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• Multiple Routers, Failover, DHCP and multiple gateways. NOT WAN-failover

  - by u_b

  I've had a look around google and this forum but could not find an answer to my question. So probably one of you can help me a little. My intended setup is: Router R1: wan connection to isp. connected backup server. provides some wireless SSID. other connected devices like printer, laptop, etc. both wired and wireless. Router R2: no wan connection to isp but connected to R2. connects mp3-streamer and music server. also serves as a wireless access point with same SSID. other than described connections only wireless connections. I would like to be able to control music even if R1 is off, e.g. with no internet connection. On the other hand I would like to access internet also in the case that R2 is off, i.e. no music access. Last but not least I would like to stream internet radio, i.e., R1 and R2 are on, and music is streamed from internet to R1 to R2 to streamer. I would like to realize all this using DHCP (also using static assignments) so i do not have to configure statically on android, laptop, etc. So my questions are: Can I make DHCP provide a list of two default gateways R1,R2? In order to make clients fallback to other gateway if currently assigned gateway is turned off? Thanks in advance, u_b

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• Apache using 100% CPU, once again

  - by CBenni

  Recently, apache2 started using 100% of CPU power: top gives me From other, similar threads, I took the tip to use mod_status. Aside from HUGE amounts of NULL requests, it gives: CPU Usage: u2.16 s1.32 cu0 cs0 - .0835% CPU load 1.2 requests/sec - 17.6 kB/second - 14.6 kB/request 8 requests currently being processed, 42 idle workers The access and error logs do not show anything surprising or intriguing at all. Note the .8% CPU usage. Another tip was to use strace: root@server:~# strace -p 1956 Process 1956 attached - interrupt to quit restart_syscall(<... resuming interrupted call ...> And remains like this for at least half an hour, without producing any additional output. Restarting apache fixed the problem for less than a second The server runs a few custom python scripts aswell as a django-powered website on apache2 (up-to-date), but even turning the scripts off (or not having them active in the first place) did not change anything. After I stopped apache and powered my server off, powered it on a few minutes afterwards and restarted all my services, the CPU usage remained low for several hours, just in order to pop up again randomly (?) The DigitalOcean CPU stats on my server are: You can see how the CPU usage was super high for almost half a day until I restarted the bot - just to remain stable for several hours and then pop up again. I am completely at a loss of words and don't know what I could do to find out what piece of my code is giving me these problems or if apache itself is the cause... Therefore I would greatly appreciate any hints to the questions: What else can I try to do? Which things might I not have checked? Is this definitely in my own code? How do you find what part of python code crashes an app via a infinite loop or similar?

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• How to handle files that don't need version control in mercurial

  - by richardh

  I am new to mercurial, and for the most part do LaTeX reports and statistical calculations in R using .csv and/or .sqlite files. Re LaTeX, all I really care is the .tex file. Re R, I don't need version control on the .csv or .sqlite files because they are static. When I do 'hg add' for a repo with a .csv and/or .sqlite file, I get a warning like: rev2.sqlite: up to 3070 MB of RAM may be required to manage this file (use 'hg revert rev2.sqlite' to cancel pending addition) So I revert and subsequently use adds like hg add -X *.sqlite. I guess I really have two questions: (1) Should I ignore these warnings? Because these large files are static, can I just add to the repo knowing that the diff files will always be empty and not worry about wasted resources? (2) If I should keep excluding these files from the repo, is there away that I can fix this option? I.E., add to my .hgrc file something that always appends an option like -I *.tex -I *.R to my 'hg add' commands? Thanks!

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• Azure Virtual Machines - what fault tolerance do they provide?

