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• Common Live Upgrade problems

  - by user12611829

  As I have worked with customers deploying Live Upgrade in their environments, several problems seem to surface over and over. With this blog article, I will try to collect these troubles, as well as suggest some workarounds. If this sounds like the beginnings of a Wiki, you would be right. At present, there is not enough material for one, so we will use this blog for the time being. I do expect new material to be posted on occasion, so if you wish to bookmark it for future reference, a permanent link can be found here. Live Upgrade copies over ZFS root clone This was introduced in Solaris 10 10/09 (u8) and the root of the problem is a duplicate entry in the source boot environments ICF configuration file. Prior to u8, a ZFS root file system was not included in /etc/vfstab, since the mount is implicit at boot time. Starting with u8, the root file system is included in /etc/vfstab, and when the boot environment is scanned to create the ICF file, a duplicate entry is recorded. Here's what the error looks like. # lucreate -n s10u9-baseline Checking GRUB menu... System has findroot enabled GRUB Analyzing system configuration. Comparing source boot environment file systems with the file system(s) you specified for the new boot environment. Determining which file systems should be in the new boot environment. Updating boot environment description database on all BEs. Updating system configuration files. Creating configuration for boot environment . Source boot environment is . Creating boot environment . Creating file systems on boot environment . Creating file system for in zone on . The error indicator ----- /usr/lib/lu/lumkfs: test: unknown operator zfs Populating file systems on boot environment . Checking selection integrity. Integrity check OK. Populating contents of mount point . This should not happen ------ Copying. Ctrl-C and cleanup If you weren't paying close attention, you might not even know this is an error. The symptoms are lucreate times that are way too long due to the extraneous copy, or the one that alerted me to the problem, the root file system is filling up - again thanks to a redundant copy. This problem has already been identified and corrected, and a patch (121431-58 or later for x86, 121430-57 for SPARC) is available. Unfortunately, this patch has not yet made it into the Solaris 10 Recommended Patch Cluster. Applying the prerequisite patches from the latest cluster is a recommendation from the Live Upgrade Survival Guide blog, so an additional step will be required until the patch is included. Let's see how this works. # patchadd -p | grep 121431 Patch: 121429-13 Obsoletes: Requires: 120236-01 121431-16 Incompatibles: Packages: SUNWluzone Patch: 121431-54 Obsoletes: 121436-05 121438-02 Requires: Incompatibles: Packages: SUNWlucfg SUNWluu SUNWlur # unzip 121431-58 # patchadd 121431-58 Validating patches... Loading patches installed on the system... Done! Loading patches requested to install. Done! Checking patches that you specified for installation. Done! Approved patches will be installed in this order: 121431-58 Checking installed patches... Executing prepatch script... Installing patch packages... Patch 121431-58 has been successfully installed. See /var/sadm/patch/121431-58/log for details Executing postpatch script... Patch packages installed: SUNWlucfg SUNWlur SUNWluu # lucreate -n s10u9-baseline Checking GRUB menu... System has findroot enabled GRUB Analyzing system configuration. INFORMATION: Unable to determine size or capacity of slice . Comparing source boot environment file systems with the file system(s) you specified for the new boot environment. Determining which file systems should be in the new boot environment. INFORMATION: Unable to determine size or capacity of slice . Updating boot environment description database on all BEs. Updating system configuration files. Creating configuration for boot environment . Source boot environment is . Creating boot environment . Cloning file systems from boot environment to create boot environment . Creating snapshot for on . Creating clone for on . Setting canmount=noauto for in zone on . Saving existing file in top level dataset for BE as //boot/grub/menu.lst.prev. Saving existing file in top level dataset for BE as //boot/grub/menu.lst.prev. Saving existing file in top level dataset for BE as //boot/grub/menu.lst.prev. File propagation successful Copied GRUB menu from PBE to ABE No entry for BE in GRUB menu Population of boot environment successful. Creation of boot environment successful. This time it took just a few seconds. A cursory examination of the offending ICF file (/etc/lu/ICF.3 in this case) shows that the duplicate root file system entry is now gone. # cat /etc/lu/ICF.3 s10u8-baseline:-:/dev/zvol/dsk/panroot/swap:swap:8388608 s10u8-baseline:/:panroot/ROOT/s10u8-baseline:zfs:0 s10u8-baseline:/vbox:pandora/vbox:zfs:0 s10u8-baseline:/setup:pandora/setup:zfs:0 s10u8-baseline:/export:pandora/export:zfs:0 s10u8-baseline:/pandora:pandora:zfs:0 s10u8-baseline:/panroot:panroot:zfs:0 s10u8-baseline:/workshop:pandora/workshop:zfs:0 s10u8-baseline:/export/iso:pandora/iso:zfs:0 s10u8-baseline:/export/home:pandora/home:zfs:0 s10u8-baseline:/vbox/HardDisks:pandora/vbox/HardDisks:zfs:0 s10u8-baseline:/vbox/HardDisks/WinXP:pandora/vbox/HardDisks/WinXP:zfs:0 Solaris 10 9/10 introduces new autoregistration file This one is actually mentioned in the Oracle Solaris 9/10 release notes. I know, I hate it when that happens too. Here's what the "error" looks like. # luupgrade -u -s /mnt -n s10u9-baseline System has findroot enabled GRUB No entry for BE in GRUB menu Copying failsafe kernel from media. 61364 blocks miniroot filesystem is Mounting miniroot at ERROR: The auto registration file does not exist or incomplete. The auto registration file is mandatory for this upgrade. Use -k argument along with luupgrade command. autoreg_file is path to auto registration information file. See sysidcfg(4) for a list of valid keywords for use in this file. The format of the file is as follows. oracle_user=xxxx oracle_pw=xxxx http_proxy_host=xxxx http_proxy_port=xxxx http_proxy_user=xxxx http_proxy_pw=xxxx For more details refer "Oracle Solaris 10 9/10 Installation Guide: Planning for Installation and Upgrade". As with the previous problem, this is also easy to work around. Assuming that you don't want to use the auto-registration feature at upgrade time, create a file that contains just autoreg=disable and pass the filename on to luupgrade. Here is an example. # echo "autoreg=disable" /var/tmp/no-autoreg # luupgrade -u -s /mnt -k /var/tmp/no-autoreg -n s10u9-baseline System has findroot enabled GRUB No entry for BE in GRUB menu Copying failsafe kernel from media. 61364 blocks miniroot filesystem is Mounting miniroot at ####################################################################### NOTE: To improve products and services, Oracle Solaris communicates configuration data to Oracle after rebooting. You can register your version of Oracle Solaris to capture this data for your use, or the data is sent anonymously. For information about what configuration data is communicated and how to control this facility, see the Release Notes or www.oracle.com/goto/solarisautoreg. INFORMATION: After activated and booted into new BE , Auto Registration happens automatically with the following Information autoreg=disable ####################################################################### Validating the contents of the media . The media is a standard Solaris media. The media contains an operating system upgrade image. The media contains version . Constructing upgrade profile to use. Locating the operating system upgrade program. Checking for existence of previously scheduled Live Upgrade requests. Creating upgrade profile for BE . Checking for GRUB menu on ABE . Saving GRUB menu on ABE . Checking for x86 boot partition on ABE. Determining packages to install or upgrade for BE . Performing the operating system upgrade of the BE . CAUTION: Interrupting this process may leave the boot environment unstable or unbootable. The Live Upgrade operation now proceeds as expected. Once the system upgrade is complete, we can manually register the system. If you want to do a hands off registration during the upgrade, see the Oracle Solaris Auto Registration section of the Oracle Solaris Release Notes for instructions on how to do that. Technocrati Tags: Oracle Solaris Patching Live Upgrade var sc_project=1193495; var sc_invisible=1; var sc_security="a46f6831";

