Cross-Platform Sharing Pains

All in all, the developers of Linux seem to have done a pretty good job of ensuring that Linux is able to integrate with other systmes. Chief among this integration has been in the realm of sharing files between Linux and Windows hosts. Overall, the CIFS support has been pretty damned good and has allowed Linux to lead in this area compared to other, proprietary *N*X OSes.

That said, Microsoft (and others) seem to like to create a moving target for the Open Source community to aim at. If you have Windows 2008-based fileservers in your operations and are trying to get you Linux hosts to mount shares coming off these systems, you hay have run into issues with doing so. This is especially so if your Windows share-servers are set up with high security settings and you're trying to use service names to reference those share servers (i.e., the Windows-based fileserver may have a name like "dcawfs0035n" but you might have an alias like "repository5").

Normally, when mounting a CIFS fileserver by its real name, you'll do something like:

# mount -t cifs "//dcawfs0035n/LXsoftware" /mnt/NAS -o domain=mydomain,user=myuser

And, assuming the credentials you supply are correct, the URI is valid and the place you're attemtping to mount to exists and isn't busy, you'll end up with that CIFS share mounted on your Linux host. However, if you try to mount it via an alias (e.g., a CNAME in DNS):

# mount -t cifs "//repository5/LXsoftware" /mnt/NAS -o domain=mydomain,user=myuser

You'll get prompted for your password - as per normal - but, instead of being rewarded with the joy of your CIFS share mounted to you Linux host, you'll get an error similar to the following:

mount error 5 = Input/output error
Refer to the mount.cifs(8) manual page (e.g.man mount.cifs)

Had you fat-fingered your password, you'd have gotten a "mount error 12" (permission denied), instead. The above results in strict name checking being performed on the share mount attempt. Because you've attempted to an alias to connect with, the name-checking will fail and you'll get the above denial. You can verify that this is the underlying cause by re-attempting the mount with the fileserver's real name. If that succeeds where the alias, failed, you'll know where to go, next.

The Microsoft-published solution is found in KB281308. To summarize, you'll need to:

• Have admin and login rights on the share-server
• Login to the share-server
• Fire up regedit
• Navigate to "HKLM\System\CurrentControlSet\Services\LanmanServer\Parameters"
• Create a new DWORD paramter named "DisableStrictNameChecking"
• Set its value to "1"
• Reboot the fileserver
• Retry your CIFS mount attempt.

At this point, your CIFS mount should succeed.

Interestingly, if you've ever tried to connect to this share from another Windows host not in the share-server's domain (e.g., from a host on different Windows domain that doesn't have cross-realm trusts set up or a standlone Windows client), you will probably have experienced connection errors, as well. Typical error messages being something on the order of "account is not allowed to logon from this resource" or just generally refusing to accept what you know to be a good set of credentials.