_Files reserved word? with Next Generation client

New Contributor

We are preparing to roll the Next Generation OneDrive out to about 23,000 users and we are currently getting feedback from a few pilot locations.

One of the comments we received today was that FOLDER names which contain an underscore do not sync using the new client.  In testing we have not found that to be correct and we have many folders with underscores working fine.  However, we did find one scenario which is failing, but which worked ok with the old Groove client:

In a folder name, if there is anything, then an underscore preceeding "file" or "files", the sync will fail in the Next Gen. client.  It will work fine with old Groove sync clients.

For example Folders called "these_files" will fail.  "This_file" will also fail.

_Files will work

_file will work.


Folder names with a percent or hash sign also do not work, but I wouldn't have expected them to. :)

Anyone else see this or know if there is a list of reserved words, or if anyone has created a program which can recurse a folder tree and warn the user if there are any noncompliant filenames?

7 Replies

Hi Nigel


Im running the OneDrive Preview 17.3.6674 on MacOS Sierra and have no problem uploading folders with _ Just tested with a folder called: This_Folder_Will_Fail

Just asked my colleague with Window 10 - OneDrive version 17.3.6517 to create a folder called This_Folder and he has no problem uploading to OneDrive

Thanks Glen.   The issue I'm seeing is specifically with using the word "Files" or "File" after an underscore following any characters

In the Next Generation client:

This folder works:    _files

This folder fails:   My_files


But when using the origional Groove client, both names sync successfully.

This came up as we are having users upgrade from the old client to the next generation client, and some are reporting that folders which have always worked with the old client are now failing with the new. 


However Vasil pointed out that "files" is a documented reserved word in the KB he noted above, when using the old client.  This is opposite to what I've seen (works in the old client but not in the new), but clearly its a combination to be avoided either way.

Hi Nigel


Just tested with a My_Files folder - No problem here

@Vasil Michev wrote:

It is, as detailed here: https://support.microsoft.com/en-us/kb/2933738

According to this info:

The following folder names can be synchronized in OneDrive for Business and SharePoint Online. However, if they’re synchronized, they may not appear when you view the library on the SharePoint Online or OneDrive for Business webpage. With some of these restrictions, you may be unable to add files or folders that have these characters while in the OneDrive for Business folder. However, if you create the files or folders outside OneDrive for Business and then drag those files or folders into the OneDrive for Business folder, the files and folders will sync but the files won't appear on the webpage.


etc. etc.

According to Glen he could upload a "My_Files" folder and provided a screenshot of the web interface as proof.

According to Microsoft he should not have been able to see the folder on the web interface (see above).


Both statements contradict each other so most likely both are false.  ;)


Seriously, it is (sort of) ok if there are some restrictions for file and folder names because they come from legacy applications where people should have know better but didn't implement a better solutions. (Special filenames were never a good idea. Localized filenames like _files and _Dateien didn't make it better.)


But pretty pretty please with a sprinkle of sugar give us meaningful error messages! If the sync client is not able to sync those files and folder it should tells us about it in the client and not on a web page which is most likely out of date when a new version of the client is published.


I have the Next Generation client preview client supporting Sharepoint site since the beginning and have no issue with it. Yesterday it update to version 17.3.6705.1122 and start having issue with 2 old syncs folders ending by _files (as coming from save of webpage).

Rename them and putting back the orginal name ending by _files solve temporary the issue but it come back after waiting some hour.

Does someone known the origin of this limitation. I understand form COM, PRN, ... files but folder ending by _files is quite common especially if you save webpage. MS doesn't want we save then due to risk within html page?