  - by Borek

  We are thinking about moving our virtual machines (Hyper-V VHDs) to Windows Azure but I haven't found much about what kind of fault tolerance that infrastructure provides. When I run VHD in Azure, I've got two questions: Is my VHD and all the data in it safe? I think that uploaded VHDs use the "Storage" infrastructure so they should be automatically replicated to multiple disks and geographically distributed but should I still make a full-image backup just to be safe? (Note that of course I will be backing up the actual data inside VMs that I care about; I just want to know if there is a chance greater than 0.0000001% that one day I will receive an email from Microsoft telling me that my VM is gone and that I should create or restore it from scratch). Do I need to worry about other things regarding the availability of my VMs? I mean, when I have an on-premise server I need to worry about the hardware itself, about the host operating system, what would happen if my router failed, if my Hyper-V's C: drive failed etc. Am I right in thinking that with Azure, their infrastructure takes care of all of this? Thanks.

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• Import data in Excel that doesn't have a row delimiter, but number of columns is known

  - by Alex B

  So i have this text file that looks something like this: Header1 Header2 Header3 Header4 A1 B1 C1 D1 A2 B2 C2 D2 and so on. When imported, I'd want the data to format itself in 4 columns. I tried the Get External Data from Text, and it successfully imports it, but it doesn't wrap it around, so it just keeps making columns for every space. I'd want it to go on the next line after 4 (in this case) elements have been added. What's the simplest way to achieve this? EDIT: My answer follows, since I'm not yet allowed to answer my own questions yet. The Excel function I needed is called indirect(). Not sure how it actually works though, so hopefully someone can help out with that, but the function call that worked for me is =INDIRECT(ADDRESS((ROW(A1)-1)*4+COLUMN(A1),1)) which i found over here: http://www.ozgrid.com/forum/showthread.php?t=101584&p=456031#post456031 Note: this required me to add the text to excel where i'd get this row full of columns, and then flip it so that i'd have a column full of rows.

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• Computer not finding hard drives on boot -sometimes-

  - by todd.pund

  Computer specs: Mobo: Gigabyte ultradurable 3 - GA-970A-UD3 Processor: First gen I7 3.2GHZ Ram: 8GB Kingston DDR3 1066 Video Card: EVGA NVidia GTX 460 1GB Hard Drive: 500MB 7200rpm x2 (can't remember brand, sorry I'm at work.) Last week my developer preview for Windows 8 ran out so I put my copy of windows 7 back on the computer. The computer at that point started suffering from frequent freezing and crashing. When I rebooted the computer sometimes it wouldn't find the system HD at all. When I looked at the post screen it seemed to show that it wasn't finding either of the HDs. Then yesterday when turning on the computer I just got GRUB as a message (not a GRUB prompt, just GRUB) I haven't had a dual boot of Linux for at least a year. I loaded windows 7 recovery console from the disk and ran: bootrec /fixboot bootrec /fixmbr Which did not help. At that point I just installed Ubuntu 13.04 over the windows 7 install and still received the GRUB post. I went into the BIOS and switched the Hard Drive priorities and then it loaded into Ubuntu fine. For several days everything was just hunky dory until I installed the Ubuntu version of Steam, install Portal and tried to run it. At that point the computer froze and after hard rebooting couldn't find the hard disks again. Then after restarting the system it loaded up fine again and no issues since. (I have not tried to launch portal again). My next thought is to remove the system hard drive and try to use the secondary as the master to see if the primary HD is bad. I'm sorry if this has been confusing, I'll answer any questions I can. Any thoughts?

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• What differences are there between "home" switches and "professional" switches?

  - by pjreddie

  Our radio station uses a PtP wireless system to stream our radio and TV signals from our studio up a hill to our transmitter. We have been having problems with warbly sound and drop outs that come from some point in this system. An engineer that occasionally visits the station thinks it could be the switches we use on each side of the PtP wireless system to connect the PtP devices to the encoders and decoders and wants us to get two of these switches: http://www.amazon.com/Netgear-JGS516-ProSafe-16-Port-Ethernet/dp/B0002CWPOK/ref=dp_return_1 The encoder/decoder setup only streams 8Mbps total so it seems like the switches we have should not be stressed out, unless they are causing sufficient latency to degrade the performance of the encoder/decoder. At each end of the connection we only have 4 connections, is there any reason we couldn't get a cheaper, "home" quality switch like this: http://www.amazon.com/D-Link-DGS-1005G-5-Port-Gigabit-Desktop/dp/tech-data/B003X7TRWE/ref=de_a_smtd Is there a significant difference that we would notice in terms of latency between these two switches? How much does the quality of the switch actually matter in this scenario? Any help is appreciated, feel free to ask questions if anything needs clarification. Thanks