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• Clustering in GlassFish with DCOM on Windows 7

  - by ByronNevins

  I've discovered that Windows 7 makes it very difficult to use DCOM and, mainly, the GlassFish clustering commands that rely on DCOM.  I spent a few days trying to solve the problems.  I don't yet have a cookbook for making DCOM work on Windows 7.  But here are a few tips and advice I've found. run asadmin setup-local-dcom -- It now comes automatically with the open source GlassFish 4.  It will write some critical registry entries for you.  run asadmin validate-dcom to test dcom 3.   When I ran validate-dcom on my Windows 7 network I saw the problem below: Successfully resolved host name to: gloin/10.28.51.10 Successfully connected to DCOM Port at port 135 on host gloin. Successfully connected to NetBIOS Session Service at port 139 on host gloin.Successfully connected to Windows Shares at port 445 on host gloin.Can not access the remote file system.  Is UAC on? : Access is denied. I discovered the actual problem is that Windows 7 no longer has the "C$" Administrative file share available by default. If "C$" isn't available then nothing will work. Here is how to expose the "C$" share: Registry Change -- this change allows “C$” to be accessed.  As soon as I set it -- the file copying started working!  [1] regkey: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System create this key, 32 bit word, with value == 1 LocalAccountTokenFilterPolicy 4.  Turn on the Remote Registry Service -- This is critical and it's easy to do. Windows 7 has it turned off by default. MyComputer-right click, manage, services, then turn on Remote Registry Service and set it to start automatically in the fture. 5. Turn off UAC: %systemroot%\system32\UserAccountControlSettings.exe 6. This is where I discovered that McAfee virus scanner blocks all the NetBios shares!  It has to be disabled.  

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• login takes long time

  - by Arkaprovo Bhattacharjee

  I am using Ubuntu 12.04 from past 12 days. In the beginning login was fast enough after I put the password it hardly takes 3 to 4 sec to enter in desktop, but now its taking like more that 40 sec to show desktop after entering password. whats the problem, is there any solution? P.S there is only two programs (psensor and jupiter) that starts automatically after login. boot.log fsck from util-linux 2.20.1 /dev/sda6: clean, 254544/3325952 files, 2133831/13285632 blocks * Stopping Userspace bootsplash[164G[ OK ] * Stopping Flush boot log to disk[164G[ OK ] * Starting mDNS/DNS-SD daemon[164G[ OK ] Skipping profile in /etc/apparmor.d/disable: usr.sbin.rsyslogd Skipping profile in /etc/apparmor.d/disable: usr.bin.firefox * Starting bluetooth daemon[164G[ OK ] * Starting network connection manager[164G[ OK ] * Starting AppArmor profiles [170G [164G[ OK ] * Stopping System V initialisation compatibility[164G[ OK ] * Starting CUPS printing spooler/server[164G[ OK ] * Starting System V runlevel compatibility[164G[ OK ] * Starting Bumblebee supporting nVidia Optimus cards[164G[ OK ] * Starting LightDM Display Manager[164G[ OK ] * Starting save kernel messages[164G[ OK ] * Starting anac(h)ronistic cron[164G[ OK ] * Starting ACPI daemon[164G[ OK ] * Starting regular background program processing daemon[164G[ OK ] * Starting deferred execution scheduler[164G[ OK ] speech-dispatcher disabled; edit /etc/default/speech-dispatcher * Starting CPU interrupts balancing daemon[164G[ OK ]

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• My Android phone isn't being detected by Ubuntu

  - by Lara

  This is what I've got from terminal, looks like it can see the phone as a USB device just fine but isn't showing up under fdisk so I can't mount it. It automounts just fine in my VMWare Windows. And Internet tethering works fine while under Linux (haven't tried under Windows). Here's lsusb: Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub Bus 002 Device 019: ID 04d9:1135 Holtek Semiconductor, Inc. Bus 001 Device 003: ID 05ca:18c0 Ricoh Co., Ltd Bus 001 Device 004: ID 0489:e00f Foxconn / Hon Hai Foxconn T77H114 BCM2070 [Single-Chip Bluetooth 2.1 + EDR Adapter] Bus 003 Device 010: ID 04e8:6860 Samsung Electronics Co., Ltd Bus 002 Device 012: ID 046d:c315 Logitech, Inc. Classic New Touch Keyboard And here's sudo fdisk -l: Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x0001ff06 Device Boot Start End Blocks Id System /dev/sda1 2048 681845797 340921875 7 HPFS/NTFS/exFAT /dev/sda2 * 681846784 845686783 81920000 83 Linux /dev/sda3 845686784 968566783 61440000 7 HPFS/NTFS/exFAT /dev/sda4 968568830 972475081 1953126 5 Extended /dev/sda5 968568832 972475081 1953125 82 Linux swap / Solaris Disk /dev/mapper/cryptswap1: 2000 MB, 2000000000 bytes 255 heads, 63 sectors/track, 243 cylinders, total 3906250 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0xbe4c2ec7 Disk /dev/mapper/cryptswap1 doesn't contain a valid partition table

