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  • Utilize two gateways on the same network same interface with load balancing

    - by RushPL
    My setup is two ISPs on a single interface and single network. I can either set my default gateway to 192.168.0.1 or 192.168.1.250 and either work. My desire is to utilize both of them with some load balancing. I have tried to follow the advice given in here http://serverfault.com/a/96586 #!/bin/sh ip route show table main | grep -Ev '^default' \ | while read ROUTE ; do ip route add table ISP1 $ROUTE done ip route add default via 192.168.1.250 table ISP1 ip route add default via 192.168.0.1 table ISP2 iptables -t mangle -A PREROUTING -j CONNMARK --restore-mark iptables -t mangle -A PREROUTING -m mark ! --mark 0 -j ACCEPT iptables -t mangle -A PREROUTING -j MARK --set-mark 10 iptables -t mangle -A PREROUTING -m statistic --mode random --probability 0.5 -j MARK --set-mark 20 iptables -t mangle -A PREROUTING -j CONNMARK --save-mark Now then I do "traceroute somehost" repeatedly I can only get route through my default route which is 192.168.1.250. Shouldn't the packets change routes in a random manner? How to debug it?

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  • Performance triage

    - by Dave
    Folks often ask me how to approach a suspected performance issue. My personal strategy is informed by the fact that I work on concurrency issues. (When you have a hammer everything looks like a nail, but I'll try to keep this general). A good starting point is to ask yourself if the observed performance matches your expectations. Expectations might be derived from known system performance limits, prototypes, and other software or environments that are comparable to your particular system-under-test. Some simple comparisons and microbenchmarks can be useful at this stage. It's also useful to write some very simple programs to validate some of the reported or expected system limits. Can that disk controller really tolerate and sustain 500 reads per second? To reduce the number of confounding factors it's better to try to answer that question with a very simple targeted program. And finally, nothing beats having familiarity with the technologies that underlying your particular layer. On the topic of confounding factors, as our technology stacks become deeper and less transparent, we often find our own technology working against us in some unexpected way to choke performance rather than simply running into some fundamental system limit. A good example is the warm-up time needed by just-in-time compilers in Java Virtual Machines. I won't delve too far into that particular hole except to say that it's rare to find good benchmarks and methodology for java code. Another example is power management on x86. Power management is great, but it can take a while for the CPUs to throttle up from low(er) frequencies to full throttle. And while I love "turbo" mode, it makes benchmarking applications with multiple threads a chore as you have to remember to turn it off and then back on otherwise short single-threaded runs may look abnormally fast compared to runs with higher thread counts. In general for performance characterization I disable turbo mode and fix the power governor at "performance" state. Another source of complexity is the scheduler, which I've discussed in prior blog entries. Lets say I have a running application and I want to better understand its behavior and performance. We'll presume it's warmed up, is under load, and is an execution mode representative of what we think the norm would be. It should be in steady-state, if a steady-state mode even exists. On Solaris the very first thing I'll do is take a set of "pstack" samples. Pstack briefly stops the process and walks each of the stacks, reporting symbolic information (if available) for each frame. For Java, pstack has been augmented to understand java frames, and even report inlining. A few pstack samples can provide powerful insight into what's actually going on inside the program. You'll be able to see calling patterns, which threads are blocked on what system calls or synchronization constructs, memory allocation, etc. If your code is CPU-bound then you'll get a good sense where the cycles are being spent. (I should caution that normal C/C++ inlining can diffuse an otherwise "hot" method into other methods. This is a rare instance where pstack sampling might not immediately point to the key problem). At this point you'll need to reconcile what you're seeing with pstack and your mental model of what you think the program should be doing. They're often rather different. And generally if there's a key performance issue, you'll spot it with a moderate number of samples. I'll also use OS-level observability tools to lock for the existence of bottlenecks where threads contend for locks; other situations where threads are blocked; and the distribution of threads over the system. On Solaris some good tools are mpstat and too a lesser degree, vmstat. Try running "mpstat -a 5" in one window while the application program runs concurrently. One key measure is the voluntary context switch rate "vctx" or "csw" which reflects threads descheduling themselves. It's also good to look at the user; system; and idle CPU percentages. This can give a broad but useful understanding if your threads are mostly parked or mostly running. For instance if your program makes heavy use of malloc/free, then it might be the case you're contending on the central malloc lock in the default allocator. In that case you'd see malloc calling lock in the stack traces, observe a high csw/vctx rate as threads block for the malloc lock, and your "usr" time would be less than expected. Solaris dtrace is a wonderful and invaluable performance tool as well, but in a sense you have to frame and articulate a meaningful and specific question to get a useful answer, so I tend not to use it for first-order screening of problems. It's also most effective for OS and software-level performance issues as opposed to HW-level issues. For that reason I recommend mpstat & pstack as my the 1st step in performance triage. If some other OS-level issue is evident then it's good to switch to dtrace to drill more deeply into the problem. Only after I've ruled out OS-level issues do I switch to using hardware performance counters to look for architectural impediments.

