RHCSA 2

RHCSA-2

LOG FILES

Log Files Location And How Do I View Logs Files

Almost all logfiles are located under /var/log directory and its sub­

directories on Linux. You can change to this directory using the cd command. You

need be the root user to view or access log files on Linux or Unix like operating

systems. You can use the following commands to see the log files:

less command

more command

cat command

grep command

tail command

zcat command

zgrep command

zmore command

How do I view log files on Linux?

Open the Terminal or login as root user using ssh command. Go to /var/log

directory using the following cd command:

To view a common log file called /var/log/messages use any one of the following command: # less /var/log/messages

# more ­f /var/log/messages # cat /var/log/messages # tail ­f /var/log/messages

# grep ­i error /var/log/messages

Common Linux log files names and usage

/var/log/messages : General message and system related stuff /var/log/auth.log : Authenication logs

/var/log/kern.log : Kernel logs

/var/log/cron.log : Crond logs (cron job) /var/log/maillog : Mail server logs

/var/log/qmail/ : Qmail log directory (more files inside this directory) /var/log/httpd/ : Apache access and error logs directory

/var/log/lighttpd/ : Lighttpd access and error logs directory /var/log/boot.log : System boot log

/var/log/mysqld.log : MySQL database server log file /var/log/secure or /var/log/auth.log : Authentication log /var/log/utmp or /var/log/wtmp : Login records file

TOP Command

Linux Top command is a performance monitoring program which is used frequently by many system administrators to monitor Linux performance and it is available under many Linux/Unix like operating systems. The top command used to dipslay all the running and active real­time processes in ordered list and updates it regularly. It display CPU usage, Memory usage, Swap Memory, Cache Size, Buffer Size, Process PID, User, Commands and much more. It also shows high memory and cpu utilization of a running processess. The top command is much userful for system administrator to monitor and take correct action when required. Let’s see top command in action. # top

2. Sorting with ­O (Uppercase Letter ‘O’)

Press (Shift+O) to Sort field via field letter, for example press ‘a‘ letter to sort process with PID (Process ID).

3. Display Specific User Process # top ­u tecmint

4. Highlight Running Process in Top

Press ‘z‘ option in running top command will display running process in color which may help you to identified running process easily.

5. Shows Absolute Path of Processes

6. Change Delay or Set ‘Screen Refresh Interval’ in Top

By default screen refresh interval is 3.0 seconds, same can be change pressing ‘d‘ option in running top command and change it as desired as shown below.

7. Kill running process with argument ‘k’

You can kill a process after finding PID of process by pressing ‘k‘ option in running top command without exiting from top window as shown below.

8. Sort by CPU Utilisation

Press (Shift+P) to sort processes as per CPU utilization. See screenshot below. 9. Renice a Process

You can use ‘r‘ option to change the priority of the process also called Renice. 10. Save Top Command Results

Press (Shift+W) to save the running top command results under /root/.toprc. 11. Getting Top Command Help

Press ‘h‘ option to obtain the top command help. 12. Exit Top Command After Specific repetition

Top output keep refreshing until you press ‘q‘. With below command top command will automatically exit after 10 number of repetition.

There are number of arguments to know more about top command you may refer man page of top command.

VmStat – Virtual Memory Statistics

Linux VmStat command used to display statistics of virtual memory, kernerl

threads

, disks, system processes, I/O blocks, interrupts, CPU activity and

much more. By default vmstat command is not available under Linux

systems you need to install a package called sysstat that includes a vmstat

program.

If vmstat and iostat commands are not available on your box, please install

sysstat

package. The vmstat, sar and iostat commands are the collection

of package included in sysstat – the system monitoring tools. The iostat

generates reports of CPU & all device statistics. You may download and

install sysstat using source tarball from link

sysstat

, but we recommend

installing through YUM command.

Install Sysstat in Linux

# yum ­y install sysstat

vmstat

_{– Summary information of Memory, Processes, Paging etc.}

iostat

– Central Processing Unit (CPU) statistics and input/output statistics

for devices and partitions

1. List Active and Inactive Memory

In the below example, there are six columns. The significant of the columns are

explained in man page of vmstat in details. Most important fields are free under memory and si, so under swap column.

# vmstat ­a

procs ­­­­­­­­­­­memory­­­­­­­­­­ ­­­swap­­ ­­­­­io­­­­ ­­system­­ ­­­­­cpu­­­­­ r b swpd free inact active si so bi bo in cs us sy id wa st

1 0 0 810420 97380 70628 0 0 115 4 89 79 1 6 90 3 0 Free – Amount of free/idle memory spaces.

si – Swaped in every second from disk in Kilo Bytes. so – Swaped out every second to disk in Kilo Bytes.

Note: If you run vmstat without parameters it’ll displays summary report since system boot.

2. Execute vmstat ‘X’ seconds and (‘N’number of times)

With this command, vmstat execute every two seconds and stop automatically after executing six intervals.

3. Vmstat with timestamps

vmstat command with ­t parameter shows timestamps with every line

printed as shown below.

$ vmstat ­t 1 5

4. Statistics of Various Counter

vmstat command and ­s switch displays summary of various event counters

and memory statistics.

$ vmstat ­s

5. Disks Statistics

vmstat with ­d option display all disks statistics.

$ vmstat ­d

6. Display Statistics in Megabytes

The vmstat displays in Megabytes with parameters ­S and M(Uppercase &

megabytes). By default vmstat displays statistics in kilobytes.

Iostat Command

1. Display CPU and I/O statistics

iostat without arguments displays CPU and I/O statistics of all partitions as shown below. # iostat

2. Shows only CPU Statistics

iostat with ­c arguments displays only CPU statistics as shown below. # iostat ­c

3. Shows only Disks I/O Statistics

iostat with ­d arguments displays only disks I/O statistics of all partitions as shown. # iostat ­d

4. Shows I/O statistics only of a single device.

By default it displays statistics of all partitions, with ­p and device name arguments displays only disks I/O statistics for specific device only as shown.

# iostat ­p sda

5. Display LVM Statistics

With ­N (Uppercase) parameter displays only LVM statistics as shown. # iostat ­N

6. iostat version.

With ­V (Uppercase) parameter displays version of iostat as shown. # iostat ­V

Note: vmstat and iostat contains number of columns and flags which may not possible to explain in details. If you want to know more about it you may refer man page of vmstat and iostat.

Lsof – List Open Files

Lsof command used in many Linux/Unix like system that is used to display list of all the open files and the processes. The open files included are disk files, network sockets, pipes, devices and processes. One of the main reason for using this command is when a disk cannot be unmounted and displays the error that files are being used or opened. With this commmand you can easily identify which files are in use. 1. List all Open Files with lsof Command

In the below example, it will show long listing of open files some of them are extracted for better understanding which displays the columns like Command, PID, USER, FD, TYPE etc.