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• Cloning a failing disk (Win 7)

  - by daveh551

  I have a Windows 7 machine with several partitions on a 1.5T drive. Windows has been complaining about disk errors and imminent failure, so I have purchased a new 2TB drive. The failing disk has not completely failed, and, in fact, I was able to boot Windows from it (after a couple tries) and examine the SMART logs - the only RED item was 1 sector being reallocated. But when I try to Clone it to the new Drive using Acronis True Image Home (2010), True Image can see the drive, the partitions, and the contents, but when it goes to actually do the clone, it says "Failed to move. Make sure the destination disk is not smaller than the source disk, and that there are not errors on the disk" (or something like that). What are some other options for simply cloning the failing drive. I'd like to clone the entire disk, but am willing to do it partition by partition if necessary. Was this a known failing of the 2010 edition of ATI, or is it really something hosed in my system. Would upgrading to the 2012 edition be likely to work any better? (I'd download the trial and try it out, but if I remember right, the cloning operation is disabled in the trial version), and I don't have enough free disk space to make an entire image.) What are some other cloning software packages if ATI won't work? Note that I'm only looking to clone the disk, not make an image as a back up - I use Ghost for that, and can fall back to that if I have to. It looks to me like CloneZilla would do the job. Any recommendations? Thanks, and if this duplicates other questions, I apologize.

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• Can you see something wrong in my .htaccess?

  - by AlexV

  OK, after many search, trial and errors I've managed to create an .htaccess that do what I wanted (see explanations and questions after the code block): <IfModule mod_rewrite.c> RewriteEngine On #1 If the requested file is not url-mapper.php (to avoid .htaccess loop) RewriteCond %{REQUEST_FILENAME} (?<!url-mapper\.php)$ #2 If the requested URI does not end with an extension OR if the URI ends with .php* RewriteCond %{REQUEST_URI} !\.(.*) [OR] RewriteCond %{REQUEST_URI} \.php.*$ [NC] #3 If the requested URI is not in an excluded location RewriteCond %{REQUEST_URI} !^/seo-urls\/(excluded1|excluded2)(/.*)?$ #Then serve the URI via the mapper RewriteRule .* /seo-urls/url-mapper.php?uri=%{REQUEST_URI} [L,QSA] </IfModule> This is what the .htaccess should do: #1 is checking that the file requested is not url-mapper.php (to avoid infinite redirect loops). This file will always be at the root of the domain. #2 the .htaccess must only catch URLs that don't end with an extension (www.foo.com -- catch | www.foo.com/catch-me -- catch | www.foo.com/dont-catch.me -- don't catch) and URLs ending with .php* files (.php, .php4, .php5, .php123...). #3 some directories (and childs) can be excluded from the .htaccess (in this case /seo-urls/excluded1 and /seo-urls/excluded2). Finally the .htaccess feed the mapper with an hidden GET parameter named uri containing the requested uri. Even if I tested and everything works, I want to know if what I do is correct (and if it's the "best" way to do it). I've learned a lot with this "project" but I still consider myself a beginner at .htaccess and regular expressions so I want to triple check it there before putting it in production...

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• Can a non-redundant RAID5 cause any serious problems (compared to RAID0)?

