`copy2` checks if `os` nodule has `chmod` and then it uses it without thinking. 

On filesystems that doesn't support `chmod` it ends with

    OSError: [Errno 95] Operation not supported: <filename>

which is not acceptable since documentation says "copy2() never returns failure".

I agree that copy2 should not fail because chmod fails. Could you please provide the entire traceback message when it fails (on both 2.7 and 3.4 or 3.5)? And what OS are you running on, and what filesystem?

It looks like the error happens because errno=95 (EOPNOTSUPP, probably) isn't in the list of errors that _copyxattr catches, while (ENOTSUP=134 on Linux) is.

I think the documentation is also incorrect. Of course copy2 can fail: what about out of disk space? I think the documentation is trying to say that copy2 never fails because it can't preserve metadata. And the wording in the docs "copy2() never returns failure" is also odd, it should say "copy2() never raises an exception because it cannot preserve file metadata".

Actually it is a remote fs mounted via samba. OS is Linux.

Tracebacks with Python versions I have:

$ python2.7
Python 2.7.11 (default, Jan 11 2016, 21:04:40) 
[GCC 5.3.1 20160101] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import shutil
>>> shutil.copy2("src", "dst")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/shutil.py", line 131, in copy2
    copystat(src, dst)
  File "/usr/lib/python2.7/shutil.py", line 100, in copystat
    os.chmod(dst, mode)
OSError: [Errno 95] Operation not supported: 'dst'
>>> 
$ python3.4
Python 3.4.4 (default, Jan  5 2016, 15:35:18) 
[GCC 5.3.1 20160101] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import shutil
>>> shutil.copy2("src", "dst")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.4/shutil.py", line 246, in copy2
    copystat(src, dst, follow_symlinks=follow_symlinks)
  File "/usr/lib/python3.4/shutil.py", line 191, in copystat
    lookup("chmod")(dst, mode, follow_symlinks=follow)
OSError: [Errno 95] Operation not supported: 'dst'
>>> 
$ python3.5
Python 3.5.1+ (default, Jan 13 2016, 15:09:18) 
[GCC 5.3.1 20160101] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import shutil
>>> shutil.copy2("src", "dst")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.5/shutil.py", line 252, in copy2
    copystat(src, dst, follow_symlinks=follow_symlinks)
  File "/usr/lib/python3.5/shutil.py", line 197, in copystat
    lookup("chmod")(dst, mode, follow_symlinks=follow)
OSError: [Errno 95] Operation not supported: 'dst'
>>>

New changeset 9585f46b97931d2640c3343dfe03aed15beb9fea by Stéphane Wirtel (Windson yang) in branch 'master':
bpo-26468: Doc: improve the documentation of shutil.copy2 when it can fail. (GH-13765)
https://github.com/python/cpython/commit/9585f46b97931d2640c3343dfe03aed15beb9fea

I have merged the PR with the change in the documentation, feel free to open a new PR for the other part of this issue.

New changeset c27bcc3b476bbda7958724376189816c4e9d19c4 by Miss Islington (bot) in branch '3.8':
bpo-26468: Doc: improve the documentation of shutil.copy2 when it can fail. (GH-13765)
https://github.com/python/cpython/commit/c27bcc3b476bbda7958724376189816c4e9d19c4