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  • How to handle Foreign Keys with Entity Framework

    - by Jack Marchetti
    I have two entities. Groups. Pools. A Group can create many pools. So I setup my Pool table to have a GroupID foreign key. My code: using (entity _db = new entity()) { Pool p = new Pool(); p.Name = "test"; p.Group.ID = "5"; _db.AddToPool(p); } This doesn't work. I get a null reference exception on p.Group. How do I go about creating a new "Pool" and associating a GroupID?

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  • Configuring DNS and IIS for multiple domains on a single server

    - by RichardS
    I might be over complicating this but...I am hosting several websites and dns for the domains on a single server: domain1.net domain1.com domain2.net I have three items which I'm trying to work out whether to achieve by DNS, by IIS hostnames(bindings), or by IIS redirect. 1. Where I have domain1.net and domain1.com, I want everything from both (all emails and web requests) to just point to the domain1.net. Can I do this at the DNS level, or do I have to set up the email as forwarders on the email server and the domain as a hostname in IIS? For example: [email protected] [email protected] www.domain1.com www.domain1.net 2. I want to make sure that requests for domain1.net and www.domain1.net both resolve to the same place. Should this be done with DNS or with multiple hostnames, or with IIS redirects? 3. If I then want to have one webmail site serving all of domains (webmail.domain1.net, webmail.domain2.net), is it best to this with a cname in DNS or with host headers in IIS?

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  • 2 GPUs (for multi-monitor setup)

    - by A Dwarf
    I have a machine to which I need to connect a second monitor. This machine currently hosts a ATI Radeon HD 4770 with two DVI adapters. The second monitor to be hooked to this machine is a VGA monitor. Until I find a DVI-VGA adpater, I'm thinking installing a second graphics card which does have a VGA adapter, an NVidia card. Can I successfully run both AMD and NVidia cards on this machine? Any specifics I must be aware of, like how to ensure the ATI card to be the main card? Operating system is Windows 7

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  • How can I make multiple displays work on my Asus UX32VD?

    - by oKtosiTe
    Original title: Why do I have two trash icons in the Unity Launcher? Whether I run Ubuntu as a live-USB or install it, I always have two trash bins on the Unity Launcher. Both work, and both open the same location. This seems a bit redundant; what could be done about it? Update: Turning auto-hide on made it obvious that I have multiple Launchers showing. With auto-hide off, they simply overlap, making it look like there's a double trash icon, but with auto-hide enabled, I can display one Launcher (and therefore one trash icon) at a time. Still, two are running simultaneously. Second update: This problem appears to be caused by the way Ubuntu handles multiple displays on my Asus UX32VD Ultrabook. Somehow, the laptop display cannot be used while my external display is connected. It is shown in the Displays list, but remains black no matter how I configure it. The external display runs at 1920x1200, the laptop monitor should run at 1920x1080. It therefore becomes obvious that the Launcher that's supposed to run on the laptop display, is actually displayed on the external monitor. Using nomodeset as a kernel parameter as indicated here makes the laptop display inaccessible altogether, detecting the external monitor as the laptop display and making resolutions other than 1920x1200 inaccessible. That is not an option.

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  • Multiple logins with pam_mount means multiple (redundant) mounts ...

    - by Jamie
    I've configured pam_mount.so to automagically mount a cifs share when users login; the problem is if a user logs into multiple times simultaneously, the mount command is repeated multiple times. This so far isn't a problem but it's messy when you look at the output of a mount command. # mount /dev/sda1 on / type ext4 (rw,errors=remount-ro) proc on /proc type proc (rw,noexec,nosuid,nodev) none on /sys type sysfs (rw,noexec,nosuid,nodev) 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) none on /dev type devtmpfs (rw,mode=0755) none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620) none on /dev/shm type tmpfs (rw,nosuid,nodev) none on /var/run type tmpfs (rw,nosuid,mode=0755) none on /var/lock type tmpfs (rw,noexec,nosuid,nodev) none on /lib/init/rw type tmpfs (rw,nosuid,mode=0755) //srv1/UserShares/jrisk on /home/jrisk type cifs (rw,mand) //srv1/UserShares/jrisk on /home/jrisk type cifs (rw,mand) //srv1/UserShares/jrisk on /home/jrisk type cifs (rw,mand) I'm assuming I need to fiddle with either the pam.d/common-auth file or pam_mount.conf.xml to accomplish this. How can I instruct pam_mount.so to avoid duplicate mountings?

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  • Multiple SSL certificates on Apache using multiple public IPs - not working

