Day 4 - File Sharing and Old Internet Services

📌 Key Takeaways

• NFS is for sharing between Unix/Linux systems, and Samba is for sharing between Linux and Windows.
• The components of Samba are SMB, CIFS, and NetBIOS. RPC belongs to NFS, so including it here makes the answer wrong.
• NFS is configured in /etc/exports, and Samba in /etc/samba/smb.conf.
• Services from before the web — Gopher (menu-based information retrieval), Usenet (newsgroups), Archie (FTP search).
• Questions repeatedly mix up the names and ask you to pick the one that differs in nature.

NFS — Between Unix Systems

   [Server]  exports /data
              │
              ▼
   [Client]  mounts it and uses it like its own directory

# Server: /etc/exports
/data  192.168.0.0/24(rw,sync)
 
exportfs -a               # apply the configuration
showmount -e server-address      # check the exported list
 
# Client
mount -t nfs server:/data /mnt

• You mount a remote directory and use it like a local one. Users do not feel that it is across a network.
• Being RPC-based is the key point that distinguishes it from Samba.

Reading One Line of /etc/exports

   /data    192.168.0.0/24(rw,sync)
   └─┬─┘    └─────┬──────┘└───┬───┘
     │            │           └── options (in parentheses, comma-separated)
     │            └────────────── who is allowed access (host or network range)
     └─────────────────────────── directory to export

• Do not put a space between the target and the parentheses. If you write 192.168.0.0/24 (rw) with a space, the range and the options get separated and write permission opens to an unintended scope.
• root_squash is the default because otherwise someone who is root on their own PC could do whatever they like with the server's shared files.
• Editing the file alone does not apply the change. Run exportfs -a (export everything) or exportfs -r (re-read and apply). exportfs -v shows the list currently being exported.

$ showmount -e 192.168.0.10
Export list for 192.168.0.10:
/data 192.168.0.0/24
 
# mount -t nfs 192.168.0.10:/data /mnt
$ df -h /mnt
Filesystem          Size  Used Avail Use% Mounted on
192.168.0.10:/data   50G   20G   30G  40% /mnt

• The mount source is written as server:directory. If the Filesystem column of df shows this form instead of a device like /dev/sda1, it is NFS.
• showmount -e is used on the client to see "what that server offers," while exportfs is used on the server to manage "what I am offering."
• NFS exchanges ownership by UID number, not by name. A file owned by alice (uid 1001) on the server appears on the client as belonging to whoever has uid 1001. The "numbers are what is stored in files" idea from Week 4 applies here as well.
• As for ports, NFS uses 2049, and rpcbind, which tells where RPC services are, uses 111.

Samba — With Windows

⚠️ In the question "Which is least related to the components of Samba?", the choices are SMB · CIFS · NetBIOS · RPC. The answer is RPC. RPC is what NFS uses; it is not a component of Samba.

smbclient -L //server               # list the shares
mount -t cifs //server/share /mnt   # mount
testparm                           # check smb.conf syntax

The Shape of smb.conf

   [global]
      workgroup = WORKGROUP
      security = user
 
   [share]
      path = /srv/share
      writable = yes
      valid users = alice

• [global], [homes], and [printers] are names with predefined meanings, and the rest are share names the administrator invents freely.
• Samba keeps a Samba password separate from the Linux account. Even if an alice account exists on Linux, you must register her with smbpasswd -a alice before she can log in to Samba.
• The two daemons divide the work — smbd handles file/printer sharing and authentication, and nmbd lets computers be found by their NetBIOS names. The ports are also split: smbd uses TCP 139 and 445, and nmbd uses UDP 137 and 138.
• The way to write a share differs by operating system. Windows uses backslashes, \\server\share, and Linux uses slashes, //server/share.
• If you connect with smbclient //server/share -U alice, the smb: \> prompt appears, and you exchange files with get and put, like FTP. It is used to pull something out briefly without mounting.
• The name Samba comes from the protocol name SMB.

NFS vs Samba

• Answer immediately: "To share with Windows?" → Samba, "To share between Unix systems?" → NFS.

• In the mount command, the word after -t and the remote notation differ. nfs uses server:/path, and cifs uses //server/share.
• NFS and Samba feel different from yesterday's FTP. NFS and Samba are used by "mounting and treating it like your own directory," while FTP is "connect and exchange files." Still, all three fall into the "file sharing/transfer" group.

Internet Services Before the Web

• Gopher is an information retrieval service from before the web (WWW) appeared. You went down through menus, so there were no hyperlinks.
• Usenet is newsgroups, and its protocol is NNTP (Network News Transfer Protocol).
• Archie is FTP search. The name looks unfamiliar, so it tends to be used as a distractor choice.

• All three are "search," but what they search differs. Pair them up as Archie–FTP and Veronica–Gopher.
• The difference between Gopher and WWW is how documents are linked. In Gopher you pick menus from the top down, while in WWW you click hyperlinks inside a document and jump anywhere. Gopher uses port 70, and WWW (HTTP) uses port 80.
• Usenet, unlike mail, is "a bulletin board that many people read together." Posts go into topic-based newsgroups separated by dots, such as comp.os.linux. The port for NNTP is 119.
• The place where Linus Torvalds first announced Linux in 1991 was also a Usenet newsgroup, comp.os.minix. This connects to the birth of Linux from Week 1.

• The four differ in spelling by only one or two letters, so they appear together in choices. Tell them apart by expanding the abbreviation — the M of SMTP is Mail, the second N of NNTP is News, the T of NTP is Time, and the M of SNMP is Management.

Grouping by Nature

These groups come up as questions exactly as they are. For example, if asked to choose the one with a different nature among WWW · SAMBA · TELNET · GOPHER: WWW and Gopher are information retrieval, TELNET is remote access, and SAMBA is file sharing, so you must read the sentence carefully to see what the grouping criterion is.

Other Services

• Remember the pairing: DHCP is automatic IP assignment, NTP is setting the time. Be careful not to confuse them with DNS (name resolution).
• DHCP's two ports are 67 for the server and 68 for the client. What DHCP hands out is not only the IP address but also the subnet mask, default gateway, and DNS server address. It is like receiving all at once the values you entered by hand in Week 9.
• Addresses are not given permanently; they are lent for a set period (a lease). If it is not renewed before the period ends, the address goes back to another computer.
• Among the services in this table, DHCP, NTP, and SNMP use UDP. They are short question-and-answer exchanges, so there is no need for TCP, which sets up a connection.

Tomorrow we tie this week's Internet services together on one page.

📖 Glossary

• NFS : A file sharing system between Unix/Linux systems. It is based on RPC and configured with /etc/exports.
• RPC : Remote Procedure Call. The communication method NFS uses.
• Samba : Software that provides file and printer sharing between Linux and Windows.
• SMB / CIFS : The file sharing protocol Samba uses and its extended specification.
• NetBIOS : The specification that handles name management in Samba.
• Gopher : A pre-web service for finding information through menus.
• Usenet : A topic-based newsgroup service. It uses the NNTP protocol.
• Archie : A service that searched for files on FTP servers.