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  • How do I stop Ubuntu Precise freezing/hanging

    - by artfulrobot
    At least once a day I lose work on my (2 different) Intel i5 machines running Ubuntu 12.04. The entire system will freeze/lock-up/hang, and never return. At this point nothing works; even the caps lock key doesn't toggle the light on the keyboard; Ctrl-Alt-F1 won't do anything either. askubuntu.com is apparently where I'm directed for support. I suspect this is a kernel bug. But I simply can't keep losing work like this, so I'm anxious to try whatever it takes to get the thing reliably working. Can you suggest something I can try to fix the problem an existing bug I can follow progress on and contribute to (from users/tester's POV) the most constructive way I can contribute to helping fix the problem, keeping in mind that I do need the computer (so can't do things that might "brick" it!)

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  • DB2 runstats not working for xml columns

    - by Keshav Prasad
    Hello, I am running runstats command to update the runtime statistics of a particular table called "CUSTOMER" in DB2. The customer has two columns- CID (integer) and INFO (xml column). After running the command, if I look into the SYSCOLDIST table, the information for column CID is populated correctly. But there is nothing filled for the INFO xml column. The same happens with a different table that has xml columns. Please help.. Thanks, -Keshav

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  • Sharing SCTP connection with multiple threads

    - by poly
    I have an application that needs to run in SCTP environment, I have a question in sharing the connection among multiple threads for packet receiving only, I've tried with the sctp_sendmsg and it worked without even locking the threads (is that been taking care of by the OS, in other words, is it thread safe to do that). I've tested many cases with the send and I can't see them out of sync. Anyway, back to the receiving, is it possible to create multiple threads and send each thread the sctp descriptor to start receiving messages? Do I need a lock here or is it ok without lock? I'm using C in linux.

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  • Alternatives to Pessimistic Locking in Cluster Applications

    - by amphibient
    I am researching alternatives to database-level pessimistic locking to achieve transaction isolation in a cluster of Java applications going against the same database. Synchronizing concurrent access in the application tier is clearly not a solution in the present configuration because the same database transaction can be invoked from multiple JVMs concurrently. Currently, we are subject to occasional race conditions which, due to the optimistic locking we have in place via Hibernate, cause a StaleObjectStateException exception and data loss. I have a moderately large transaction within the scope of my refactoring project. Let's describe it as updating one top-level table row and then making various related inserts and/or updates to several of its child entities. I would like to insure exclusive access to the top-level table row and all of the children to be affected but I would like to stay away from pessimistic locking at the database level for performance reasons mostly. We use Hibernate for ORM. Does it make sense to start a single (perhaps synchronous) message queue application into which this method could be moved to insure synchronized access as opposed to each cluster node using its own, which is a clear race condition hazard? I am mentioning this approach even though I am not confident in it because both the top-level table row and its children could also be updated from other system calls, not just the mentioned transaction. So I am seeking to design a solution where the top-level table row and its children will all somehow be pseudo-locked (exclusive transaction isolation) but at the application and not the database level. I am open to ideas and suggestions, I understand this is not a very cut and dried challenge.