    - by St. Even
    I need configure multiple SSL certificates on a single Apache server. I already know that I need multiple external IP addresses as I cannot use SNI (only running Apache 2.2.3 on this server). I assumed that I had everything configured correctly, unfortunately things are not working as they should (or maybe I should say, as I expected them to work)... In my httpd.conf I have: NameVirtualHost *:80 NameVirtualHost *:443 Lets say my public IP is 12.0.0.1 and my private IP is 192.168.0.1. When I use the public IP in my vhost my default website is being shown instead the one defined in my vhost, e.g.: <VirtualHost 12.0.0.1:443> ServerAdmin [email protected] ServerName blablabla.site.com DocumentRoot /data/sites/blablabla.site.com ErrorLog /data/sites/blablabla.site.com-error.log #CustomLog /data/sites/blablabla.site.com-access.log common SSLEngine On SSLCertificateFile /etc/httpd/conf/ssl/blablabla.site.com.crt SSLCertificateKeyFile /etc/httpd/conf/ssl/blablabla.site.com.key SSLCertificateChainFile /etc/httpd/conf/ssl/blablabla.site.com.ca-bundle <Location /> SSLRequireSSL On SSLVerifyDepth 1 SSLOptions +StdEnvVars +StrictRequire </Location> </VirtualHost> When I use the private IP in my vhost everything works as it should (the website defined in my vhost is being shown), e.g.: <VirtualHost 192.168.0.1:443> ...same as above... </VirtualHost> My server is listening on all interfaces: [root@grbictwebp02 httpd]# netstat -tulpn | grep :443 tcp 0 0 0.0.0.0:443 0.0.0.0:* LISTEN 5585/httpd What am I doing wrong? If I cannot get this to work I cannot continue to add the second SSL certificate on the other public IP... If more information is required just let me know!

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  • why does vb.net not support multiple inheritance?

    - by isolatedIterator
    I've seen some discussion on why c# does not implement multiple inheritance but very little as to why it isn't supported in vb. I understand that both c# and vb are compiled down to intermediary language and so they both need to share similar restrictions. The lack of multiple inheritance in VB seems to have been given as one reason for the lack of the feature in dot net. Does anyone know why VB doesn't support multiple inheritance? I'm hoping for a bit of history lesson and discussion on why this was never considered for VB.

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  • why does vb not support multiple inheritance?

    - by isolatedIterator
    I've seen some discussion on why c# does not implement multiple inheritance but very little as to why it isn't supported in vb. I understand that both c# and vb are compiled down to intermediary language and so they both need to share similar restrictions. The lack of multiple inheritance in VB seems to have been given as one reason for the lack of the feature in dot net. Does anyone know why VB doesn't support multiple inheritance? I'm hoping for a bit of history lesson and discussion on why this was never considered for VB.

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  • is multiple inheritance a compiler writers problem? - c++

    - by Dr Deo
    i have been reading about multiple inheritance http://stackoverflow.com/questions/225929/what-is-the-exact-problem-with-multiple-inheritance http://en.wikipedia.org/wiki/Diamond_problem http://en.wikipedia.org/wiki/Virtual_inheritance http://en.wikipedia.org/wiki/Multiple_inheritance But since the code does not compile until the ambiguity is resolved, doesn't this make multiple inheritance a problem for compiler writers only? - how does this problem affect me in case i don't want to ever code a compiler

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  • Specifying both multiple targets and multiple build files with ant or subant in 1.6

    - by Paul Marshall
    I'm trying to unify a build process, running one build to get multiple packages. My first shot at this is just having a central build script call <ant or <subant on each project's build.xml file. I'm using Ant 1.6, and I've run into a funny problem: either I use the <ant task, and I can specify multiple targets but not multiple build files, or I use the <subant task, and I can specify multiple build files but not multiple targets. I realize there's a few solutions here already: Just upgrade to Ant 1.7 already; <antcall can do multiple targets there. Edit the separate project build files to have a variety of top-level targets, so I can call each individual file with just one target, and use <antcall. Copy-paste a lot of <ant tasks, with a little help from <macrodef to help the sanity. Is there something I've missed, that will allow me to do what I want from this single central build.xml without a) editing individual project files, b) writing lots of repetitive code, or c) upgrading Ant, and that d) doesn't require editing every time I add a new project?

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  • Drupal 6: Group multiple values in tpl.php

    - by Jozzeh
    When using the date and views module, you can specify in views (using row style fields) 'group multiple values'. Which is default on. If you turn it off, you get multiple nodes each with a date. For example: - 24th March ------- node1 - 25th March ------- node1 What I'm trying to figure out is: what if you are not using fields but node as Row style. How do you implement this not-group-multiple-values in your type-node.tpl.php?

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  • How to enable multiple displays with Catalyst drivers in Ubuntu 13.04?

    - by Lokitez
    First, I installed Ubuntu 13.04. I have an ATI Radeon HD 7850. The open source drivers allowed multiple displays, but were horrendously laggy (even opening a browser window took several seconds). When I installed the Catalyst proprietary drivers, performance was perfect. The only problem is that trying to enable dual-monitors in the Catalyst center was grayed out and in the Ubuntu settings resulted in the resolution error. Is there any way around this?

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  • 12.10 upgrade broke brightness keys [closed]

    - by Chris Morgan
    I have been running Ubuntu (64-bit) on my HP 6710b laptop (Core 2 Duo with integrated graphics) for several years, and the backlight brightness keys have always worked. Since I upgraded to Ubuntu 12.10 earlier today, those keys do not work any more. The secondary function keys: Fn+F3: sleep; still works (and considerably faster than ever before!) Fn+F8: battery info; still works Fn+F9: reduce brightness; stopped working in 12.10 Fn+F10: increase brightness; stopped working in 12.10 It may also be worth while mentioning that X does not appear to be receiving the brightness events at all, or at least not sending them out further. (This I detected with a key logger I wrote for a Uni project, which uses X's Record extension; it is informed of the sleep and battery info keystrokes, but doesn't receive the brightness ones at all.) In the mean time, I know that I can use the Brightness & Lock settings screen to alter the brightness. (Wow! I can suddenly make my backlight darker than I could before—I can go right down to turning the backlight off, something I couldn't do before... but this model has a fairly dim screen, so I don't expect to use that much, if ever.) How can I get the brightness keys working again? This question is probably strongly related to I can't control my Brightness in HP Compaq 6710s.

