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• switch OFF syn cookies

  - by Nick

  We have several servers they have public IP's, but work together (one is with Load Balancer, orther with Apache Web server, other with MySQL and so on. Most of the ports are fire-walled, so only "local" servers can be connect there. However ALL servers have some ports that must be publicly open. We have SYN Cookies enabled and from time to time we got: possible SYN flooding on port 8080. Sending cookies. Port 8080 is not public. How we can switch OFF SYN Cookies for some ports (e.g. 8080, 3306 etc) or from some sources (e.g. our servers), but in same time SYN Cookies to be switched ON for all other ports, e.g. port 80. We found this similar problem, except our servers are with public IP's: SYN cookies on internal machines

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• How to keep program always in memory (no swapping)

  - by Yossarian

  I'm using KeePass (on Windows 7) for storing passwords. The application is running on my laptop almost 100% of the time, but I'm using it rarely. The problem is, that activating the window after long time takes huge amount of time, I'd say that OS realized the application is no longer used and swapped it. I don't want OS to swap my KeePass (because of the loading lag, and also because of security - I don't like the idea of password keeping program's memory to be stored anywhere on HDD). Is there any possibility how to tell OS not to swap some program? Or, is this achievable by some programming?

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• Remote I/O costs with a Content Delivery Network

  - by x711Li

  As far as I know, the time complexity of scanning a directory and the amount of files in said directory are correlated due to I/O costs. Would the administrative costs of placing the files in a hashed directory tree for uploading/downloading files through a CDN API be worth it for the added efficiency? For instance, given a filename foo.mp3, the MD5 hash for this is 10ebb1120767e9de166e0f5905077cb1. Thus, storing foo.mp3 in ./10/eb/foo.mp3 would allow for less files per directory (assuming MD5 generates patterns with in Base36, this allows for 36^2 root directories with 36^2 subdirectories each and little chance of hash collision) Considering the directories themselves are not loaded, would the I/O costs of directory scanning still exist with direct uploading/downloading?

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• Computer hangs on start-up, but re-start always works

  - by user10604

  I press the power switch; the fans start whirring; then precisely nothing happens. The monitor lights (I have two monitors) blink to indicate that they aren't receiving any signal - no BIOS splash screen, nothing. This scenario occurs about 80 percent of the time, the other 20 percent being normal starts. Noticing that the computer has not started properly, I press the power switch for four seconds to turn the computer off, and then I press it again to start the computer for the second time. It always starts normally the second time. Always. The power supply is a 750W from SilverStone. The motherboard is a Gigabyte P55A-UD3P. The video card is an Asus EN9800GT. There's 8 GB of RAM. I don't know what other information might be pertinent. Help!

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• How do I get the machine name from an IP via Multicast DNS?

  - by Adam

  I have a list of IP addresses on a network, and most of them support multicast DNS. I'd like to be able to resolve the server name instead of just having the IP address. ping computer.local 64 bytes from 192.168.0.52: icmp_seq=1 ttl=64 time=5.510 ms 64 bytes from 192.168.0.52: icmp_seq=2 ttl=64 time=5.396 ms 64 bytes from 192.168.0.52: icmp_seq=3 ttl=64 time=5.273 ms Works, but I'd like to be able to determine that name from the IP. Also the devices don't necessarily broadcast any services, but definitely do support mDNS broadcast. So looking through services won't work.

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• Sending a large number of mails causing problems on CentOS 6 / Plesk 10

  - by papakost

  I have a VPS running CentOS 6. When the system tries to send daily newsletter, after some time (e.g. after sending about 2000 emails), I get error "Unable to send mail" and the system memory goes really high. Till this moment, the mails are delivered normally. The rest symptoms are: I cannot see anything on /var/log/maillog (File seems not to be written) All files on /var/spool/mail have 0 bytes size. From time to time on httpd log I get errors like: /usr/sbin/sendmail: error while loading shared libraries: libc.so.6: cannot open shared object file: Error 23 "Activate mail service on domain" setting in Plesk is deactivated. Any idea on what's going wrong here?

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• How do you create a SQL query in Excel 2007 with a dynamic date range?

