How To Enable EPEL Repository in RHEL/CentOS 6/5

Why we use EPEL (Extra Packages for Enterprise Linux) repository ?
Provides lots of open source packages to install via Yum.
Epel repo is 100% open source and free to use.
It does not provide any core duplicate packages and no compatibility issues.
All epel packages are maintained by Fedora repo.

First, you need to download the file using Wget and then install it using RPM on your system to enable the EPEL repository. Use below links based on your Linux OS versions. (Make sure you must be root user).

For RHEL/CentOS 6 32-64 Bit
## RHEL/CentOS 6 32-Bit ##
# wget http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
# rpm -ivh epel-release-6-8.noarch.rpm
## RHEL/CentOS 6 64-Bit ##
# wget http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
# rpm -ivh epel-release-6-8.noarch.rpm
For RHEL/CentOS 5 32-64 Bit
## RHEL/CentOS 5 32-Bit ##
# wget http://download.fedoraproject.org/pub/epel/5/i386/epel-release-5-4.noarch.rpm
# rpm -ivh epel-release-5-4.noarch.rpm
## RHEL/CentOS 5 64-Bit ##
# wget http://download.fedoraproject.org/pub/epel/5/x86_64/epel-release-5-4.noarch.rpm
# rpm -ivh epel-release-5-4.noarch.rpm
For RHEL/CentOS 4 32-64 Bit
## RHEL/CentOS 4 32-Bit ##
# wget http://download.fedoraproject.org/pub/epel/4/i386/epel-release-4-10.noarch.rpm
# rpm -ivh epel-release-4-10.noarch.rpm
## RHEL/CentOS 4 64-Bit ##
# wget http://download.fedoraproject.org/pub/epel/4/x86_64/epel-release-4-10.noarch.rpm
# rpm -ivh epel-release-4-10.noarch.rpm
How Do I Verify EPEL Repo?
# yum repolist
Loaded plugins: fastestmirror, priorities, refresh-packagekit, security
Loading mirror speeds from cached hostfile
epel/metalink                                            | 5.6 kB     00:00
 * base: centos.aol.in
 * epel: mirror.neu.edu.cn
 * extras: mirrors.digipower.vn
 * remi: fr2.rpmfind.net
 * rpmforge: mir01.syntis.net
 * updates: centos.aol.in
base                                                     | 3.7 kB     00:00
epel                                                     | 4.2 kB     00:03
epel/primary_db                                          | 5.8 MB     01:13
extras                                                   | 3.4 kB     00:00
rpmforge                                                 | 1.9 kB     00:00
updates                                                  | 3.4 kB     00:00
updates/primary_db                                       | 1.3 MB     00:29
repo id        repo name                                               status
base           CentOS-6 - Base                                          6,327+40
epel           Extra Packages for Enterprise Linux 6 - x86_64          9,712+518
extras         CentOS-6 - Extras                                              14
remi           Les RPM de remi pour Enterprise Linux 6 - x86_64        200+1,174
rpmforge       RHEL 6 - RPMforge.net - dag                              4,627+23
updates        CentOS-6 - Updates                                         254+43
repolist: 21,134
How Do I Use EPEL Repo?
You need to use YUM command for searching and installing packages. For example we search for Zabbix package using epel repo, lets see it is available or not under epel.
# yum --enablerepo=epel info zabbix
Sample Output
Available Packages
Name       : zabbix
Arch       : i386
Version    : 1.4.7
Release    : 1.el5
Size       : 1.7 M
Repo : epel
Summary    : Open-source monitoring solution for your IT infrastructure
URL        : http://www.zabbix.com/
License    : GPL
Description: ZABBIX is software that monitors numerous parameters of a network
Let’s install Zabbix package using epel repo option –enablerepo=epel switch.
# yum --enablerepo=epel install zabbix
Note: The epel configuration file is located under /etc/yum.repos.d/epel.repo.
This way you can install as many as high standard open source packages using EPEL repo

lsof Command Examples (Identify Open Files)

lsof stands for List Open Files.

It is easy to remember lsof command if you think of it as “ls + of”, where ls stands for list, and of stands for open files.

It is a command line utility which is used to list the information about the files that are opened by various processes. In unix, everything is a file, ( pipes, sockets, directories, devices, etc.). So by using lsof, you can get the information about any opened files.

1. Introduction to lsof

Simply typing lsof will provide a list of all open files belonging to all active processes.

#  lsof

COMMAND  PID       USER   FD      TYPE     DEVICE  SIZE/OFF       NODE NAME

init       1       root  cwd       DIR        8,1      4096          2 /

init       1       root  txt       REG        8,1    124704     917562 /sbin/init

init       1       root    0u      CHR        1,3       0t0       4369 /dev/null

init       1       root    1u      CHR        1,3       0t0       4369 /dev/null

init       1       root    2u      CHR        1,3       0t0       4369 /dev/null

init       1       root    3r     FIFO        0,8       0t0       6323 pipe

By default One file per line is displayed. Most of the columns are self explanatory. We will explain the details about couple of cryptic columns (FD and TYPE).