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  • Configuring JPA Primary key sequence generators

    - by pachunoori.vinay.kumar(at)oracle.com
    This article describes the JPA feature of generating and assigning the unique sequence numbers to JPA entity .This article provides information on jpa sequence generator annotations and its usage. UseCase Description Adding a new Employee to the organization using Employee form should assign unique employee Id. Following description provides the detailed steps to implement the generation of unique employee numbers using JPA generators feature Steps to configure JPA Generators 1.Generate Employee Entity using "Entities from Table Wizard". View image2.Create a Database Connection and select the table "Employee" for which entity will be generated and Finish the wizards with default selections. View image 3.Select the offline database sources-Schema-create a Sequence object or you can copy to offline db from online database connection. View image 4.Open the persistence.xml in application navigator and select the Entity "Employee" in structure view and select the tab "Generators" in flat editor. 5.In the Sequence Generator section,enter name of sequence "InvSeq" and select the sequence from drop down list created in step3. View image 6.Expand the Employees in structure view and select EmployeeId and select the "Primary Key Generation" tab.7.In the Generated value section,select the "Use Generated value" check box ,select the strategy as "Sequence" and select the Generator as "InvSeq" defined step 4. View image   Following annotations gets added for the JPA generator configured in JDeveloper for an entity To use a specific named sequence object (whether it is generated by schema generation or already exists in the database) you must define a sequence generator using a @SequenceGenerator annotation. Provide a unique label as the name for the sequence generator and refer the name in the @GeneratedValue annotation along with generation strategy  For  example,see the below Employee Entity sample code configured for sequence generation. EMPLOYEE_ID is the primary key and is configured for auto generation of sequence numbers. EMPLOYEE_SEQ is the sequence object exist in database.This sequence is configured for generating the sequence numbers and assign the value as primary key to Employee_id column in Employee table. @SequenceGenerator(name="InvSeq", sequenceName = "EMPLOYEE_SEQ")   @Entity public class Employee implements Serializable {    @Id    @Column(name="EMPLOYEE_ID", nullable = false)    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator="InvSeq")   private Long employeeId; }   @SequenceGenerator @GeneratedValue @SequenceGenerator - will define the sequence generator based on a  database sequence object Usage: @SequenceGenerator(name="SequenceGenerator", sequenceName = "EMPLOYEE_SEQ") @GeneratedValue - Will define the generation strategy and refers the sequence generator  Usage:     @GeneratedValue(strategy = GenerationType.SEQUENCE, generator="name of the Sequence generator defined in @SequenceGenerator")

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  • How to manage primary key while updating [migrated]

    - by Subin Jacob
    In the following table primaryKeyColumn is primary key. To maintain the data history I always uses the values with WHERE condition(WHERE StatusColumn=1) And will set the StatusColumn to 0 if the data is edited (So that I could keep the previous data). But the problem is, if I update it to 0 , I can't insert the same key to primarykeycolumn since the column validated for primary keys. How can I manage these kind of validations? what the mistake I did in this design? primaryKeyColumn ValueColumn StatusColumn ---------------- ----------- ------------ 2 Name1 1 3 Name2 1 4 Name3 0

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  • Cannot add custom keyboard shortcut

    - by krasilich
    I'm trying to assign custom shortcut to launch my own script (I don't need it in terminal window, just launch it) So, I went to Settings - Keyboard - Shortcuts - Custom Shortcuts, pressed the button with "+" and entered the name of shortcut and the command itself. But then I cannot bind keys to that shortcut. I selected a new row and pressed needed keys (Shift + F3) and nothing happens. I can change the keys for system shortcuts, but do not have any luck with my own. Any ideas?

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  • Can not add custom keyboard shortcut

    - by krasilich
    I'm trying to assign custom shortcut to lunch my own script (I don't need it in terminal window, just lunch it) So, I went to Settings - Keyboard - Shortcuts - Custom Shortcuts press the button with "+" and enter the name of shortcut and the command itself. But then I cannot bind keys to that shortcut. I select new row and press needed keys (Shift + F3) and nothing happens. I can change the keys for system shortcuts, but do not have any luck with my own. Any ideas?

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  • Difference between multiple NS and NS having multiple A

    - by Jake
    I found this Can an NS Record Point To Multiple A Records?, but wonders what is the difference, if any. For example: mydomain.com. IN NS ns1.myhost.com. mydomain.com. IN NS ns2.myhost.com. ns1.myhost.com. IN A 111.222.333.1 ns2.myhost.com. IN A 111.222.333.2 versus mydomain.com. IN NS ns.myhost.com. ns.myhost.com. IN A 111.222.333.1 ns.myhost.com. IN A 111.222.333.2 EDIT: actually, come to think of it, it could be said the same for MX records. Any breaking differences? EDIT 2: then again, MX allow use of priority values so its a different case, in that one-ip-per-domain is more useful sometimes.