  - by leemes

  I used to have a three-disc RAID5 (mdadm) in my computer for personal media storage (music, videos, photos, programs, games, ...). It had three discs with 750 GB each, resulting in an array capacity of 1.5 TB. One day (one year ago), I needed one of those discs to install another operating system. I thought, I don't need the redundancy anymore since I backup the most important stuff (personal photos e.g.) on an external disc anyway. So I decided to remove one of the three discs without converting the RAID to RAID0 or even two separate discs, because I had no temporary storage (since one cannot simply convert the RAID5 to RAID0 AFAIK). So now, for about one year, I have a non-redundant RAID5 with 2 of 3 discs running. Sometimes, one of the discs has a defective contact at the power cable or something similar causing the drive to stop working temporarily (I don't know exactly what it is). Since it still works when rebooting the computer and in most cases by calling some mdadm commands, it wasn't that problematic. Note that the data is not very critical, since I still have a backup of the most important stuff. But in the last few weeks, one of the drives fails very frequently (every few hours), so it gets really annoying to manage this. My questions are: Is there any disadvantage (apart from the annoying management) of a non-redundant RAID5 (with one drive less than typical) over a RAID0? If I understand it correctly, both have no redundancy and the same capacity. On a temporary drive failure, I can restart the array in both cases, assuming that the drive itself still works after the failure. Can it happen that the drive contents alter on a drive failure, making the array inconsistent? If so, can I tell mdadm to check the array for failures (without a file system level checking tool)? Since the drive most probably only has a defective contact causing it to fail for a second only, can I tell mdadm to automatically restart the array, so I will not even notice the failure if no application wanted to access the file system during the failure?

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• Windows 8 install app for multiple user accounts

  - by Robert Graves

  I purchased Adera episode 2 intending to play through it with my son. We each have our own user account on the same PC. When my son logged in, he was prompted to purchase the app which I had already purchased, installed, and played on the same PC. So I checked the Terms of Use. After selecting an app in the store, there is a Terms of Use link on the left side under the Install button. It is almost impossible to identify it as a link unless you put your mouse over it. The Terms of Use are standard across all apps in the store, not specific to particular apps. The terms of use indicates that the app may be installed on up to five devices, but says nothing about multiple user accounts on those devices. However, this Microsoft blog article indicates that it is allowed. Say, for example, that your family has a shared PC. You have previously used your Microsoft account to purchase a game that all your kids like to play. You can install it for each of your kids by having each of them sign in to their Windows accounts on the shared PC, then launch the Store and sign in to the Store using your own Microsoft account. There, you’ll see all your apps and you can re-install the app on your kid’s Windows account. Installing apps on multiple user accounts on a shared PC still only counts as one of the five allowable PCs where you can install apps. So I have two questions: Is it permissible under the Terms of Use to install the app under multiple accounts on the same device? If so, how do I do so given that my son has already signed into the store using his own Microsoft account.

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• Any ideas why Ettercap filters aren't seeing packet data?

  - by Bryan

  I'm using an Ettercap filter to detect a query response coming back from a particular service on a remote machine. When I see a response from the service, I'm searching through the data in the packet to see if an offset is a specific value, and if so I'm changing the value at another offset. Trouble is, when I try this on a new virtual machine I built my Ettercap filter's no longer getting any data in the DATA.data variable available to it. if(ip.proto == TCP && tcp.src == 17867) { msg("Response seen!\n"); if(DATA.data + 2 == "\0x01") { msg("Flag detected!\n"); DATA.data + 5 = 0x09; } } The filter's getting applied to the traffic because "Response seen!" messages get printed out by Ettercap. However, "Flag detected!" messages do not. I think DATA.data is indeed empty because if I change my second "if" statement to check for DATA.data == "" then the "Flag detected!" message gets printed. Any ideas why this may be happening?! Also, if this is the wrong site to be asking questions like this, please let me know. I wasn't sure if it fit better here or somewhere like superuser or serverfault. By the way, this is a cross-post from StackOverflow... I should have posted on this forum instead I think. :)

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• Excel controls not visible for certain users

