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This post is aimed to help administrators to keep Linux home directories in a centralized location and mounting them when needed by using the Automounter.
NOTE: Each user should have unique uid/gid

NFS Server:
Any NFS Server will do just fine.
I will use NetApp NFS since this is for a production environment.

RHEL Client:
RHEL 5.3 64bit

john uid=2100 gid=2100
alex uid=2101 gid=2101

NetApp NFS Server Setup:
1) Create a volume to host your home directories

filer> vol create homedirs aggr1 200g

2) Enter the following in your /etc/exports file to export this to the specific RHEL client.

filer> exportfs -p, /vol/homedirs
filer> exportfs -a

RHEL Client Configuration:

1) As root mount the volume anywhere in the system. (This is only to create the home directories and assign the proper ownership, then unmount.)
[root@rhelbox ~]# mkdir /mnt/homedirs
[root@rhelbox ~]# mount ny1afilerd1:/vol/homedirs /mnt/homedirs/
[root@rhelbox ~]# mount

filer:/vol/homedirs on /mnt/homedirs type nfs (rw,

2) Create the home directories and assign proper ownership
[root@rhelbox ~]# mkdir /mnt/homedirs/{john,alex}

[root@rhelbox ~]# id john
uid=2100(john) gid=2100 groups=2100
[root@rhelbox ~]# chown 2100:2100 /mnt/homedirs/john/

[root@rhelbox ~]# id alex
uid=2101(alex) gid=2101 groups=2101
[root@rhelbox~]# chown 2101:2101 /mnt/homedirs/alex/

3) Copy the files from /etc/skel to the new home directory
[root@rhelbox ~]# for i in john alex; do cp /etc/skel/.* /mnt/homedirs/$i/; done

4) Unmount the temporary folder
[root@rhelbox~]# umount /mnt/homedirs
[root@rhelbox~]# rmdir /mnt/homedirs

5) Configure the Automounter
Enter the following in /etc/auto.master
/home /etc/auto.home –timeout=60

Create /etc/auto.home and populate as follows:
* -fstype=nfs,rw,nosuid,soft

6) Restart the automounter
[root@rhelbox ~]# service autofs restart

7) That should be it, lets give it a try
[root@rhelbox ~]# su – john
[john@rhelbox ~]$ ls -A
.bash_history .bash_logout .bash_profile .bashrc

I needed to send confidential data to other people via the Internet, so it needs to be encrypted.

GPG is the free implementation of the OpenPGP(Preety Good Privacy) standard defined by RFC4880.
It provides a way to encrypt data using a public/private key infrastructure. You can set a Web of Trust with the people you need to share data, get their public keys, send them your public key and start encrypting and decrypting as I will show you in this guide.
GPG is available is diferent platforms including Linux, MAC, Windows(Binary version as well as in Cygwin).
you can use the OS of your choice, just make sure GPG is installed

For this demo I am using a Mac with OS 10.6

1) Make sure you have GPG installed, otherwise downloaded from
To check type:

2) Generate your Private/Public Key Pair

You will get a warning about the expiration if you selected the default, which means it never expires.
If you want it to expire then change the value(eg 3m) will expire in 3 months.

Enter Real Name, Email and a Comment.
Try to make this as unique as possible as this will have an inpact in how your key is identified

Select an empty Passphrase UNLESS you dont mind to be prompted everytime for the passphrase
Now Just wait a few seconds while the key is generated, Move the mouse and type on the keyboard to increase the randomness.

In Case you get:
Not enough random bytes available.
Please do some other work to give the OS a chance to collect more entropy! (Need 284 more bytes)

DON’T PANIC, Just do stuff in your PC, write things to disk, log in to another terminal with a different user, etc.
Just do different things, that collect more entropy.

OK the set up is done, Now we need to give people in our Web of Trust (Fancy terminology for “people we trust and trust us”) our public key so they can encrypt data with our public key, so we can open it using our Private Key and
we need to get their public key to encrypt data with their public key so that they can open it using their Private Key

For Example:
If I(John) need to send an encrypted document to Ann, I need to have her Public Key, Encrypt the Data with her Public key so she can decrypt it using her Private key. It’s all about the Private/Public Key Pairs.

3) Give the people you trust your public key and get their public key
You can get the public Key by any means, including the internet, email, etc.
The public key is supposed to be public, But on the other hand, guard your Private Key with your life, it should be only readable by the owner and no one else.

Check your keys by listing them:

Now Export that key into a file:
-r option tells gpg which public key to export in case you generated more than one Private/Public Key Pairs.
-o tells the output filename
–armor option is to output in a format that is understood by many applications, otherwise it will be output in gpg raw format

The contents of the file should look like this:

Version: GnuPG v1.4.10 (Darwin)


4) Send that public key file to your friend and your friend will send you his public key exported from his system.
When you get his Public Key (his file), then you need to import it into your key ring like this:
Lets say Ann Dexter sent me through email her public key file called

Listing the keys will yield

5) We want to encrypt secret.txt using Ann’s Pubilc Key
And it is as simple as:

This will generate a secret.txt.asc file which is the encrypted version of secret.txt AND Signed so the recipient can verify it came from you
This file can ONLY be decrypted with Ann Dexter PRIVATE KEY, you CAN’T decrypt it because you ONLY posses Ann Dexter’s Public Key but NOT her Private Key.

