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• one 16K random read I/O issues 2 scsi I/O (16K and 4K) requests in linux

  - by hiroyuki

  I noticed weird issue when benchmarking random read I/O for files in linux (2.6.18). The Benchmarking program is my own program and it simply keeps reading 16KB of a file from a random offset. I traced I/O behavior at system call level and scsi level by systemtap and I noticed that one 16KB sysread issues 2 scsi I/Os as following. SYSPREAD random(8472) 3, 0x16fc5200, 16384, 128137183232 SCSI random(8472) 0 1 0 0 start-sector: 226321183 size: 4096 bufflen 4096 FROM_DEVICE 1354354008068009 SCSI random(8472) 0 1 0 0 start-sector: 226323431 size: 16384 bufflen 16384 FROM_DEVICE 1354354008075927 SYSPREAD random(8472) 3, 0x16fc5200, 16384, 21807710208 SCSI random(8472) 0 1 0 0 start-sector: 1889888935 size: 4096 bufflen 4096 FROM_DEVICE 1354354008085128 SCSI random(8472) 0 1 0 0 start-sector: 1889891823 size: 16384 bufflen 16384 FROM_DEVICE 1354354008097161 SYSPREAD random(8472) 3, 0x16fc5200, 16384, 139365318656 SCSI random(8472) 0 1 0 0 start-sector: 254092663 size: 4096 bufflen 4096 FROM_DEVICE 1354354008100633 SCSI random(8472) 0 1 0 0 start-sector: 254094879 size: 16384 bufflen 16384 FROM_DEVICE 1354354008111723 SYSPREAD random(8472) 3, 0x16fc5200, 16384, 60304424960 SCSI random(8472) 0 1 0 0 start-sector: 58119807 size: 4096 bufflen 4096 FROM_DEVICE 1354354008120469 SCSI random(8472) 0 1 0 0 start-sector: 58125415 size: 16384 bufflen 16384 FROM_DEVICE 1354354008126343 As shown above, one 16KB pread issues 2 scsi I/Os. (I traced scsi io dispatching with probe scsi.iodispatching. Please ignore values except for start-sector and size.) One scsi I/O is 16KB I/O as requested from the application and it's OK. The thing is the other 4KB I/O which I don't know why linux issues that I/O. of course, I/O performance is degraded by the weired 4KB I/O and I am having trouble. I also use fio (famous I/O benchmark tool) and noticed the same issue, so it's not from the application. Does anybody know what is going on ? Any comments or advices are appreciated. Thanks

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• Recommendations for good Unix MTA / groupware solutions? [closed]

  - by Jez

  Possible Duplicate: Exchange server replacement that runs on Linux I'm setting up a Debian server, and one of the things I need on it is an MTA. I don't want to use something like Exim or Postfix because I want something that ties in SMTP, POP3, and IMAP all in one (a la Microsoft Exchange). Most MTAs also seem to be hellishly difficult to configure. Try and read the Exim documentation; you could do a university degree on it (I'm not kidding). When you can get an HTTP server like Cherokee which is easy to configure and has a nice web interface, do MTAs or groupware solutions need to be that hard? I'm aware that some people think "the Unix way" is to have lots of different interacting pieces of software (like maybe an SMTP MTA, POP3 service, webmail service, and overarching manager to tie them all together), but I think this is a situation where that just makes things a lot harder to deal with and one large software suite fits in much more nicely. So, I'm looking for good open source software suites that will run on Debian that: Combine (at least) SMTP, POP3, and IMAP Are easy(ish) to configure Have a nice configuration web interface or GUI Are not defunct projects I don't mind if it's groupware and offers calendaring too, but I would only be using the e-mail functionality for now. Another nice-to-have would be built-in webmail (if we're combining a bunch of functionality, why not?) Note however that I do NOT need Outlook support. I am not really looking for an "Exchange replacement drop-in". The suites I've found so far that seem to match the above criteria (and have appropriate licenses) are Citadel, Kolab, and Zimbra. I'd appreciate anyone who has experience with any of these giving me the pros and cons of them, such as how easy they are to configure and what their performance is like. I'd also appreciate any other suggestions for solutions that fulfil my criteria that I may have missed out.