  - by Nossidge

  One of the users of an Excel program I've written is having a weird problem. None of the control objects (Command Button, ComboBox, etc.) are visible to him when he opens the file on his laptop. He is using Excel 2003, the same version I used to create the program, and enables macros using the pop-up when the file loads. I have Googled this, and have found these people who seem to be having the exact same problem, with various versions of Excel. Unfortunately, none of their questions were answered. I can't really explain it any better than this user: If I enter design mode and pull a control from the control toolbar onto a sheet all I see are the drag handles. When not in design mode I have to feel around with the mouse and can click the button which executes the button click code correctly and opens another sheet where again I have to feel around for the buttons to return me to the original sheet. The button I managed to click is now visible but as soon as I click anywhere on the sheet it disappears. I have verified that the visible property of the buttons is set and that the Show All Objects on the Options View tab is selected. If I pull buttons from the Forms toolbar onto a sheet they are visible. If I try to find Objects using F5 when not in design mode Excel reports no objects on the sheet. So, Super Users, can you help? UPDATE: Thanks for your replies, but much like the person in the ozgrid link, the problem has gone away. Not sure why it went, but I can confirm that the user rebooted again and also started up other Excel files that didn't contain controls in the interim. Perhaps that fixed it, or maybe it'll be back again. I'll keep udating with progress, and close if the problem doesn't reoccur for the next few days. Thanks again.

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• Can a website see/know my MAC address even if I use a VPN?

  - by ilhan

  I have searched other results and read many of them but I could not get an enough information. My question is that can a website see my MAC address or can they have an information about that I'm the same person under these conditions: I am using a VPN and I use two IPs: first one is normal one, the second one is the VPN's IP. I use two browsers to hide behind browser fingerprinting. I use both browsers with Incognito Mode. I always use one for normal IP, one for the VPN IP. I do not know that if the website uses cookies or not. But can they collect an enough information to prove that these two identities belong to same person? Is there any other way for them to see that I am the same person? I use different IPs, different browsers and I use both browsers in incognito mode. I even changed one of browsers language to only English. So even if they collect my info from browser, they will see two browsers using different languages. (Addition after edit): So I have changed my IP and browser information and the website can not reach this information anymore to prove that I am the same person using two accounts. Then let's come to the title: Can they see my MAC address? Because I think that it is the last way that they can identify me and my main question is that. I wrote the information above to mention that I changed IPs and I have some precautions to avoid browser fingerprinting (btw my VPN provider already has a service about blocking it). I wrote them because I read similar advices in some related questions but my question is that can they see my MAC address (or anything else that can make me detected) despite all these precautions. And lastly, Is there an extra way to be anonymized that I can do? For example, can my system clock or anything else give an information? Thanks in advance.

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• Expanding iSCSI LUNs (NTFS)

  - by Fatih

  I have a 4TB iSCSI LUN that formated as NTFS in Windows 2008. I've shared this formated volume as a folder over SMB. When the capacity of this volume is not enough, I have to add more iSCSI LUNs, but the end-users must see only the folder that I've shared before. So, when I expand the NTFS volume that is currently 4TB, with more iSCSI LUNS(for example 2 more 4TB LUN), if one of the luns is failed, or missing, will all of my data in the folder be lost? I imagine that the expanding ntfs volume is like RAID 0(striped). if it is like RAID 0, then all my data will be lost when one of the luns is failed, or missing. In brief, there are two questions in here: 1- What will be happened, if one of the luns is missing in an expanded ntfs volume? 2- Is there another way to merge all of iscsi luns as only a folder, in that way the users don't see any extra folder even if I add extra iscsi luns to the file server.(I don't mention about DFS) Regards.

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• Which default Database Systems come installed in Microsoft VS2010 Express?