# lsof

Sections and it’s values are self­explanatory. However, we’ll review FD & TYPE columns more precisely. FD – stands for File descriptor and may seen some of the values as:

cwd current working directory rtd root directory

txt program text (code and data) mem memory­mapped file

Also in FD column numbers like 1u is actual file descriptor and followed by u,r,w of it’s mode as: r for read access.

w for write access.

u for read and write access.

TYPE – of files and it’s identification. DIR – Directory

REG – Regular file

CHR – Character special file. FIFO – First In First Out

2. List User Specific Opened Files

The below command will display the list of all opened files of user tecmint. # lsof ­u tecmint

3. Find Processes running on Specific Port

To find out all the running process of specific port, just use the following command with option ­i. The below example will list all running process of port 22.

# lsof ­i TCP:22

4. List Only IPv4 & IPv6 Open Files

In below example shows only IPv4 and IPv6 network files open with separate commands.

# lsof ­i 4 # lsof ­i 6

5. List Open Files of TCP Port ranges 1­1024

To list all the running process of open files of TCP Port ranges from 1­1024. # lsof ­i TCP:1­1024

6. Exclude User with ‘^’ Character

Here, we have excluded root user. You can exclude a particular user using ‘^’ with command as shown above.

7. Find Out who’s Looking What Files and Commands?

Below example shows user tecmint is using command like ping and /etc directory . # lsof ­i ­u tecmint

8. List all Network Connections

The following command with option ‘­i’ shows the list of all network connections ‘LISTENING & ESTABLISHED’.

# lsof ­i

9. Search by PID

The below example only shows whose PID is 1 [One]. # lsof ­p 1

10. Kill all Activity of Particular User

Sometimes you may have to kill all the processes for a specific user. Below command will kills all the processes of tecmint user.

# kill ­9 `lsof ­t ­u tecmint`

Note: Here, it’s not possible to give example of all available options, this guide is only to show how lsof command can be use. You may refer man page of lsof command to know more about it.

Tcpdump – Network Packet Analyzer

Tcpdump one of the most widely used command­line network packet analyzer or packets sniffer program that is used capture or filter TCP/IP packets that received or transferred on a specific interface over a network. It also provides a option to save captured packages in a file for later analysis.

How to Install tcpdump in Linux

Many of Linux distributions already shipped with tcpdump tool, if in case you don’t have it on systems, you can install it using following Yum command.

# yum install tcpdump

1. Capture Packets from Specific Interface

The command screen will scroll up until you interrupt and when we execute tcpdump command it will captures from all the interfaces, however with ­i switch only capture from desire interface. # tcpdump ­i eth0

2. Capture Only N Number of Packets

When you run tcpdump command it will capture all the packets for specified interface, until you Hit cancel button. But using ­c option, you can capture specified number of packets. The below example will only capture 6 packets.

# tcpdump ­c 5 ­i eth0

3. Print Captured Packets in ASCII

The below tcpdump command with option ­A displays the package in ASCII format. It is a character­ encoding scheme format.

4. Display Available Interfaces

To list number of available interfaces on the system, run the following command with ­D option.

# tcpdump ­D

5. Display Captured Packets in HEX and ASCII

The following command with option ­XX capture the data of each packet, including its link level header in HEX and ASCII format.

# tcpdump ­XX ­i eth0

6. Capture and Save Packets in a File

As we said, that tcpdump has a feature to capture and save the file in a .pcap format, to do this just execute command with ­w option.

# tcpdump ­w 0001.pcap ­i eth0 7. Read Captured Packets File

To read and analyze captured packet 0001.pcap file use the command with ­r option, as shown below.

# tcpdump ­r 0001.pcap

8. Capture IP address Packets

To capture packets for a specific interface, run the following command with option ­n. # tcpdump ­n ­i eth0

9. Capture only TCP Packets.

To capture packets based on TCP port, run the following command with option tcp. # tcpdump ­i eth0 tcp

10. Capture Packet from Specific Port

Let’s say you want to capture packets for specific port 22, execute the below command by specifying port number 22 as shown below.

# tcpdump ­i eth0 port 22

11. Capture Packets from source IP

To capture packets from source IP, say you want to capture packets for 192.168.0.2, use the command as follows.

# tcpdump ­i eth0 src 192.168.0.2

12. Capture Packets from destination IP

To capture packets from destination IP, say you want to capture packets for 50.116.66.139, use the command as follows.

# tcpdump ­i eth0 dst 50.116.66.139

This article may help you to explore tcpdump command in depth and also to capture and analysis packets in future. There are number of options available, you can use the options as per your requirement.

Netstat – Network Statistics

Netstat is a command line tool for monitoring incoming and outgoing network packets statistics as well as interface statistics. It is very useful tool for every system

administrator to monitor network performance and troubleshoot network related problems.

1. Listing all the LISTENING Ports of TCP and UDP connections Listing all ports (both TCP and UDP) using netstat ­a option. # netstat ­a | more

2. Listing TCP Ports connections

Listing only TCP (Transmission Control Protocol) port connections using netstat ­at. # netstat ­at

3. Listing UDP Ports connections

Listing only UDP (User Datagram Protocol ) port connections using netstat ­au. # netstat ­au

4. Listing all LISTENING Connections

Listing all active listening ports connections with netstat ­l. # netstat ­l

5. Listing all TCP Listening Ports

Listing all active listening TCP ports by using option netstat ­lt. # netstat ­lt

6. Listing all UDP Listening Ports

Listing all active listening UDP ports by using option netstat ­lu. # netstat ­lu

7. Listing all UNIX Listening Ports

Listing all active UNIX listening ports using netstat ­lx. # netstat ­lx

8. Showing Statistics by Protocol

Displays statistics by protocol. By default, statistics are shown for the TCP, UDP, ICMP, and IP protocols. The ­s parameter can be used to specify a set of protocols.

# netstat ­s

9. Showing Statistics by TCP Protocol

Showing statistics of only TCP protocol by using option netstat ­st. # netstat ­st

10. Showing Statistics by UDP Protocol # netstat ­su

11. Displaying Service name with PID

Displaying service name with their PID number, using option netstat ­tp will display “PID/Program Name”. # netstat ­tp

12. Displaying Promiscuous Mode

Displaying Promiscuous mode with ­ac switch, netstat print the selected information or refresh screen every five second. Default screen refresh in every second.

13. Displaying Kernel IP routing

Display Kernel IP routing table with netstat and route command. # netstat ­r

14. Showing Network Interface Transactions

Showing network interface packet transactions including both transferring and receiving packets with MTU size.