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• 12.04 Wi-Fi not working correctly with Intel Pro/Wireless 3945ABG

  - by Jerel

  This is a very strange problem. The only time the Wi-Fi works is when I have the wired connection connected. I have a Dell 6400/e1505 with the Broadcom BCM 4401-B0 internal NIC, and the Intel Pro/Wireless 3945ABG Wi-Fi adapter. I was on 10.0.4 LTS before, and I remember having to screw around to get the Wi-Fi to work, but that was years ago, and now it's acting even stranger than it did back then. If I boot up with the wire connected, the Wi-Fi starts up. If I boot up without the wire connected, the Wi-Fi won't start at all. If after booting with the wire connected, and the Wi-Fi starts up, I then disable the wireless, the wired connection works fine. Without the wire connected, dmesg shows the iwl3945 driver loading and starting with no errors, and the wireless adapter activated. Running rfkill list shows no blocks, but there is no connection to my Wi-Fi. Help! I am more confused than a chameleon in a bag of Skittles.

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• Why does 12.04 upgrade abort with out of space error when I have lots of it?

  - by Kristian Thomsen

  When upgrading Ubuntu from 11.10 to 12.04 I discovered an unexpected problem. The upgrade was stopped because there wasn't enough free space for the installation. I managed to free some space and do the upgrade but now a prompt appears after logging in saying I'm out of space. This prompt asks me if I want to examine the problem. The "Disk Usage Analyser" is opened. In the top it says: Total filesystem capacity: 47.0 GB (used: 13.5 GB available: 33.4 GB) Folder -- Usage -- Size / -- 100% -- 12.5 GB usr -- 44.8 % -- 5.6 GB home -- 30.3 % -- 3.8 GB lib -- 13.0 % -- 1.6 GB var -- 9.1 % -- 1.1 GB boot 2.5 % 309.5 GB and a lot of small contributors like: etc, opt, sbin, bin etc. I do not really understand this problem since the analyser in the top says that I have 33.4 GB left in this file system. What can I do to make Ubuntu use the remaining space? Running df -i in the terminal gives: Filesystem Inodes IUsed IFree IUse% Mounted on /dev/sda7 610800 576874 33926 95% / udev 213451 563 212888 1% /dev tmpfs 218524 486 218038 1% /run none 218524 3 218521 1% /run/lock none 218524 7 218517 1% /run/shm /dev/sda8 2264752 16371 2248381 1% /home The output of df -h Filesystem Size Used Avail Use% Mounted on /dev/sda7 9,3G 7,8G 1,1G 88% / udev 993M 4,0K 993M 1% /dev tmpfs 401M 884K 400M 1% /run none 5,0M 0 5,0M 0% /run/lock none 1003M 152K 1002M 1% /run/shm /dev/sda8 35G 4,0G 29G 13% /home /dev/sda2 101G 64G 37G 64% /media/A2C8E28BC8E25CD3 Running sudo fdisk -l gives Disk /dev/sda: 160.0 GB, 160041885696 bytes 255 heads, 63 sectors/track, 19457 cylinders, total 312581808 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000080 Device Boot Start End Blocks Id System /dev/sda1 63 96389 48163+ de Dell Utility /dev/sda2 * 98304 210434488 105168092+ 7 HPFS/NTFS/exFAT /dev/sda3 210436094 312576704 51070305+ f W95 Ext'd (LBA) /dev/sda5 306279288 312576704 3148708+ dd Unknown /dev/sda6 210436096 214341631 1952768 82 Linux swap / Solaris /dev/sda7 214343680 233873407 9764864 83 Linux /dev/sda8 233875456 306278399 36201472 83 Linux Partition table entries are not in disk order

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• Javascript: Machine Constants Applicable?

  - by DavidB2013

  I write numerical routines for students of science and engineering (although they are freely available for use by anybody else as well) and am wondering how to properly use machine constants in a JavaScript program, or if they are even applicable. For example, say I am writing a program in C++ that numerically computes the roots of the following equation: exp(-0.7x) + sin(3x) - 1.2x + 0.3546 = 0 A root-finding routine should be able to compute roots to within the machine epsilon. In C++, this value is specified by the language: DBL_EPSILON. C++ also specifies the smallest and largest values that can be held by a float or double variable. However, how does this convert to JavaScript? Since a Javascript program runs in a web browser, and I don't know what kind of computer will run the program, and JavaScript does not have corresponding predefined values for these quantities, how can I implement my own version of these constants so that my programs compute results to as much accuracy as allowed on the computer running the web browser? My first draft is to simply copy over the literal constants from C++: FLT_MIN: 1.17549435082229e-038 FLT_MAX: 3.40282346638529e+038 DBL_EPSILON: 2.2204460492503131e-16 I am also willing to write small code blocks that could compute these values for each machine on which the program is run. That way, a supercomputer might compute results to a higher accuracy than an old, low-level, PC. BUT, I don't know if such a routine would actually reach the computer, in which case, I would be wasting my time. Anybody here know how to compute and use (in Javascript) values that correspond to machine constants in a compiled language? Is it worth my time to write small programs in Javascript that compute DBL_EPSILON, FLT_MIN, FLT_MIN, etc. for use in numerical routines? Or am I better off simply assigning literal constants that come straight from C++ on a standard Windows PC?

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• Preffered lambda syntax?

  - by Roger Alsing

  I'm playing around a bit with my own C like DSL grammar and would like some oppinions. I've reserved the use of "(...)" for invocations. eg: foo(1,2); My grammar supports "trailing closures" , pretty much like Ruby's blocks that can be passed as the last argument of an invocation. Currently my grammar support trailing closures like this: foo(1,2) { //parameterless closure passed as the last argument to foo } or foo(1,2) [x] { //closure with one argument (x) passed as the last argument to foo print (x); } The reason why I use [args] instead of (args) is that (args) is ambigious: foo(1,2) (x) { } There is no way in this case to tell if foo expects 3 arguments (int,int,closure(x)) or if foo expects 2 arguments and returns a closure with one argument(int,int) - closure(x) So thats pretty much the reason why I use [] as for now. I could change this to something like: foo(1,2) : (x) { } or foo(1,2) (x) -> { } So the actual question is, what do you think looks best? [...] is somewhat wrist unfriendly. let x = [a,b] { } Ideas?