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• Outdoor WiFi Mesh Topology vs. Repeaters

  - by IronJaxor

  Here's the current configuration in our organization (which I believe is incorrect): We have a number of Cisco 1500 series AP's (22 in total), that are mounted outdoors to provide seamless WiFi coverage over a large area. Each AP however has its own physical ethernet connection back to the WLC (All the AP's are marked as Root AP's). They are all broadcasting the same SSID. We have tried to stagger the channel selection but because there are only three non-overlapping channels to choose from, and in some areas the density of AP's is quite high, there is multiple places of channel interference. With this configuration we experience 100-150 disconnects from clients every day. (Our clients are mobile so they move throughout the coverage area constantly). My idea is to switch the AP's to the same channel thereby forming a wireless mesh, use the built in functionality of the 1500 series to use 802.11a as the backhaul, designate one or two AP's as root AP's and wire them back to the WLC. Thereby forming a WiFi mesh, which if I'm not mistaken is the point of the 1500 series in the first place! I am however completely new at WiFi networks and wondering if I am simply mistaken in what I believe my proposed changes will enable, or if there is a better way to tackle the WiFi topology.

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• Start Chrome by command line, but adding some arguments to make it login into your Google account automatically

  - by jim

  Is there a way to start Chrome calling it from the command line (using Linux), but providing it some argument to make it login into some Google account automatically? I'm looking for something like google-chrome -account foo -pass bar that I can easily put in a bash script later. A little background: I have a laptop connected to my TV, which is currently using just a mouse for user interaction. There's no google account logged in by default, and that's the way I want to keep it, so my kids can't come across videos and pictures in google and youtube that they are not supposed to see (e.g.: adult content, or anything marked as not appropriate for kids by the google's safe search filters). The bad thing about this is that there are some music videos in youtube that requires you to be logged in to see, usually those we (the adults) used to sing when playing karaoke... as the only input available is a mouse, I'm looking for a way to start with my google account without having to type the whole thing usin the on-screen keyboard. You may think "Why you can't use the keyboard, if the laptop is right there?". Well, it's in a kind of uncomfortable position - too high for me without a chair or something, as it's right above the furniture in where the TV is located. Is there a way to make this scriptable? If not, do you know any other workaround? Note: using the remember me after logging off or alike options are discarded, as the safe-search chrome version must be always the default version to run.

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• Large scale file replication with an option to "unsubscribe" from a replicated file on a given machine

  - by Alexander Gladysh

  I have a 100+ GB files per day incoming on one machine. (File size is arbitrary and can be adjusted as needed.) I have several other machines that do some work on these files. I need to reliably deliver each incoming file to the worker machines. A worker machine should be able to free its HDD from a file once it is done working with it. It is preferable that a file would be uploaded to the worker only once and then processed in place, and then deleted, without copying somewhere else — to minimize already high HDD load. (Worker itself requires quite a bit of bandwidth.) Please advise a solution that is not based on Java. None of existing replication solutions that I've seen can do the "free HDD from the file once processed" stuff — but maybe I'm missing something... A preferable solution should work with files (from the POV of our business logic code), not require the business logic to connect to some queue or other. (Internally the solution may use whatever technology it needs to — except Java.)

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• GroupWise 6.5 IMAP Service Shuts Down-Needs Constant Restarting

  - by Jeffrey Majette

  I have an issue with my aging (and soon to be replaced) GroupWise 6.5 system. The IMAP service in the GWIA tends to periodically shut down, requiring that I restart the service. When IMAP is down, my end users who use Blackberry BIS cannot send or receive email on their devices. It's a royal pain to have to restart the IMAP service several times a day. The GWIA logs do not seem to indicate a problem. I thought I was on to something yesterday. I discovered that the gwia.cfg file located in SYS:SYSTEM was actually from GW 6.0. The gwia.cfg in DOMAIN\WPGATE\GWIA was titled for GW 6.5 when opening the file for editing. I changed the generic placeholder info in the file to match my environment and restarted the gwia. However, it made no difference in performance. The IMAP service shuts down about 30 minutes after the last restart. I know this version of GW is antiquated. We are in the process of migrating to Google Apps. But, if anyone has an idea that could fix this issue, I and my end user community would be forever grateful!