  - by Jordan

  I am trying to create a reporting spreadsheet that can print reports for a given time period. The query below works, but when I try to use a "?" parameter in place of the date, I get an error after selecting a cell containing my date. If I use single quotes ('?') I get a conversion from string to date/time failure, if I don't (?) I get a syntax error near @p1. Eventually I will need either a start and end date or a formula adding a month or shift to the starting date/time to filter the data down to important information. The query was built in Microsoft Query. SELECT FloatTable.DateAndTime, TagTable.TagName FROM master.dbo.FloatTable FloatTable, master.dbo.TagTable TagTable WHERE FloatTable.TagIndex = TagTable.TagIndex AND ((FloatTable.DateAndTime={ts '2012-06-01 00:00:00'})) Any assistance would be much appreciated. Thanks in advance.

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• Cloud hosting and single hardware point of failure?

  - by PeterB

  From talking to sales I thought Rackspace Cloud was running on a SAN and compute nodes (as VMWare's offerings do), only to find out it doesn't, so when the host server goes down for maintenance all cloud servers on the server go down (in our case for 2.5 hours). I understand Amazon EC2 also has this single-server point of failure. Which cloud hosting solutions don't rely on a single server? I've yet to find a list by architecture Is there a term that distinguishes between these types of 'cloud'? Is one of these 'grid computing' and the other 'virtualisation'? Can a SAN backed solution provide the same reliability as 2 mirrored cloud servers on (say) Rackspace Cloud? I am more familiar with the VMWare architecture and would like to understand the advantages and disadvantages of each approach. I understand the standard architecture is to have multiple cloud servers and mirrored data between them; until we need multiple database servers I'm wondering if a SAN/node hosting solution would provide the lack of downtime we need without the added complexity.

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• Reducing storage cost by moving old files to external USB HDDs. Your thoughts?

  - by cparker4486

  I've got about 300GB of pictures and marketing data that is rarely accessed and I'd like to get it off my main storage. I was thinking to simply add two external USB HDDs to the server and move all the files to one of the drives. The second drive would be the backup destination for the first drive. I'm working with Server 2003 R2 SP2. This will help me free a good amount of space on my main storage as well as reduce the complexity, backup window, and usage of my backups to tape.

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• How do I log file system read/writes by filename in Linux?

  - by Casey

  I'm looking for a simple method that will log file system operations. It should display the name of the file being accessed or modified. I'm familiar with powertop, and it appears this works to an extent, in so much that it show the user files that were written to. Is there any other utilities that support this feature. Some of my findings: powertop: best for write access logging, but more focused on CPU activity iotop: shows real time disk access by process, but not file name lsof: shows the open files per process, but not real time file access iostat: shows the real time I/O performance of disk/arrays but does not indicate file or process

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• Greater than or equal check when using Group Policy Preferences and Item Level Targeting in the Registry

  - by edusysadmin

  I'm implementing some screen saver configurations via Group Policy Preferences (on Win7 Enterprise x64 desktops). The desired configuration is to have users be able to adjust their screen saver and screen saver time out, but not allow them to select non screen saver or a time out higher than 45min. I've found a great write-up for configuration of the screen saver (link) but cannot find a way to configure the time out. I cannot find a way to have the item level targeting compare the reg key HKCU\Control Panel\Desktop\ScreenSaveTimeOut value and force an over-write of the key if configured above 45min/2700seconds. Anyone else tried something like this or found a means to do this?

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• When resizing Windows Explorer on Windows 8 it crashes?

  - by Tural Teyyuboglu

  I have following problem: When I try to change size of any explorer window from maximized to some size getting following screen It blinks 20-30 times, then crashes. Also it changes it's size every time into this square size. Here is event viewer result: The program Explorer.EXE version 6.2.9200.16384 stopped interacting with Windows and was closed. To see if more information about the problem is available, check the problem history in the Action Center control panel. Process ID: 10f8 Start Time: 01cd9e3e189fe3d1 Termination Time: 0 Application Path: C:\Windows\Explorer.EXE Report Id: ea71d13a-0a32-11e2-be92-3859f90026b6 Faulting package full name: Faulting package-relative application ID: What can be issue? Is there any way to fix explorer crashes? Or only way is reinstalling windows?

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• Windows 2003 Server Suddenly Drops Connections to everything but PING and port 80 (webserver)

  - by Urda

  Hi, I'm running a Windows 2003 Dedicated server, and the box has been rock solid for more than 2 years now. Just recently, I have had an issue where after a certain ammount of time the server will just stop accepting connections on all ports except 80, and still responds to pings. If you surf to a static HTML page on the box, you can display it. If you pull up a PHP file that has an outside database connection, it fails. RDP refuses to connect, and LogMeIn reports that "The connection was reset" The only fix at this time is to have the provider physically reboot my box to correct the issue. The event log doesn't seem to be leaving helpful messages, and I am at a lost to what is causing this error since I have not installed any new software in months on it. Any tips or help would be appreciated to tracking down this issue. I don't mind updating the question as responses come in, I just do not know where to start troubleshooting because it seems random at this time.