  - by Tonygts

  Appreciate all advice 0n the following questions Which database systems (Ms SQL 2008, MS SQL Compact, or others) comes installed with VS2010 Express edition. SQL Server 2008 R2 Express is free, can we install and integrate with VS2010 Express? How to uninstall those database already come installed? I have installed VS2010 express on Windows 7; just VS2010 components (VB, C#, C++ and Web Developer) and without installing any other things like SQL Express. In the Console Panel-Program & Features' window, the installed list is shown below: Microsoft SQL Server 2008 Setup Support File Microsoft SQL Server 2008 Browser Microsoft SQL Server VSS Writer Microsoft SQL Server Database Publishing Wizard 1.4 Microsoft ASP.NET MVC2 - VWD Express 2010 Tools Microsoft SQL Server 2008 Management Objects Microsoft SQL Server Compact 3.5 SP2 ENU Microsoft SQL Server System CLR Types Microsoft Silverlight 3 SDK Microsoft ASP.NET MVC 2 Microsoft Visual Studio 2010 ADO.NET Entity Framework Tools Visual Studio 2010 Tools doe SQL Server Compact 3.5 SP2 ENU Web Deployment Tool Microsoft Visual Web Developer 2010 Express - ENU Microsoft Visual C++ 2010 Express - ENU Microsoft Visual C# 2010 Express - ENU Microsoft Visual Visual Basic 2010 Express - ENU Microsoft SQL Server 2008 As you can see, Microsoft SQL Server 2008 (last line) and near the top, Microsoft SQL Server Compact 3.5 SP2 ENU and many of their related SQL components such as Microsoft SQL Server 2008 R2 Management Objects are also installed. These are actually installed by installing VS2010 Express, but I have no idea how to use them or verify their valid existence from VS2010. Also, do I have to uninstall them before I install SQL Server 2008 R2, which is the latest version I believe? And what tool is needed to manage and create data source and tables?

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• Cloning to a smaller hard drive with DDRescue

  - by krebshack

  I am currently working with a 700 GB Seagate hard drive that's beginning to fail. I'll call this "SDB" from now on. I'd like to clone it while I'm still able to. However, the only hard drive that I have available is a 500 GB WD hard drive. I'll call this "SDC" from now on. The partition scheme on SDB is as follows: 9.77 GB is allocated to a recovery partition and the remaining 688.87 GB is allocated to a Windows partition. Both are formatted using NTFS. There is no partition scheme on SDC. I know how to clone one hard drive to another using DDRescue but I've only done it using hard drives that are the same size. For your reference, I'll normally use the command "ddrescue -v -r 3 /dev/sdb /dev/sdc example.log". I'd like to know if it's possible to do this with DDRescue. I've read the manual from GNU (http://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html) and I haven't seen anything indicating that it is possible. I'm just looking for some confirmation that this is a correct impression. If it's not possible, then it would be helpful if any of y'all would be able to make some work around suggestions. But please don't feel obligated to do that. I don't want to have my one thread bogged down with two many questions.

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• Remote reboot of windows to knoppix

  - by user64452

  I am attempting to develop an Auditing application. This audit application will be employed on windows networks. The Audit will need to discover Hardware and software details of all machines attached to the network (including Printers) I do not want to have to install this application on each workstation. The audit app. needs to discover all the ip addresses of all the networked workstations. I have been prototyping this app for the last couple of months and have decided to try a new tack Is this possible? a). You have a windows network, min Windows XP sp3 and upwards b). Maximum of 100 Networked machines (if that matters) c). I need to remotely reboot each WINDOWS machine in turn on the entire network and get it to startup using UNIX, say knoppix for example! d). however the knoppix live cd is only available from one of the networked machines Questions... Morphology? Longevity? Incept dates? Cheers DD

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• What are the typical methods used to scale up/out email storage servers?

  - by nareshov

  Hi, What I've tried: I have two email storage architectures. Old and new. Old: courier-imapds on several (18+) 1TB-storage servers. If one of them show signs of running out of disk space, we migrate a few email accounts to another server. the servers don't have replicas. no backups either. New: dovecot2 on a single huge server with 16TB (SATA) storage and a few SSDs we store fresh mails on the SSDs and run a doveadm purge to move mails older than a day to the SATA disks there is an identical server which has a max-15min-old rsync backup from the primary server higher-ups/management wanted to pack in as much storage as possible per server in order to minimise the cost of SSDs per server the rsync'ing is done because GlusterFS wasn't replicating well under that high small/random-IO. scaling out was expected to be done with provisioning another pair of such huge servers on facing disk-crunch issues like in the old architecture, manual moving of email accounts would be done. Concerns/doubts: I'm not convinced with the synchronously-replicated filesystem idea works well for heavy random/small-IO. GlusterFS isn't working for us yet, I'm not sure if there's another filesystem out there for this use case. The idea was to keep identical pairs and use DNS round-robin for email delivery and IMAP/POP3 access. And if one the servers went down for whatever reasons (planned/unplanned), we'd move the IP to the other server in the pair. In filesystems like Lustre, I get the advantage of a single namespace whereby I do not have to worry about manually migrating accounts around and updating MAILHOME paths and other metadata/data. Questions: What are the typical methods used to scale up/out with the traditional software (courier-imapd / dovecot)? Do traditional software that store on a locally mounted filesystem pose a roadblock to scale out with minimal "problems"? Does one have to re-write (parts of) these to work with an object-storage of some sort - such as OpenStack object storage?