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  • Is this a ridiculous way to structure a DB schema, or am I completely missing something?

    - by Jim
    I have done a fair bit of work with relational databases, and think I understand the basic concepts of good schema design pretty well. I recently was tasked with taking over a project where the DB was designed by a highly-paid consultant. Please let me know if my gut intinct - "WTF??!?" - is warranted, or is this guy such a genius that he's operating out of my realm? DB in question is an in-house app used to enter requests from employees. Just looking at a small section of it, you have information on the users, and information on the request being made. I would design this like so: User table: UserID (primary Key, indexed, no dupes) FirstName LastName Department Request table RequestID (primary Key, indexed, no dupes) <...> various data fields containing request details UserID -- foreign key associated with User table Simple, right? Consultant designed it like this (with sample data): UsersTable UserID FirstName LastName 234 John Doe 516 Jane Doe 123 Foo Bar DepartmentsTable DepartmentID Name 1 Sales 2 HR 3 IT UserDepartmentTable UserDepartmentID UserID Department 1 234 2 2 516 2 3 123 1 RequestTable RequestID UserID <...> 1 516 blah 2 516 blah 3 234 blah The entire database is constructed like this, with every piece of data encapsulated in its own table, with numeric IDs linking everything together. Apparently the consultant had read about OLAP and wanted the 'speed of integer lookups' He also has a large number of stored procedures to cross reference all of these tables. Is this valid design for a small to mid-sized SQL DB? Thanks for comments/answers...

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  • How to solve this problem starting new Opera-windows on dual monitor-setup?

    - by Mnementh
    I use Opera and have a setup with two monitors. If I want to open a new URL opera -newwindow URL. The outcome differs, if I execute this command in a program on the same screen where Opera is, or on the other. On the same screen everything is fine. I get the message opera: Activated running instance and the new window with the URL is opened. On the other screen, I get a dialog with the following message: It appears another opera instance is using the same configuration directory because its lock file is active: /home/(my name)/.opera/lock and the URL is not shown. That's not only from console, also if I click a link in E-Mail or so. How can I fix this? Window-manager is awesome, if it does make a difference.

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  • Multiple columns in a single index versus multiple indexes

    - by Tim Coker
    The short version of my question is what's the difference between three indexes each indexing a single column and one index indexing three columns. Background follows. I'm primarily a programmer but have to do DBA work because we don't have a DBA. I'm evaluating our indexes versus the queries run against a particular table. The table as 3 columns that I'm often filtering against or getting the max value of. Most of the time the queries look like select max(col_a) from table where col_b = 'avalue' or select col_c from table where col_b = 'avalue' and col_a = 'anothervalue' All columns are independently indexed. My question is would I see any difference if I had an index that indexed col_b and col_a together since they can appear in a where clause together?

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  • Network interface selection

    - by Antonino
    Hello. Suppose I have more than a network interfaces and I want to selectively use them per application. eth0 is the standard interface with the standard gateway in the main routing table eth1 is another interface with a different gateway. Suppose I launch an application as a user "user_eth1". I used the following set of rules for iptables / ip rules. IPTABLES: iptables -t mangle -A OUTPUT -m user --uid-owner user_eth1 -j MARK --set-mark 100 iptables -t nat -A POSTROUTING -m user -uid-owner -o eth1 user_eth1 -j SNAT --to-source <eth_ipaddress> IPRULE: ip rule add fwmark 100 lookup table100 and i build "table100" as follows (no doubts on that) ip route show table main | grep -Ev ^default | while read ROUTE; do ip route add table table100 $ROUTE; done ip route add default via <default_gateway> table table100 It doesn't work at all. What's wrong with this? Thank you in advance!