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• Servers/Websites Keep Going Down

  - by Tyler Johnson

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

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• Standing and sitting while using a computer at work

  - by Adam Batkin

  I would like to be able to comfortably switch between sitting and standing while at work (I'm a software developer, so I spend most of my day in front of a computer). For the past couple of months I have been using a large elevated stand that sits on my desk (designed expressly for this purpose) containing my keyboard and mouse, and my monitors have been raised as high as possible and aimed upwards. So I can stand all day and I'm pretty comfortable (my right wrist may be at too much of an angle when it's on my mouse, but that's a separate issue). The only problem is that sometimes I want to be able to sit. I can easily place my keyboard and mouse back down under the elevated stand, but I have to look up pretty steeply and that is uncomfortable and makes it difficult to see the screens since they are tilted upwards. My monitor mounts are difficult to adjust quickly/easily, so I can't just re-aim them. I would of course love one of those hydraulic standing/sitting desks (cost isn't the problem). But I'm in a row of "trader-style" desks where it's basically a very long surface with people sitting at 6-foot intervals. What type of equipment do you recommend? I suppose the best thing would be some sort of monitor stand (it must be able to hold 2-3 LCDs) that can easily be lowered and raised. But any other suggestions are also welcome.

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• windows: force user to use specific network adapter

  - by Chad

  I'm looking for a configuration/hack to force a particular application or all traffic from a particular user to use a specific NIC. I have an legacy client/server app that has a "security feature" that limits connections based on IP address. I'm trying to find a way to migrate this app to a terminal server environment. The simple solution is for the development team to update the code in the application, however in this case that's not an option. I was thinking I might be able to install VMware NIC's installed for each user on the terminal server and do some type of scripting to force that user account to use a specific NIC. Anybody have any ideas on this? EDIT 1: I think I have a hack to work around my specific problem, however I'd love to hear of a more elegant solution. I got lucky in that the software reads the server IP address out of a config file. So I'm going to have to make a config file for each user and make a customer programs files for each user. Then add a VMware NIC for each user and make each server IP address reside on a different subnet. That will force the traffic for a particular user to a particular IP address, however its really messy and all the VM NIC's will slow down the terminal server. I'll setup a proof of concept Monday and let the group know how it affects performance.

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• Setting up a global MySQL Cluster in the cloud

  - by GregB

  I'm giving the question an overhaul to more specifically identify where I need help. I use two tools to manage a bunch of cloud server: Puppet and Rundeck. Both of these can be configured to use a mysql backend. I'd like to setup an instance of each application in both the U.S., and the U.K., treating the U.K. servers as hot stand-bys in case of failure in the U.S. I want to use a MySql cluster so that the data is automatically replicated from the U.S. to the U.K. Because these are hot standbys, high performance is not a goal. Redundancy and data integrity are most important. My question revolves around the setup of the mysql cluster. I want to run three servers, each one running a data node, a sql node, and a management node. Is this a valid configuration for mysql server? If so, could someone point me in the right direction for creating such a setup? I've downloaded the offical tarball, and the official debian, and the documentation for them contradicts many of the online tutorials. I'm installing on Ubuntu 10.04.

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• What mobile phones are viable for a "nerdy" person? [closed]

  - by Blixt

  This community wiki is for determining a list of good mobile phone choices if you are "nerdy" (definition follows.) As a point of reference, the almost two years old N95 8GB will be used. Mostly because that's what I can most relate to since I've had it since it came out. Today, iPhone and other modern mobile phones really out-shine it in usability and interface. However, it still does everything I want it to do (and here's the definition of "nerdy"; modify as needed): Syncs contacts, calendar, tasks and mail in the background Can run multiple installable applications in the background (Google Maps with Latitude, for example) Good amount of space for music etc. Lets you develop your own little toy applications (Python; not to mention it can also run an Apache server with a public URL!) Tethering! Supports Flash (maybe not very important, but it has its uses) Has a manufacturer that believes in the nerdiness! (The people at Nokia Labs make lots of cool stuff and share early versions with the community and are generally open) A high resolution screen (at least 320x240) Special hardware features such as an accelerometer and GPS What's missing from the N95 8GB but still qualifies as good, "nerdy", qualities: 7.2 Mbit/s (or faster) internet through HSDPA or HSPA+. A good web browser that can do most of the stuff a desktop browser can (especially render sites properly and run JavaScript correctly) Touch (especially multi-touch) More special hardware features such as a compass Intuitive and fluent user interface (Shiny stuff) Ability to configure it to trust root certificates of my own choice A processor fast enough to run Quake 3! =)