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  • Running Multiple sites with multiple domains apache

    - by PsychoData
    I am having a rough time running apache and using multiple domain names here is a snippet of my config file. I keep getting a error saying that NameVirtualHost has no VirtualHosts. I want them both running on the same IP and I'm not sure why this doesn't work. I've been digging through the documentation for VirtualHosts, NameVirtualHost, and apache's page about name based virtual hosting. That example in the name based page is almost exactly my config! What am I doing wrong? Listen *:80 NameVirtualHost *:80 <VirtualHost *:80> ServerName www.sample1.net DocumentRoot /var/www/sample1-net </VirtualHost> <VirtualHost *:80> ServerName www.example2.net DocumentRoot /var/www/example2-net </VirtualHost>

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  • Beginner Geek: How to Use Multiple Monitors to Be More Productive

    - by Chris Hoffman
    Many people swear by multiple monitors, whether they’re geeks or just people who need to be productive. Why use just one monitor when you can use two or more and see more at once? Additional monitors allow you to expand your desktop, getting more screen real estate for your open programs. Windows makes it very easy to set up additional monitors, and your computer probably has the necessary ports. Why Use Multiple Monitors? Multiple monitors give you more screen real estate. Hook up multiple monitors to a computer and you can move your mouse back and forth between them, dragging programs between monitors as if you had an extra-large desktop. People who swear by multiple monitors use them to display multiple things on-screen at a time. Rather than Alt+Tabbing and task switching to glance at another window, you can just look over with your eyes and then look back to the program you’re using. Some examples of use cases for multiple monitors include: Coders who want to view their code on one display with the other display reserved for documentation. They can just glance over at the documentation and look back at their primary workspace. Anyone who needs to view something while working. Viewing a web page while writing an email, viewing another document while writing an something, or working with two large spreadsheets and having both visible at once. People who need to keep an eye on information, whether it’s email or up-to-date statistics, while working. Gamers who want to see more of the game world, extending the game across multiple displays. Geeks who just want to watch a video on one screen while doing something else on the other screen. Hooking Up Multiple Monitors Hooking up an additional monitor to your computer should be very simple. Most new computers come with more than one port for a monitor — whether DVI, HDMI, the older VGA port, or a mix. Some computers may include splitter cables that allow you to connect multiple monitors to a single port. Most laptops also come with ports that allow you to hook up an external monitor. Plug a monitor into your laptop’s DVI or VGA port and Windows will allow you to use both your laptop’s integrated display and the external monitor at once. This all depends on the ports your computer has and how your monitor connects. If you have an old VGA monitor lying around and you have a modern laptop with only DVI or HDMI connectors, you may need an adapter that allows you to plug your monitor’s VGA cable into the new port. Be sure to take your computer’s ports into account before you get another monitor for it. Managing Multiple Monitors With Windows Windows makes using multiple monitors easy. Just plug the monitor into the appropriate port on your computer and Windows should automatically extend your desktop onto it. You can now just drag and drop windows between monitors. To control how this works, right-click your Windows desktop and select Screen resolution. Choose an option from the Multiple displays box. The Extend option extends your desktop onto an additional monitor, while the other options are mainly useful if you’re using an additional monitor for presentations — for example, you could mirror your laptop’s desktop onto a large monitor or blank your laptop’s screen while it’s connected to a larger display. Be sure to arrange your monitors properly so Windows understands how your monitors are physically positioned. Windows 8 allows you to extend your Windows taskbar across multiple monitors. You’ll find this option in the taskbar’s options window — right-click the taskbar and select Properties. You can also choose where you want Windows to display taskbar buttons for open programs — on any monitor’s taskbar or only on the taskbar on the associated monitor. Windows 7 doesn’t have these convenient features built-in — your second monitor won’t have a taskbar. To extend your taskbar onto an additional monitor, you’ll need a third-party utility like the free and open-source Dual Monitor Taskbar. If you just have a single monitor, you can also use the Aero Snap feature to quickly place multiple Windows applications side by side. On Windows 7 or 8, press Windows Key + Left or Windows Key + Right to make the current window take up the left or right half of your display. You could also drag any window’s title bar to the left or right edges of your screen and release the window. How useful this feature is depends on your monitor’s size and resolution. If you have a large, high-resolution monitor, it will allow you to see a lot. If you have a smaller laptop monitor with the seemingly standard 1366×768 resolution, you won’t be able to see much of each snapped window at once, so snapping windows may not be practical. Image Credit: Chance Reecher on Flickr, Camp Atterbury Joint Maneuver Training Center on Flickr, Xavier Caballe on Flickr     

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  • Ancillary Objects: Separate Debug ELF Files For Solaris