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  • How can I get my ATI / AMD drivers to work with any kernel above 3.2.0.x?

    - by TorakTu
    How can I get my ATI / AMD drivers to work with any kernel above 3.2.0.x ? WHAT DID WORK Installed original AMD64 version of Ubuntu 12.04 ISO image. Burned DVD and installed which shown kernel 3.2.0-23 to begin with. Got 5.1 surround sound working. Got ATI ( Now its AMD ) video drivers installed for my Radeon HD R6870 Video card from AMD's website. fglrxinfo came up and reported as normal. THE PROBLEM Kernel 3.2.0.x kept locking up so I tried higher kernel versions. But ATI / AMD Drivers do not install on any kernel Above 3.2.0.x WHAT I HAVE TRIED I have gone over this tutorial many times ( https://help.ubuntu.com/community/BinaryDriverHowto/ATI ) and it doesn't work on ANY kernel except 3.2.0.x. The problems I am having here are that the ATI / AMD drivers working for the 12.04 Precise with kernel 3.2.0-23 and 24, But the computer kept locking up. Although all my games would work, the lock ups were random and were constant. So I looked all over the web for 3 days trying to find an answer and the lock up issue was said to just update the kernel. So I did. Have tried many kernels. All of them .. no lock ups. BUT the Restricted AMD drivers from the AMD website will not install. And none of the OpenSource AMD drivers have EVER installed no matter what Kernel or version I tried. EXAMPLE OUTPUT OF 3D TYPE OF ERRORS Javax.media.opengl.GLException: glXGetConfig failed: error code GLX_NO_EXTENSION at com.sun.opengl.impl.x11.X11GLDrawableFactory.glXGetConfig(X11GLDrawableFactory.java:651) at com.sun.opengl.impl.x11.X11GLDrawableFactory.xvi2GLCapabilities(X11GLDrawableFactory.java:350) at com.sun.opengl.impl.x11.X11GLDrawableFactory.chooseGraphicsConfiguration(X11GLDrawableFactory.java:174) at javax.media.opengl.GLCanvas.chooseGraphicsConfiguration(GLCanvas.java:520) at javax.media.opengl.GLCanvas.<init>(GLCanvas.java:131) at haven.HavenPanel.<init>(HavenPanel.java:68) at haven.HavenPanel.<init>(HavenPanel.java:78) at haven.MainFrame.<init>(MainFrame.java:182) at haven.MainFrame.main2(MainFrame.java:306) at haven.MainFrame.access$100(MainFrame.java:34) at haven.MainFrame$7.run(MainFrame.java:360) at java.lang.Thread.run(Thread.java:722) And of course this is what fglrxinfo shows : X Error of failed request: BadRequest (invalid request code or no such operation) Major opcode of failed request: 139 (ATIFGLEXTENSION) Minor opcode of failed request: 66 () Serial number of failed request: 13 Current serial number in output stream: 13 EDIT : I forgot to mention that I DID look at this post over the last few days and it did not help.

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

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

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  • Parse text file on click and display

    - by John R
    I am thinking of a methodology for rapid retrieval of code snippets. I imagine an HTML table with a setup like this: one two ... ten one oneTwo() oneTen() two twoOne() twoTen() ... ten tenOne() tenTwo() When a user clicks a function in this HTML table, a snippet of code is shown in another div tag or perhaps a popup window (I'm open to different solutions). I want to maintain only one PHP file named utitlities.php that contains a class called 'util'. This file & class will hold all the functions referenced in the above table (it is also used on various projects and is functional code). A key idea is that I do not want to update the HTML documentation everytime I write/update a new function in utilities.php. I should be able to click a function in the table and have PHP open the utilities file, parse out the apropriate function and display it in an HTML window. Questions: 1) I will be coding this in PHP and JavaScript but am wondering if similar scripts are available (for all or part) so I don't reinvent the wheel. 2) Quick & easy Ajax suggestions appreciated too (probably will use jquery, but am rusty). 3) Methodology for parsing out the functions from the utilities.php file (I'm not to good with regex).