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• Absence Management White Papers to Assist with your Implementations

  - by Carolyn Cozart

  Absence Management Setup – Additional Resources PeopleSoft is committed to helping our customers sharing our knowledge expertise in our applications. We have prepared a collection of documents (White Papers) containing examples, tips, and techniques to help you when making important decisions during your Absence Management implementation.   These documents can all be found on My Oracle Support. Absence Management Entitlement and Take Setup This document (Document ID 1493866.1) provides an overview of how to set up the main components of Absence Management, such as Absence Entitlement and Take elements, as well as other supporting elements relevant to your Absence Management implementation. Absence Management System Elements This document (Document ID 1493879.1) provides an overview of the system elements related to Absence Management. System elements are building blocks used during the design and construction of your Absence Rules. Knowing how they work and when to use them should help you expedite the implementation of your Absence Policy rules in your company Absence Management Self Service Setup This document (Document ID 1493867.1) provides an overview and guidance on some of the important areas when setting up Absence Self Service. Throughout this document we are providing examples of different configurations supported in Self Service. 

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• Review: Data Modeling 101

  I just recently read “Data Modeling 101”by Scott W. Ambler where he gave an overview of fundamental data modeling skills. I think this article was excellent for anyone who was just starting to learn or refresh their skills in regards to the modeling of data.  Scott defines data modeling as the act of exploring data oriented structures.  He goes on to explain about how data models are actually used by defining three different types of models. Types of Data Models Conceptual Data Model  Logical Data Model (LDMs) Physical Data Model(PDMs) He further expands on modeling by exploring common data modeling notations because there are no industry standards for the practice of data modeling. Scott then defines how to actually model data by expanding on entities, attributes, identities, and relationships which are the basic building blocks of data models. In addition he discusses the value of normalization for redundancy and demoralization for performance. Finally, he discuss ways in which Developers and DBAs can become better data modelers through the use of practice, and seeking guidance from more experienced data modelers.

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• Full screen blackout using allegro in codeblocks

  - by Armando Ortiz

  I'm very interested in game programming and I'm taking my first steps alone. So I installed allegro. Although Dev-C++ didn't work, Code::Blocks compiled successfully. I started out with this basic program: #include <allegro.h> int main(){ allegro_init(); install_keyboard(); set_gfx_mode( GFX_AUTODETECT, 640, 480, 0, 0); readkey(); return 0; } END_OF_MAIN(); The problem comes in when I try to run it. It opens the little window as always, but rapidly blacks out my whole screen. I press any key and it takes me back to the little window telling me that it finished, which means the program worked. But I try any other program with allegro, like: #include <allegro.h> int x = 10; int y = 10; int main(){ allegro_init(); install_keyboard(); set_gfx_mode( GFX_AUTODETECT, 640, 480, 0, 0); while ( !key[KEY_ESC] ){ clear_keybuf(); acquire_screen(); textout_ex( screen, font, " ", x, y, makecol( 0, 0, 0), makecol( 0, 0, 0) ); if (key[KEY_UP]) --y; else if (key[KEY_DOWN]) ++y; else if (key[KEY_RIGHT]) ++x; else if (key[KEY_LEFT]) --x; textout_ex( screen, font, "@", x, y, makecol( 255, 0, 0), makecol( 0, 0, 0) ); release_screen(); rest(50); } return 0; } END_OF_MAIN(); And the same thing happens over and over again! Is there something I'm doing wrong?

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• cannot mount root filesystem on 10.04

  - by howaryoo

  I tried to apply the recommendation of question: Kernel Panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) After running that command: sudo mount --bind /dev /mnt/dev I get this error message: mount: mount point /mnt/dev does not exist fdisk -l returns /dev/sda1 /dev/sda2 /dev/sda5 do I need to mount sda2 and sda5? Edited after @psusi's comment: /dev/sda1 is the boot file system It seems that I need to mount sda2 or sda5. Here is what I tried: (I tried this on a virtual machine so the sda(s) are now vda(s) ) ubuntu@ubuntu:~$ sudo fdisk -l Disk /dev/vda: 19.3 GB, 19327352832 bytes 16 heads, 63 sectors/track, 37449 cylinders Units = cylinders of 1008 * 512 = 516096 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x0008eece Device Boot Start End Blocks Id System /dev/vda1 * 3 496 248832 83 Linux Partition 1 does not end on cylinder boundary. /dev/vda2 498 37448 18622465 5 Extended Partition 2 does not end on cylinder boundary. /dev/vda5 498 37448 18622464 8e Linux LVM ubuntu@ubuntu:~$ ubuntu@ubuntu:~$ ubuntu@ubuntu:~$ sudo mount -t ext4 /dev/vda5 /mnt mount: wrong fs type, bad option, bad superblock on /dev/vda5, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so ubuntu@ubuntu:~$ sudo mount -t ext2 /dev/vda5 /mnt mount: wrong fs type, bad option, bad superblock on /dev/vda5, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so ubuntu@ubuntu:~$ Any info that can help me rescue that server would be greatly appreciated!

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• External USB hard-drive changing drive letter

  - by Sydius

  I have a Seagate FreeAgent Go external USB hard drive that was mounted but mysteriously decided to reconnect itself: Sep 30 15:07:06 feinman kernel: [243901.551604] usb 1-1.2: USB disconnect, device number 3 Sep 30 15:07:06 feinman kernel: [243901.553828] sd 6:0:0:0: [sdb] Synchronizing SCSI cache Sep 30 15:07:06 feinman kernel: [243901.553893] sd 6:0:0:0: [sdb] Result: hostbyte=DID_NO_CONNECT driverbyte=DRIVER_OK Sep 30 15:07:10 feinman kernel: [243905.336557] usb 1-1.2: new high-speed USB device number 4 using ehci_hcd Sep 30 15:07:10 feinman kernel: [243905.431219] scsi7 : usb-storage 1-1.2:1.0 Sep 30 15:07:11 feinman kernel: [243906.427207] scsi 7:0:0:0: Direct-Access Seagate FreeAgent Go 0148 PQ: 0 ANSI: 4 Sep 30 15:07:11 feinman kernel: [243906.428303] sd 7:0:0:0: Attached scsi generic sg1 type 0 Sep 30 15:07:11 feinman kernel: [243906.430317] sd 7:0:0:0: [sdc] 625142447 512-byte logical blocks: (320 GB/298 GiB) Sep 30 15:07:11 feinman kernel: [243906.430860] sd 7:0:0:0: [sdc] Write Protect is off Sep 30 15:07:11 feinman kernel: [243906.430865] sd 7:0:0:0: [sdc] Mode Sense: 1c 00 00 00 Sep 30 15:07:11 feinman kernel: [243906.431386] sd 7:0:0:0: [sdc] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA Sep 30 15:07:11 feinman kernel: [243906.493674] sdc: sdc1 Sep 30 15:07:11 feinman kernel: [243906.496109] sd 7:0:0:0: [sdc] Attached SCSI disk It changed from sdb to sdc, causing a number of problems for me. What can I do to further track down the cause? I thought it might be a problem with it sleeping but when I cat /sys/class/scsi_disk/6\:0\:0\:0/allow_restart, I see that it's already 1.

