OPS335: File Servers

FILE SERVER RESOURCES

Online References:

• File Server Notes (Week 9 class notes)
• NSF Security (List of tips regarding NSF and security)

OVERVIEW

In OPS235, you learned how to install and configure an SSH server to be able to use utilities such as ssh, scp and sftp. Although the sftp utility is useful for transferring files between different computers via the Internet, it is not considered useful or efficient for accessing files on servers that are connected over a local network.

Two popular protocols called Network File Server (NFS) and Samba (SMB) are used to provide high speed file access between servers on a local network. The NFS protocol allows a user to access files on another server in a local network in a similar way that local files on a same server are accessed. The Samba open-source software is used to access files from Windows servers using a combination of Windows protocols including NetBIOS, SMB, etc.

This lab will focus on installing, configuring and using NFS and Samba to access files between different servers on a local network.

INVESTIGATION 1: USING AUTOMOUNT WITH NFS

In this investigation, we will set up an NFS server on our VM2 machine. We will then set up an NFS client on our VM3 machine and be able to view and import files within the VM2 /home directories from the VM3 machine.

Prerequistites
Due to the changes made in lab3, you will now need your vm1 running (as the DNS server) in order for any of your virtual machines to be able to use the internet.

Setting up the NFS Server

Perform the following tasks:

1. Make certain that all of your MVs are running.
2. Switch to your VM2 machine.
3. Although nsf is already on your VM when you installed it, we will install additional utilities for nsf. Issue the following command:
   yum install nfs-utils
4. The /etc/exports file allows you to restrict the access to servers to access files for security purposes. Edit /etc/exports file, and replace all contents of the file with the following:
   /home 192.168.x.4(rw,root_squash,insecure)
   
   
5. Start enable your nfs service (now known as nfs-server.service).
6. Build the server's list of exports:
   exportfs -r
   
   
7. Run and record the output of the following commands:
   exportfs
   showmount -e
   
   
8. You will have to adjust your firewall settings on your VM2 machine to allow NFS to work.
   Run the netstat command in order to determine the ports needed and issue the appropriate iptables command(s).

Setting up & Testing the NFS Client

Perform the following tasks:

1. Ensure the VM guest network is functioning properly. You can use the "host cbc.ca" command to see if DNS queries are being answered.
2. Ensure you have full connectivity to the internet.
3. Again, you should not have to install any NFS software.
4. Add the following line to the bottom of the /etc/fstab file on your VM3 machine:
   192.168.x.3:/home /home nfs4 defaults 0 0

Warning:
Do not change any other lines in this file. Do not change any lines in /etc/fstab on your host machine. Doing so can make your machine fail to boot.

1. Run the following command to avoid an error that would be caused by logging in while root_squash is active:
   setsebool -P
   use_nfs_home_dirs 1
   
   
2. Logout of vm03 and shut it down.

Testing NFS mounts on your client

• Restart vm03 and login using your learnid.

• Check that the home directory is mounted

mount | grep /home

• If it is not, try running 'mount /home' as root and observe any errors.
• On vm03, create an empty file using the touch command.

touch empty_file_created_on_vm03

• Now shutdown vm03.
• Now on the NFS server, us ls -l in your learnid's home directory to check for the file you just created.

Setting up Automount on the VM

On vm03 as root perform the following tasks:

• Comment or remove the line from /etc/fstab that you entered earlier.
• With a server installation of Fedora 22, you will not need to install autofs, but on other installations you might need:

dnf install autofs

• Move the existing file /etc/auto.master:

mv /etc/auto.master /etc/auto.master.orig

• This is a great way to keep a back up in case you need to restore the file in the future. Now create another:

vi /etc/auto.master

• Add only the following line:

/home   /etc/auto.home   --timeout=60

• Create the file /etc/auto.home and add ONLY the following line:

*        -fstype=nfs4,rw,nosuid,soft      192.168.x.3:/home/&

• Start autofs, and ensure the service will automatically start at boot.

• Log out of vm3 and log back in using your learn account.
• Open a terminal and enter the command:

mount | grep home

• How does it differ from the previous mount?
• Create another empty file with the name

touch another_empty_file_from_vm03

• Run and record the output of the command

df -hT

• Back on the nfs server run and record the output of ls -l in your home directory.
• You should see the files you created on vm03.
• You may encounter errors with SELinux during the lab (though it has not been a problem recently). It is required that you leave it running. Use the following commands to determine what booleans need to be flipped.

audit2allow < /var/log/audit/audit.log
audit2why < /var/log/audit/audit.log

Setting up Automount on the other VM

• Now that you have VM3 automatically mounting home directories from VM2, configure VM1 to do the same.

