I'm trying to share a folder on one Ubuntu machine with another Ubuntu machine on the same home network. When I right click on the folder and choose Sharing Options, it tells me I need to install Windows network sharing services in order to share folders. What does Windows have to do with this? I'm not trying to share with a Windows machine...
You're right, this can be confusing. So let me try to clarify the terms first of all:
The way Windows shares files and printers is called SMB. The people from the SAMBA project have implemented all of Microsoft's protocols and specifications for Linux. Ubuntu therefore supports the same sort of file sharing as Windows, which is called Samba.
So, when the Sharing Options dialogue asks you to install the packages, you're not actually installing any Microsoft software or anything like that. Go ahead and do it, it's perfectly safe.
You can try to just enable sharing before you follow Salih Emin's instructions; if it doesn't work, you will get a simple warning, you can then do the steps Salih describes if needed. I have tried it on a freshly installed and up-to-date system, and I indeed needed to do this.
At present, there is a small bug in Lucid which is listed in Launchpad: bug #536766. This bug doesn’t prompt the user to install the necessary packages needed to complete the file sharing set-up. Until that is addressed, here is a quick workaround.
You need to install libapache2-mod-dnssd and restart. Click this link to install it, or find libapache2-mod-dnssd in the Software Centre.
Once you have it installed, head over to System → Preferences → Personal file Sharing, and check the 'Share public files on network' box.
Once that is all done, you should then be able to view all other computers on your network that have allowed public file sharing within the Public folder. Just click on Places → Network, and there you should see all available computers and their shared Public folders.
Double-clicking on the server icon will mount the relevant public folder on your desktop.
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I believe that's what SAMBA packages are listed under, or it's at lest part of their description. As an alternative, you can try Preferences->File Sharing which I believe uses a different mechanism. Samba is a handy thing to have installed though.