# netstat ­i

15. Showing Kernel Interface Table

Showing Kernel interface table, similar to ifconfig command. # netstat ­ie

16. Displaying IPv4 and IPv6 Information

Displays multicast group membership information for both IPv4 and IPv6. # netstat ­g

17. Print Netstat Information Continuously

To get netstat information every few second, then use the following command, it will print netstat information continuously, say every few seconds.

18. Finding non supportive Address

Finding un­configured address families with some useful information.

# netstat ­­verbose

19. Finding Listening Programs

Find out how many listening programs running on a port.

# netstat ­ap | grep http

20. Displaying RAW Network Statistics

# netstat ­­statistics ­­raw

That’s it, If you are looking for more information and options about

netstat command, refer netstat manual docs or use man netstat

command to know all the information.

IPTraf – Real Time IP LAN Monitoring

IPTraf is an open source console­based real time network (IP LAN)

monitoring utility for Linux. It collects a variety of information such as

IP traffic monitor that passes over the network, including TCP flag

information, ICMP details, TCP/UDP traffic breakdowns, TCP

connection packet and byne counts. It also gathers information of

general and detaled interface statistics of TCP, UDP, IP, ICMP, non­IP, IP

checksum errors, interface activity etc.

Installing IPTraf

IPTraf is part of the Linux distribution and can be installed on RHEL,

CentOS and Fedora server’s using yum command from terminal.

# yum install iptraf

IPTraf Usage

Once IPTraf installed, run the following command from the terminal to

launch an ascii based menu interface that will allow you to view

current IP traffic monitoring, General interface statistics, Detailed

interface statistics, Statistical breakdowns, Filters and also provide

some configure options where you can configure as per your need.

#iptraf

IPTraf Startup Screen

The iptraf interactive screen, displays a menu system with different options to choose from. Here are the some screenshots that shows real time IP traffic counts and interface statistics etc.

� IP traffic monitor

� General interface statistics � Detailed interface statistics � Statistical breakdowns

� LAN station monitor � Configure

IPTraf Options

Using “iptraf -i” will immediately start the IP traffic monitor on a particular interface. For example, the following command will start the IP traffic on interface eth0. This is the primary interface card that attached to your system. Else you can also monitor all your network interface traffic using argument as “iptraf -i all“.

# iptraf ­i eth0

IPTraf Eth0 Monitoring

Similarly, you can also monitor TCP/UDP traffic on a specific interface, using the following command.

Psacct or Acct – Monitor User Activity

� The psacct or acct package provides several features for monitoring process activities. � ac command prints the statistics of user logins/logouts (connect time) in hours.

� lastcomm command prints the information of previously executed commands of user. � accton commands is used to turn on/off process for accounting.

� sa command summarizes information of previously executed commands. � last and lastb commands show listing of last logged in users.

� Using command “ac -d” will prints out the total login time in hours by day­wise. � Using command “ac -p” will print the total login time of each user in hours.

� To get the total login statistics time of user “tecmint” in hours, use the command as. # ac tecmint � The following command will prints the day­wise total login time of user “tecmint” in hours. # ac ­

d tecmint

� Print All Account Activity Information # sa � Print Individual User Information # sa ­u � Print Number of Processes # sa ­m

� Print Sort by Percentage # sa ­c

� List Last Executed Commands of User # lastcomm tecmint � Search Logs for Commands # lastcomm ls

RPM

RPM (Red Hat Package Manager) utility for Red Hat based systems like (RHEL, CentOS and Fedora).

The tool allows system administrators and users to install, update, uninstall, query, verify and manage system software packages in Unix/Linux operating systems. The RPM formerly known as .rpm file, that includes compiled software programs and libraries needed by the packages. This utility only works with packages that built on .rpm format. is an default open source and most popular package management

Some Facts about RPM (RedHat Package Manager)

� RPM is free and released under GPL (General Public License).

� RPM keeps the information of all the installed packages under /var/lib/rpm database.

� RPM is the only way to install packages under Linux systems, if you’ve installed packages using source code, then rpm won’t manage it.

� RPM deals with .rpm files, which contains the actual information about the packages such as: what

it is, from where it comes, dependencies info, version info etc. There are five basic modes for RPM command

� Install It is used to install any RPM package.

� Remove It is used to erase, remove or un-install any RPM package. � Upgrade It is used to update the existing RPM package.

� Verify It is used to query about different RPM packages. � Query It is used for the verification of any RPM package.

Where to find RPM packages

Below is the list of rpm sites, where you can find and download all RPM

packages.

�

http://rpmfind.net

�

http://www.redhat.com

�

http://freshrpms.net/

�

http://rpm.pbone.net/

How to Mount RPM Packages from cdrom iso image

#mount /dev/sr0 /mnt

#cd /mnt

#ls

#cd Package

#ls

1. How to Check an RPM Signature Package

# rpm --checksig pidgin-2.7.9-5.el6.2.i686.rpm

2. How to Install an RPM Package

# rpm -ivh pidgin-2.7.9-5.el6.2.i686.rpm

RPM command and options

-i : install a package

-v : verbose for a nicer display

3. How to check dependencies of RPM Package before Installing

# rpm -qpR BitTorrent-5.2.2-1-Python2.4.noarch.rpm

RPM command and options -q : Query a package

-p : List capabilities this package provides.

-R: List capabilities on which this package depends..

4. How to Install a RPM Package Without Dependencies

# rpm -ivh --nodeps BitTorrent-5.2.2-1-Python2.4.noarch.rpm

5. How to check an Installed RPM Package

Using -q option with package name, will show whether an rpm installed or not.

# rpm -q BitTorrent

6. How to List all files of an installed RPM package

To view all the files of an installed rpm packages, use the -ql (query list) with rpm command.

7. How to List Recently Installed RPM Packages

Use the following rpm command with -qa (query all) option, will list all the recently installed

rpm packages.

# rpm -qa --last

8. How to List All Installed RPM Packages

Type the following command to print the all the names of installed packages on your Linux system.

# rpm –qa

9. How to Upgrade a RPM Package

If we want to upgrade any RPM package “–U” (upgrade) option will be used.

One of the major advantages of using this option is that it will not only upgrade

the latest version of any package, but it will also maintain the backup of the

older package so that in case if the newer upgraded package does not run the

previously installed package can be used again.

10. How to Remove a RPM Package

To un-install an RPM package, for example we use the package name nx, not the original package

name nx-3.5.0-2.el6.centos.i686.rpm. The -e (erase) option is used to remove package.

# rpm -evv nx

11. How to Remove an RPM Package Without Dependencies

The –nodeps (Do not check dependencies) option forcefully remove the rpm package from the

system. But keep in mind removing particular package may break other working applications.

