Linux and Samba in a Federal Lab

Using Linux and Samba for research on extremely small lasers called VCSELs.
NFS

Again, the parameter analyzer talks NFS, so the next step was configuring that. The /etc/exports file needed just one line:

/home/guest/hptestdata 192.168.10.29(rw)

The hptestdata directory was created under guest's home directory, and nfsd was restarted. This line allows only the one IP address to mount the directory. Appropriate information was entered into the parameter analyzer's front panel and the mount button pushed. Of course it didn't work the first time. After just a minute of diagnosis, syncing the ID numbers on the analyzer to the guest account solved the problem. Total time to configure NFS was less than five minutes.

Samba

Samba is an amazing product that can do many things. This is a simple application, and the /etc/smb.conf is shown in Listing 1.

Listing 1. /etc/smb.conf

Of course, crucial security information like network domain has been changed in this and /etc/exports. The key parts in the file are creating the hptestdata share and making it read-only. The read-only part is to prevent users from accidentally deleting data. We periodically purge, but only after assurances from all the users. The other part of Samba is modifying the boot-up files so nmbd is killed. With the network configuration we are setting up, we don't want to see the machine on the network. Therefore we don't want nmbd to provide name services. See your distribution's documentation for the appropriate file to configure. For Red Hat 6.2, we modified S91smb and commented out the nmbd startup lines by placing a # at the beginning of the appropriate lines. To remind myself of this network configuration, I also changed the echo line in the file to say that smbd was not starting. Normally the script will output that nmbd is starting. Access is restricted to our domain only so outside access is prevented. Total time to configure was several hours of tweaking.

NT Setup

The final configuration step was on the NT box. We haven't seen this trick anywhere else so we think it's pretty neat. We created a data share for the Linux machine. This is where the users will go for data from their desktops. Then we made a network shortcut using UNC (universal naming convention) and put it into the data share. To be honest, to do this we made the Samba share visible on the network for just a minute and created a shortcut in the directory. It was easier for us to do that than fight getting the double backslashes correct. When the user accesses the NT server, he or she sees the shared folder. Double-clicking there shows a directory. Double-clicking on the directory brings the user to the Linux box with the test data, without realizing it. This trick is necessary because Windows cannot share out a network drive that it has mounted. My original plan was to have the NT box map the Samba share to a drive and then share that out. Total time to configure was five minutes, after realizing that Windows can't share out a mapped drive and we employed this trick.

Conclusion

Linux and Samba filled a requirement of the lab that couldn't be supported otherwise. The method is transparent to the users because they go to the same central place for data; it's as secure as the branch's NT server, and it was literally built for free since we used 100% scavenged equipment.

Future

This scheme still suffers slightly from security. A savvy computer user could look at the properties of the network shortcut and then use that to make a shortcut directly to the Samba server, bypassing the NT security. An alternative would be to use the Linux box and smbmount to mount a share from the NT server and export that using NFS to the test device. We were able to mount the NT share on the Linux box, export that with NFS and then mount that on the 4155B. The problem still remaining is writing to that share, even using options with smbmount. Hopefully, in the near future we will have some time to tackle this aspect again.

Resources

Brian Gollsneider is a student at the University of Maryland working on a PhD in electrical engineering. He works with the researchers at the Army Research Laboratory investigating VCSELs. Brian Gollsneider may be reached via e-mail at gollsneb@glue.umd.edu.

Mike Martin is a student at the University of Maryland working on a BS in electrical engineering. He works with the researchers at the Army Research Laboratory investigating VCSELs.

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