Record steps, commands, and your observations in INVESTIGATION 1 in your OPS335 lab log-book

Configuring a Samba Server on Linux

• On your VM 2 install Samba

 dnf install samba samba-client

• Create a backup of the file /etc/samba/smb.conf, and create a new one that includes only the following:

[global]
workgroup = <yourlearnid>.org 
server string = "put your real name here without the quotes"
encrypt passwords = yes
smb passwd file = /etc/samba/smbpasswd
  
[home]
comment = "put your real name here without the quotes"
path = /home/<learnid>
public = no
writable = yes
printable = no
create mask = 0765

• Now add a parameter to the global section that will limit access to the share so that only machines in your virtual network and those in the lab room will be able to access it.
• Add a parameter to the home section so that only your user account can access that share.
• Create a Samba password for user <learnid> with the command

smbpasswd -a <learnid>

• If you need to, you can change a user's password by using the command

smbpasswd <username>

• Confirm the user you created has been added using the following command

pdbedit -L -v

• Test and review your configuration with the command

testparm

• You can now start your Samba server (smb.service) and ensure it will start at boot.
• Modify the firewall on VM2 to allow samba traffic.
• Test if you have a connection with the command

smbclient -U <learnid> -L vm2

• It will show you a list of all available shares.

Connecting to a Linux SMB Server from a Linux Client

There are many ways that a Linux client can connect to an SMB server.

Using smbclient

• In a full installation you should not need to install samba-client on your host, but if it is not present then do so.
• You will also need to install the cifs-utils package to be able to mount the filesystem.
• From the host use the "smbclient" command in a terminal window.

smbclient '\\vm2\home' -U <learnid>

• After entering your password you should get a prompt similar to

smb: \>

• Enter the ls command to see a list of the files in your home directory - you may receive the following error.

smb: \> ls
NT_STATUS_ACCESS_DENIED listing \*

• SE Linux should be in Enforcing and will need to be adjusted (on the samba server) for this to work.

 setsebool -P samba_enable_home_dirs 1

• Once you have access to the directory use the get and put commands (similar to ftp) to move files.
• When you are finished close the connection.

Using 'mount -t cifs'

• The next way is to use the mount command.
• Use the mount command on the host to mount your home directory

mkdir /tmp/vm2-home
mount -t cifs //vm2/home /tmp/vm2-home -o username=<learnid>
ls /tmp/vm2-home

Using Nautilus to browse Samba shares

• Use the "Places" menu from the desktop and open 'Browse Network'.
• From the menu in the side-bar of the files tool, choose 'Connect to Server'.
• Enter 'smb://vm2/home' as the location, and enter your samba password in the prompt.
  • Where vm2 is the name of the server, and home is the name of the directory it is sharing.
• After you have checked that you can access your files, unmount the share by right-clicking its icon in the side-bar and clicking 'Unmount'.

Using a browser

• You can also use a web browser with support for the SMB protocol such as Konqueror.
  • Note that firefox does not have such support.
• If Konqueror is not installed then install it with the command:

yum install kdebase

• Start Konqueror, the web/file browser, and in the address bar enter the following

smb://vm2/home

• Enter your username and password when prompted.
• Double click on a file you have some text in.
  • Open it with gedit, make some changes, and save it.
  • When prompted, choose to upload the file.
• Close Konqueror.
• cat the file on your VM2 to ensure the changes were properly uploaded.

Connecting to a Linux SMB Server from a Windows Client (Windows 7)

• Power up a Windows 7 system in the lab and login using your LEARN username and password.
• Add the prerouting and forwarding rules to your Centos host's iptables necessary to redirect samba traffic from outside your network to your VM 2.
• Open up Explorer and Right click on Computer > Map network drive.. > Select a Drive Letter and '\\<ip-address-of-host>\home' > you will then be asked for your username and password.
• You should now be able to browser, drag and drop your files to and from the Windows machine.

COMPLETING THE LAB

Arrange proof that ...

EXPLORATION QUESTIONS

1. What does the no_root_squash option for an NFS mount mean?
2. Explain the meaning of the defaults option in an fstab entry. What do the numbers mean at the end?
3. What is the function of the 'exportfs' command?
4. What is the purpose of the 'showmount' command?
5. What is the meaning of the "timeout=60" phrase?
6. What is the meaning of the asterisk (*) in the file /etc/auto.home?
7. What is the meaning of the ampersand (&) in the file /etc/auto.home?
8. What is the role of the /etc/mtab file on the nfs server?
9. What port does nfs-server use?
10. What is the purpose of the testparm command?
11. What does SMB stand for? CIFS?
12. What does the text inside square brackets in the smb.conf file mean? (e.g., "[home]").
13. Explain the meaning of the line "create mask = 0765" in the smb.conf file?
14. What does the smbpasswd command do?
15. What did the setsebool command do?