# rpm -ev --nodeps vsftpd

12. How to Query a file that belongs which RPM Package

Let’s say, you have list of files and you would like to find out which package belongs to these files. For example, the following command with -qf (query file) option will show you a file /usr/bin/htpasswd is

own by package httpd-tools-2.2.15-15.el6.centos.1.i686.

13. How to Query a Information of Installed RPM Package

Let’s say you have installed an rpm package and want to know the information about the package. The following -qi (query info) option will print the available information of the

installed package.

# rpm -qi vsftpd

14. Get the Information of RPM Package Before Installing

You have download a package from the internet and want to know the information of a package before installing. For example, the following option -qip (query info package) will print the information of a

package sqlbuddy.

# rpm -qip sqlbuddy-1.3.3-1.noarch.rpm

15. How to Query documentation of Installed RPM Package

To get the list of available documentation of an installed package, use the following command with option -qdf (query document file) will display the manual pages related to vmstat package.

16. How to Verify a RPM Package

Verifying a package compares information of installed files of the package against the rpm database. The

-Vp (verify package) is used to verify a package.

# rpm -Vp sqlbuddy-1.3.3-1.noarch.rpm

17. How to Verify all RPM Packages

Type the following command to verify all the installed rpm packages.

# rpm –Va

18. How to Import an RPM GPG key

To verify RHEL/CentOS/Fedora packages, you must import the GPG key. To do so, execute the

following command. It will import CentOS 6 GPG key.

# rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

19. How to List all Imported RPM GPG keys

To print all the imported GPG keys in your system, use the following command.

20. How To rebuild Corrupted RPM Database

Sometimes rpm database gets corrupted and stops all the functionality of rpm and other

applications on the system. So, at the time we need to rebuild the rpm database and restore it with the help of following command.

# cd /var/lib

# rm __db*

# rpm --rebuilddb

YUM

YUM (Yellow dog Updater Modified) is an open source command-line as well as

graphical based package management tool for RPM (RedHat Package Manager)

based Linux systems. It allows users and system administrator to easily install, update, remove or search software packages on a systems. It was developed and released by

Seth Vidal under GPL (General Public License) as an open source, means anyone can

allowed to download and access the code to fix bugs and develop customized

packages. YUM uses numerous third party repositories to install packages

automatically by resolving their dependencies issues.

Syntax

yum [options] [command] [package ...]

repository:A repository is a collection of rpms under some sort of filesystem tree. For most purposes associated with yum, the repository will have two more important

characteristics. It has had the command createrepo run on the tree, which extracts and encodes all of the metadata that yum relies on in order to function. Also, the tree, and is made accessible by URL from a server (which means as one or more of

http://my.web.server/path, ftp://my.ftp.server/path, file://full/file/path to the repository tree).

S.No RPM YUM

1

If we want to install an application(Ex: apache), rpm need to install all the packages required for this application, these packages may vary from 1 rpm to several rpm’s depending on shared rpm packages.

Install an application with single command Ex: yum install httpd

2 RPM package dependencies is bit tough YUM resolves dependencies with ease

3 Batch installation of applications is possible with one command

YUM command can install number of applications in one single command

Ex: yum install httpd vsftpd 4 RPM can not handle updated software

installation automatically

Does YUM install updates of the existing packages by using

yum install upgrade

5 Can not connect to online repositories Can connect to on­line repositories to get latest software before installing the applications

Create Repository: Step:1 # mount 192.168.0.254:/soft /mnt # cd /mnt #ls # df ­Th 192.168.0.254:/soft nfs 5.0G 3.6G 1.2G 77% /mnt #cd /Packages #rpm ­ivh vsftpd­2.2.2­11.el6.x86_64.rpm # cp ­rvf /mnt/Packages/ /var/ftp/pub/ # ls ­l /var/ftp/pub/ Step 2:

(i) # rpm -ivh createrepo-0.9.8-5.el6.noarch.rpm

(ii) # rpm -ivh deltarpm-3.5-0.5.20090913git.el6.x86_64.rpm

(iii) # rpm -ivh python-deltarpm-3.5-0.5.20090913git.el6.x86_64.rpm

To Create a repo

# createrepo . (or)

# createrepo -v /var/ftp/pub/

Step 3

Now Crate a repository # cd /etc/yum.repos.d/ # vim redhat.repo [redhat] baseurl=file:///software enabled=1 gpgcheck=0 :wq! Note :

enabled =1 ---> get repodata from (1 from local 0 - from web site) gpgcheck=0 --> Key checking ( 0 - no need key, 1 - need Key)

# yum clean all

# yum clean dbcache # yum repolist

#service vsftpd restart #chkconfig vsftpd on

II Method for centralized yum Server creation

#ln -s /var/ftp/pub/ /var/www/html/ # vim /etc/yum.repos.d/redhat.repo [redhat]

baseurl=ftp://127.0.0.1/pub/ (or) http://server ip/pub/ enabled=1

gpgcheck=0 :wq!

# yum clean all

# yum clean dbcache # yum repolist

Client server repos id configuration

# vim /etc/yum.repos.d/admin.repo [admin]

baseurl=ftp://yum server ip/pub/ (or) http://serverip/pub/ enabled=1

gpgcheck=0 :wq!

# yum clean all

# yum clean dbcache # yum repolist

1. Install a Package with YUM

To install a package called

Firefox 14, just run the below command it will

automatically find and install all required dependencies for Firefox.

# yum install firefox

The above command will ask confirmation before installing any package on

your system. If you want to install packages automatically without asking any

confirmation, use option -y as shown in below example.

# yum -y install firefox

2. Removing a Package with YUM

To remove a package completely with their all dependencies, just run the

following command as shown below.

# yum remove firefox

Same way the above command will ask confirmation before removing a

3. Updating a Package using YUM

Let’s say you have outdated version of

MySQL package and you want

to update it to the latest stable version. Just run the following command

it will automatically resolves all dependencies issues and install them.

# yum update mysql

4. List a Package using YUM

Use the list function to search for the specific package with name. For

example to search for a package called

openssh

, use the command.

# yum list openssh

To make your search more accurate, define package name with their

version, in case you know. For example to search for a specific version

openssh-4.3p2

of the package, use the command.

5. Search for a Package using YUM

If you don’t remember the exact name of the package, then use search

function to search all the available packages to match the name of the

package you specified. For example, to search all the packages that

matches the word .

# yum search vsftpd

6. Get Information of a Package using YUM

Say you would like to know information of a package before installing

it. To get information of a package just issue the below command.

# yum info firefox

7. List all Available Packages using YUM

To list all the available packages in the Yum database, use the below command.

8. List all Installed Packages using YUM

To list all the installed packages on a system, just issue below command, it will

display all the installed packages.