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• Lost files after installing Ubuntu

  - by Joshua Rosato

  I installed Ubuntu on my laptop over windows, I had 2 partitions on one hard disk. It seems like my second partition is gone with all my files. How can I recover the old files? They weren't on the same partition as Windows. I read that the partition has probably just not been mounted so ran sudo fdisk -l to find all the partitions and then ran sudo mount, however I can't tell from the results of sudo mount what is not mounted and I am also unsure how to mount it once I find the unmounted partition. sudo fdisk -l - Results Disk /dev/sda: 250.1 GB, 250059350016 bytes 255 heads, 63 sectors/track, 30401 cylinders, total 488397168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x0002c6dc Device Boot Start End Blocks Id System /dev/sda1 * 2048 486322175 243160064 83 Linux /dev/sda2 486324222 488396799 1036289 5 Extended /dev/sda5 486324224 488396799 1036288 82 Linux swap / Solaris sudo mount - Results /dev/sda1 on / type ext4 (rw,errors=remount-ro) proc on /proc type proc (rw,noexec,nosuid,nodev) sysfs on /sys type sysfs (rw,noexec,nosuid,nodev) none on /sys/fs/cgroup type tmpfs (rw) none on /sys/fs/fuse/connections type fusectl (rw) none on /sys/kernel/debug type debugfs (rw) none on /sys/kernel/security type securityfs (rw) udev on /dev type devtmpfs (rw,mode=0755) devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620) tmpfs on /run type tmpfs (rw,noexec,nosuid,size=10%,mode=0755) none on /run/lock type tmpfs (rw,noexec,nosuid,nodev,size=5242880) none on /run/shm type tmpfs (rw,nosuid,nodev) none on /run/user type tmpfs (rw,noexec,nosuid,nodev,size=104857600,mode=0755) none on /sys/fs/pstore type pstore (rw) systemd on /sys/fs/cgroup/systemd type cgroup (rw,noexec,nosuid,nodev,none,name=systemd) gvfsd-fuse on /run/user/1000/gvfs type fuse.gvfsd-fuse (rw,nosuid,nodev,user=joshy1)

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• Why unhandled exceptions are useful

  - by Simon Cooper

  It’s the bane of most programmers’ lives – an unhandled exception causes your application or webapp to crash, an ugly dialog gets displayed to the user, and they come complaining to you. Then, somehow, you need to figure out what went wrong. Hopefully, you’ve got a log file, or some other way of reporting unhandled exceptions (obligatory employer plug: SmartAssembly reports an application’s unhandled exceptions straight to you, along with the entire state of the stack and variables at that point). If not, you have to try and replicate it yourself, or do some psychic debugging to try and figure out what’s wrong. However, it’s good that the program crashed. Or, more precisely, it is correct behaviour. An unhandled exception in your application means that, somewhere in your code, there is an assumption that you made that is actually invalid. Coding assumptions Let me explain a bit more. Every method, every line of code you write, depends on implicit assumptions that you have made. Take this following simple method, that copies a collection to an array and includes an item if it isn’t in the collection already, using a supplied IEqualityComparer: public static T[] ToArrayWithItem( ICollection<T> coll, T obj, IEqualityComparer<T> comparer) { // check if the object is in collection already // using the supplied comparer foreach (var item in coll) { if (comparer.Equals(item, obj)) { // it's in the collection already // simply copy the collection to an array // and return it T[] array = new T[coll.Count]; coll.CopyTo(array, 0); return array; } } // not in the collection // copy coll to an array, and add obj to it // then return it T[] array = new T[coll.Count+1]; coll.CopyTo(array, 0); array[array.Length-1] = obj; return array; } What’s all the assumptions made by this fairly simple bit of code? coll is never null comparer is never null coll.CopyTo(array, 0) will copy all the items in the collection into the array, in the order defined for the collection, starting at the first item in the array. The enumerator for coll returns all the items in the collection, in the order defined for the collection comparer.Equals returns true if the items are equal (for whatever definition of ‘equal’ the comparer uses), false otherwise comparer.Equals, coll.CopyTo, and the coll enumerator will never throw an exception or hang for any possible input and any possible values of T coll will have less than 4 billion items in it (this is a built-in limit of the CLR) array won’t be more than 2GB, both on 32 and 64-bit systems, for any possible values of T (again, a limit of the CLR) There are no threads that will modify coll while this method is running and, more esoterically: The C# compiler will compile this code to IL according to the C# specification The CLR and JIT compiler will produce machine code to execute the IL on the user’s computer The computer will execute the machine code correctly That’s a lot of assumptions. Now, it could be that all these assumptions are valid for the situations this method is called. But if this does crash out with an exception, or crash later on, then that shows one of the assumptions has been invalidated somehow. An unhandled exception shows that your code is running in a situation which you did not anticipate, and there is something about how your code runs that you do not understand. Debugging the problem is the process of learning more about the new situation and how your code interacts with it. When you understand the problem, the solution is (usually) obvious. The solution may be a one-line fix, the rewrite of a method or class, or a large-scale refactoring of the codebase, but whatever it is, the fix for the crash will incorporate the new information you’ve gained about your own code, along with the modified assumptions. When code is running with an assumption or invariant it depended on broken, then the result is ‘undefined behaviour’. Anything can happen, up to and including formatting the entire disk or making the user’s computer sentient and start doing a good impression of Skynet. You might think that those can’t happen, but at Halting problem levels of generality, as soon as an assumption the code depended on is broken, the program can do anything. That is why it’s important to fail-fast and stop the program as soon as an invariant is broken, to minimise the damage that is done. What does this mean in practice? To start with, document and check your assumptions. As with most things, there is a level of judgement required. How you check and document your assumptions depends on how the code is used (that’s some more assumptions you’ve made), how likely it is a method will be passed invalid arguments or called in an invalid state, how likely it is the assumptions will be broken, how expensive it is to check the assumptions, and how bad things are likely to get if the assumptions are broken. Now, some assumptions you can assume unless proven otherwise. You can safely assume the C# compiler, CLR, and computer all run the method correctly, unless you have evidence of a compiler, CLR or processor bug. You can also assume that interface implementations work the way you expect them to; implementing an interface is more than simply declaring methods with certain signatures in your type. The behaviour of those methods, and how they work, is part of the interface contract as well. For example, for members of a public API, it is very important to document your assumptions and check your state before running the bulk of the method, throwing ArgumentException, ArgumentNullException, InvalidOperationException, or another exception type as appropriate if the input or state is wrong. For internal and private methods, it is less important. If a private method expects collection items in a certain order, then you don’t necessarily need to explicitly check it in code, but you can add comments or documentation specifying what state you expect the collection to be in at a certain point. That way, anyone debugging your code can immediately see what’s wrong if this does ever become an issue. You can also use DEBUG preprocessor blocks and Debug.Assert to document and check your assumptions without incurring a performance hit in release builds. On my coding soapbox… A few pet peeves of mine around assumptions. Firstly, catch-all try blocks: try { ... } catch { } A catch-all hides exceptions generated by broken assumptions, and lets the program carry on in an unknown state. Later, an exception is likely to be generated due to further broken assumptions due to the unknown state, causing difficulties when debugging as the catch-all has hidden the original problem. It’s much better to let the program crash straight away, so you know where the problem is. You should only use a catch-all if you are sure that any exception generated in the try block is safe to ignore. That’s a pretty big ask! Secondly, using as when you should be casting. Doing this: (obj as IFoo).Method(); or this: IFoo foo = obj as IFoo; ... foo.Method(); when you should be doing this: ((IFoo)obj).Method(); or this: IFoo foo = (IFoo)obj; ... foo.Method(); There’s an assumption here that obj will always implement IFoo. If it doesn’t, then by using as instead of a cast you’ve turned an obvious InvalidCastException at the point of the cast that will probably tell you what type obj actually is, into a non-obvious NullReferenceException at some later point that gives you no information at all. If you believe obj is always an IFoo, then say so in code! Let it fail-fast if not, then it’s far easier to figure out what’s wrong. Thirdly, document your assumptions. If an algorithm depends on a non-trivial relationship between several objects or variables, then say so. A single-line comment will do. Don’t leave it up to whoever’s debugging your code after you to figure it out. Conclusion It’s better to crash out and fail-fast when an assumption is broken. If it doesn’t, then there’s likely to be further crashes along the way that hide the original problem. Or, even worse, your program will be running in an undefined state, where anything can happen. Unhandled exceptions aren’t good per-se, but they give you some very useful information about your code that you didn’t know before. And that can only be a good thing.