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• iptables: How to combine DNAT and SNAT to use a secondary IP address?

  - by Que_273

  There are lots of questions on here about iptables DNAT/SNAT setups but I haven't found one that solves my current problem. I have services bound to the IP address of eth0 (e.g. 192.168.0.20) and I also have a IP address on eth0:0 (192.168.0.40) which is shared with another server. Only one server is active, so this alias interface comes and goes depending on which server is active. In order to get traffic accepted by the service a DNAT rule is used to change the destination IP. iptables -t nat -A PREROUTING -d 192.168.0.40 -p udp --dport 7100 -j DNAT --to-destination 192.168.0.20 I also wish all outbound traffic from this service to appear to come from the shared IP, so that return responses will work in the event of a active-standby failover. iptables -t nat -A POSTROUTING -p udp --sport 7100 -j SNAT --to-source 192.168.0.40 My problem is that the SNAT rule is not always run. Inbound traffic causes a connection tracking entry like this. [root]# conntrack -L -p udp udp 17 170 src=192.168.0.185 dst=192.168.0.40 sport=7100 dport=7100 src=192.168.0.20 dst=192.168.0.185 sport=7100 dport=7100 [ASSURED] mark=0 secmark=0 use=2 which means the POSTROUTING chain is not run and outbound traffic leaves with the real IP address as the source. I am thinking I can set up a NOTRACK rule in the raw table to prevent conntracking for this port number, but is there a better or more efficient way to make this work? Edit - Alternative question: Is there a way (in CentOS/Linux) to have an interface that can be bound to but not used, such that it can be attached to the network or detached when a shared IP address is swapped between servers?

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• Is Ubuntu a bad distro for a standalone mysql database server?

  - by DhruvPathak

  I read an article here : http://www.mysqlperformanceblog.com/2011/12/08/which-linux-distribution-for-mysql-server/ On the other end there are Debian and Ubuntu. Both use tool called dpkg for package management. There isn’t a month that I log in to a system based on either distribution where there are no issues with packages consistency. Unfinished installations, unresolved conflicts are so common that it’s just beyond simple negligence. The packaging system is just not robust enough. Another problem is that one broken package may block you from installing or uninstalling anything else. Imagine that someone left system in such shape, you prepared for downtime, stopped MySQL and… error – text editor has not been properly installed, so you cannot upgrade MySQL either until the problem is fixed. In a stressful situation when downtime clock ticks – annoying at best We prefer Ubuntu server because of familiarity and Ubuntu also being development environment. Questions: Is Ubuntu used commonly in production for a mysql database server ? Is it worth the trouble ever to have one distro eg Ubuntu in web server, and another say Red Hat in database server ? Or Is a homogenous server pool a better choice ?

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• How can I prevent a DDOS attack on Amazon EC2?

  - by cwd

  One of the servers I use is hosted on the Amazon EC2 cloud. Every few months we appear to have a DDOS attack on this sever. This slows the server down incredibly. After around 30 minutes, and sometimes a reboot later, everything is back to normal. Amazon has security groups and firewall, but what else should I have in place on an EC2 server to mitigate or prevent an attack? From similar questions I've learned: Limit the rate of requests/minute (or seconds) from a particular IP address via something like IP tables (or maybe UFW?) Have enough resources to survive such an attack - or - Possibly build the web application so it is elastic / has an elastic load balancer and can quickly scale up to meet such a high demand) If using mySql, set up mySql connections so that they run sequentially so that slow queries won't bog down the system What else am I missing? I would love information about specific tools and configuration options (again, using Linux here), and/or anything that is specific to Amazon EC2. ps: Notes about monitoring for DDOS would also be welcomed - perhaps with nagios? ;)

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• How can I monitor network traffic?