# yum list installed | less

9. Yum Provides Function

Yum provides function is used to find which package a specific file

belongs to. For example, if you would like to know the name of the

package that has the /etc/httpd/conf/httpd.conf.

# yum provides /etc/httpd/conf/httpd.conf

10. Check for Available Updates using Yum

To find how many of installed packages on your system have updates

available, to check use the following command.

11. Update System using Yum

To keep your system up-to-date with all security and binary package updates,

run the following command. It will install all latest patches and security

updates to your system.

# yum update

12. List all available Group Packages

In Linux, number of packages are bundled to particular group. Instead of

installing individual packages with yum, you can install particular group that

will install all the related packages that belongs to the group. For example to

list all the available groups, just issue following command.

# yum grouplist

13. Install a Group Packages

To install a particular package group, we use option as groupinstall. Fore

example, to install “MySQL Database“, just execute the below command.

14. Update a Group Packages

To update any existing installed group packages, just run the following

command as shown below.

# yum groupupdate 'DNS Name Server‘

15. Remove a Group Packages

To delete or remove any existing installed group from the system, just use

below command.

# yum groupremove 'DNS Name Server‘

16. List Enabled Yum Repositories

To list all enabled Yum repositories in your system, use following option.

# yum repolist

16. List all Enabled and Disabled Yum Repositories

The following command will display all enabled and disabled yum repositories

on the system.

17. Install a Package from Specific Repository

To install a particular package from a specific enabled or disabled repository, you must

use --enablerepo option in your yum command. For example to Install PhpMyAdmin

3.5.2 package, just execute the command.

# yum --enablerepo=epel install phpmyadmin

18. Interactive Yum Shell

Yum utility provides a custom shell where you can execute multiple commands.

19. Clean Yum Cache

By default yum keeps all the repository enabled package data in /var/cache/yum/ with each sub-directory, to clean all cached files from enabled repository, you need to run the following command regularly to clean up all the cache and make sure that there is

nothing unnecessary space is using. We don’t want to give the output of the below command, because we like to keep cached data as it is.

# yum clean all

20. View History of Yum

To view all the past transactions of yum command, just use the following command.

Mount the ISO image into server # mount /dev/sr0 /mnt #df /mnt #cd Packages #rpm –ivh createrepo……rpm #rpm –ivh deltarpm………rpm #rpm –ivh python-deltarpm……rpm #rpm –ivh vsftpd……rpm

Copy the packages into /var/ftp/pub/

#cp –rvf /mnt/Packages/ /var/ftp/pub/

Note: The cp command will take a while so the -v flag will show what it is doing Create the local repo with createrepo command

#createrepo –v /var/ftp/pub/

Set up your local repository

Now you have the repo created you can use it on the local system by setting up a repo conf file for it. Use your editor of choice (which is vi of course) to create repo

#vi /etc/yum.repos.d/rhel7.repo [rhel7] name=Local repo baseurl=file:///var/ftp/pub enabled=1 gpgcheck=0

Note: The three / is in the file URL. The enabled set to 1 so that it will not get repository in

online and it will get it from locally, gpgcheck is set to zero so that it will not look for signatures.

Confirm the repo is now available locally

#yum clean all

#yum clean dbcache #yum repolist

Centralized yum Server Configuration

# systemctl start vsftpd # systemctl status vsftpd

We are going to use the default anonymous ftp configuration so the repo needs to be made available via /var/ftp/pub .

Before all that though we have to test vsftpd is working and set up the firewall rules if applicable….

# systemctl status firewalld

If you are not using a firewall then you can skip the commands below that allow the ftp service

#firewall-cmd --get-default-zone

public

# firewall-cmd --query-service=ftp

no

# firewall-cmd --query-service=ftp --permanent

If the service is not allowed then add it both in the runtime config and the permanent config.

# firewall-cmd --add-service=ftp

success

# firewall-cmd --add-service=ftp –permanent

success

# firewall-cmd --query-service=ftp

yes

# firewall-cmd --query-service=ftp --permanent

yes

You can now test vsftp by going to a remote server and using an ftp client to login

anonymously. ( You can also test it locally ). If you don’t have an ftp client you can install a basic command line one using

#yum install ftp

You should be able to log in anonymous users and see the root directory. ( Which is chrooted to /var/ftp/ by default).

Set up your ftp repository #vi /etc/yum.repos.d/rhel7.repo [ftprepo] name=ftp baseurl=ftp://127.0.0.1/pub enabled=1 gpgcheck=0

Note: The three / is in the file URL. The enabled set to 1 so that it will not get repository in

online and it will get it from locally, gpgcheck is set to zero so that it will not look for signatures.

Confirm the repo is now available through ftp

#yum clean all

#yum clean dbcache #yum repolist

Client server repos id configuration

# vim /etc/yum.repos.d/admin.repo

[admin]

baseurl=ftp://yum server ip/pub enabled=1

gpgcheck=0 :wq!

# yum clean all

# yum clean dbcache # yum repolist

Cron format is a simple, yet powerful and flexible way to define time and frequency of various actions. nnCron make active use of cron format in both classic and extended modes.

Traditional (inherited from Unix) cron format consists of five fields separated by white spaces: <Minute> <Hour> <Day_of_the_Month> <Month_of_the_Year> <Day_of_the_Week>

nnCron can use both traditional and "enhanced" version of cron format, which has an additional (6th) field: <Year> <Minute> <Hour> <Day_of_the_Month> <Month_of_the_Year> <Day_of_the_Week> <Year>

A user can select the format he would like to use by selecting or unselecting the Year field checkbox on General tab in

Options dialog (which can be opened by doublecliking the nnCron icon in system tray). By default, nnCron uses the

enhanced format.

The following graph shows what it consists of: * * * * * *

| | | | | |

| | | | | +-- Year (range: 1900-3000)

| | | | +---- Day of the Week (range: 1-7, 1 standing for Monday) | | | +--- Month of the Year (range: 1-12)

| | +--- Day of the Month (range: 1-31) | +--- Hour (range: 0-23) +--- Minute (range: 0-59)

• Any of these 6 fields may be an asterisk (*). This would mean the entire range of possible values, i.e. each minute, each hour, etc. In the first four fields, nnCron users can also use "nonstandard"

character ? (question mark), described here.

• Any field may contain a list of values separated by commas, (e.g. 1,3,7) or a range of values (two integers separated by a hyphen, e.g. 1-5).

• After an asterisk (*) or a range of values, you can use character / to specify that values are repeated over and over with a certain interval between them. For example, you can write "0-23/2" in Hour field to specify that some action should be performed every two hours (it will have the same effect as "0,2,4,6,8,10,12,14,16,18,20,22"); value "*/4" in Minute field means that the action should be performed every 4 minutes, "1-30/3" means the same as "1,4,7,10,13,16,19,22,25,28".

