looking at my times the site is going up/down this may be one of the reasons? I have the dvp Nitro package at Media Temple (http://mediatemple.net/webhosting/nitro/). So at this point I would request some help in trying to figure out what the cause of this is, and how I can go about pinpointing this issue. ANY HELP is greatly appreciated.

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• Redirecting a single request to another pages, ignoring www subdomain

  - by Petter Brodin

  I have a site running on IIS 7.5 that does an automatic redirect from 'http://mysite.com/whatever.aspx' to 'http://www.mysite.com/whatever.aspx' On the site, there is a lot of traffic to an old URL that I want to redirect to the front page, index.aspx: 'http://mysite.com/foo/bar/index.cgi%something=asdf&somethingelse=qwerty' The problem is that no matter what I try, I can only get the redirect to work with the www subdomain. If I use the URL without www, I just end up at 'http://www.mysite.com/404.aspx' Any ideas? Thanks in advance for all help! Edit3: it seems like the browser caching the redirect response was messing with me, so edit2 is wrong. See my response below. Edit2: disregard edit1, it doesn't seem like it's working after all. Edit: here's some further info: using this article I've managed to redirect from 'http://mysite.com/foo/bar/index.cgi' to 'http://www.mysite.com/index.aspx', but if I add the query string parameters, it still redirects to 'http://www.mysite.com/404.aspx' Isn't there a way to catch all requests to the cgi file, including query string parameters?

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• Juniper router dropping pings to external interface

  - by Alexander Garden

  My organization has a Juniper SSG20-WLAN that routes our traffic to the outside world. We've been having intermittent problems with our internet connection so I wrote up a Python script to ping the internal interface of the router, the external interface, a couple of our internal servers, the ISP router our router talks to, their upstream provider, and Google and Yahoo for good measure. It does that about every minute. What I have found is that when our internet goes out, our Juniper router ceases responding to pings on the external interface. Everything past that is, of course, unreachable. The internal interface and our internal servers continue to echo back without interruption. None of the counters indicate dropped packets of any type. They all look normal. The logs complain about VIP servers being unavailable but otherwise nothing indicative of network issues. My questions are these: Does this exonerate our ISP? Or, contrawise, might a problem with the connection be causing the external interface to go down? Is there somewhere else in the SSG20, beside the system log and counters, that might help me track down info on the problem? UPDATE: Turned out that one of the switches between my monitoring box and the router was a router itself, and occasionally diverting from the gateway to itself. Kudos to those who made suggestions along those lines. Not really sure which answer to mark as accepted, as it was really stuff in the comments that turned out to be right. Thanks for the suggestions.

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• Performance data collection for short-running, ephemeral servers

  - by ErikA

  We're building a medical image processing software stack, currently hosted on various AWS resources. As part of this application, we have a handful of long-running servers (database, load balancers, web application, etc.). Collecting performance data on those servers is quite simple - my go-to- recipe of Nagios (for monitoring/notifications) and Munin (for collection of performance data and displaying trends) will work just fine. However - as part of this application, we are constantly starting up and terminating compute instances on EC2. In typical usage, these compute instances start up, configure themselves, receive a job from a message queue, and then get to work processing that job, which takes anywhere from 15 minutes to over 8 hours. After job completion, these instances get terminated, never to be heard from again. What is a decent strategy for collecting performance data on these short-lived instances? I don't necessarily need monitoring on them - if they fail for whatever reason, our application will detect this and handle re-starting the job on another instance or raising the flag so an administrator can take a look at things. However, it still would be useful to collect information like CPU (user, idle, iowait, etc.), memory usage, network traffic, disk read/write data, etc. In our internal database, we track the instance ID of the machine that runs each job, and it would be quite helpful to be able to look up performance data for a specific instance ID for troubleshooting and profiling. Munin doesn't seem like a great candidate, as it requires maintaining a list of munin nodes in a text file - far from ideal for an environment with a high amount of churn, and for the short amount of time each node will be running, I'd rather keep the full-resolution data indefinitely than have RRD water down the data over time. In the end, my guess is that this will require a monitoring engine that: uses a database (MySQL, SQLite, etc.) for configuration and data storage exposes an API for adding/removing hosts and services Are there other things I should be thinking about when evaluating options? Perhaps I'm over-thinking this, though, and just ought to run sar at 1-minute intervals on these short-lived instances and collect the sar db files prior to termination.