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• Automatic TRIM vs. manual TRIM

  - by Eike Cochu

  I am currently trying to find out how to trim with my new TP and was wondering about the difference of manual/online trimming. Here is my setup: ThinkPad T430s with SSD Samsung 830, 128GB and Xubuntu 12.10, here are some outputs to check if trim will work on my system (got these from here: http://wiki.ubuntuusers.de/SSD/TRIM) root@eike-tp:~# sudo hdparm -I /dev/sda | grep -i TRIM * Data Set Management TRIM supported (limit 8 blocks) First, I tried the online trimming: How to enable TRIM? my fstab with discard inserted: UUID=d6c49c17-a4f1-466c-9f7e-896c20db3bba / ext4 discard,noatime,errors=remount-ro 0 1 # swap was on /dev/sda5 during installation UUID=a0322f5f-c6c1-4896-863f-668f0638d8cf none swap sw 0 0 tmpfs /tmp tmpfs defaults,noatime,mode=1777 0 0 I tried to test if it works (but I don't get any zeroes when I try it with /dev/sda), but found out that this method is only possible with SSD type 2 and I seem to have type 3. So I don't know if it works or not. The Ubuntuwiki (first link) recommends manual trimming, so I set up a daily cronjob instead of discard: #!/bin/sh LOG=/var/log/batched_discard.log echo "*** $(date -R) ***" >> $LOG fstrim -v / >> $LOG the wiki article suggests weekly or daily. Now to my questions: How often executes the automated trim? How often is recommended? Online vs. manual trimming? Thank you for your help

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• HTG Explains: What Are Computer Algorithms and How Do They Work?

  - by YatriTrivedi

    Unless you’re into math or programming, the word “algorithm” might be Greek to you, but it’s one of the building blocks of everything you’re using to read this article. Here’s a quick explanation of what they are, and how they work. Disclaimer: I’m not a math or computer science teacher, so not all of the terms I use are technical. That’s because I’m trying to explain everything in plain English for people aren’t quite comfortable with math. That being said, there is some math involved, and that’s unavoidable. Math geeks, feel free to correct or better explain in the comments, but please, keep it simple for the mathematically disinclined among us. Image by Ian Ruotsala Latest Features How-To Geek ETC How To Make Hundreds of Complex Photo Edits in Seconds With Photoshop Actions How to Enable User-Specific Wireless Networks in Windows 7 How to Use Google Chrome as Your Default PDF Reader (the Easy Way) How To Remove People and Objects From Photographs In Photoshop Ask How-To Geek: How Can I Monitor My Bandwidth Usage? Internet Explorer 9 RC Now Available: Here’s the Most Interesting New Stuff Lucky Kid Gets Playable Angry Birds Cake [Video] See the Lord of the Rings Epic from the Perspective of Mordor [eBook] Smart Taskbar Is a Thumb Friendly Android Task Launcher Comix is an Awesome Comics Archive Viewer for Linux Get the MakeUseOf eBook Guide to Speeding Up Windows for Free Need Tech Support? Call the Star Wars Help Desk! [Video Classic]

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• What decent email client would you recommend (at least better than Thunderbird)?

