"directory junction" vs "directory symbolic link"?

382

A junction is definitely not the same thing as a directory symbolic link, although they behave similarly. The main difference is that, if you are looking at a remote server, junctions are processed at the server and directory symbolic links are processed at the client. Also see Matthew's comment on the fact that this means symbolic links on the local file system can point to remote file systems.

Suppose that on a machine named Alice you were to put a junction point c:\myjp and a directory symbolic link c:\mysymlink, both pointing to c:\targetfolder. While you're using Alice you won't notice much difference between them. But if you're using another machine named Bob, then the junction point

\\Alice\c$\myjp will point to \\Alice\c$\targetfolder

but the symbolic link

\\Alice\c$\mysymlink will point to \\Bob\c$\targetfolder

(Caveat: by default, the system doesn't follow symlinks on remote volumes, so in most cases the second example will actually result in either "File Not Found" or "The symbolic link cannot be followed because its type is disabled.")

The difference between a directory symbolic link and a file symbolic link is simply that one represents a directory and one represents a file. Since the target of the link doesn't need to exist when the link is created, the file system needs to know whether to tell applications that it is a directory or not.

It should also be noted that creating a symbolic link requires special privilege (by default, only available to elevated processes) whereas creating a junction only requires access to the file system.

Harry Johnston

Posted 2011-10-05T03:28:14.963

Reputation: 5 054

I'm confused about the junction link above. Is the source of that folder on Bob's computer? – Mallow – 2014-07-24T15:55:19.640

2@Mallow I think everything is on Alice's computer. Bob is merely a client accessing Alice – user193130 – 2014-07-24T16:10:25.103

1Regard writing style, when comparing two things, it's clearer to unfamiliar people to explicitly state which goes with which. The following is confusing: "One is foo foo, and the other is bar bar"... (so... which one?) – ahnbizcad – 2015-08-09T21:08:06.490

@ahnbizcad: I really don't think it necessary to spell out explicitly that the directory symbolic link represents a directory and the file symbolic link represents a file. It's hardly likely to be the other way around! – Harry Johnston – 2015-08-09T21:20:59.000

@Harry Johnston, can you say more about " junctions are processed at the server and directory symbolic links are processed at the client" or where you got this from? – Daan – 2015-09-14T09:22:36.267

@Daan: the fact that symbolic links cross SMB is documented in What's new in SMB?. I don't know of any documentation that explicitly states that junction points don't, but it is inherent in the way they are implemented and I did find Create the SYSVOL Root and Staging Areas Junction Point which otherwise wouldn't work. (Mostly though, it's just experience.)

– Harry Johnston – 2015-09-14T19:52:19.937

@Harry Johnston, the reason I asked is because I had a problem with using junctions and symbolic links in my webserver, I posted the question here: http://serverfault.com/questions/722381/iis-server-directory-not-writable-via-symbolic-link-compared-to-directory-junct

– Daan – 2015-09-15T08:33:01.347

was there something else about safety or not wit deleting them? – barlop – 2016-06-11T17:10:23.190

It's possible to create a file symlink to a directory though. This still works in Cygwin, however if you don't explicitly set it to a /D, then apps like Windows explorer doesn't realise it's a directory symlink and show it as a directory and allow traversal. – CMCDragonkai – 2017-02-07T02:43:49.417

apparently win xp and prior had a danger issue re deleting junctions. http://cects.com/overview-to-understanding-hard-links-junction-points-and-symbolic-links-in-windows/ Safest thing is a suggestion here that'd apply to symbolic links or junctions or whatever, https://superuser.com/questions/167076/how-can-i-delete-a-symbolic-link add an underscore or rename, the actual non-link target directory, then the link or junction thing, shows as empty and delete it with eg rmdir or

– barlop – 2017-09-22T11:19:33.527

@barlop, AFAIK, you can always delete a junction or directory symbolic link with rmdir, you don't need to make it appear to be empty first. – Harry Johnston – 2017-09-22T22:04:05.737

@HarryJohnston I didn't say you had to. My point is that it's safer to temporarily rename the target. so that a)one is not deleting the wrong one(the target when one means to delete the junction and only the junction), and b)that link documents that XP and win2K3 and prior, had an issue where deleting a junction deleted the target directory itself too. So it's safer from the perspective of behaviour of prior Win OSs and human error. – barlop – 2017-09-23T05:59:42.990

@HarryJohnston Also do you know of a quick way to test if a directory is a link(unless one made a batch file with a command like this) https://stackoverflow.com/questions/18883892/batch-file-windows-cmd-exe-test-if-a-directory-is-a-link-symlink so without a quick easy check, I suppose if one can quickly check then one can do it safely (putting aside the issue with previous OSs like XP and Win2K3 and prior)

– barlop – 2017-09-23T06:05:34.513

1@barlop, rmdir should be safe, I'm pretty sure it only ever deletes the junction, not the target. It certainly won't delete any content unless you specify /s. I would normally just use dir (on the parent directory) to see whether something is a junction point. In some cases that might not be convenient, I suppose. – Harry Johnston – 2017-09-23T06:44:52.777