Now You can send the secret.txt.asc to Ann using any means you want, email, ftp, etc.

6) Ann Dexter got your encrypted file, how does she decrypt it?
Since she posseses the Private Key she can just do the following:

And She will get the following the following output indicating that the Private key was used to Decrypt the file.

gpg: encrypted with 2048-bit ELG-E key, ID AB00C1A4, created 2008-04-01 “Ann Dexter (Systems) ”

Ann should now have the secret.txt file ready and decrypted

This guide helps measure the network throughput and bandwidth between two hosts in the same network, different networks and across different data centers.

This specifically helped me when I needed to know how much throughput the company network had between headquarters data center and the Disaster Recovery data center which where in different states and I wanted to calculate how long would it take to replicate our SAN between the sites, about 60TB of data.

The tool I used for this is called iPerf (, this tool includes both the Server and Client, I am running this tool from a RHEL 5.3 system.

You can find a RHEL/Centos binary for this tool at

A Java based Graphical iperf tool can be found at, which can be run on a Windows system, with the Java runtime environment.

Now let’s get to the steps on how to measure network throughput.

1) Set up the iperf server

I am utilizing a RHEL 5.3 for the server.

Install iperf:

[root@remote]# rpm -Uvh

Run iperf as server:

[root@remote ~]# iperf -s
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)

Now that the iperf server is running, install the client at the other office.

2) Set up the iperf client on RHEL

Install iperf on RHEL:

[root@local]# rpm -Uvh

Run iperf as client on RHEL:

iperf has many great options, you can see all the options by doing # iperf -h

I usually use the following options to determine throughput:

[root@local ~]# iperf -c -fk // is the remote server -fk is to present as kbps
Client connecting to, TCP port 5001
TCP window size: 16.0 KByte (default)
[ 3] local port 38124 connected with port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.3 sec 37680 KBytes 30029 Kbits/sec

Server screen Output:

Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
[ 4] local port 5001 connected with port 38124
[ 4] 0.0-10.9 sec 36.8 MBytes 28.3 Mbits/sec

Using the -r option to “Do a bidirectional test individually”

[root@local ~]# iperf -c -fk -r
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
Client connecting to, TCP port 5001
TCP window size: 16.0 KByte (default)
[ 5] local port 41973 connected with port 5001
[ ID] Interval Transfer Bandwidth
[ 5] 0.0-10.1 sec 27744 KBytes 22580 Kbits/sec
[ 4] local port 5001 connected with port 55521
[ 4] 0.0-10.1 sec 48160 KBytes 39093 Kbits/sec

Server screen Output:

Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
[ 4] local port 5001 connected with port 41973
[ 4] 0.0-10.7 sec 27.1 MBytes 21.3 Mbits/sec
Client connecting to, TCP port 5001
TCP window size: 16.0 KByte (default)
[ 4] local port 55521 connected with port 5001
[ 4] 0.0-10.0 sec 47.0 MBytes 39.3 Mbits/sec

Using the -d option to “Do a bidirectional test simultaneously”

[root@local ~]# iperf -c -fk -d
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
Client connecting to, TCP port 5001
TCP window size: 16.0 KByte (default)
[ 5] local port 41974 connected with port 5001
[ 4] local port 5001 connected with port 40886
[ ID] Interval Transfer Bandwidth
[ 5] 0.0-10.1 sec 37872 KBytes 30648 Kbits/sec
[ 4] 0.0-10.4 sec 12856 KBytes 10132 Kbits/sec

Server screen Output:

Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
[ 4] local port 5001 connected with port 41974
Client connecting to, TCP port 5001
TCP window size: 16.0 KByte (default)
[ 6] local port 40886 connected with port 5001
[ 6] 0.0-10.4 sec 12.6 MBytes 10.2 Mbits/sec
[ 4] 0.0-10.7 sec 37.0 MBytes 28.9 Mbits/sec

3) Set up the iperf client on Windows

Download the JPerf client

Unzip and Run the jperf.bat, you will see a graphical interface, just enter the ip of the server and you are good to go.

You can adjust your client’s options, Dual = -d , Trade= -r in the command line client:

Server screen Output:

Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
[ 4] local port 5001 connected with port 2606
[ 4] 0.0-10.0 sec 2.52 MBytes 2.12 Mbits/sec

This posting will help you configuring multipathing on RHEL 5.3 for LUNs carved from a NetApp SAN. For this guide I am using a C-Class blade system with QLogic HBA cards.

1) Make sure you have the packages needed by RHEL, otherwise install them.