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  • Installing Ubuntu 12.10 on new computer with Windows 8

    - by rft183
    I recently purchased a new HP computer (P6-2330) with Windows 8. I have tried unsuccessfully to install Ubuntu 12.10 64bit alongside Windows 8. The computer is UEFI with Secure Boot enabled. I've tried following the instruction at https://help.ubuntu.com/community/UEFI. I am able to get the GRUB menu to show up. However, as soon as I press Enter on either Try Ubuntu or Install Ubuntu, the screen goes blank. Nothing works at all, not even the Num Lock or Caps Lock keys on the keyboard. I have to use the power button to restart the computer. Does anyone have any suggestions on how to get Ubuntu installed? To clarify, I have actually tried installing using both a USB stick and a DVD. The USB stick gave a blank screen, while the DVD gave the error message "Empty Security Header" after pressing Enter at the GRUB screen.

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  • Storing User-uploaded Images

    - by Nyxynyx
    What is the usual practice for handling user uploaded photos and storing them on the database and server? For a user profile image: After receiving the image file from user, rename file to <image_id>_<username> Move image to /images/userprofile Add img filename to a table users containing their profile details like first_name, last_name, age, gender, birthday For a image for a review done by user: After receiving the image file from user, rename file to <image_id>_<review_id> Move image to /images/reviews Add img filename to a table reviews containing their profile details like review_id, review_content, user_id, score. Question 1: How should I go about storing the image filenames if the user can upload multiple photos for a particular review? Serialize? Question 2: Or have another table review_images with columns review_id, image_id, image_filename just for tracking images? Will doing a JOIN when retriving the image_filename from this table slow down performance noticeably? Question 3: Should all the images be stored in a single folder? Will there be a problem when we have 100K photos in the same folder? Is there a more efficient way to go about doing this?

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  • Sql Server 2008 Create Foreign Key Manually

    - by tgriffiths
    I have inherited an old database which wasn't designed very well. It is a Sql Server 2008 database which is missing quite a lot of Foreign Key relationships. Below shows two of the tables, and I am trying to manually create a FK relationship between dbo.app_status.status_id and dbo.app_additional_info.application_id I am using SQL Server Management Studio when trying to create the relationship using the query below USE myDatabase; GO ALTER TABLE dbo.app_additional_info ADD CONSTRAINT FK_AddInfo_AppStatus FOREIGN KEY (application_id) REFERENCES dbo.app_status (status_id) ON DELETE CASCADE ON UPDATE CASCADE ; GO However, I receive this error when I run the query The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_AddInfo_AppStatus". The conflict occurred in database "myDatabase", table "dbo.app_status", column 'status_id'. I am wondering if the query is failing because each table already contains approximately 130,000 records? Please help. Thanks.

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  • Parse text file on click - and then display

    - by John R
    I am thinking of a methodology for rapid retrieval of code snippets. I imagine an HTML table with a setup like this: one two ... ten one oneTwo() oneTen() two twoOne() twoTen() ... ten tenOne() tenTwo() When a user clicks a function in this HTML table, a snippet of code is shown in another div tag or perhaps a popup window (I'm open to different solutions). I want to maintain only one PHP file named utitlities.php that contains a class called 'util'. This file & class will hold all the functions referenced in the above table (it is also used on various projects and is functional code). A key idea is that I do not want to update the HTML documentation everytime I write/update a new function in utilities.php. I should be able to click a function in the table and have PHP open the utilities file, parse out the apropriate function and display it in an HTML window. Questions: 1) I will be coding this in PHP and JavaScript but am wondering if similar scripts are available (for all or part) so I don't reinvent the wheel. 2) Quick & easy Ajax suggestions appreciated too (probably will use jquery, but am rusty). 3) Methodology for parsing out the functions from the utilities.php file (I'm not to good with regex).