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• perform command substitution in MS-DOS

  - by wiggin200

  I wonder how you can make in MS-DOS a command substitution Command substitution is a very powerful concept of the UNIX shell. It is used to insert the output of one command into a second command. E.g. with an assignment: $ today=$(date) # starts the "date" command, captures its output $ echo "$today" Mon Jul 26 13:16:02 MEST 2004 This can also be used with other commands besides assignments: $ echo "Today is $(date +%A), it's $(date +%H:%M)" Today is Monday, it's 13:21 This calls the date command two times, the first time to print the week-day, the second time for the current time. I need to know to do that in MS-DOS, (I already know that there is a way to perform something like that using as part of the for command, but this way is much more obfuscated and convoluted

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• Dynamically changing one-node Cassandra cluster to two nodes

  - by Jason Axelson

  So I have an application that will be very dormant most of the time but will need high-bursting a few days out of the month. Since we are deploying on EC2 I would like to keep only one Cassandra server up most of the time and then on burst days I want to bring one more server up (with more RAM and CPU than the first) to help serve the load. What is the best way to do this? Should I take a different approach? Some notes about what I plan to do: Bring the node up and repair it immediately After the burst time is over decommission the powerful node Use the always-on server as the seed node My main question is how to get the nodes to share all the data since I want a replication factor of 2 (so both nodes have all the data) but that won't work while there is only one server. Should I bring up 2 extra servers instead of just one?

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• Windows Server 2008 freezes when I run programs as administrator

  - by user5795

  I am working on a machine running Windows Server 2008. Every program I have tried to run (firefox, notepad, wordpad) works fine, but if I right-click on any item on the desktop or the start menu and select "Run as Administrator" it freezes. I can move the mouse around and open/close the start menu, but the items in the start menu do not change color when the mouse hovers over them. I googled for answers for some time but had no luck. Does anyone have any ideas that I could try? (Update: I forgot to mention that the machine is virtual and I am using VMWare Workstation. In order to answer the questions below, I have been going to the same snapshot of the system each time. This lets me start the system in the exact same place each time in order to answer your questions and test.) (Update: When I run any process as administrator and it freezes, I can start task manager, but I cannot see the new process (notepad, etc...) )

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• What is your approach to draw a representation of your network ?

  - by Kartoch

  Hello, I'm looking to the community to see how people are drawing their networks, i.e. using symbols to represent complex topology. You can have hardware approach, where every hardware unit are represented. You can also have "entity" approach, where each "service" is shown. Both are interesting but it is difficult to have both on the same schema (but this is needed, especially using virtualization environment). Furthermore, it is difficult to have complex informations on such representation. For instance security parameters (encrypted link, need for authentication) or specific details (protocol type, ports, encapsulation). So my question is: where your are drawing a representation of your network, what is your approach ? Are you using methodology and/or specific softwares ? What is your recommendations for information to put (or not) ? How to deal with the complexity when the network becomes large and/or you want to put a lot of information on it ? Examples and links to good references will be appreciated.

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• Altering specific configuration values in the On-Screen Keyboard of Windows 7

  - by fnst

  I have to use the On-Screen Keyboard of Windows 7 for typing: (In case you haven't used it yet, you can get it via: All Programs - Accessories - Ease of Access - On-Screen Keyboard or simply search for "osk.exe") It offers a feature to "hover" about the buttons. Microsoft describes it as the following: In hovering mode, you use a mouse or joystick to point to a key for a predefined period of time, and the selected character is typed automatically. There is my specific problem. The predefined period of time is too long to be useful for me. The minimum amount of time is 0.5 seconds (max. 3 seconds). Is there any way to alter this value to something < 0.5? For example via editing the registry? Edit: The entry *'HKEY_CURRENT_USER\Software\Microsoft\Osk\HoverPeriod'* cannot be set lower than 500 ms. Any helpful tip would be great!