2) Install QLogic Drivers if needed, or utilize RHEL drivers. In my case I am using HP C-Class blades with Qlogic HBA cards. HP drivers can be found at the HP site, driver is called hp_sansurfer. I am utilizing RHEL built in drivers, but you can install the HP/QLogic drivers as follows:

3) If Qlogic HBA, install the SanSurfer CLI, this is very useful program for doing things with QLogic HBA cards, it can be downloaded at QLogic website, install as follows:

4) Install NetApp Host Utilities Kit, the package is a tar.gz file, you can find it at the now site

Open it and run the install shell script

5) Once Everything is installed on the host, create the LUN and ZONE it from the NetApp, Brocade(SAN Fabric),Host

6) Once it has been Zoned and mapped correctly, verify if your RHEL host can see it.

7) Utilize NetApp tools to see LUN connectivity

8 ) Utilize NetApp tools to check multipathing, not set yet

Time to configure multipathing

9) Start the multipath daemon

10) Find you WWID, this will be needed in the configuration if you want to alias it.

Comment out the blacklist in the default /etc/multipath.conf, otherwise you will NOT see anything.

11) Now you are ready to configure /etc/multipath.conf

Exclude (blacklist) all the devices that do not correspond to any
LUNs configured on the storage controller and which are mapped to
your Linux host. There are 2 methods:
Block by WWID
Block by devnode
In this case I am blocking by devnode since I am using HP and know my devnode RegEx
Also configure the device and alias(optional).
The full /etc/multipath.conf will look like this:

12) Restart multipath and make sure it starts automatically:

13) Verify multipath is working

14) Now you can access the LUN by using the mapper

15) Format it to your liking and mount it

16 ) If you want it to be persistent after reboots put it on /etc/fstab and make sure multipathd start automatically.

17) If possible reboot to check it mounts correctly after reboots.

You have added a new disk or increased the size of your LUN, or increased the size of the virtual disk in case of virtual machines, and now you need to increase the partition, the Logical Volume and the filesystem in order to be able to use the new space.

In this post I go through the steps necessary to make this happen in a RHEL 5.3 system.

The LUN I will increase has 20GB and it had an LVM partition. I decided to increase the LUN size to 72GB and this is how it looks now.

[root@server~]# fdisk -lu
Disk /dev/sdb: 77.3 GB, 77309411328 bytes
255 heads, 63 sectors/track, 9399 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sdb1 * 1 2611 20971488 8e Linux LVM

I need to perform the following steps in order to be able to use the new space.

1. Increase the size of the partition using fdisk

[root@server ~]# fdisk /dev/sdb

Command (m for help): u //Change the display to sectors
Changing display/entry units to sectors
Command (m for help): p //Print the current partition table for that drive
Disk /dev/sdb: 77.3 GB, 77309411328 bytes
255 heads, 63 sectors/track, 9399 cylinders, total 150994944 sectors
Units = sectors of 1 * 512 = 512 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 * 64 41943039 20971488 8e Linux LVM
Command (m for help): d //Delete the partition information, we will recreate
Selected partition 1
Command (m for help): n //Create partition
Command action
e extended
p primary partition (1-4)
p //In this case it is primary
Partition number (1-4): 1 // In this case it is the first partition on the drive
First sector (63-150994943, default 63): 64 //Align partition if used on NetApp
Last sector or +size or +sizeM or +sizeK (64-150994943, default 150994943):
Using default value 150994943
Command (m for help): t //Change type from Linux(default) to Linux LVM
Selected partition 1
Hex code (type L to list codes): 8e //Linux LVM partition type
Changed system type of partition 1 to 8e (Linux LVM)
Command (m for help): p //Print again to double check
Disk /dev/sdb: 77.3 GB, 77309411328 bytes
255 heads, 63 sectors/track, 9399 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 9400 75497440 8e Linux LVM
Command (m for help): w //Write the partition table
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks.

2. You need to reboot for the changes to take place, or just run

server# partprobe

3. Make LVM acknowledge the new space

[root@server ~]# pvresize /dev/sdb1

4. Check that the Volume group shows the new space

[root@server ~]# vgs
VG #PV #LV #SN Attr VSize VFree
vg0 1 2 0 wz–n- 71.97G 52.00G

5. Extend the logical volume:
make it total of 28G in this example

[root@server~]# lvresize -L 28G /dev/mapper/vg0-lvhome
Extending logical volume lvhome to 28.00 GB
Logical volume lvswap successfully resized

You can also take all the free space available

[root@server ~]# lvresize -l +100%FREE /dev/mapper/vg0-lvhome
Extending logical volume lvhome to 67.97 GB
Logical volume lvhome successfully resized

6. Use the rest for whatever partition you want

[root@server~]# lvcreate -l 100%FREE -n lvdata vg0

7. Resize the Filesystem

[root@server~]# resize2fs /dev/mapper/vg0-lvhome
resize2fs 1.39 (29-May-2006)
Filesystem at /dev/mapper/vg0-lvhome is mounted on /home; on-line resizing required
Performing an on-line resize of /dev/mapper/vg0-lvhome to 9953280 (4k) blocks.
The filesystem on /dev/mapper/vg0-lvhome is now 9953280 blocks long.