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• Exchange 2003 Internet Mail Size Limits

  - by scampbell

  I have unsuccessfully tried to increase per user incoming mail size settings by editing their user account settings on our Exchange server, but large incoming mail from external domains is still blocked using the default global settings. After reading here: http://support.microsoft.com/default.aspx?scid=kb;en-us;322679 I see that All Internet e-mail messages use the global setting for limits on sending and on receiving. The message categorizer evaluates the sender's sending limit and the recipient's receiving limit. In example 2 earlier, a user with a user mailbox limit of 3 MB could receive messages from another user with a 3-MB sending limit. Because Internet users use the global setting, they can send only a 2-MB message. Which to me is madness! Surely if I want to allow a user to receive mail up to a certain size then I should be able to set it as such? Is there a specific way of getting round this? Would setting the global defaults high and setting a lower, say 10MB, limit on the SMTP connector do the trick? Thanks.

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• VPS Memory Exchausted Even With Light Settings

  - by user101570

  Linux noob here. I have a 256MB VPS on Ubuntu 11.04 server and when I run "free -m" the result shows all memory being used (including the second line re: buffers/cache). I found this very strange, considering I only have 5 Apache processes running each chewing up about 20MB each. MYSQL is taking up 30MB. To my knowledge, and according to "top", I have no other memory hogs operating. Settings that may be relevant: PHP memory_limit = 32M MYSQL key_buffer = 16M Prefork MPM Maxclients = 10 So when I reviewed these settings, I naturally thought maxclients was too high, so I tried switching it to 5. Now not only does my memory still show as being 100% used, my website loads much, much slower, despite not getting any traffic aside from mine at the moment. I don't understand this. I thought a single Apache process handles all requests from a client received within the "KeepAliveTimeout" window, which I've set to 2 seconds. With my initial config. of 10 maxclients, my page load times are around .3ms, so a single process should handle that no problem, correct? So next I went to an extreme level of 1 for maxclients. My memory is still at 100% usage and my site loads painfully slow. I'm a noob at a complete loss here. According to the many tutorials I've read on basic server setup, I should be good to go. Help! Please! Edit: total used free shared buffers cached Mem: 256 256 0 0 0 0 -/+ buffers/cache: 256 0 Swap: 0 0 0

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• 150 TB and growing, but how to grow?

  - by seandavi

  My group currently has two largish storage servers, both NAS running debian linux. The first is an all-in-one 24-disk (SATA) server that is several years old. We have two hardware RAIDS set up on it with LVM over those. The second server is 64 disks divided over 4 enclosures, each a hardware RAID 6, connected via external SAS. We use XFS with LVM over that to create 100TB useable storage. All of this works pretty well, but we are outgrowing these systems. Having build two such servers and still growing, we want to build something that allows us more flexibility in terms of future growth, backup options, that behaves better under disk failure (checking the larger filesystem can take a day or more), and can stand up in a heavily concurrent environment (think small computer cluster). We do not have system administration support, so we administer all of this ourselves (we are a genomics lab). So, what we seek is a relatively low-cost, acceptable performance storage solution that will allow future growth and flexible configuration (think ZFS with different pools having different operating characteristics). We are probably outside the realm of a single NAS. We have been thinking about a combination of ZFS (on openindiana, for example) or btrfs per server with glusterfs running on top of that if we do it ourselves. What we are weighing that against is simply biting the bullet and investing in Isilon or 3Par storage solutions. Any suggestions or experiences are appreciated.

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• ASP.Net Session Timing Out Rapidly

  - by Zac

  We have an ASP.Net 3.5 website running on Windows Server 2008 with IIS7. The session timeout period for this site is configured to be 20 minutes - however, it is currently lasting for between 40 and 50 seconds. After researching the problem we investigated several configuration values which could be involved in the timeout period but none of them are set to less than 20 minutes. The areas we look are as follows: web.config system.web/sessionState element (20 minutes). web.config system.web/authentication/forms element (not present, defaults to 30 minutes). Sites/{website}/ASP/Session Properties/Time-out (20 minutes). Application Pools/{appPool}/Advanced Settings/Process Model/Idle Time-out (20 minutes). We've also noted that the CPU is staying around 0% and that RAM usage is flat-lining around 1.07 GB (of 8 GB available) - so there is no performance-based reason for IIS to be recycling the Application Pool as far as we can tell. Are there any settings we've overlooked which could cause the session timeouts to be expiring so quickly? EDIT A couple of additional points: This is not occurring in development, only on the server. The session is not sliding (i.e. if we refresh the page a few times it still times out approximately 40 - 50 seconds after the session was created.