@HarryJohnston ah yes you're right. good idea re rmdir(without /s), and rm, and re dir on the parent.. I see even dir c:\blahsymboliclink will just show the symbolic link.. so it's not like with dir c:\windows which does dir c:\windows*.* dir c:\blahsymboliclink will show whether it's a symbolic link or not. dir c:\blahsymbolic link is a bit like dir c:\windo* or ls -ld blah it won't list the contents of the symbolic link directory itself unless you dod ...*.* or were within it. – barlop – 2017-09-23T07:40:15.273

13Just to be clear: there may well be other subtler functional differences between directory junctions and directory symbolic links. The remote vs. local thing is just the most obvious from a user (as opposed to a developer) perspective. – Harry Johnston – 2011-10-05T04:02:18.620

Sry I find the second paragraph quite ambiguous. If I create a symbolic link testlink on the client, which links to the c:\test folder on the server, doesn't testlink (symbolic link) also allow me to see the contents of the C:\test folder on the server? – Pacerier – 2011-10-05T05:31:03.797

1@Pacerier the difference is where they are resolved. If you create a symbolic link on your local machine then you won't notice the difference. If you shared out your computer then a junction would resolve to your computer when viewed from another but a symbolic link would resolve to theirs – Matthew Steeples – 2011-10-05T07:43:24.770

13@MatthewSteeples do you mean that if I create a symbolic link C:\testlink (which points to C:\test on my computer) and someone remote access my computer and clicks on C:\testlink, it would resolve to the C:\test on HIS computer, Whereas if I create a directory junction C:\testlink (which points to C:\test on my computer), and someone remote access my computer and clicks on C:\testlink) it would lead him to the C:\test on my computer? Or did I get it the wrong way round? – Pacerier – 2011-10-05T08:19:46.027

3@Pacerier that's right. You've got it the right way round in your example – Matthew Steeples – 2011-10-05T08:41:24.173

I've edited my answer to expand on the example, hopefully it is clearer now. – Harry Johnston – 2011-10-05T22:38:36.547

2@Matthew ic, so that means that symbolic links are useless – Pacerier – 2011-10-06T13:13:30.227

9@Pacerier in this context yes, but symbolic links allow you to have a folder on your computer that points to a network share (because they're resolved client side). Eg C:\MyNetworkShare could actually point to \Alice\Share – Matthew Steeples – 2011-10-06T14:57:36.263

7@MatthewSteeples but couldn't we create a directory junction C:\MyNetworkShare which points to \\Alice\Share as well? – Pacerier – 2011-10-07T10:44:04.710

9@Pacerier, no, junction points have to be local. – Harry Johnston – 2011-10-08T00:05:26.347

@HarryJohnston I see your point now – Pacerier – 2011-10-08T00:52:23.403

1Also: suppose a machine has two network cards, and so is known on the network by two different names. (E.g. a subnet of high-end calculation servers, each with one 100MB card on the larger, main network, and each with 40GB cards on a smaller network connecting them to the file server for inter-calc cummunication). Consider a junction on the file-server Svr: G:\jnctn -> G:\trgt. If the server is known as SvrA on the 100MB network and SrvB on the 40GB network, and G:\ is shared as Shr, then \SvrA\shr\jnctn and \SvrB\shr\jnctn both resolve to G:\trgt on the server. – David I. McIntosh – 2014-06-03T18:32:42.783

1And the key thing about this is: they resolve on the same network as the original access. That is, \SvrA\shr\jnctn resolves, in effect, to \SvrA\shr\trgt, i.e. resolves on the 100MB network, and \SrvB\shr\jnctn resolves to \Svrb\shr\trgt, i.e. resolves on the 40GB network. If you were to create a symbolic link that still works for external access, you would need to link as G:\jnctn -> \SrvA\shr\tgt or \SrvB\shr\tgt, and so you are deciding the network access in the link itself. This may be desirable or may be exactly what you don't want! – David I. McIntosh – 2014-06-03T18:37:32.183

3That is so weird. Even relative symbolic links don't work remotely. E.g. I create a directory d:\_tmp\data. Create link like so: d:\_tmp>mklink /d data-link data. Remote user has full access to d:\_tmp and all its subfolders BUT he will still not be able to open d:\_tmp\data-link. – Nux – 2016-08-19T11:18:14.833

4That is because when a symbolic link gets evaluated client-side it would be pointing to d:\_tmp\data on the client, not the server. – apraetor – 2016-09-24T12:13:55.347

I think the reason why it's weird is clear. But I agree with @Nux that it IS weird, at least in the case of relative symlinks. – Jon Coombs – 2017-03-21T22:36:03.357

1Complex talk hurts brain -- I like charts I love this sentence, and the chart too. – Luke – 2019-06-24T01:08:24.417