    - by Ali Bahrami
    We introduced a new object ELF object type in Solaris 11 Update 1 called the Ancillary Object. This posting describes them, using material originally written during their development, the PSARC arc case, and the Solaris Linker and Libraries Manual. ELF objects contain allocable sections, which are mapped into memory at runtime, and non-allocable sections, which are present in the file for use by debuggers and observability tools, but which are not mapped or used at runtime. Typically, all of these sections exist within a single object file. Ancillary objects allow them to instead go into a separate file. There are different reasons given for wanting such a feature. One can debate whether the added complexity is worth the benefit, and in most cases it is not. However, one important case stands out — customers with very large 32-bit objects who are not ready or able to make the transition to 64-bits. We have customers who build extremely large 32-bit objects. Historically, the debug sections in these objects have used the stabs format, which is limited, but relatively compact. In recent years, the industry has transitioned to the powerful but verbose DWARF standard. In some cases, the size of these debug sections is large enough to push the total object file size past the fundamental 4GB limit for 32-bit ELF object files. The best, and ultimately only, solution to overly large objects is to transition to 64-bits. However, consider environments where: Hundreds of users may be executing the code on large shared systems. (32-bits use less memory and bus bandwidth, and on sparc runs just as fast as 64-bit code otherwise). Complex finely tuned code, where the original authors may no longer be available. Critical production code, that was expensive to qualify and bring online, and which is otherwise serving its intended purpose without issue. Users in these risk adverse and/or high scale categories have good reasons to push 32-bits objects to the limit before moving on. Ancillary objects offer these users a longer runway. Design The design of ancillary objects is intended to be simple, both to help human understanding when examining elfdump output, and to lower the bar for debuggers such as dbx to support them. The primary and ancillary objects have the same set of section headers, with the same names, in the same order (i.e. each section has the same index in both files). A single added section of type SHT_SUNW_ANCILLARY is added to both objects, containing information that allows a debugger to identify and validate both files relative to each other. Given one of these files, the ancillary section allows you to identify the other. Allocable sections go in the primary object, and non-allocable ones go into the ancillary object. A small set of non-allocable objects, notably the symbol table, are copied into both objects. As noted above, most sections are only written to one of the two objects, but both objects have the same section header array. The section header in the file that does not contain the section data is tagged with the SHF_SUNW_ABSENT section header flag to indicate its placeholder status. Compiler writers and others who produce objects can set the SUNW_SHF_PRIMARY section header flag to mark non-allocable sections that should go to the primary object rather than the ancillary. If you don't request an ancillary object, the Solaris ELF format is unchanged. Users who don't use ancillary objects do not pay for the feature. This is important, because they exist to serve a small subset of our users, and must not complicate the common case. If you do request an ancillary object, the runtime behavior of the primary object will be the same as that of a normal object. There is no added runtime cost. The primary and ancillary object together represent a logical single object. This is facilitated by the use of a single set of section headers. One can easily imagine a tool that can merge a primary and ancillary object into a single file, or the reverse. (Note that although this is an interesting intellectual exercise, we don't actually supply such a tool because there's little practical benefit above and beyond using ld to create the files). Among the benefits of this approach are: There is no need for per-file symbol tables to reflect the contents of each file. The same symbol table that would be produced for a standard object can be used. The section contents are identical in either case — there is no need to alter data to accommodate multiple files. It is very easy for a debugger to adapt to these new files, and the processing involved can be encapsulated in input/output routines. Most of the existing debugger implementation applies without modification. The limit of a 4GB 32-bit output object is now raised to 4GB of code, and 4GB of debug data. There is also the future possibility (not currently supported) to support multiple ancillary objects, each of which could contain up to 4GB of additional debug data. It must be noted however that the 32-bit DWARF debug format is itself inherently 32-bit limited, as it uses 32-bit offsets between debug sections, so the ability to employ multiple ancillary object files may not turn out to be useful. Using Ancillary Objects (From the Solaris Linker and Libraries Guide) By default, objects contain both allocable and non-allocable sections. Allocable sections are the sections that contain executable code and the data needed by that code at runtime. Non-allocable sections contain supplemental information that is not required to execute an object at runtime. These sections support the operation of debuggers and other observability tools. The non-allocable sections in an object are not loaded into memory at runtime by the operating system, and so, they have no impact on memory use or other aspects of runtime performance no matter their size. For convenience, both allocable and non-allocable sections are normally maintained in the same file. However, there are situations in which it can be useful to separate these sections. To reduce the size of objects in order to improve the speed at which they can be copied across wide area networks. To support fine grained debugging of highly optimized code requires considerable debug data. In modern systems, the debugging data can easily be larger than the code it describes. The size of a 32-bit object is limited to 4 Gbytes. In very large 32-bit objects, the debug data can cause this limit to be exceeded and prevent the creation of the object. To limit the exposure of internal implementation details. Traditionally, objects have been stripped of non-allocable sections in order to address these issues. Stripping is effective, but destroys data that might be needed later. The Solaris link-editor can instead write non-allocable sections to an ancillary object. This feature is enabled with the -z ancillary command line option. $ ld ... -z ancillary[=outfile] ...By default, the ancillary file is given the same name as the primary output object, with a .anc file extension. However, a different name can be provided by providing an outfile value to the -z ancillary option. When -z ancillary is specified, the link-editor performs the following actions. All allocable sections are written to the primary object. In addition, all non-allocable sections containing one or more input sections that have the SHF_SUNW_PRIMARY section header flag set are written to the primary object. All remaining non-allocable sections are written to the ancillary object. The following non-allocable sections are written to both the primary object and ancillary object. .shstrtab The section name string table. .symtab The full non-dynamic symbol table. .symtab_shndx The symbol table extended index section associated with .symtab. .strtab The non-dynamic string table associated with .symtab. .SUNW_ancillary Contains the information required to identify