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  • Laptop Display Not Working

    - by etrask
    Hello, I just purchased this laptop. It is working fine but I want to use Xubuntu on it. I managed to get 10.04 installed and running but it did not recognize/use the wireless card. So I want to try 10.10. However, every time I try, the screen goes black and never comes back on. I have tried the Live CD and Alternate install CDs, for both Ubuntu and Xubuntu 10.10. After I select "Install Ubuntu" or "Try Ubuntu", the screen blacks out and never displays anything. So I deleted "quiet" and "splash" off the command line to see what messages would come up. A bunch of text flies by but it ends at: [time] TCP established hash table entries: 524288 (order: 11, 8388608 bytes) [time] TCP bind hash table entries 65536 (order: 8, 1048576 bytes) [time] TCP: Hash tables configured (established 524288 bind 65536) [time] TCP reno registered [time] UDP hash table entries: 2048 (order: 4, 65536 bytes) [time] UDP-Lite hash table entries: 2048 (order: 4, 65536 bytes) [time] NET: Registered protocol family 1 And freezes here forever. I have tried nomodeset, vga=771, and xforcevesa with no progress. Is my video card simply not going to work with this distro? It seems strange that 10.04 would work fine but not 10.10. Any help is appreciated, thank you.

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  • route http and ssh traffic normally, everything else via vpn tunnel

    - by Normadize
    I've read quite a bit and am close, I feel, and I'm pulling my hair out ... please help! I have an OpenVPN cliend whose server sets local routes and also changes the default gw (I know I can prevent that with --route-nopull). I'd like to have all outgoing http and ssh traffic via the local gw, and everything else via the vpn. Local IP is 192.168.1.6/24, gw 192.168.1.1. OpenVPN local IP is 10.102.1.6/32, gw 192.168.1.5 OpenVPN server is at {OPENVPN_SERVER_IP} Here's the route table after openvpn connection: # ip route show table main 0.0.0.0/1 via 10.102.1.5 dev tun0 default via 192.168.1.1 dev eth0 proto static 10.102.1.1 via 10.102.1.5 dev tun0 10.102.1.5 dev tun0 proto kernel scope link src 10.102.1.6 {OPENVPN_SERVER_IP} via 192.168.1.1 dev eth0 128.0.0.0/1 via 10.102.1.5 dev tun0 169.254.0.0/16 dev eth0 scope link metric 1000 192.168.1.0/24 dev eth0 proto kernel scope link src 192.168.1.6 metric 1 This makes all packets go via to the VPN tunnel except those destined for 192.168.1.0/24. Doing wget -qO- http://echoip.org shows the vpn server's address, as expected, the packets have 10.102.1.6 as source address (the vpn local ip), and are routed via tun0 ... as reported by tcpdump -i tun0 (tcpdump -i eth0 sees none of this traffic). What I tried was: create a 2nd routing table holding the 192.168.1.6/24 routing info (copied from the main table above) add an iptables -t mangle -I PREROUTING rule to mark packets destined for port 80 add an ip rule to match on the mangled packet and point it to the 2nd routing table add an ip rule for to 192.168.1.6 and from 192.168.1.6 to point to the 2nd routing table (though this is superfluous) changed the ipv4 filter validation to none in net.ipv4.conf.tun0.rp_filter=0 and net.ipv4.conf.eth0.rp_filter=0 I also tried an iptables mangle output rule, iptables nat prerouting rule. It still fails and I'm not sure what I'm missing: iptables mangle prerouting: packet still goes via vpn iptables mangle output: packet times out Is it not the case that to achieve what I want, then when doing wget http://echoip.org I should change the packet's source address to 192.168.1.6 before routing it off? But if I do that, the response from the http server would be routed back to 192.168.1.6 and wget would not see it as it is still bound to tun0 (the vpn interface)? Can a kind soul please help? What commands would you execute after the openvpn connects to achieve what I want? Looking forward to hair regrowth ...