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• Mysqld shutting down by itself

  - by AJ Naidas

  I'm running a Wordpress Blog that gets medium-high traffic. It is hosted in an Ubuntu Server 2GB Memory 2 Core Processor 40GB SSD Disk, 3TB Transfer. The problem is that MySQL shuts down by itself after an hour or two. I had to restart mysql each and every time this happens. I checked the logs and this is what I found: 140612 6:48:14 [Warning] Using unique option prefix myisam-recover instead of myisam-recover-options is deprecated and will be removed in a future release. Please use the full name instead. 140612 6:48:14 [Note] Plugin 'FEDERATED' is disabled. 140612 6:48:14 InnoDB: The InnoDB memory heap is disabled 140612 6:48:14 InnoDB: Mutexes and rw_locks use GCC atomic builtins 140612 6:48:14 InnoDB: Compressed tables use zlib 1.2.3.4 140612 6:48:14 InnoDB: Initializing buffer pool, size = 1.4G InnoDB: mmap(1502412800 bytes) failed; errno 12 140612 6:48:14 InnoDB: Completed initialization of buffer pool 140612 6:48:14 InnoDB: Fatal error: cannot allocate memory for the buffer pool 140612 6:48:14 [ERROR] Plugin 'InnoDB' init function returned error. 140612 6:48:14 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. 140612 6:48:14 [ERROR] Unknown/unsupported storage engine: InnoDB 140612 6:48:14 [ERROR] Aborting 140612 6:48:14 [Note] /usr/sbin/mysqld: Shutdown complete judging by this line: 140612 6:48:14 InnoDB: Fatal error: cannot allocate memory for the buffer pool I suspect that this is a memory problem, but I would like to hear from the experts here before I conclude. Is this a lack of memory problem? Do you think the value of max_connections in my.cnf (currently 100) is a potential cause and needs increasing? TIA.

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• How to detect/list rogue computers connected to a WIFI network without access to the Wifi Router interface? [migrated]

  - by JJarava

  This is what I believe to be an interesting challenge :) A relative (that leaves a bit too far to go there in person) is complaining that their WIFI/Internet network performance has gone down abysmally lately. She'd like to know if some of the neighbors are using her wifi network to access the internet but she's not too technically savvy. I know that the best way to prevent issues would be to change the Router password, but it's a bit of a PITA having to re-configure all wifi devices... and if the uninvited guest broke the password once, they can do it again... Her wifi router/internet connection is provided by the telco, and remotely managed so she can log-on to their telco account's page and remotely change the router's Wifi password, but doesn't have access to the router status page/config/etc unless she opts out of the telco's remote support and mainteinance service... So, how could she check if there are guests in the wifi with this restrictions and in the most "point and click way"? In this case I'd probably use nmap to look for other devices in the network, but I'm not sure if that's the easiest way to do it. I'm not a wifi expert, so I don't know if there are any wifi-scanning utils that can tell us who's talking to the router... Lastly, she's a Windows user as I guess that'll influence the choice of tools available Any suggestions more than welcome Regards!

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• Does having TRIM enabled affect other hard drives on a computer (and how do you know when Windows is using it)?

  - by Breakthrough

  I recently purchased a solid state drive (an OCZ Vertex 2 (80 GB)) to use as my primary operating system partition. I also have three other SATA hard drives of assorted sizes. I successfully installed Windows 7 Professional onto the SSD (works awesome, great response time and transfer rate), and used the other three HDDs for data storage. I was browsing through the Bible of OCZ SSDs, and noticed the following in Section 60-76 - Tweaks and TRIM: Q. How do I know if TRIM is enabled on my OCZ SSD? A. In Windows 7, go to start/run/cmd), type the following: fsutil.exe behaviour query DisableDeleteNotify It should respond back with: DisableDeleteNotify=0 if TRIM support is ready and active. If it's not, then type: fsutil.exe behavior set DisableDeleteNotify 0 After a bit of searching on Google, I found similar results elsewhere (set DisableDeleteNotify to 0, which makes sense since for TRIM to work, the solid-state drive needs to be notified when deletes occur (for the garbage collector) unlike a normal hard drive). When I run the query on fsutil, I get the following result: DisableDeleteNotify = 48 Following the instructions I found, I set this to 0 instead of 48. However, I am beginning to wonder. Is this all the proof I really need that the OS is using TRIM? Also, since this applies globally for the computer, is TRIM data being sent to the other hard drives connected to the computer? And if so, would this cause any degradation in disk performance?