  - by matteo

  I've used Thunderbird for years. I keep a huge number of emails. I move them to folders to organize or archive them, but I don't delete anything so I have hundreds of thousands of messages. I like the way TB is conceived, and the way it works as long as the volume of data is small. But it just doesn't scale. It has a lot of ridiculous design flaws such that, for example, any time consuming operation blocks the whole UI completely (and you don't even know for how long) as if everything was implemented in a single monolythic all-tasks-are-blocking way. I'm tired of it. So what is the alternative that you would recommend as an email client program with all the usual basic features one expects from any email client program? Important: I mainly use POP3, much much more than IMAP, and my main account is on gmail. This question is not intended to be a rant against TB (I admit it is, as a side effect); I have highlighted its weaknesses BECAUSE the answer I'm looking for is a recomendation for a program that doesn't suffer from these issues.

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• disk space worngly displayed after installing LVM disk

  - by Ubuntuser

  I installed ubuntu server using LVM partitioning on a 1 TB hard disk. However, after installation, i can only see 10 Gig space here is the fidsk output ` # fdisk -l Disk /dev/sda: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00041507 Device Boot Start End Blocks Id System /dev/sda1 * 1 10 71680 83 Linux Partition 1 does not end on cylinder boundary. /dev/sda2 10 121602 976689152 8e Linux LVM Disk /dev/dm-0: 10.7 GB, 10737418240 bytes 255 heads, 63 sectors/track, 1305 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Disk /dev/dm-0 doesn't contain a valid partition table Disk /dev/dm-1: 2147 MB, 2147483648 bytes 255 heads, 63 sectors/track, 261 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Disk /dev/dm-1 doesn't contain a valid partition table You have new mail in /var/mail/root and df -h output df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/system-root 9.9G 6.6G 2.8G 71% / devtmpfs 1.9G 232K 1.9G 1% /dev tmpfs 1.9G 4.0K 1.9G 1% /dev/shm /dev/sda1 68M 22M 43M 34% /boot tmpfs 6.0G 0 6.0G 0% /var/spool/asterisk/monitor You have new mail in /var/mail/root ` any way to increase this space without reisntalling?

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• How can a usb be detected but not show up anywhere?

  - by George Mauer

  I started the morning by trying to create a bootable usb using a 2gb stick and the startup disk creator. It seemed to run through the whole process just fine until it got to a screen that read something like "Creating memory partion" and which sat on 100% for about 45 minutes before I hit cancel and removed the usb stick. Now the usb stick is not being detected as storage or...anything (even on my windows pc) though it does show up in the syslog. Allow me to demonstrate. We start with the usb not plugged in: [georgemauer@ubuntu:~]$ sudo fdisk -l (04-04 16:01) Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x994bdc0f Device Boot Start End Blocks Id System /dev/sda1 2048 27650047 13824000 27 Hidden NTFS WinRE /dev/sda2 * 27650048 27854847 102400 7 HPFS/NTFS/exFAT /dev/sda3 27854848 976771119 474458136 7 HPFS/NTFS/exFAT I plug in the usb: [georgemauer@ubuntu:~]$ tail -f /var/log/syslog ***Snip*** Apr 4 15:01:18 ubuntu wpa_supplicant[1136]: WPA: Group rekeying completed with 00:24:36:ad:e7:3f [GTK=TKIP] Apr 4 15:02:29 wpa_supplicant[1136]: last message repeated 3 times Apr 4 15:02:29 ubuntu kernel: [22122.788133] usb 2-1: new high speed USB device number 13 using ehci_hcd Apr 4 15:02:29 ubuntu kernel: [22122.923873] scsi10 : usb-storage 2-1:1.0 Apr 4 15:02:29 ubuntu mtp-probe: checking bus 2, device 13: "/sys/devices/pci0000:00/0000:00:13.2/usb2/2-1" Apr 4 15:02:30 ubuntu mtp-probe: bus: 2, device: 13 was not an MTP device Apr 4 15:02:30 ubuntu kernel: [22123.926154] scsi 10:0:0:0: Direct-Access GENERIC USB Mass Storage 1.00 PQ: 0 ANSI: 2 Apr 4 15:02:30 ubuntu kernel: [22124.105118] sd 10:0:0:0: Attached scsi generic sg1 type 0 Apr 4 15:02:30 ubuntu kernel: [22124.108212] sd 10:0:0:0: [sdb] Attached SCSI removable disk but then: [georgemauer@ubuntu:~]$ ls /mnt -alF (04-04 16:02) total 8 drwxr-xr-x 2 root root 4096 2011-04-21 12:51 ./ drwxr-xr-x 26 root root 4096 2012-03-31 13:16 ../ [georgemauer@ubuntu:~]$ ls /media -alF (04-04 16:03) total 8 drwxr-xr-x 2 root root 4096 2012-04-04 12:18 ./ drwxr-xr-x 26 root root 4096 2012-03-31 13:16 ../ What could be going on and how do I recover my usb key?

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• Pygame: Save a list of objects/classes/surfaces

  - by Sam Tubb

  I am working on a game, in which you can create mazes. You place blocks on a 16x16 grid, while choosing from a variety of block to make the level with. Whenever you create a block, it adds this class: class Block(object): def __init__(self,x,y,spr): self.x=x self.y=y self.sprite=spr self.rect=self.sprite.get_rect(x=self.x,y=self.y) to a list called instances. I tried shelving it to a .bin file, but it returns some error dealing with surfaces. How can I go about saving and loading levels? Any help is appreciated! :) Here is the whole code for reference: import pygame from pygame.locals import * #initstuff pygame.init() screen=pygame.display.set_mode((640,480)) pygame.display.set_caption('PiMaze') instances=[] #loadsprites menuspr=pygame.image.load('images/menu.png').convert() b1spr=pygame.image.load('images/b1.png').convert() b2spr=pygame.image.load('images/b2.png').convert() currentbspr=b1spr curspr=pygame.image.load('images/curs.png').convert() curspr.set_colorkey((0,255,0)) #menu menuspr.set_alpha(185) menurect=menuspr.get_rect(x=-260,y=4) class MenuItem(object): def __init__(self,pos,spr): self.x=pos[0] self.y=pos[1] self.sprite=spr self.pos=(self.x,self.y) self.rect=self.sprite.get_rect(x=self.x,y=self.y) class Block(object): def __init__(self,x,y,spr): self.x=x self.y=y self.sprite=spr self.rect=self.sprite.get_rect(x=self.x,y=self.y) while True: #menu items b1menu=b1spr.get_rect(x=menurect.left+32,y=48) b2menu=b2spr.get_rect(x=menurect.left+64,y=48) menuitems=[MenuItem(b1menu,b1spr),MenuItem(b2menu,b2spr)] screen.fill((20,30,85)) mse=pygame.mouse.get_pos() key=pygame.key.get_pressed() placepos=((mse[0]/16)*16,(mse[1]/16)*16) if key[K_q]: if mse[0]<260: if menurect.right<255: menurect.right+=1 else: if menurect.left>-260: menurect.left-=1 else: if menurect.left>-260: menurect.left-=1 for e in pygame.event.get(): if e.type==QUIT: exit() if menurect.right<100: if e.type==MOUSEBUTTONUP: if e.button==1: to_remove = [i for i in instances if i.rect.collidepoint(placepos)] for i in to_remove: instances.remove(i) if not to_remove: instances.append(Block(placepos[0],placepos[1],currentbspr)) for i in instances: screen.blit(i.sprite,i.rect) if not key[K_q]: screen.blit(curspr,placepos) screen.blit(menuspr,menurect) for item in menuitems: screen.blit(item.sprite,item.pos) if item.rect.collidepoint(mse): if pygame.mouse.get_pressed()==(1,0,0): currentbspr=item.sprite pygame.draw.rect(screen, ((255,0,0)), item, 1) pygame.display.flip()