the primary and ancillary objects, and to identify the object being examined. The primary object and all ancillary objects contain the same array of sections headers. Each section has the same section index in every file. Although the primary and ancillary objects all define the same section headers, the data for most sections will be written to a single file as described above. If the data for a section is not present in a given file, the SHF_SUNW_ABSENT section header flag is set, and the sh_size field is 0. This organization makes it possible to acquire a full list of section headers, a complete symbol table, and a complete list of the primary and ancillary objects from either of the primary or ancillary objects. The following example illustrates the underlying implementation of ancillary objects. An ancillary object is created by adding the -z ancillary command line option to an otherwise normal compilation. The file utility shows that the result is an executable named a.out, and an associated ancillary object named a.out.anc. $ cat hello.c #include <stdio.h> int main(int argc, char **argv) { (void) printf("hello, world\n"); return (0); } $ cc -g -zancillary hello.c $ file a.out a.out.anc a.out: ELF 32-bit LSB executable 80386 Version 1 [FPU], dynamically linked, not stripped, ancillary object a.out.anc a.out.anc: ELF 32-bit LSB ancillary 80386 Version 1, primary object a.out $ ./a.out hello worldThe resulting primary object is an ordinary executable that can be executed in the usual manner. It is no different at runtime than an executable built without the use of ancillary objects, and then stripped of non-allocable content using the strip or mcs commands. As previously described, the primary object and ancillary objects contain the same section headers. To see how this works, it is helpful to use the elfdump utility to display these section headers and compare them. The following table shows the section header information for a selection of headers from the previous link-edit example. Index Section Name Type Primary Flags Ancillary Flags Primary Size Ancillary Size 13 .text PROGBITS ALLOC EXECINSTR ALLOC EXECINSTR SUNW_ABSENT 0x131 0 20 .data PROGBITS WRITE ALLOC WRITE ALLOC SUNW_ABSENT 0x4c 0 21 .symtab SYMTAB 0 0 0x450 0x450 22 .strtab STRTAB STRINGS STRINGS 0x1ad 0x1ad 24 .debug_info PROGBITS SUNW_ABSENT 0 0 0x1a7 28 .shstrtab STRTAB STRINGS STRINGS 0x118 0x118 29 .SUNW_ancillary SUNW_ancillary 0 0 0x30 0x30 The data for most sections is only present in one of the two files, and absent from the other file. The SHF_SUNW_ABSENT section header flag is set when the data is absent. The data for allocable sections needed at runtime are found in the primary object. The data for non-allocable sections used for debugging but not needed at runtime are placed in the ancillary file. A small set of non-allocable sections are fully present in both files. These are the .SUNW_ancillary section used to relate the primary and ancillary objects together, the section name string table .shstrtab, as well as the symbol table.symtab, and its associated string table .strtab. It is possible to strip the symbol table from the primary object. A debugger that encounters an object without a symbol table can use the .SUNW_ancillary section to locate the ancillary object, and access the symbol contained within. The primary object, and all associated ancillary objects, contain a .SUNW_ancillary section that allows all the objects to be identified and related together. $ elfdump -T SUNW_ancillary a.out a.out.anc a.out: Ancillary Section: .SUNW_ancillary index tag value [0] ANC_SUNW_CHECKSUM 0x8724 [1] ANC_SUNW_MEMBER 0x1 a.out [2] ANC_SUNW_CHECKSUM 0x8724 [3] ANC_SUNW_MEMBER 0x1a3 a.out.anc [4] ANC_SUNW_CHECKSUM 0xfbe2 [5] ANC_SUNW_NULL 0 a.out.anc: Ancillary Section: .SUNW_ancillary index tag value [0] ANC_SUNW_CHECKSUM 0xfbe2 [1] ANC_SUNW_MEMBER 0x1 a.out [2] ANC_SUNW_CHECKSUM 0x8724 [3] ANC_SUNW_MEMBER 0x1a3 a.out.anc [4] ANC_SUNW_CHECKSUM 0xfbe2 [5] ANC_SUNW_NULL 0 The ancillary sections for both objects contain the same number of elements, and are identical except for the first element. Each object, starting with the primary object, is introduced with a MEMBER element that gives the file name, followed by a CHECKSUM that identifies the object. In this example, the primary object is a.out, and has a checksum of 0x8724. The ancillary object is a.out.anc, and has a checksum of 0xfbe2. The first element in a .SUNW_ancillary section, preceding the MEMBER element for the primary object, is always a CHECKSUM element, containing the checksum for the file being examined. The presence of a .SUNW_ancillary section in an object indicates that the object has associated ancillary objects. The names of the primary and all associated ancillary objects can be obtained from the ancillary section from any one of the files. It is possible to determine which file is being examined from the larger set of files by comparing the first checksum value to the checksum of each member that follows. Debugger Access and Use of Ancillary Objects Debuggers and other observability tools must merge the information found in the primary and ancillary object files in order to build a complete view of the object. This is equivalent to processing the information from a single file. This merging is simplified by the primary object and ancillary objects containing the same section headers, and a single symbol table. The following steps can be used by a debugger to assemble the information contained in these files. Starting with the primary object, or any of the ancillary objects, locate the .SUNW_ancillary section. The presence of this section identifies the object as part of an ancillary group, contains information that can be used to obtain a complete list of the files and determine which of those files is the one currently being examined. Create a section header array in memory, using the section header array from the object being examined as an initial template. Open and read each file identified by the .SUNW_ancillary section in turn. For each file, fill in the in-memory section header array with the information for each section that does not have the SHF_SUNW_ABSENT flag set. The result will be a complete in-memory copy of the section headers with pointers to the data for all sections. Once this information has been acquired, the debugger can proceed as it would in the single file case, to access and control the running program. Note - The ELF definition of ancillary objects provides for a single primary object, and an arbitrary number of ancillary objects. At this time, the Oracle Solaris link-editor only produces a single ancillary object containing all non-allocable sections. This may change in the future. Debuggers and other observability tools should be written to handle the general case of multiple ancillary objects. ELF Implementation Details (From the Solaris Linker and Libraries Guide) To implement ancillary objects, it was necessary to extend the ELF format to add a new object type (ET_SUNW_ANCILLARY), a new section type (SHT_SUNW_ANCILLARY), and 2 new section header flags (SHF_SUNW_ABSENT, SHF_SUNW_PRIMARY). In this section, I will detail these changes, in the form of diffs to the Solaris Linker and Libraries manual. Part IV ELF Application Binary Interface Chapter 13: Object File Format Object File Format Edit Note: This existing section at the beginning of the chapter describes the ELF header. There's a table of object file types, which now includes the new ET_SUNW_ANCILLARY type. e_type Identifies the object file type, as listed in the following table. NameValueMeaning ET_NONE0No file type ET_REL1Relocatable file ET_EXEC2Executable file ET_DYN3Shared object file ET_CORE4Core file ET_LOSUNW0xfefeStart operating system specific range ET_SUNW_ANCILLARY0xfefeAncillary object file ET_HISUNW0xfefdEnd operating system specific range ET_LOPROC0xff00Start