To be completed by 2/28/2008
Practical Exercises

1. Setup your desktop machine as NFS server and your cluster node as NFS client, following the instructions below.

Install the NFS related packages by using apt-get.
On your desktop: 
apt-get install portmap nfs-common nfs-kernel-server
On the node: 
apt-get install portmap nfs-common
On your desktop, create a directory on top of your home directory to export it, for example, 
mkdir /home/exports
chmod 755 /home/exports
Create a dummy user and give its owhership to the directory: 
/usr/sbin/groupadd -g 666 jonny
/usr/sbin/useradd -m -s /bin/bash -u 666 -g 666 jonny
chown jonny:jonny /home/exports/
Copy some files from /etc into directory /home/exports and give them ownership "jonny": 
cp /etc/hosts /home/exports
cp /etc/nsswitch.conf /home/exports
cp /etc/inetd.conf /home/exports
Then 
cp /etc/securetty /home/exports
and live its root ownreship.
Modify file /etc/exports to include export of directory /home/exports to your node, for example, node02: 
/home/exports  node02(rw)
Make sure your node and its IP address are included in /etc/hosts file. Start portmap and NFS services: 
/etc/init.d/portmap start
/etc/init.d/nfs-common start
/etc/init.d/nfs-kernel-server start
Make sure the services are running by executing command rpcinfo: 
rpcinfo -p
You should see the following: 
   program vers proto   port
    100000    2   tcp    111  portmapper
    100000    2   udp    111  portmapper
    100003    2   udp   2049  nfs
    100003    3   udp   2049  nfs
    100021    1   udp   1046  nlockmgr
    100021    3   udp   1046  nlockmgr
    100021    4   udp   1046  nlockmgr
    100005    1   udp   1047  mountd
    100005    1   tcp   1925  mountd
    100005    2   udp   1047  mountd
    100005    2   tcp   1925  mountd
    100005    3   udp   1047  mountd
    100005    3   tcp   1925  mountd
    100024    1   udp   1048  status
    100024    1   tcp   1926  status
Login remotely to your node machine via rsh or ssh and run rpcinfo pointing it at your desktop, for example: 
rpcinfo -p unisys02
If you see the same output as on the NFS server, it means the server allows you to access the portmap and its rpc services. Check what directories are exported to you from the server: 
/sbin/showmount -e unisys02
It should show 
/home/exports node02
Now you are ready to mount its directory on the node. Create a new mounting point and mount the exported directory onto it: 
mkdir /home/exports
mount unisys02:/home/exports /home/exports
To make sure the directory has been mounted, run command 
df -h
The mounted directory shows up in the bottom of the file systems list: 
unisys02:/home/exports   494M   78M  390M  17% /home/exports
To see who is the owner of the files in the directory, run command 
ls -l /home/exports/
Since there is no user with UID=666 and GID=666 on the node, the mounted directory would belong to a non-existent user: 
ls -l /home/exports/
total 5
-rw-r--r--    1 666      666           104 Feb 10 19:32 hosts
-rw-r--r--    1 666      666          1750 Feb 10 19:32 nsswitch.conf
-rw-------    1 root     root          114 Feb 10  2003 securetty
-rw-r--r--    1 666      666           289 Feb 10 19:32 inetd.conf
Create user jonny with UID=GID=667 and try to change the ownership of the directory on the node: 
chown jonny:jonny /home/exports
Does it work? Why?

Change the UID and GID of jonny to be consistent with those on the NFS server: 
/usr/sbin/groupmod -g 666 jonny
/usr/sbin/usermod -u 666 -g 666 jonny
Become user jonny then step into directory /home/exports: 
su jonny
cd /home/exports
and see if you can create files in this directory. Unmount the directory, 
umount /home/exports
Modify file /etc/fstab by including a new entry with /home/exports: 
unisys02:/home/exports  /home/exports   nfs     rw      0    0
Then run 
mount -a
Check if it is mounted 
df -h
Remove the entry from /etc/fstab and unmount the directory. If the directory can not get unmounted and you receive error message "device is busy", check what processes hold the directory by executing command fuser: 
/bin/fuser -m (file_system)
For example, 
 /bin/fuser -m /mnt/nfs
Kill these processes and try to unmount the directory again.
Try to avoid NFS mounting through /etc/fstab. Use either manual mount or automount.

2. Mount the directory on the node again. Shutdown the NFS server on your desktop: 
/etc/init.d/nfs-kernel-server stop
Try to access the NFS mounted directory, for example, with ls.
Try Ctrl_C to unfreeze the terminal.
Start the NFS server on you desktop 
/etc/init.d/nfs-kernel-server start
and try to access the directory again.

3. Repeat exercise #2 using options rw,intr,hard in command mount.

4. Repeat exercise #2 using options rw,intr,soft in command mount. Wait for 30 - 60 seconds until it times out.

5. Observing stale file handle error.
On the NFS server, create a new directory tree under NFS exported directory: 
mkdir -p /home/exports/test/demo
On the client, step into the directory: 
cd /home/exports/test
ls
On the NFS server, remove directory test with its subdirectory: 
cd /home/exports
rm -rf test
On the client, run 
ls

6. Finding the optimal write and read block sizes (wsize, rsize).
Modify /etc/exports on the NFS server to allow root access to the exported directory on the client: 
/home/exports  node02(rw,no_root_squash)
Re-export the directory 
/usr/sbin/exportfs -ra
On the client node, mount the directory with read and write block sizes option rsize=1024,wsize=1024: 
mount -o rsize=1024,wsize=1024 unisys02:/home/exports /home/exports
To make sure the directory is accessible, run command 
 ls -l /home/exports
Check the time (real time) it would take to write 1.6 MB file over the NFS: 
time dd if=/dev/zero of=/home/exports/testfile bs=16k count=100
Check how long it would take to read this file: 
time dd if=/home/exports/testfile of=/dev/null bs=16k
Unmount the directory.
Repeat the same procedure with rsize = wsize = 2048, 4096, 5125, 8192, 10240, block sizes (they are N*1024 Bytes).
What is the optimal block size?

7. Protecting portmap with tcp_wrappers.
Unmount the NFS directory on the node. On the NFS server, put entry for portmap into /etc/hosts.deny: 
portmap: ALL
Try mounting the directory on the node. On the NFS server, in file /etc/hosts.allow, put entry allowing to mount the directory on your node: 
portmap: 192.168.5.22

8. Install autofs on the node machine (NFS client). 
apt-get install autofs
Configure the master map file, /etc/auto.master, and specify the timeout 60 seconds: 
/mnt   /etc/auto.exports  --timeout=60
Make sure directory /mnt already exists.

Configure the indirect map file, /etc/auto.exports: 
exports  -rw,hard,intr  unisys16:/home/exports

Restart or reload autofs: 
/etc/init.d/autofs restart

Access the file system and check if it gets mounted: 
cd /mnt/exports
df
Run command df -h again after about a minute.

9. Read Chapter 28

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