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• Tips for achieving "continual" delivery

  - by Ben

  A team is experiencing difficulty releasing software on a frequent basis (once every week). What follows is a typical release timeline: During the iteration: Developers work on stories on the backlog on short-lived (this is enthusiastically enforced) feature branches based on the master branch. Developers frequently pull their feature branches into the integration branch, which is continually built and tested (as far as the test coverage goes) automatically. The testers have the ability to auto-deploy integration to a staging environment and this occurs multiple times per week, enabling continual running of their test suites. Every Monday: there is a release planning meeting to determine which stories are "known good" (based on the testers' work), and hence will be in the release. If there is a known issue with a story, the source branch is pulled out of integration. no new code (only bug fixes requested by the testers) may be pulled into integration on this Monday to ensure the testers have a stable codebase to cut a release from. Every Tuesday: The testers have tested the integration branch as much as they possibly can have given the time available and there are no known bugs so a release is cut and pushed out to the production nodes slowly. This sounds OK in practise, but we have found that it is incredibly difficult to achieve. The team sees the following symptoms "subtle" bugs are found on production that were not identified on the staging environment. last minute hot-fixes continue into the Tuesday. problems on the production environment require roll-backs which blocks continued development until a successful live deployment is achieved and the master branch can be updated (and hence branched from). I think test coverage, code quality, ability to regression test quickly, last minute changes and environmental differences are at play here. Can anyone offer any advice regarding how best to achieve "continual" delivery?

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• Foreach loop with 2d array of objects

  - by Jacob Millward

  I'm using a 2D array of objects to store data about tiles, or "blocks" in my gameworld. I initialise the array, fill it with data and then attempt to invoke the draw method of each object. foreach (Block block in blockList) { block.Draw(spriteBatch); } I end up with an exception being thrown "Object reference is not set to an instance of an object". What have I done wrong? EDIT: This is the code used to define the array Block[,] blockList; Then blockList = new Block[screenRectangle.Width, screenRectangle.Height]; // Fill with dummy data for (int x = 0; x <= screenRectangle.Width / texture.Width; x++) { for (int y = 0; y <= screenRectangle.Height / texture.Width; y++) { if (y >= screenRectangle.Height / (texture.Width*2)) { blockList[x, y] = new Block(1, new Rectangle(x * 16, y * 16, texture.Width, texture.Height), texture); } else { blockList[x, y] = new Block(0, new Rectangle(x * 16, y * 16, texture.Width, texture.Height), texture); } } }

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• What triggered the popularity of lambda functions in modern mainstream programming languages?

  - by Giorgio

  In the last few years anonymous functions (AKA lambda functions) have become a very popular language construct and almost every major / mainstream programming language has introduced them or is planned to introduce them in an upcoming revision of the standard. Yet, anonymous functions are a very old and very well-known concept in Mathematics and Computer Science (invented by the mathematician Alonzo Church around 1936, and used by the Lisp programming language since 1958, see e.g. here). So why didn't today's mainstream programming languages (many of which originated 15 to 20 years ago) support lambda functions from the very beginning and only introduced them later? And what triggered the massive adoption of anonymous functions in the last few years? Is there some specific event, new requirement or programming technique that started this phenomenon? IMPORTANT NOTE The focus of this question is the introduction of anonymous functions in modern, main-stream (and therefore, maybe with a few exceptions, non functional) languages. Also, note that anonymous functions (blocks) are present in Smalltalk, which is not a functional language, and that normal named functions have been present even in procedural languages like C and Pascal for a long time. Please do not overgeneralize your answers by speaking about "the adoption of the functional paradigm and its benefits", because this is not the topic of the question.

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• Cannot Restore GRUB (Ubuntu 11.04 + Win 7)

  - by Benny

  I'm trying to fix GRUB on my PC, but I'm running into serious issues doing so. Any help would be greatly appreciated as I'm completely crippled right now. Here is the sequence of events for this PC: Installed Windows 7 Split full disk into two partitions (one for win7 and one for multimedia) Long time passed Split one of the partitions into two again Installed Ubuntu 11.04 on new partition A little time passed Windows 7 acting up, reinstall Ubuntu GRUB gone Tried restoring GRUB by mounting and grub-install from live USB Tried switching to a live CD instead of USB (thinking it might be the drive) Now I don't see GRUB and I'm getting "input/output" errors An example i/o error: ubuntu@ubuntu:~$ sudo fdisk -l Disk /dev/sda: 750.2 GB, 750156374016 bytes 255 heads, 63 sectors/track, 91201 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0xbe86aff6 Device Boot Start End Blocks Id System /dev/sda1 * 1 48727 391393280 7 HPFS/NTFS /dev/sda2 48727 77063 227612647+ 7 HPFS/NTFS /dev/sda3 77063 91202 113566721 5 Extended /dev/sda5 77063 90622 108908544 83 Linux /dev/sda6 90622 91202 4657152 82 Linux swap / Solaris ubuntu@ubuntu:~$ sudo mount /dev/sda5 /mnt ubuntu@ubuntu:~$ sudo grub-install --root-directory=/mnt /dev/sda mkdir: cannot create directory `/mnt/boot': Input/output error ubuntu@ubuntu:~$ cd /mnt ubuntu@ubuntu:/mnt$ ls ls: cannot access etc: Input/output error

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