FD – Represents the file descriptor. Some of the values of FDs are,

cwd – Current Working Directory

txt – Text file

mem – Memory mapped file

mmap – Memory mapped device

NUMBER – Represent the actual file descriptor. The character after the number i.e ’1u’, represents the mode in which the file is opened. r for read, w for write, u for read and write.

TYPE – Specifies the type of the file. Some of the values of TYPEs are,

REG – Regular File

DIR – Directory

FIFO – First In First Out

CHR – Character special file

For a complete list of FD & TYPE, refer man lsof.

2. List processes which opened a specific file

You can list only the processes which opened a specific file, by providing the filename as arguments.

#  lsof /var/log/syslog

COMMAND  PID   USER   FD   TYPE DEVICE SIZE/OFF   NODE NAME

rsyslogd 488 syslog    1w   REG    8,1     1151 268940 /var/log/syslog

3. List opened files under a directory

You can list the processes which opened files under a specified directory using ‘+D’ option. +D will recurse the sub directories also. If you don’t want lsof to recurse, then use ‘+d’ option.

#  lsof +D /var/log/

COMMAND   PID   USER  FD   TYPE DEVICE SIZE/OFF   NODE NAME

rsyslogd  488 syslog   1w   REG    8,1     1151 268940 /var/log/syslog

rsyslogd  488 syslog   2w   REG    8,1     2405 269616 /var/log/auth.log

console-k 144   root   9w   REG    8,1    10871 269369 /var/log/ConsoleKit/history

4. List opened files based on process names starting with

You can list the files opened by process names starting with a string, using ‘-c’ option. -c followed by the process name will list the files opened by the process starting with that processes name. You can give multiple -c switch on a single command line.

#  lsof -c ssh -c init

COMMAND    PID   USER   FD   TYPE DEVICE SIZE/OFF   NODE NAME

init         1       root  txt    REG        8,1   124704  917562 /sbin/init

init         1       root  mem    REG        8,1  1434180 1442625 /lib/i386-linux-gnu/libc-2.13.so

init         1       root  mem    REG        8,1    30684 1442694 /lib/i386-linux-gnu/librt-2.13.so

ssh-agent 1528 prakash  1u   CHR        1,3      0t0    4369 /dev/null

ssh-agent 1528 prakash   2u   CHR        1,3      0t0    4369 /dev/null

ssh-agent 1528 prakash    3u  unix 0xdf70e240      0t0   10464 /tmp/ssh-sUymKXxw1495/agent.1495

5. List processes using a mount point

Sometime when we try to umount a directory, the system will say “Device or Resource Busy” error. So we need to find out what are all the processes using the mount point and kill those processes to umount the directory. By using lsof we can find those processes.

#   lsof /home

The following will also work.

#   lsof +D /home/

6. List files opened by a specific user

In order to find the list of files opened by a specific users, use ‘-u’ option.

# lsof -u prakash

COMMAND    PID       USER   FD   TYPE     DEVICE SIZE/OFF       NODE NAME

update-no 1892 prakash   20r  FIFO        0,8      0t0      14536 pipe

update-no 1892 prakash   21w  FIFO        0,8      0t0      14536 pipe

bash      1995  prakash cwd    DIR        8,1     4096     393218 /home/prakash

Sometimes you may want to list files opened by all users, expect some 1 or 2. In that case you can use the ‘^’ to exclude only the particular user as follows

#   lsof -u ^ prakash

COMMAND    PID       USER   FD      TYPE     DEVICE  SIZE/OFF       NODE NAME

rtkit-dae 1380      rtkit    7u     0000        0,9         0       4360 anon_inode

udisks-da 1584       root  cwd       DIR        8,1      4096          2 /

The above command listed all the files opened by all users, expect user ‘prakash’.

7. List all open files by a specific process

You can list all the files opened by a specific process using ‘-p’ option. It will be helpful sometimes to get more information about a specific process.

#  lsof -p 1753

COMMAND  PID       USER   FD   TYPE DEVICE SIZE/OFF    NODE NAME

bash    1753 prakash  cwd    DIR    8,1     4096  393571 /home/prakash/test.txt

bash    1753 prakash  rtd    DIR    8,1     4096       2 /

bash    1753 prakash  255u   CHR  136,0      0t0       3 /dev/pts/0

8. Kill all process that belongs to a particular user

When you want to kill all the processes which has files opened by a specific user, you can use ‘-t’ option to list output only the process id of the process, and pass it to kill as follows

#  kill -9 `lsof -t -u prakash`

The above command will kill all process belonging to user ‘prakash’, which has files opened.