processor-specific range ET_HIPROC0xffffEnd processor-specific range Sections Edit Note: This overview section defines the section header structure, and provides a high level description of known sections. It was updated to define the new SHF_SUNW_ABSENT and SHF_SUNW_PRIMARY flags and the new SHT_SUNW_ANCILLARY section. ... sh_type Categorizes the section's contents and semantics. Section types and their descriptions are listed in Table 13-5. sh_flags Sections support 1-bit flags that describe miscellaneous attributes. Flag definitions are listed in Table 13-8. ... Table 13-5 ELF Section Types, sh_type NameValue . . . SHT_LOSUNW0x6fffffee SHT_SUNW_ancillary0x6fffffee . . . ... SHT_LOSUNW - SHT_HISUNW Values in this inclusive range are reserved for Oracle Solaris OS semantics. SHT_SUNW_ANCILLARY Present when a given object is part of a group of ancillary objects. Contains information required to identify all the files that make up the group. See Ancillary Section. ... Table 13-8 ELF Section Attribute Flags NameValue . . . SHF_MASKOS0x0ff00000 SHF_SUNW_NODISCARD0x00100000 SHF_SUNW_ABSENT0x00200000 SHF_SUNW_PRIMARY0x00400000 SHF_MASKPROC0xf0000000 . . . ... SHF_SUNW_ABSENT Indicates that the data for this section is not present in this file. When ancillary objects are created, the primary object and any ancillary objects, will all have the same section header array, to facilitate merging them to form a complete view of the object, and to allow them to use the same symbol tables. Each file contains a subset of the section data. The data for allocable sections is written to the primary object while the data for non-allocable sections is written to an ancillary file. The SHF_SUNW_ABSENT flag is used to indicate that the data for the section is not present in the object being examined. When the SHF_SUNW_ABSENT flag is set, the sh_size field of the section header must be 0. An application encountering an SHF_SUNW_ABSENT section can choose to ignore the section, or to search for the section data within one of the related ancillary files. SHF_SUNW_PRIMARY The default behavior when ancillary objects are created is to write all allocable sections to the primary object and all non-allocable sections to the ancillary objects. The SHF_SUNW_PRIMARY flag overrides this behavior. Any output section containing one more input section with the SHF_SUNW_PRIMARY flag set is written to the primary object without regard for its allocable status. ... Two members in the section header, sh_link, and sh_info, hold special information, depending on section type. Table 13-9 ELF sh_link and sh_info Interpretation sh_typesh_linksh_info . . . SHT_SUNW_ANCILLARY The section header index of the associated string table. 0 . . . Special Sections Edit Note: This section describes the sections used in Solaris ELF objects, using the types defined in the previous description of section types. It was updated to define the new .SUNW_ancillary (SHT_SUNW_ANCILLARY) section. Various sections hold program and control information. Sections in the following table are used by the system and have the indicated types and attributes. Table 13-10 ELF Special Sections NameTypeAttribute . . . .SUNW_ancillarySHT_SUNW_ancillaryNone . . . ... .SUNW_ancillary Present when a given object is part of a group of ancillary objects. Contains information required to identify all the files that make up the group. See Ancillary Section for details. ... Ancillary Section Edit Note: This new section provides the format reference describing the layout of a .SUNW_ancillary section and the meaning of the various tags. Note that these sections use the same tag/value concept used for dynamic and capabilities sections, and will be familiar to anyone used to working with ELF. In addition to the primary output object, the Solaris link-editor can produce one or more ancillary objects. Ancillary objects contain non-allocable sections that would normally be written to the primary object. When ancillary objects are produced, the primary object and all of the associated ancillary objects contain a SHT_SUNW_ancillary section, containing information that identifies these related objects. Given any one object from such a group, the ancillary section provides the information needed to identify and interpret the others. This section contains an array of the following structures. See sys/elf.h. typedef struct { Elf32_Word a_tag; union { Elf32_Word a_val; Elf32_Addr a_ptr; } a_un; } Elf32_Ancillary; typedef struct { Elf64_Xword a_tag; union { Elf64_Xword a_val; Elf64_Addr a_ptr; } a_un; } Elf64_Ancillary; For each object with this type, a_tag controls the interpretation of a_un. a_val These objects represent integer values with various interpretations. a_ptr These objects represent file offsets or addresses. The following ancillary tags exist. Table 13-NEW1 ELF Ancillary Array Tags NameValuea_un ANC_SUNW_NULL0Ignored ANC_SUNW_CHECKSUM1a_val ANC_SUNW_MEMBER2a_ptr ANC_SUNW_NULL Marks the end of the ancillary section. ANC_SUNW_CHECKSUM Provides the checksum for a file in the c_val element. When ANC_SUNW_CHECKSUM precedes the first instance of ANC_SUNW_MEMBER, it provides the checksum for the object from which the ancillary section is being read. When it follows an ANC_SUNW_MEMBER tag, it provides the checksum for that member. ANC_SUNW_MEMBER Specifies an object name. The a_ptr element contains the string table offset of a null-terminated string, that provides the file name. An ancillary section must always contain an ANC_SUNW_CHECKSUM before the first instance of ANC_SUNW_MEMBER, identifying the current object. Following that, there should be an ANC_SUNW_MEMBER for each object that makes up the complete set of objects. Each ANC_SUNW_MEMBER should be followed by an ANC_SUNW_CHECKSUM for that object. A typical ancillary section will therefore be structured as: TagMeaning ANC_SUNW_CHECKSUMChecksum of this object ANC_SUNW_MEMBERName of object #1 ANC_SUNW_CHECKSUMChecksum for object #1 . . . ANC_SUNW_MEMBERName of object N ANC_SUNW_CHECKSUMChecksum for object N ANC_SUNW_NULL An object can therefore identify itself by comparing the initial ANC_SUNW_CHECKSUM to each of the ones that follow, until it finds a match. Related Other Work The GNU developers have also encountered the need/desire to support separate debug information files, and use the solution detailed at http://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html. At the current time, the separate debug file is constructed by building the standard object first, and then copying the debug data out of it in a separate post processing step, Hence, it is limited to a total of 4GB of code and debug data, just as a single object file would be. They are aware of this, and I have seen online comments indicating that they may add direct support for generating these separate files to their link-editor. It is worth noting that the GNU objcopy utility is available on Solaris, and that the Studio dbx debugger is able to use these GNU style separate debug files even on Solaris. Although this is interesting in terms giving Linux users a familiar environment on Solaris, the 4GB limit means it is not an answer to the problem of very large 32-bit objects. We have also encountered issues with objcopy not understanding Solaris-specific ELF sections, when using this approach. The GNU community also has a current effort to adapt their DWARF debug sections in order to move them to separate files before passing the relocatable objects to the linker. The details of Project Fission can be found at http://gcc.gnu.org/wiki/DebugFission. The goal of this project appears to be to reduce the amount of data seen by the link-editor. The primary effort revolves around moving DWARF data to separate .dwo files so that the link-editor never encounters them. The details of modifying the DWARF data to be usable in this form are involved — please see the above URL for details.