• In Month and Day of Week fields, you can use names of months or days of weeks abbreviated to first three letters ("Jan,Feb,...,Dec" or "Mon,Tue,...,Sun") instead of their numeric values.

How to Add/Edit Crontab

To add or update job in crontab, use below command. It will open crontab file in editor where job can be added/updated.

# crontab -e

By default it will edit crontab entries of current logged in user. To edit other user crontab use command as below

# crontab -u username -e

Change EDITOR environment variable to change your default editor.

How to List Crontab

To view crontab entries of current user use following command . # crontab -l

To view crontab entries of other user use following command . # crontab -u username –l

20 Useful Crontab Examples:

1. Schedule a cron to execute at 2am daily.

This will be useful for scheduling database backup on daily basis. 0 2 * * * /bin/sh backup.sh

2. Schedule a cron to execute twice a day.

Below example command will execute at 5AM and 5PM daily. You can specify multiple time stamp by comma seprated.

0 5,17 * * * /scripts/script.sh

3. Schedule a cron to execute on every minutes.

Generally we don’t require any script to execute on every minutes but in some case you may need to configure it. * * * * * /scripts/script.sh

4. Schedule a cron to execute on every Sunday at 5 PM.

This type of cron are useful for doing weekly tasks, like log rotation etc. 0 17 * * sun /scripts/script.sh

5. Schedule a cron to execute on every 10 minutes.

If you want to run your script on 10 minutes interval, can configure like below. These type of crons are useful for monitoring.

*/10 * * * * /scripts/monitor.sh

*/10: means to on each 10 minutes. Same as if you want to execute on every 5 minutes use */5.

6. Schedule a cron to execute on selected months.

Some times we required to schedule a task to be execute for selected months only. Below example script will run on January, May and August months.

7. Schedule a cron to execute on selected days.

If you required to schedule a task to be execute for selected days only. Below example will run on each Sunday and Friday at 5PM .

0 17 * * sun,fri /script/script.sh

8. Schedule a cron to execute on first sunday of every month.

To schedule a script to execute a script on first sunday only is not possible by time parameter, But we can use condition in command fields to do it.

0 2 * * sun [ $(date +\%d) -le 07 ] && /script/script.sh

9. Schedule a cron to execute on every four hours.

If you want to run script on 4 hours interval. It can be configure like below. 0 */4 * * * /scripts/script.sh

10. Schedule a cron to execute twice on every Sunday and Monday.

To schedule a task to execute twice on Sunday and Monday only. Use following settings to do it. 0 4,17 * * sun,mon /scripts/script.sh

11. Schedule a cron to execute on every 30 Seconds.

To schedule a task to exectue on every 30 seconds is not possible by time parameters, But it can be done by schedule same cron twice like below.

* * * * * /scripts/script.sh

* * * * sleep 30; /scripts/script.sh

12. Schedule a multiple tasks in single cron.

To configure multiple tasks with single cron, Can be done by seprating tasks by semicolon ( ; ). * * * * * /scripts/script.sh; /scripts/scrit2.sh

12. Schedule a multiple tasks in single cron.

To configure multiple tasks with single cron, Can be done by separating tasks by semicolon ( ; ). * * * * /scripts/script.sh; /scripts/scrit2.sh

13. Schedule a tasks to execute on yearly ( @yearly ).

@yearly timestamp is similar to “0 0 1 1 *”. It will execute task on first minute of every year, It may useful to send new year greetings :)

@yearly /scripts/script.sh

14. Schedule a tasks to execute on monthly ( @monthly ).

@monthly timestamp is similar to “0 0 1 * *”. It will execute task on first minute of month. It may useful to do monthly tasks like pay the bills and invoicing to customers.

@monthly /scripts/script.sh

15. Schedule a tasks to execute on Weekly ( @weekly ).

@weekly timestamp is similar to “0 0 1 * *”. It will execute task on first minute of month. It may useful to do weekly tasks like cleanup of system etc.

@weekly /bin/script.sh

16. Schedule a tasks to execute on daily ( @daily ).

@daily timestamp is similar to “0 0 * * *”. It will execute task on first minute of every day, It may useful to do daily tasks.

17. Schedule a tasks to execute on hourly ( @hourly ).

@hourly timestamp is similar to “0 * * * *”. It will execute task on first minute of every hour, It may usefull to do hourly tasks.

@hourly /scripts/script.sh

18. Schedule a tasks to execute on system reboot ( @reboot ).

@reboot is usefull for those tasks which you want to run on your system startup. It will be same as system startup scripts. It is usefull for starting tasks in background automatically.

@reboot /scripts/script.sh

19. Redirect Cron Results to specified email account.

By default cron sends details to current user where cron is scheduled. If you want to redirect it to your other account, can be done by setup MAIL variable like below

# crontab -l MAIL=bob

0 2 * * * /script/backup.sh

20. Taking backup of all crons to plain text file.

I recommend to keep backup of all jobs entry in a file. It this is a way to recover crons if you lost them.

Check current scheduled cron:

# crontab -l MAIL=rahul

# crontab -l MAIL=rahul

0 2 * * * /script/backup.sh

Backup cron to text file:

# crontab -l > cron-backup.txt # cat cron-backup.txt

MAIL=rahul

0 2 * * * /script/backup.sh

Removing current scheduled cron:

# crontab -r # crontab -l

no crontab for root

Restore crons from text file:

# crontab cron-backup.txt # crontab -l

MAIL=rahul

AT

While working on Linux systems we preferred crontab for scheduling jobs generally. There are another utility command is very useful for scheduling one time tasks. It reads commands from standard input or

script/file which can be executed later once. But we can’t use at command for any recurring tasks. For recurring tasks use Linux crontab.

At command can be useful for shutdown system at specified time, Taking one time backup, sending email as reminder at specified time etc. This article will help you to understand the working of at command with useful examples.

Commands used with at:

at : execute commands at specified time. atq : lists the pending jobs of users.

atrm : delete jobs by their job number. 1. Schedule first job using at command

Below example will schedule “ls ­l” command to be executed on next 9:00 AM once. # at 9:00 AM

at> ls ­l at> ^d

job 3 at 2013­03­23 09:00 Use ^d to exit from at prompt.

2. List the scheduled jobs using atq

When we list jobs by root account using atq , it shows all users jobs in result. But if we execute it from non root account, it will show only that users jobs.

