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September 4, 2006

Importance of Loopback Device

As is typical, I found myself helping out a friend with their Debian box. For whatever, reason (which would become apparent later) he was not able to access the server from his network. I was clear that Samba was running and that once the windows clients were authenticated to the network using the same username and passwd... Accessing the Linux server resources would be trivial.

After perusing /var/log/samba, I discovered the following error:
open_oplock_ipc: Failed to get local UDP socket for address

Hmmm. The failure didn't immediately jump out, so off to trusty google.
It seems that there is use for the loopback device after all. Actually, I had not given it much thought. I always thought of the loopback device as a 'virtual' device, that simply is required to handle localhost. It seems that samba cannot function without enabling the network loopback device.

A simple 'ifconfig -a' revealed that loopback wasn't enabled. Easy enough to fix.
Running as root '/sbin/ifconfig lo up' resolved that matter.
However, the next step was to make sure that the device remained active.

So I next modified /etc/init.d/networking', and added 'ifup lo eth0' and assigned loopback device to first (only) ethernet device.

Next, I made a few modifications to /etc/smb.conf
Made sure that I synced passwd b/t windows and linux.

Once I completed the modifications, I ran 'testparm' and 'smbclient -L hostname' to dump the current samba configuration and active shares to stdout.

The output was as expected, hence problem resolved.

Posted by AG at September 4, 2006 1:51 AM