One of the best diagnostic tools for debugging problems is Samba itself. You can use the -d option for both smbd and nmbd to specify the debug level at which to run. See the man pages for smbd, nmbd, and smb.conf for more information regarding debugging options. The debug level (log level) can range from 1 (the default) to 10 (100 for debugging passwords).

Another helpful method of debugging is to compile Samba using the gcc -g flag. This will include debug information in the binaries and allow you to attach gdb to the running smbd/nmbd process. To attach gdb to an smbd process for an NT workstation, first get the workstation to make the connection. Pressing ctrl-alt-delete and going down to the domain box is sufficient (at least, the first time you join the domain) to generate a LsaEnumTrustedDomains. Thereafter, the workstation maintains an open connection and there will be an smbd process running (assuming that you haven't set a really short smbd idle timeout). So, in between pressing ctrl-alt-delete and actually typing in your password, you can attach gdb and continue.

Some useful Samba commands worth investigating are:

$ testparm | more
$ smbclient -L //{netbios name of server}

Tcpdump was the first UNIX sniffer with SMB support. It is a command-line utility and now, its SMB support is somewhat lagging that of ethereal and tethereal.

Ethereal is a graphical sniffer, available for both UNIX (Gtk) and Windows. Ethereal's SMB support is quite good. For details on the use of ethereal, read the well-written Ethereal User Guide.

Figure 39.1. Starting a Capture.

Listen for data on ports 137, 138, 139, and 445. For example, use the filter port 137, port 138, port 139, or port 445 as seen in Starting a Capture snapshot.

A console version of ethereal is available as well and is called tethereal.

Figure 39.2. Main Ethereal Data Window.

For tracing things on Microsoft Windows NT, Network Monitor (aka Netmon) is available on Microsoft Developer Network CDs, the Windows NT Server install CD, and the SMS CDs. The version of Netmon that ships with SMS allows for dumping packets between any two computers (i.e., placing the network interface in promiscuous mode). The version on the NT Server install CD will only allow monitoring of network traffic directed to the local NT box and broadcasts on the local subnet. Be aware that Ethereal can read and write Netmon formatted files.