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  • Can zlib.crc32 or zlib.adler32 be safely used to mask primary keys in URLs?

    - by David Eyk
    In Django Design Patterns, the author recommends using zlib.crc32 to mask primary keys in URLs. After some quick testing, I noticed that crc32 produces negative integers about half the time, which seems undesirable for use in a URL. zlib.adler32 does not appear to produce negatives, but is described as "weaker" than CRC. Is this method (either CRC or Adler-32) safe for usage in a URL as an alternate to a primary key? (i.e. is it collision-safe?) Is the "weaker" Adler-32 a satisfactory alternative for this task? How the heck do you reverse this?! That is, how do you determine the original primary key from the checksum?

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  • How to change a primary key in SQL to auto_increment?

    - by Jian Lin
    I have a table in MySQL that has a primary key: mysql> desc gifts; +---------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------------+-------------+------+-----+---------+-------+ | giftID | int(11) | NO | PRI | NULL | | | name | varchar(80) | YES | | NULL | | | filename | varchar(80) | YES | | NULL | | | effectiveTime | datetime | YES | | NULL | | +---------------+-------------+------+-----+---------+-------+ but I wanted to make it auto_increment. The following statement failed. How can it be modified so that it can work? thanks mysql> alter table gifts modify giftID int primary key auto_increment; ERROR 1068 (42000): Multiple primary key defined

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  • Using Rails, how can I set my primary key to not be an integer-typed column?

    - by Rudd Zwolinski
    I'm using Rails migrations to manage a database schema, and I'm creating a simple table where I'd like to use a non-integer value as the primary key (in particular, a string). To abstract away from my problem, let's say there's a table employees where employees are identified by an alphanumeric string, e.g. "134SNW". I've tried creating the table in a migration like this: create_table :employees, {:primary_key => :emp_id} do |t| t.string :emp_id t.string :first_name t.string :last_name end What this gives me is what seems like it completely ignored the line t.string :emp_id and went ahead and made it an integer column. Is there some other way to have rails generate the PRIMARY_KEY constraint (I'm using PostgreSQL) for me, without having to write the SQL in an execute call? NOTE: I know it's not best to use string columns as primary keys, so please no answers just saying to add an integer primary key. I may add one anyway, but this question is still valid.

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