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• Windows Virtual Machine ping reply fails the first few times

  - by user28471

  I am running a windows Web Server 2008 virtual machine. When I try to ping it from another windows machine the ping reply comes straight back with 100% success. But when I try to ping it from one of the Linux boxes, the ping reply fails with partial or 100% loss the first couple of time and succeeds the third time onwards. I know it is quite strange but can any one think anything that could be causing it. Could anything in the Windows Domain Security or Firewall be "taking time" to allow responding to the ping request? In fact even the firewall is turned off on the virtual machine.

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• Why does this PowerShell script hang?

  - by jshin47

  Today I had to use Start-Sleep many times so I thought I would create a shortcut function for it, sleep($time). However, whenever I entered the function it never exits! It must be an issue with either the data type for the argument for Start-Sleep or the way I am declaring the function. Instead of posting the whole script, I've posted this useless one that would make a familiar beep pattern if it worked: function beep { Write-Host `a } function sleep { param([int]$time) Start-Sleep -m $time } beep sleep(300) beep sleep(200) beep sleep(50) beep sleep(300) beep sleep(450) beep sleep(200) beep

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• What does this error mean (Can't create TCP/IP socket (24))?

  - by user105196

  I have web server with OS RHEL 6.2 and Mysql 5.5.23 on another server and the web server can read from Mysql server without problem, but some time I got this error: [Sun Sep 23 06:13:07 2012] [error] [client XXXXX] DBI connect('XXXX:192.168.1.2:3306','XXX',...) failed: Can't create TCP/IP socket (24) at /var/www/html/file.pm line 199. my question : What does this error mean (Can't create TCP/IP socket (24))? is it OS error or Mysql error ? perl -v This is perl, v5.10.1 (*) built for x86_64-linux-thread-multi mysql -V mysql Ver 14.14 Distrib 5.5.23, for Linux (x86_64) using readline 5.1 su - mysql -s /bin/bash -c 'ulimit -a' core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 127220 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 10240 cpu time (seconds, -t) unlimited max user processes (-u) 1024 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited

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• Personal Browsing Monitor Software [closed]

  - by jmadden93

  Anyone know of any personal browsing monitor software? I'd like to be able to monitor my own browsing habbits and the time I spend on entertainment, vs work vs educational sites. Something that offers more than simply looking at the history feature built into browsers. It would be nice if it gave you a breakdown of how much time you spend on certain categories of sites like social media, vs video, vs. news, productivity, etc. I think it would be useful to know how one spends their time.

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• SSH - SFTP/SCP only + additional command running in background

  - by Chris

  there are many solutions described to get ur SSH-connection forced to only run SFTP by modifying the sshd_config by adding a new group match and give that new group a Forcecommand internal-sftp Well that works great but i would love to have a little more feature. My servers automatically ban IP's which try to connect often in a short time. So when you use any SFTP-Client, which opens multiple connections to work faster it can get banned instandly by the server for a long time. The servers have a script to whitelist users by administrator. I've modified this script to whitelist the user, which runs the script. All i need to do is now get the server to execute that script, when somebody logins. On SSH it's no problem, just put it in .bashrc or something like, but the Forcecommand don't runs these scripts on login. Is there any way to run such a shellscript before or at the same time as the Forcecommand get fired?

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• Is there a way to get a shared spreadsheet to update without closing and reopening?

  - by Mike

  Using Excel 2010, I have a spreadsheet that is used by 3 different people at any one time. But if one person has the spreadsheet open on there PC the other people can only view it as read only. I have since shared the workbook and put the spreadsheet on a shared network drive and now they can all view the spreadsheet at the same time and edit it at the same time. The problem is that nobody can see the changes that the other users have made unless the close out of the spreadsheet and open it up again to view the changes. I have checked the settings of the shared workbook and on the advanced tab have tick the option that updates the information every 5 minutes but the information does not update until you close out and open the spreadsheet back up again. How can I fix this problem?

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• Windows XP occasionally hangs for 2-3 minutes as the splash screen fades in.

  - by marcusw

  This is a bit of a rare problem, I have not been able to debug or fix it or find anyone else with the issue. I hope someone here can help me out. Once in a while, I boot up Windows XP from the first partition of the first disk (using grub, the computer dual-boots ubuntu) and it hangs as the Windows XP splash image fades in, leaving the screen with a dim image of the splash screen. After 2-3 minutes, it continues to boot as normal, no error messages or strange behavior. I have noticed that this happens about 75% of the time when the last time the computer was shut down it was from Ubuntu, and maybe 5-10% of the time otherwise. I have looked at system logs as far as I was able, and did not find anything the miss. What is causing this and how can I fix it?

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