Similarly you can also use ‘-t’ in many ways. For example, to list process id of a process which opened /var/log/syslog can be done by

#  lsof -t /var/log/syslog

489

Talking about kill, did you know that there are 4 Ways to Kill a Process?

9. Combine more list options using OR/AND

By default when you use more than one list option in lsof, they will be ORed. For example,

#  lsof -u prakash -c init

COMMAND    PID       USER   FD   TYPE     DEVICE SIZE/OFF       NODE NAME

init         1       root  cwd    DIR        8,1     4096          2 /

init         1       root  txt    REG        8,1   124704     917562 /sbin/init

bash      1995 prakash    2u   CHR      136,2      0t0          5 /dev/pts/2

bash      1995 prakash 255u   CHR      136,2      0t0          5 /dev/pts/2

...

The above command uses two list options, ‘-u’ and ‘-c’. So the command will list process belongs to user ‘prakash’ as well as process name starts with ‘init’.

But when you want to list a process belongs to user ‘prakash’ and the process name starts with ‘init’, you can use ‘-a’ option.

#  lsof -u prakash -c init -a

The above command will not output anything, because there is no such process named ‘init’ belonging to user ‘prakash’.

10. Execute lsof in repeat mode

lsof also support Repeat mode. It will first list files based on the given parameters, and delay for specified seconds and again list files based on the given parameters. It can be interrupted by a signal.

Repeat mode can be enabled by using ‘-r’ or ‘+r’. If ‘+r’ is used then, the repeat mode will end when no open files are found. ‘-r’ will continue to list,delay,list until a interrupt is given irrespective of files are opened or not.

Each cycle output will be separated by using ‘=======’. You also also specify the time delay as ‘-r’ | ‘+r’.

#  lsof -u prakash -c init -a -r5

COMMAND   PID       USER   FD   TYPE DEVICE SIZE/OFF    NODE NAME

inita.sh 2971 prakash  cwd    DIR    8,1     4096  393218 /home/prakash

inita.sh 2971 prakash rtd    DIR    8,1     4096       2 /

inita.sh 2971 prakash  txt    REG    8,1    83848  524315 /bin/dash

inita.sh 2971 prakash  mem    REG    8,1  1434180 1442625 /lib/i386-linux-gnu/libc-2.13.so

inita.sh 2971 prakash  mem    REG    8,1   117960 1442612 /lib/i386-linux-gnu/ld-2.13.so

inita.sh 2971 prakash    0u   CHR  136,4      0t0       7 /dev/pts/4

inita.sh 2971 prakash    1u   CHR  136,4      0t0       7 /dev/pts/4

inita.sh 2971 prakash   2u   CHR  136,4      0t0       7 /dev/pts/4

inita.sh 2971 prakash   10r   REG    8,1       20  393578 /home/prakash/inita.sh

In the above output, for the first 5 seconds, there is no output. After that a script named “inita.sh” is started, and it list the output.

Finding Network Connection

Network connections are also files. So we can find information about them by using lsof.

11. List all network connections

You can list all the network connections opened by using ‘-i’ option.

#  lsof -i

COMMAND    PID  USER   FD   TYPE DEVICE SIZE/OFF NODE NAME

avahi-dae  515 avahi   13u  IPv4   6848      0t0  UDP *:mdns

avahi-dae  515 avahi   16u  IPv6   6851      0t0  UDP *:52060

cupsd     1075  root    5u  IPv6  22512      0t0  TCP ip6-localhost:ipp (LISTEN)

You can also use ‘-i4′ or ‘-i6′ to list only ‘IPV4′ or ‘IPV6‘ respectively.

12. List all network files in use by a specific process

You can list all the network files which is being used by a process as follows

# lsof -i -a -p 234

You can also use the following

# lsof -i -a -c ssh

The above command will list the network files opened by the processes starting with ssh.

13. List processes which are listening on a particular port

You can list the processes which are listening on a particular port by using ‘-i’ with ‘:’ as follows

# lsof -i :25

COMMAND  PID        USER   FD   TYPE DEVICE SIZE NODE NAME

exim4   2541 Debian-exim    3u  IPv4   8677       TCP localhost:smtp (LISTEN)

14. List all TCP or UDP connections

You can list all the TCP or UDP connections by specifying the protocol using ‘-i’.

# lsof -i tcp; lsof -i udp;

15. List all Network File System ( NFS ) files

You can list all the NFS files by using ‘-N’ option. The following lsof command will list all NFS files used by user ‘prakash’.