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• What hardware would I need (approx) to run ESXi server?

  - by mr.b

  Hi, I am considering to purchase off-the-shelf commodity hardware in order to build server that will host virtual machines using ESXi server. Intended purpose for this server is NOT mission critical tasks. It will have to run perhaps 20-50 Windows XP/Vista/7 virtual machines (in total, but closer to 20 figure). Each guest would have to have 1-2 GB of ram, and probably two-three times more disk space than guest OS needs with clean install and all updates applied (that would be around 6-8 GB for XP, and i believe closer to 10-15 for win7). Those guests will act as a test ground for a new product that is network management software, thus guests will idle most of their time once initially loaded, but if I give them some task to complete, they should be able to perform reasonably well. Now, from what I have learned... CPU is usually not much of an issue (6 cores would do it), memory should not be lacking, but doesn't have to be sum of all guests, because of overcommitment... That leads me to IO, which is, as it seems, the bottleneck. Since I have very little experience with ESXi (and ESX, too) server, I'd like to ask: How much memory could I save by overcommitment, and how does it affect performance? Is 6-core cpu enough to run above described system? Would it be possible to run entire server off two (or even one) SSD drives (to host system virtual disks, with few additional HDDs (2-3) in RAID 0 to be used as secondary storage? I read somewhere that ESXi allows having something like "master image", essentially virtual machine that is "deployed" many times, so that disk space can be saved by having only differences stored by specific guests, instead of copying around whole virtual disks. Is this true, and how can this help me? Are there any other things I need to take into consideration when building this off-the-shelf solution? I should probably mention here that I'm fully aware of issues like SPOF regarding power supply, raid 0, etc, but since it's only a testing ground and not a production system, it's not so important for me. Thanks, B.

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• ssh hangs on "Last login" line

  - by Pavel H

  This happened for the first time three days ago - I ssh to the server, authenticate using a password, get the welcome message but it remains hanging on the "Last login:..." line. The command line doesn't show and the server doesn't react to my input. Other services on the server keep working ok (apache, tomcat, database, ..). The box has an out-of-band management using which I was able to restart it. After the restart the ssh worked ok again and I didn't find anything suspicious in the logs. Three days later the same problem occurs on this box again, and newly on yet another server in the cluster - 100% same symptoms. Both servers have about 2 month old installation of Debian Squeeze (6.0.2) and the problem never occurred before despite frequent ssh-ing, so it should not be a problem of settings. We haven't been installing anything new for quite some time now. I also made sure there is enough disk space on both servers. Since it started to happen all of a sudden on two servers at about the same time, I suspect some bug may have been introduced via Debian updates, yet I haven't been able to find anyone with the same problem. Most similar issues I have found: ssh freezes at the "Last Login Line" - in our case everything worked fine until recently, so nothing related to settings should be our problem. Diskspace checked, I couldn't check the memory but I would expect something would be in the logs if the system had been running out of it. Remote Fedora system unresponsive, odd but consistent behavior when trying to log in - problem with high load on the server; unlike in this case, nothing changes even if I wait for 10+ minutes

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• Find which files an apache process is writing to?

