I have just seen the most remarkable thing in a deep corner of my large archive disk: a single directory containing two entries (subdirectories) with the same name and same inode number.

% ls -liaF path/to/directory/with/duplicate/entries
total 56
1227293 drwxr-xr-x  1 jdlh  staff    264  3 Jan  2016 ./
1227288 drwxr-xr-x  1 jdlh  staff    264  3 Jan  2016 ../
1227364 drwxr-xr-x  1 jdlh  staff    264 20 Feb  2009 .externalToolBuilders/
1227364 drwxr-xr-x  1 jdlh  staff    264 20 Feb  2009 .externalToolBuilders/
1227367 -rw-rw-rw-  1 jdlh  staff    859 20 Feb  2009 other_files

There are two entries named externalToolBuilders/ in this directory. They appear to share the same inode number, so they refer to the same thing, not just to two things which share the same name.

When I try to copy this directory to another file system volume using Finder, I get an error that "a directory with the name .externalToolBuilders already exists. The copy aborts at that point. I can refer to both entries with a single wildcard like diff -rq .ext*, and the command treats this as expanding to two arguments.

However, I can use some command line commands like cp -r, referring to the duplicate subdirectory, and only one of the entries gets copied.

It looks like this directory was expanded from a .zip archive. It is possible that the .zip archive was constructed incorrectly to have two entries with the same name, that the archive utility did not catch the mistake, but that Finder did.

[Update after more investigation: the problem is observed in directories which were not expanded from a .zip archive. The problem is observed in several locations, but all observed examples are on a volume hosted by a QNAP Network Attached Storage (NAS) appliance, served to Mac OS through netatalk AFP support.]

Has anyone seen this on a Mac OS file system before? I find it most curious. How can it be constructed at will? Are there known drawbacks of it? How can one clean it up?

I have just seen the most remarkable thing in a deep corner of my large archive disk: a single directory containing two entries (subdirectories) with the same name and same inode number.

% ls -liaF path/to/directory/with/duplicate/entries
total 56
1227293 drwxr-xr-x  1 jdlh  staff    264  3 Jan  2016 ./
1227288 drwxr-xr-x  1 jdlh  staff    264  3 Jan  2016 ../
1227364 drwxr-xr-x  1 jdlh  staff    264 20 Feb  2009 .externalToolBuilders/
1227364 drwxr-xr-x  1 jdlh  staff    264 20 Feb  2009 .externalToolBuilders/
1227367 -rw-rw-rw-  1 jdlh  staff    859 20 Feb  2009 other_files

There are two entries named externalToolBuilders/ in this directory. They appear to share the same inode number, so they refer to the same thing, not just to two things which share the same name.

When I try to copy this directory to another file system volume using Finder, I get an error that "a directory with the name .externalToolBuilders already exists". The copy aborts at that point. I can refer to both entries with a single wildcard like diff -rq .ext*, and the command treats this as expanding to two arguments.

However, I can use some command line commands like cp -r, referring to the duplicate subdirectory, and only one of the entries gets copied.

It looks like this directory was expanded from a .zip archive. It is possible that the .zip archive was constructed incorrectly to have two entries with the same name, that the archive utility did not catch the mistake, but that Finder did.

[Update after more investigation: the problem is observed in directories which were not expanded from a .zip archive. The problem is observed in several locations, but all observed examples are on a volume hosted by a QNAP Network Attached Storage (NAS) appliance, served to Mac OS through netatalk AFP support.]

Has anyone seen this on a Mac OS file system before? I find it most curious. How can it be constructed at will? Are there known drawbacks of it? How can one clean it up?

I have just seen the most remarkable thing in a deep corner of my large archive disk: a single directory containing two entries (subdirectories) with the same name and same inode number.

% ls -liaF path/to/directory/with/duplicate/entries
total 56
1227293 drwxr-xr-x  1 jdlh  staff    264  3 Jan  2016 ./
1227288 drwxr-xr-x  1 jdlh  staff    264  3 Jan  2016 ../
1227364 drwxr-xr-x  1 jdlh  staff    264 20 Feb  2009 .externalToolBuilders/
1227364 drwxr-xr-x  1 jdlh  staff    264 20 Feb  2009 .externalToolBuilders/
1227367 -rw-rw-rw-  1 jdlh  staff    859 20 Feb  2009 other_files

There are two entries named externalToolBuilders/ in this directory. They appear to share the same inode number, so they refer to the same thing, not just to two things which share the same name.

When I try to copy this directory to another file system volume using Finder, I get an error that "a directory with the name .externalToolBuilders already exists. The copy aborts at that point. I can refer to both entries with a single wildcard like diff -rq .ext*, and the command treats this as expanding to two arguments.

However, I can use some command line commands like cp -r, referring to the duplicate subdirectory, and only one of the entries gets copied.

It looks like this directory was expanded from a .zip archive. It is possible that the .zip archive was constructed incorrectly to have two entries with the same name, that the archive utility did not catch the mistake, but that Finder did.

Has anyone seen this on a Mac OS file system before? I find it most curious. How can it be constructed at will? Are there known drawbacks of it? How can one clean it up?

I have just seen the most remarkable thing in a deep corner of my large archive disk: a single directory containing two entries (subdirectories) with the same name and same inode number.

% ls -liaF path/to/directory/with/duplicate/entries
total 56
1227293 drwxr-xr-x  1 jdlh  staff    264  3 Jan  2016 ./
1227288 drwxr-xr-x  1 jdlh  staff    264  3 Jan  2016 ../
1227364 drwxr-xr-x  1 jdlh  staff    264 20 Feb  2009 .externalToolBuilders/
1227364 drwxr-xr-x  1 jdlh  staff    264 20 Feb  2009 .externalToolBuilders/
1227367 -rw-rw-rw-  1 jdlh  staff    859 20 Feb  2009 other_files

There are two entries named externalToolBuilders/ in this directory. They appear to share the same inode number, so they refer to the same thing, not just to two things which share the same name.

When I try to copy this directory to another file system volume using Finder, I get an error that "a directory with the name .externalToolBuilders already exists. The copy aborts at that point. I can refer to both entries with a single wildcard like diff -rq .ext*, and the command treats this as expanding to two arguments.

However, I can use some command line commands like cp -r, referring to the duplicate subdirectory, and only one of the entries gets copied.

It looks like this directory was expanded from a .zip archive. It is possible that the .zip archive was constructed incorrectly to have two entries with the same name, that the archive utility did not catch the mistake, but that Finder did.

[Update after more investigation: the problem is observed in directories which were not expanded from a .zip archive. The problem is observed in several locations, but all observed examples are on a volume hosted by a QNAP Network Attached Storage (NAS) appliance, served to Mac OS through netatalk AFP support.]

Has anyone seen this on a Mac OS file system before? I find it most curious. How can it be constructed at will? Are there known drawbacks of it? How can one clean it up?