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• iptables -- OK, **now** am I doing it right?

  - by Agvorth

  This is a follow up to a previous question where I asked whether my iptables config is correct. CentOS 5.3 system. Intended result: block everything except ping, ssh, Apache, and SSL. Based on xenoterracide's advice and the other responses to the question (thanks guys), I created this script: # Establish a clean slate iptables -P INPUT ACCEPT iptables -P FORWARD ACCEPT iptables -P OUTPUT ACCEPT iptables -F # Flush all rules iptables -X # Delete all chains # Disable routing. Drop packets if they reach the end of the chain. iptables -P FORWARD DROP # Drop all packets with a bad state iptables -A INPUT -m state --state INVALID -j DROP # Accept any packets that have something to do with ones we've sent on outbound iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT # Accept any packets coming or going on localhost (this can be very important) iptables -A INPUT -i lo -j ACCEPT # Accept ICMP iptables -A INPUT -p icmp -j ACCEPT # Allow ssh iptables -A INPUT -p tcp --dport 22 -j ACCEPT # Allow httpd iptables -A INPUT -p tcp --dport 80 -j ACCEPT # Allow SSL iptables -A INPUT -p tcp --dport 443 -j ACCEPT # Block all other traffic iptables -A INPUT -j DROP Now when I list the rules I get... # iptables -L -v Chain INPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 0 0 DROP all -- any any anywhere anywhere state INVALID 9 612 ACCEPT all -- any any anywhere anywhere state RELATED,ESTABLISHED 0 0 ACCEPT all -- lo any anywhere anywhere 0 0 ACCEPT icmp -- any any anywhere anywhere 0 0 ACCEPT tcp -- any any anywhere anywhere tcp dpt:ssh 0 0 ACCEPT tcp -- any any anywhere anywhere tcp dpt:http 0 0 ACCEPT tcp -- any any anywhere anywhere tcp dpt:https 0 0 DROP all -- any any anywhere anywhere Chain FORWARD (policy DROP 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain OUTPUT (policy ACCEPT 5 packets, 644 bytes) pkts bytes target prot opt in out source destination I ran it and I can still log in, so that's good. Anyone notice anything major out of wack?

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• Suddenly getting lock timeouts with MySQL

  - by Marc Hughes

  We've got a web app hosted on Amazon Web services. Our database is a multi-az RDS MySQL server running 5.1.57 and 3-4 app servers talk to it. Today, we started seeing a lot of errors along the lines of "Lock wait timeout exceeded; try restarting transaction" - almost 1% of POST requests are seeing this. There have been no modifications to the code running on the site. There have been no schema changes. We haven't had a big spike in traffic. I've been looking at the processes running, and none seem out of control. I tried scaling our RDS instance from a small to a large, with no effect. Two days ago, Amazon had some outages. As part of the recovery from that, our RDS server, and our app servers ended up in different availability zones, but all within the same region. But yesterday, everything was fine so I'm not convinced that's related. The lock timeouts are in different types of requests and occur in different InnoDB tables. I have noticed the number of open connections jumped when we started seeing problems, but they may be a symptom and not a cause. What are my next steps in debugging this?

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• How can I create a VLAN on my extreme switch for a separate subnet/domain?

  - by drpcken

  I'm putting together a small active directory implementation for a buddy of mine. I currently have 2 servers (one is the primary domain controller) and a couple clients. I need to test and run updates on every machine on this domain, but I would have plug them into my current LIVE domain to get it internet access. From what I've read having two separate domains on a single subnet is a bad idea (even though it is temporary) so I don't want to risk messing anything up on my production domain. I'm pretty sure I can create a separate VLAN on my extreme 48 port switch and plug this smaller domain into it on a different subnet, but I don't know the commands. Both subnets would need internet access of course (one of the things I can't wrap my head around is routing internet traffic between subnets (gateway is on production subnet). Switch is a Summit x450e-48p My production domain is on subnet 192.168.200.0. My new domain I want to put online would go into subnet 192.168.10.0. A shove in the right direction would be greatly appreciated. Thank you!