  - by WIndy Weather

  I have a home network with about 10 devices including BluRay player [netflix] and both windows and linux machines. I need to collect network traffic statistics so that if questions come up about how much traffic I'm using I have the answer independent of my ISP. I've looked at DD-WRT, but I see that even buying a new router that will be supported is a problem since I might get the wrong version of the hardware. I have a DIR-655 and a DIR-501 - neither of which is supported. I don't mind buying new hardware, but it looks like a crap-shoot to get one that will work. DD-WRT looks like a bad solution unless someone knows of a place to get a router that is guaranteed to work. Does someone know of an arduino or other SBC solution? I have plenty of NAT routers already, so I just need traffic statistics for external traffic. The network is GBit Ethernet inside and Cable / soon to be DSL outside. The DIR-655 only gives me "packets", not bytes transferred oddly enough. Thanks, ww

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• Can I regenerate the rsa key for SSH access to a Cisco router? Or should I completely erase the SSH config?

  - by Josh

  I have a production 2691 that I administer via telnet. I'd like to change that to SSH. Looking at the config, it looks like there have been keys generated in the past. I think the history here is SSH was set up, they had issues connecting, and fell back to telnet. There are a number of crypto entries, including the following: crypto pki trustpoint Gateway-2691.xxx.com enrollment selfsigned subject-name cn=IOS-Gateway-2691.xxx.com revocation-check none rsakeypair Gateway-2691.xxx.com I've also got this going... Gateway-2691#sh ip ssh SSH Disabled - version 1.99 %Please create RSA keys (of atleast 768 bits size) to enable SSH v2. Authentication timeout: 120 secs; Authentication retries: 3 Gateway-2691# My question is simply, can I run crypto key generate rsa again to set it up again? Is there a way to negate or no all of the previous ssh config so that I can start fresh there? I may be asking the wrong questions, as I'm learning here. As for the SSH how-to, I'm sure I can find information in many places. I'm just basically wondering if I need to start fresh, or if I can pick up where the last attempt at SSH config left off.

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• 403 Forbiden on Apache (CentOS) Server

  - by pouya

  These are my VM setup: HOST: windows 7 ultimate 32bit GUEST: CentOs 6.3 i386 Virtualization soft: Oracle virtualBox 4.1.22 Networking: NAT -> (PORT FORWARD: HOST:8080 => GUEST:80) Shared Folder: centos all the project files goes into shared folder and for each project file a virtualhost conf file is created in /etc/httpd/conf.d/ like /etc/httpd/conf.d/$domain I wasn't able to see anything in my browser before disabling both windows firewall and iptables in centos after that if i type for example: http://www.$domain:8080/ all i see is: Forbidden You don't have permission to access / on this server. Apache/2.2.15 (CentOS) Server at www.$domain.com Port 8080 A sample Virtual Host conf file: <VirtualHost *:80> #General DocumentRoot /media/sf_centos/path/to/public_html ServerAdmin webmaster@$domain ServerName www.$domain ServerAlias $domain *.$domain #Logging ErrorLog /var/log/httpd/$domain-error.log CustomLog /var/log/httpd/$domain-access.log combined #mod rewrite RewriteEngine On RewriteLog /var/log/httpd/$domain-rewrite.log RewriteLogLevel 0 </VirtualHost> centos shared folder is availabe to guest at /media/sf_centos These are file permissons for sf_centos: drwxrwx--- root vboxsf vboxsf group includes: apache and root So these are my questions: 1- How to solve Forbidden Problem? 2- How to setup both host and guest firewalls? 3- How can i improve this developement environment to simulate production environment as much as possible specially security improvements?

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