# atq

3 2013­03­23 09:00 a root 5 2013­03­23 10:00 a rahul 1 2013­03­23 12:00 a root

Fields description: First filed: job id

Second filed: Job execution date third filed: Job execution time

Last field: User name, under which job is scheduled. 3. Remove scheduled job using atrm

You can remove any at job using atrm using their job id. # atrm 3

# atq

5 2013­03­23 10:00 a rahul 1 2013­03­23 12:00 a root

4. Check the content of scheduled at job

atq command only shows the list of jobs but if you want to check what script/commands are scheduled with that task, below example will help you.

# at ­c 5

In above example 5 is the job id. Examples of at Command:

Example 1: Schedule task at coming 10:00 AM. # at 10:00 AM

Example 2: Schedule task at 10:00 AM on coming Sunday. # at 10:00 AM Sun

Example 3: Schedule task at 10:00 AM on coming 25’th July. # at 10:00 AM July 25

Example 4: Schedule task at 10:00 AM on coming 22’nd June 2015. # at 10:00 AM 6/22/2015

Example 5: Schedule task at 10:00 AM on same date at next month. # at 10:00 AM next month

Example 6: Schedule task at 10:00 AM tomorrow. # at 10:00 AM tomorrow

Example 7: Schedule task at 10:00 AM tomorrow. # at 10:00 AM tomorrow

Example 8: Schedule task to execute just after 1 hour. # at now + 1 hour

Example 9: Schedule task to execute just after 30 minutes. # at now + 30 minutes

Example 10: Schedule task to execute just after 1 and 2 weeks. # at now + 1 week

# at now + 2 weeks

Example 11: Schedule task to execute just after 1 and 2 years. # at now + 1 year

# at now + 2 years

Example 12: Schedule task to execute at mid night. # at midnight

NTP

NTP Server

PORT NUMBER: 123

Definition: In computer networking, NTP is a system to synchronize time

of day computer clocks across the Internet.

a) The NTP system is based on Internet time servers, computers with

access to atomic clocks such as those operated by the U.S.

government. These NTP servers run a software service that provides

the clock's time of day to client computers over

UDP

port 123. NTP

supports a hierarchy of multiple server levels to handle a large load of

client requests.

b) The protocol includes algorithms to accurately adjust the time of day

being reported to account for Internet network transmission delays.

c) Computers running Windows, Mac OS X and Linux operating

systems can be configured to use an NTP server. Starting with Linux

OS, for example, on terminal type “system-config-date” option

contains an NTP server, which allows choosing an NTP server and

turning time synchronization on or off.

NTP CLIENT

USING TEXT METHOD:

# yum install chrony* ­y # vim /etc/chrony.conf

server classroom.example.com iburst # systemctl restart chronyd.service

# firewall­cmd ­­permanent –add­service=ntp # firewall­cmd –reload

# chronyc sources ­v # timedatectl

USING GRAPHICAL METHOD:

Synchronize date and time over the network­­­>click it NTP Servers

­­­> PRESS add and type into box

classroom.example.com[OR]172.25.254.254 ­­­> Give Enter Advanced options

speedup initial synchronization ­­­> Click this& apply

# firewall­cmd ­­permanent –add­service=ntp # firewall­cmd ­­reload

# chronyc sources ­v # timedatectl

LDAP

� LDAP PORT NUMBER: 389

� LDAPS PORT NUMBER: 636

• Global Catalog is available by default on ports 3268, and 3269 for

LDAPS.

• LDAP stands for Lightweight Directory Access Protocol. As the name

suggests, it is a lightweight protocol for accessing directory services,

specifically X.500­based directory services. LDAP runs over TCP/IP or

other connection oriented transfer services.

• What kind of information can be stored in the directory? The LDAP

information model is based on entries. An entry is a collection of

attributes that has a globally­unique Distinguished Name (DN). The DN

is used to refer to the entry unambiguously. Each of the entry's

attributes has a type and one or more values. The types are typically

mnemonic strings, like "cn" for common name, or "mail" for email

address. The syntax of values depend on the attribute type.

LDAP CLIENT

USING GRAPHICAL METHOD:

# yum install sssd* authconfig* autofs* ­y # systemctl enable sssd.service

# systemctl start sssd.service ­­­>sssd is not active now # authconfig­gtk

User account database : LDAP

Ldap Search base DN : dc=example,dc=com

Ldap server : ldaps://classroom.example.com

Use TLS to encrypted connection ­­­>Tick it ­­­>Click Download certicficate

url: http://classroom.example.com/pub/EXAMPLE­CA­CERT Authendication method : LDAP password

# systemctl restart sssd.service

# firewall­cmd ­­permanent –add­service=sssd # firewall­cmd ­­reload

AUTO MOUNT:

# vim /etc/auto.master /misc /etc/auto.misc

/home/guests /etc/auto.misc # vim /etc/auto.misc

ldapuserX ­rw,soft,intr classroom.example.com:/home/guests/ldapuserX # systemctl restart autofs.service

# firewall­cmd ­­permanent –add­service=autofs # firewall­cmd –reload

USING TEXT METHOD:

# authconfig­tui

─────────┤ Authentication Configuration ├─────────────────┐ │

│ User Information Authentication │[ ] Cache Informa�on [*] Use MD5 Passwords │[*] Use LDAP [*] Use Shadow Passwords │[ ] Use NIS [*] Use LDAP Authentication │[ ] Use IPAv2 [ ] Use Kerberos

│[ ] Use Winbind [ ] Use Fingerprint reader │[ ] Use Winbind Authentication [*] Local authorization is sufficient │ │ ┌────────┐ ┌──────┐ │ │ Cancel │ │ Next │ │ └────────┘ └──────┘ │ ­­­>PRESS NEXT

│

[*] Use TLS

│

│

Server: ldaps://classroom.example.com

│

│

Base DN: dc=example,dc=com

│

­­­> PRESS OK

­­­> PRESS OK

# cd /etc/openldap/cacerts/

# wget http://172.25.254.100/pub/EXAMPLE­CA­CERT

# systemctl restart sssd.service

# firewall­cmd ­­permanent –add­service=sssd

# firewall­cmd –reload

AUTO MOUNT:

# vim /etc/auto.master /misc /etc/auto.misc

/home/guests /etc/auto.misc # vim /etc/auto.misc

ldapuserX ­rw,soft,intr classroom.example.com:/home/guests/ldapuserX # systemctl restart autofs.service

# firewall­cmd ­­permanent –add­service=autofs # firewall­cmd –reload

Virtualization

• Virtualization is the creation of a virtual (rather than actual) version of

something, such as an operating

, a server, a storage device or network

resources.

• Why should we use virtualization

• Consolidation ­ It means combining multiple software workloads on one

computer system. You can run various virtual machines in order to save

money and power (electricity).

• Testing ­ You can test various configuration. You can create less resource

hungry and low priority virtual machines (VM). Often, I test new Linux

distro inside VM. This is also good for students who wish to learn new

operating systems and programming languages / database without making

any changes to working environment. At my work place I give developers

virtual test machines for testing and debugging their software.