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• How to stop NAT dropping idle connections?

  - by WGH

  I have a TCP connection that can be idle for many hours. The traffic is flowing from the server to the client only. One might say it's kind of push notification. My home router, however, tends to drop the connection silently after 20 minutes (the value of /proc/sys/net/netfilter/nf_conntrack_tcp_timeout_established). The server detects the loss once it tries to send anything (I assume it receives RST from the router itself). As client never sends anything, it never detects the loss. RFC 5382 "NAT Behavioral Requirements for TCP" states the following: A NAT can check if an endpoint for a session has crashed by sending a TCP keep-alive packet and receiving a TCP RST packet in response. It makes sense. It's much more effective than sending keep-alives by the host itself (as only NAT knows its own timeout). And probably not hard to implement. Is there any NAT solutions implementing this? It would be great if there was a way to enable this in iptables.

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• Completely unintuitive Apache/PHP memory-freeing behavior

  - by David

  Okay, this one's weird. I have a Turnkey Linux server with a gig of dedicated RAM. It's running WP3.2 with a boatload of plug-ins. It's a new site, so it has very limited traffic (other than search engines, maybe 20 hits a week). Now, for a few weeks, every few days, it would max out on main RAM, start eating up virtual RAM, and then crash. It's had this behavior for a while and I've been trying to figure out which element was causing the crash. Nine days ago, I pointed my external server monitor to this server. I wrote a 5-line HTML file (not PHP and not WP) that the server monitor accesses every minute, to see if the server is up. So, now, nine days later, the server has been rock solid, up all the time, no memory leak at all. I changed NOTHING on the server itself to see this behavior change. Have you EVER seen anything like this? All the server monitor is doing is retrieving a single, super-simple HTML file and all the memory leak problems have gone away. Weird, eh?

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• When should NTPd broadcast/broadcastclient be used instead of client/server or peer modes?

  - by Luke404

  The NTP deamon if often used in its simplest mode, which is client/server: you specify one or more server directives in your ntp.conf and your clients will use those servers. In addition to that, when you run your own NTP servers, it is good practice to peer them together, so if one of them looses connectivity to its upstream servers, it will get time from its peers. But NTPd can also work with broadcast and/or multicast distribution of time data, with the documentation stating: broadcast and multicast modes are intended for configurations involving one or a few servers and a possibly very large client population The documentation also says elsewhere: It is possible and frequently useful to configure a host as both broadcast client and broadcast server. A number of hosts configured this way and sharing a common broadcast address will automatically organize themselves in an optimum configuration based on stratum and synchronization distance. I can see one obvious administrative benefit: you don't have to manually specify and update your list of NTP servers in the clients ntp.conf, so to me it looks tempting to use broadcast mode even for a small client population (say 5+ clients with 3~4 servers). I expect network traffic to be a little higher with broadcasts instead of client/server associations, but given the usual gigabit ethernet LAN the impact should be negligible unless you have a very very large number of hosts in the same broadcast domain. At the end of the day, when should broadcast mode be used or avoided? Are there pros and cons I haven't seen?

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• Computer not POSTing "randomly"?

