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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for February 2nd, 2016

ElectriFly | SafeCharge LiPo Battery Charge Bag

Posted by jpluimers on 2016/02/02

http://www.electrifly.com/miscproducts/gpmp0751.html

Posted in Uncategorized | Leave a Comment »

I don’t care about cookies

Posted by jpluimers on 2016/02/02

https://chrome.google.com/webstore/detail/i-dont-care-about-cookies/fihnjjcciajhdojfnbdddfaoknhalnja

Posted in Uncategorized | Leave a Comment »

Windows: removing file and directory reparse points (symbolic links, directory links, junctions, hard links)

Posted by jpluimers on 2016/02/02

The interwebs is full of posts telling about how to create file and directory junctions**.

But there is little information about removing them and even less being correct: some suggest to del a directory junction (which just deletes everything in it but the junction).

Finally there is little information about listing all junctions, so lets start with that:

Deleting a link depends on the kind of link, not the kind of source.

Since symlink and hardlinks are for files, and directory symlink and junctions are for directories, this is how:

  • Delete a file symlink or hardlink by using DEL.
  • Delete a directory symlink or junction using RMDIR.

SysInternals – I wrote about them before – has a great junction tool. It can be used to create, delete and (optionally recursively) list reparse points. All usages allow for file and directory junctions.

More about reparse points

This is about the **: actually they are reparse points; for files they are symlinks, for directories mostly junctions, but sometimes symlinks.

And actually the reason I wrote this blog post. As you also have hardlinks. Some combinations of files and directories with these kinds of links fail.

Lets first go to see what kind of links there are on a fresh Windows system.

This is the only directory symlink: C:\Users\All Users and junction will show it like this:

.\\?\C:\\Users\All Users: SYMBOLIC LINK
   Print Name     : C:\ProgramData
   Substitute Name: \??\C:\ProgramData

It is unlike this directory junction C:\Users\Default User which junction will show as this:

\\?\C:\\Users\Default User: JUNCTION
   Print Name     : C:\Users\Default
   Substitute Name: C:\Users\Default

Together with C:\Users\Default and C:\Users\desktop.ini they are hidden, so you need the /AH flag to show them using DIR (as a gist, since WordPress still screws up less than and greater than):


Directory of C:\Users
08/22/2013 04:45 PM <SYMLINKD> All Users [C:\ProgramData]
09/30/2013 06:27 AM <DIR> Default
08/22/2013 04:45 PM <JUNCTION> Default User [C:\Users\Default]
08/22/2013 05:34 PM 174 desktop.ini

view raw

show-hidden-files-in-users.bat

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When you look at the examples below, it is odd to see that C:\Users\All Users is a SYMLINK and not a SYMLINKD as it points to a directory.

And yes, there are not so and very subtle differences between SYMLINKD and JUNCTION.

Lets show some examples.

The examples are hopefully more complete than the complete guide.

Since symlinks are client side created and not verified until use, you can actually use mklink to create both file and directory symbolic links for a file. DIR shows them as SYMLINK or SYMLINKD.

A SYMLINK to a file actually works, but a SYMLINKD or JUNCTION to a file gives you an Access Denied error. Hardlinks get the attributes of the source (so delete hidden hardlinks using the DEL /AH option).

Example batch file:

view raw

show-mklink-symlink-symlinkd-junction-junction-hardlink-on-file.bat

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Example output:

view raw

show-mklink-symlink-symlinkd-junction-junction-hardlink-on-file.bat.txt

hosted with ❤ by GitHub

When you try this for directories, you are in for a few small surprises.

A SYMLINK to a directory neither works as file nor as directory. A SYMLINKD or JUNCTION to a directory works. Hardlinks don’t work for directories with reason: limit the risk of cycles.

Example batch file:

view raw

show-mklink-symlink-symlinkd-junction-junction-hardlink-on-file.bat

hosted with ❤ by GitHub

Example output:

view raw

show-mklink-symlink-symlinkd-junction-junction-hardlink-on-file.bat.txt

hosted with ❤ by GitHub

Conclusion

  • symlink and hardlink can be used as files, but not as directories.
  • files referenced through symlinkd and junction behave as empty directories.
  • symlinkd and junction can be used as directories, but not as files.
  • directories referenced as symlink are not usable.
  • directories cannot function as hardlink source.
  • hardlinks to files inherited their attributes.

–jeroen

Posted in Batch-Files, Development, Scripting, Software Development | 2 Comments »

 
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