• Security and Isolation ­ If mail server or any other app gets cracked, only

that VM will be under control of the attacker. Also, isolation means

open Source Linux Virtualization Software

1. Openvz

2. Xen

3. Kernel­based Virtual Machine (KVM)

4. Linux­Vserver

5. VirtualBox

6. Bochs

7. User Mode Linux (UML)

Proprietary Linux Virtualization Software

1. VMware ESX Server and VMWare Server

2. Citrix XenServer, Oracle VM, Sun xVM

3. Parallels Virtuozzo Containers

Kernel­Based

Virtual Machine (KVM)

• A kernel­based virtual machine (KVM) is a virtualization infrastructure built for Linux OS and designed to operate on x86­based processor architecture.

KVM is developed by Red Hat Corporation to provide a virtualization solution and services on the Linux operating system platform. KVM is designed over the primary Linux OS kernel.

• Explains Kernel­Based Virtual Machine (KVM)

• KVM is a type of hypervisor that enables, emulates and provides for the creation of virtual machines on operating systems. These machines are built on top of the Linux kernel, using operating systems such as Linux, Ubuntu and Fedora. KVM can be installed on all x86 processors and provide separate instruction set extensions for Intel and AMD processors.

KVM supports multiple different guest operating system images including Linux Kernel, Windows, BSD and Solaris. It also allocates separate virtualized computing resources for each virtual machine such as the processor, storage, memory, etc.

KVM Bridge Setup

Bridging requires the bridge­utils package to be installed on the server. To check if it's installed, do the following:

#rpm ­q bridge­utils

If you get an output ­ it's installed, if not, it needs installing: #yum install bridge­utils

Before setting up your bridge, the contents of /etc/sysconfig/network­scripts/ifcfg­eth0 will look like the following: DEVICE=eth0 TYPE=ETHERNET NAME=“System eth0” BOOTPROTO=static HWADDR=00:27:0E:09:0C:B2 IPADDR=192.168.0.254 NETMASK=255.255.255.0 ONBOOT=yes

To back up your current ifcfg­eth0 before modification: 1. Run the following command:

#cp /etc/sysconfig/network­scripts/ifcfg­eth0 /etc/sysconfig/network­scripts/backup­ ifcfg­eth0

2.Create the bridge file:

#vim /etc/sysconfig/network­scripts/ifcfg­br0 3. Copy parts of ifcfg­eth0 to it:

DEVICE=br0 TYPE=Bridge BOOTPROTO=static BROADCAST=192.168.0.255 IPADDR=192.168.0.254 NETMASK=255.255.255.0 ONBOOT=yes

4. Save that file and edit ifcfg­eth0:

#vim /etc/sysconfig/network­scripts/ifcfg­eth0

5. Remove the networking parts and specify the bridge: DEVICE=eth0

HWADDR=00:27:0E:09:0C:B2 ONBOOT=yes

BRIDGE=br0

6. Bridge is setup. Make sure that the changes are correct and restart the networking: #/etc/init.d/network restart

7. Once it's restarted you see the new bridge using the ifconfig command: # ifconfig

To check whether your CPU supports the hardware virtualization, execute the following command.

# egrep '(vmx|svm)' /proc/cpuinfo

Install KVM packages using your distro specific package management tool (for example, yum on RedHat and CentOS).

# yum install kvm

Once you install the main kvm package, install the following KVM related packages that will help you to manage the VMs on your system.

# yum install qemu­kvm python­virtinst libvirt libvirt­python virt­manager libguestfs­ tools

virt­install tool is used to create the VM. This tool can be used in both interactive or non­interactive mode.

In the following example, I passed all the required values to create an VM as

command line parameters to the virt­install command.

# virt­install \

­n myRHELVM1 \

­­description "Test VM with RHEL 6" \

­­os­type=Linux \

­­os­variant=rhel6 \

­­ram=2048 \

­­vcpus=2 \

­­disk path=/var/lib/libvirt/images/myRHELVM1.img,bus=virtio,size=10 \

­­graphics none \

­­cdrom /var/rhel­server­6.5­x86_64­dvd.iso (or) ­­

location=http://.com/pub/rhel6/x86_64/ \

In the above virt-install command:

• n Name of your virtual machine

• description Some valid description about your VM. For example: Application server, database

server, web server, etc.

• os-type OS type can be Linux, Solaris, Unix or Windows.

• os-variant Distribution type for the above os­type. For example, for linux, it can be rhel6, centos6,

ubuntu14, suse11, fedora6 , etc. For windows, this can be win2k, win2k8, win8, win7 • ram Memory for the VM in MB

• vcpu Total number of virtual CPUs for the VM.

• disk path=/var/lib/libvirt/images/myRHELVM1.img,bus=virtio,size=10 Path where the VM image

files is stored. Size in GB. In this example, this VM image file is 10GB.

• graphics none This instructs virt­install to use a text console on VM serial port instead of graphical

VNC window. If you have the xmanager set up, then you can ignore this parameter.

• cdrom Indicates the location of installation image. You can specify the NFS or http installation

location (instaed of –cdrom). For example, –location=http://.com/pub/rhel6/x86_64/

• network bridge:br0 This example uses bridged adapter br0. It is also possible to create your own

network on any specific port instead of bridged adapter. If you want to use the NAT then use something like below for the network parameter with the virtual network name known as

VMnetwork1. All the network configuration files are located under /etc/libvirt/qemu/networks/ for the virtual machines. For example: –network network=VMnetwork1

KVM Migrations

Creating a Copy of the Virtual Server

• To find the correct LV that needs being backed up, you can use lvdisplay in

SSH on the source node:

# lvdisplay

• Shut­down the source VPS either using SolusVM or the command line:

• #virsh shutdown <servername>

Create the backup:

• #dd if=/dev/vps/kvm101_img | gzip | dd of=/home/kvm101_backup.gz

bs=4096

Transfer to the Destination Node

• On the destination node we need to create a logical volume the same size

as the original one:

#lvcreate ­n kvm101_img ­­size 10G /dev/vps

Transfer the backup to the destination server:

Restoring the Virtual Server

• Once you have transferred the backup of your VPS to the

destination server you can restore the backup to the new

LV:

#dd if=/home/kvm101_backup.gz | gzip ­d | dd

of=/dev/vps/kvm101_img bs=4096

VNC

Virtual Network Computing

VNC by default uses TCP port 5900+N, where N is

the display number (usually :0 for a physical

display). Several implementations also start a

basic HTTP server on port 5800+N to provide a

VNC viewer as a Java applet, allowing easy

connection through any Java­enabled web

browser.