  - by smoth190

  I have a custom built PC that is exhibiting some...odd... behavior, something I've never seen before. It was working fine one day, and the next day, it wouldn't start. Seeing as I wanted an upgrade anyway, I purchased a new motherboard that was compatible with all my parts. While replacing the motherboard, I accidentally damaged the CPU. Well, I wanted a new one anyway... so I got a new one. Seeing as I was replacing a ton of parts already, I bought a new PSU because the old one was super loud. When I slapped it all together, it starts up, lights, fans, drives, they all start. But I get no display from the monitor. No beeps, which I believe means it doesn't POST. I figured it was the RAM, because after removing the sound card and graphics card, there was nothing else that I hadn't replaced. When I remove both sticks of RAM, I get a continuous beeping, and according to the mobo handbook, means no RAM. So I think the mobo is functional, or atleast partly. I bought new RAM, but it still didn't work. I tried 3 monitors, with both VGA and DIV. So it's probably not the monitor, either. Now, let me get to the random part. Every 20 or so boots (I should also mention, for about 3 out of 5 boots I have to unplug the PC because it won't powerdown via the button), it will POST and I'll get display. Then, after about 2 or 3 resets, it won't work again. This confuses me so much, because even when I change nothing, it will/will not work. My thought is that maybe it has something to do with the RAM not clearing or something. I also reset the CMOS battery, incase that had anything to do with it, but no eval. I found some weird suggestion online about holding the power button for 30 seconds while it was unplugged. That did nothing, but I didn't expect it would... I've replaced just about the entire computer, and all the parts are compatible. Done about everything I can think of, but nothing has worked. Hopefully someone can help me here. And as I side note: When I do get my computer to boot, it says my hardware has changed and I have to re-activate windows. But it says I have to call Microsoft to do it. So I get this fancy automated voice that asks me to enter in a code into windows, then it asks me "How many computers have you activated with this copy of Windows?". Well, I had it on my computer before I replaced everything, so I said 1. Then he yelled at me for violating my 1-use license. I dunno what's going on there, do I have to re-purchase Windows 7? And they wonder why people pirate software... That's just a bonus question, though. Specs: 8GB of DDR2 RAM (Corsair) AMD CPU (I don't know what GHz or model because I can't find the box... (I think its 4 cores of 2.8Ghz) ASRock A785GM-LE Motherboard

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• ipv6 reverse DNS delegation

  - by user1709492

  I currently have 2001:1973:2303::/48 assigned to me and i'll be assigning /64's to customer's I'd like to have 1 zonefile for the /48 where i can essentially point / redirect query to different nameservers. Example ( Desired effect ) 2001:1973:2303:1234::/64 -> ns1.example.com, ns2.example.com 2001:1973:2303:2345::/64 -> ns99.example2.com, ns100.example2.com 2001:1973:2303:4321::/64 -> ns1.cust1.com, ns2.cust1.com Current /48 zonefile $TTL 3h $ORIGIN 3.0.3.2.3.7.9.1.1.0.0.2.ip6.arpa. @ IN SOA ns3.example.ca. ns4.example.ca. ( 2011071030 ; serial 3h ; refresh after 3 hours 1h ; retry after 1 hour 1w ; expire after 1 week 1h ) ; negative caching TTL of 1 hour IN NS ns3.example.ca. IN NS ns4.example.ca. 1234 IN NS ns1.example.com. NS ns2.example.com. 2345 IN NS ns99.example2.com. NS ns100.example2.com. 4321 IN NS ns1.cust1.com. NS ns2.cust1.com. Where am i going wrong ? My request seems simple to me atleast. To put it in terms of firewalling i want to redirect traffic client queries 2001:1973:2303:4321::1 - ns3.example.ca sees the request and redirects the query to ns1.cust1.com - ns1.cust1.com answers the query with omg.itworks.ca ( provided ns1.cust1.com is properly configured.

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• mod_fcgi in virtualmin: graceful kill fail, sending SIGKILL?

  - by mgjk

  Yesterday around 1am, our server ground to a crawl. This doesn't happen often, but I'm trying to get to the bottom of it. There is no unusual traffic volume, no unusual processes running, just all of the sudden the server started killing fcgid processes. [Thu Aug 02 01:17:32 2012] [warn] mod_fcgid: process 26460 graceful kill fail, sending SIGKILL ... for as many fcgid processes as we have... CPU idle fell to 0% and I/O seemed to take up most of the load. The issue lasted about 5 minutes. I suspect there was some swap activity, although I'm not sure if it was due to killed processes being swapped in to die, or if it was because some process ramped up memory usage faster than my process watching scripts can see them. The oom-killer wasn't triggered (at least it's not logged), so I think this was Apache for some reason restarting the processes. This is not regular, and nothing obvious appears in cron. Is there a normal Apache process which might cause this? We run dozens of different sites, and it was late at night, so volume was very, very low. (maybe 200 requests in a 10 minute period).

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