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  • Does LINQ require significantly more processing cycles and memory than lower-level data iteration techniques?

    - by Matthew Patrick Cashatt
    Background I am recently in the process of enduring grueling tech interviews for positions that use the .NET stack, some of which include silly questions like this one, and some questions that are more valid. I recently came across an issue that may be valid but I want to check with the community here to be sure. When asked by an interviewer how I would count the frequency of words in a text document and rank the results, I answered that I would Use a stream object put the text file in memory as a string. Split the string into an array on spaces while ignoring punctuation. Use LINQ against the array to .GroupBy() and .Count(), then OrderBy() said count. I got this answer wrong for two reasons: Streaming an entire text file into memory could be disasterous. What if it was an entire encyclopedia? Instead I should stream one block at a time and begin building a hash table. LINQ is too expensive and requires too many processing cycles. I should have built a hash table instead and, for each iteration, only added a word to the hash table if it didn't otherwise exist and then increment it's count. The first reason seems, well, reasonable. But the second gives me more pause. I thought that one of the selling points of LINQ is that it simply abstracts away lower-level operations like hash tables but that, under the veil, it is still the same implementation. Question Aside from a few additional processing cycles to call any abstracted methods, does LINQ require significantly more processing cycles to accomplish a given data iteration task than a lower-level task (such as building a hash table) would?

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  • dhcp3-server (dhcpd) is tampering with host NIC

    - by user61000
    Hi all, I have a debian box that is serving as a router (using iptables NAT). When first turned on, everything works fine for a few minutes. Then the dhcp server assigns an IP (other than 192.168.0.1) to its' host NIC, eth0. This is NOT what I want. I just want dhcp3-server to listen on eth0, not assign it an IP, and changes the kernel routing table. This of course ruins the NAT capablities of the box. How can I tell the dhcp3-server NOT to do this? Thanks Before dhcp3-server tampers with eth0, the IP is 192.168.0.1, and the routing table looks like this: ~# netstat -r Kernel IP routing table Destination Gateway Iface 192.168.0.0 * eth0 173.33.220.0 * eth1 default 173.33.220.1 eth1 After dhcp3-server tampers with eth0, the IP is 192.168.0.3, and the routing table looks like this: ~# netstat -r Kernel IP routing table Destination Gateway Iface 192.168.0.0 * eth0 173.33.220.0 * eth1 default 192.168.0.1 eth0 default 173.33.220.1 eth1 SETUP Outbound NIC is eth1 Internal NIC is eth0 /etc/network/interfaces ... iface eth0 inet static address 192.168.0.1 netmask 255.255.255.0 /etc/default/dhcp3-server INTERFACES="eth0"

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  • Corrupt mysql system tables

    - by psynnott
    I am having issues with the columns_priv table in the mysql system database. I cannot add new users currently. I have tried repairing it using mysqlcheck --auto-repair --all-databases --password but I get the following output: mysql.columns_priv Error : Incorrect file format 'columns_priv' error : Corrupt Is there any other way to repair this table, or how do I go about replacing it with a blank table? What would I lose by doing that? Thank you Edit (Additional Info) mysqld is currently using 100% cpu constantly. Looking at show processlist, I get: mysql> show processlist; +-----+------------------+-----------+-------+---------+------+-------------------+------------------------------------------------------------------------------------------------------+ | Id | User | Host | db | Command | Time | State | Info | +-----+------------------+-----------+-------+---------+------+-------------------+------------------------------------------------------------------------------------------------------+ | 5 | debian-sys-maint | localhost | mysql | Query | 1589 | Opening tables | ALTER TABLE tables_priv MODIFY Column_priv set('Select','Insert','Update','References') COLL | | | 752 | root | localhost | NULL | Query | 0 | NULL | show processlist | +-----+------------------+-----------+-------+---------+------+-------------------+------------------------------------------------------------------------------------------------------+ 2 rows in set (0.00 sec)

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