  - by Haluk

  We have this apache process which becomes io-bound time to time. Using atop, we can see it is a write operation. Using lsof -p <PID> we can see a list of files open by the httpd process. First we thought "log" files must be the problem. So we turned them off just to test. However write operations still continues. We will continue testing a few other things. For instance we use php session variables a lot. Maybe php session files are getting all the writing. But is there a way to quickly identify files which get written to by the httpd process? This way we can focus our efforts on those files. UPDATE: We used the strace command as suggested. Here are two lines from the output. write(23, "\27\0\0\0\3SET CHARACTER SET utf8", 27) = 27 write(23, "\17\0\0\0\3SET NAMES utf8", 19) = 19 We do not have a mysql process on this server. So is strace also showing what is being written to an ethernet port? UPDATE2: During high io load, the process which consumes most of the write resources gives the following output to strace -e trace=write -p <PID>: --- SIGCHLD (Child exited) @ 0 (0) --- write(9, "!", 1) = 1 write(19, "OPTIONS * HTTP/1.0\r\nUser-Agent: Apache (internal dummy connection)\r\n\r\n", 70) = 70 However I cannot figure out where these are being written to.

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• toshiba a200 laptop hangs/freezes when plugged in

  - by tapan

  The subject says it all. It is the exact same problem as described here. I had asked a similar question before here. My system specs etc, everything is here. My problem is just that I cannot afford to get it fixed right now. I just need for the laptop to be kind of usable for 2-3 more months. It worked perfectly for 3 months or so in ubuntu recovery mode. Now it hangs/freezes every hour. I spend 8 hours a day on an average on my laptop. So i just want it to last at least that long. If the laptop is not plugged in in recovery mode / regular ubuntu mode, it freezes in 5 mins and the screen becomes all weird. With my windows 7 OS, it works perfectly on battery but hangs instantly as soon as it is plugged in. Also now, a high cpu usage doesn't help anymore. Any strategy or suggestions i could employ to extend the duration for which it doesn't freeze ?

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• How to get back the themes feature in Windows XP?

  - by Martín M.

  When I try to set a visual style in Windows XP (the standard Luna, for example), I get one of these two: "Access denied" error. It works, but when I restart the computer, I get the Classic look again, with no errors. Also, the "Windows and icons" dropdown is grayed out in the "Appearance". This is a list of things I have tried, with no results: Making sure "Use visual styles on windows" is checked on System Properties Advanced Performance. Restarting the "Themes" service. It starts cleanly, no errors. Applying these two fixes: Kelly's Corner and tweaks.com. Running sfc /scannow and checking the integrity of uxtheme.dll against a clean installation of XP Restoring the whole \Windows\Resources\Themes directory. Creating a new user. The new user does not seem to suffer this problem. Maybe this is the solution, create a new user and migrating all the data, but it would be a pain, and I would prefer reinstalling the whole thing. I am using Windows XP Professional SP3, with no spyware, no virus, and no other visible malfunctions. How can I fix this?

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• ubuntu's average load never below "0.00 0.01 0.05"

  - by Karma Fusebox

  I have several ubuntu 12.04 VMs running on a ubuntu 12.04 KVM host. Those of the virtual machines that are totally idle with no services (except syslog and the other "small" standard stuff of a fresh installation) show a constant load of "0.00 0.01 0.05" in top/htop as average 1/5/15. When there are "real" applications running, the load averages behave perfectly normal but they never fall below the mentioned values. While this doesn't affect performance at all and could easily be ignored, it screws up the monitoring graphs in a very annoying way: (Notice how load15 behaves nicely if 0.05 for a short time in the right half of the pic) Unfortunately I don't know what diagnostic outputs might be helpful for you, so here's some default stuff: # top top - 16:31:01 up 1:05, 1 user, load average: 0.00, 0.01, 0.05 Tasks: 62 total, 1 running, 61 sleeping, 0 stopped, 0 zombie Cpu(s): 0.2%us, 0.2%sy, 0.0%ni, 99.2%id, 0.5%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 1019464k total, 73452k used, 946012k free, 6140k buffers Swap: 0k total, 0k used, 0k free, 22504k cached . # free -m total used free shared buffers cached Mem: 995 72 923 0 6 21 -/+ buffers/cache: 43 951 Swap: 0 0 0 . # iostat -x /dev/vda Linux 3.2.0-32-virtual (vm3) 11/15/2012 _x86_64_ (2 CPU) avg-cpu: %user %nice %system %iowait %steal %idle 0.25 0.00 0.65 0.20 0.24 98.66 Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util vda 0.14 0.12 0.51 0.22 6.74 1.46 22.50 0.02 23.26 20.64 29.30 7.63 0.56 Need something else? Has anyone ever seen this behavior? Might this be a bug in kvm/ubuntu/kernel 3.x in the end? Thanks a lot!

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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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