# lsof -N -u prakash -a

Mount Windows/USB NTFS Partition in RHEL/CentOS/Fedora

First you need to enable EPEL (Extra Packages for Enterprise Linux) Repository. You may refer the article on how to enable EPEL  Repository under RHEL, CentOS and Fedora systems.
To mount any NTFS based filesystem, you need to install a tool called NTFS3G. Before heading up for installation let’s understand NTGS3G.
What is NTFS3G
NTFS3G is an open source cross-platform, stable, GPL licensed, POSIX, NTFS R/W driver used in Linux. It provides safe handling of Windows NTFS file systems viz create, remove, rename, move files, directories, hard links, etc.
Once EPEL is installed and enabled, let’s install ntfs-3g package using the below command with root user.
# yum -y install ntfs-3g
Fuse Install
Next, install and load FUSE driver to mount detected devices with below command. FUSE module is included in the kernel itself in version 2.6.18-164 or newer.
# yum install fuse
# modprobe fuse
Identify NTFS Partition
Once fuse module is loaded, type below command to find out NTFS Partitions in Linux.
# fdisk -l
  Device   Boot      Start    End      Blocks   Id  System
 /dev/sda1   *         1      121602   976760032+   7  HPFS/NTFS
Mount NTFS partition
First create a mount point to mount the NTFS partition.
# mkdir /mnt/usb
Simply run the following command to mount the partition. Replace sda1 with your actual partition found.
# mount -t ntfs-3g /dev/sda1 /mnt/usb
Once it’s mounted on /mnt/ntfs, you may use regular Linux ls -l command to list the content of mounted filesystem.
# ls -l
If you want to make mount point permanent at the boot time, then simple add the following line at the end of /etc/fstab file. This will remain as permanent.
/dev/sda1    /mnt/usb    ntfs-3g        defaults    0    0
Umount NTFS Partition
Simply, use the following command to unmount the mounted partition.
# umount /mnt/usb

How to Enable SRIOV of IBM Servers and Blade Servers BIOS

What is SR-IOV? The short answer is that SR-IOV is a specification that allows a PCIe device to appear to be multiple separate physical PCIe devices. The SR-IOV specification was created and is maintained by the PCI SIG, with the idea that a standard specification will help promote interoperability.

Step 1: Power on the system, and press F1 to enter the Setup utility.
Step 2: Select System Settings and then Network.
Step 3: Under the Network Device List, select the device to be configured and press Enter to see all the Network Device options (Figure 1).

Step 4: Select the device’s description and press Enter to configure the device 
Step 5: From the selection menu, select Advanced Mode and press Enter to change the value.
Step 6: Choose Enable and press Enter.
Step 7: On the same selection menu, select Controller Configuration and press Enter to enter the configuration menu.
Step 8: Select Configure SRIOV and hit Enter.
Step 9: On the Configure SRIOV page, press Enter to toggle the values
Step 10: Select Enable and press Enter
Step 11: Select Save Current Configurations and press Enter.
Step 12: Press Esc to exit the menu. Then, click Save to save the configuration.
Step 13: Reboot the system.

Setting up an SSL secured Webserver with CentOS

1. Getting the required software
For an SSL encrypted web server you will need a few things. Depending on your install you may or may not have OpenSSL and mod_ssl, Apache's interface to OpenSSL. Use yum to get them if you need them.
# yum install mod_ssl openssl
Yum will either tell you they are installed or will install them for you.
2. Generate a self-signed certificate
Using OpenSSL we will generate a self-signed certificate. If you are using this on a production server you are probably likely to want a key from Trusted Certificate Authority, but if you are just using this on a personal site or for testing purposes a self-signed certificate is fine. To create the key you will need to be root so you can either su to root or use sudo in front of the commands
# Generate private key 
openssl genrsa -out ca.key 1024 
# Generate CSR 
openssl req -new -key ca.key -out ca.csr
# Generate Self Signed Key
openssl x509 -req -days 365 -in ca.csr -signkey ca.key -out ca.crt
# Move the files to the correct locations
# mv ca.crt /etc/pki/tls/certs
# mv ca.key /etc/pki/tls/private/ca.key
# mv ca.csr /etc/pki/tls/private/ca.csr
Then we need to update the Apache SSL configuration file
# vi +/SSLCertificateFile /etc/httpd/conf.d/ssl.conf
Change the paths to match where the Key file is stored. If you've used the method above it will be
SSLCertificateFile /etc/pki/tls/certs/ca.crt
Then set the correct path for the Certificate Key File a few lines below. If you've followed the instructions above it is:
SSLCertificateKeyFile /etc/pki/tls/private/ca.key
Quit and save the file and then restart Apache
# /etc/init.d/httpd restart
All being well you should now be able to connect over https to your server and see a default Centos page. As the certificate is self signed browsers will generally ask you whether you want to accept the certificate. Firefox 3 won't let you connect at all but you can override this.
Restart Apache again using 
# /etc/init.d/httpd restart