The virsh command is an alternative command to manage a Red Hat Enterprise Linux 5 KVM environment using a Command Line Interface(CLI). The virsh command is provided as part of the libvirt API which provides a common API to applications requiring standardized access to interact with KVM using a stable interface.

The following are basic and commonly used virsh commands:

help	 print help
list	 list domains
create	 create a domain from an XML file
start	 start a previously created inactive domain
destroy	 destroy a domain
define	 define (but do not start) a domain from an XML file
domid	 convert a domain name or UUID to domain id
domuuid	 convert a domain name or id to domain UUID
dominfo	 domain information
domname	 convert a domain id or UUID to domain name
domstate domain state
quit	 quit this interactive terminal
reboot	 reboot a domain
restore	 restore a domain from a saved state in a file
resume	 resume a domain
save	 save a domain state to a file
shutdown gracefully shutdown a domain
suspend	 suspend a domain
undefine undefine an inactive domain

List running guest VMs

Type the following command:

# virsh list

Sample outputs:

Id  Name                 State
----------------------------------
1   VM01                 running
2   VM02	         running

Staring a guest VM

Type the following command:

# virsh start VM01

Shutddowwn a guest VM

Type the following command:

# virsh shutdown VM01

Or, you can forcefully stop a guest VM with following command:

# virsh destroy VM01

Rebooting a guest VM

Type the following command:

# virsh reboot VM01

The post How To Start / Shutdown / Reboot Guest Operating Systems With virsh Command On KVM appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

#!/bin/bash
# Under RedHat / Centos

if [ $# -gt 0 ]
then
	MIN=$1
else
	MIN=8
fi

DEL=`expr $RANDOM % 5`
LEN=`expr $MIN + $DEL`
cat /dev/urandom | tr -dc "a-zA-Z0-9@#*=[]" | dd  bs=$LEN count=1 2>/dev/null
echo;

The post Linux Random Password Generator With Bash Script appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

#!/bin/sh
# A simple shell to build a Firewall anti SYN Flood
# Under CentOS, Fedora and RHEL / Redhat Enterprise Linux
# servers.
# ----------------------------------------------------------------------------
# Written by LongVNIT 
# (c) 2009 lifeLinux under GNU GPL v2.0+

IPT="iptables"
MODPROBE="modprobe"
IF="eth0"
IP="192.168.1.112"
PORT="22 80 443"
CHECK_TIME=60
BAN_TIME=120
HITCOUNT=10
MOD="ip_tables ip_conntrack iptable_filter ipt_state"

# Load Module
for M in $MOD
do
	$MODPROBE $M
done

# Flush IPTables
$IPT -F
$IPT -X
$IPT -P INPUT DROP
$IPT -P OUTPUT ACCEPT
$IPT -P FORWARD DROP

# Define SYN_CHECK CHAIN
$IPT -N SYN_CHECK

# BAN IP IN 
$IPT -t mangle -A PREROUTING -p TCP -d $IP -m recent --name SYN --update --seconds $BAN_TIME --hitcount $HITCOUNT -j DROP

# DROP INVALID PACKET
$IPT -A INPUT -p TCP ! --syn -m state --state NEW -j DROP

# ACCPET ALL ESTABLISHED PACKET
$IPT -A INPUT -i $IF -m state --state ESTABLISHED -j ACCEPT

# CHECK SYN
for P in $PORT
do
	$IPT -A INPUT -i $IF -p TCP -d $IP --dport $P -m state --state NEW -j SYN_CHECK
done

# ACCEPT
for P in $PORT
do
	$IPT -A INPUT -i $IF -p TCP -d $IP --dport $P -m state --state NEW -j ACCEPT
done

# SYN_CHECK CHAIN
$IPT -A SYN_CHECK -m recent --set --name SYN
$IPT -A SYN_CHECK -m recent --name SYN --update --seconds $CHECK_TIME --hitcount $HITCOUNT -j LOG --log-level 5 --log-prefix "SYN_FLOOD"
$IPT -A SYN_CHECK -m recent --name SYN --update --seconds $CHECK_TIME --hitcount $HITCOUNT -j DROP

The post Anti SYN Flood with IPTables appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

configure: error: xml2-config not found. Please check your libxml2 installation.

yum install libxml2-devel.x86_64

configure: error: Cannot find OpenSSL’s

yum install openssl-devel.x86_64

configure: error: Could not find pcre.h in /usr/local

yum install pcre-devel.x86_64

configure: error: Could not find pcre.h in /usr/local

"--with-pcre-regex=/usr/include" \

configure: error: Could not find libpcre.(a|so) in /usr/include

"--with-pcre-regex=/usr" \

configure: error: Please reinstall the libcurl distribution –
easy.h should be in /include/curl/

yum install curl-devel.x86_64

configure: error: libjpeg.(a|so) not found.

yum install libjpeg-devel.x86_64

configure: error: libpng.(a|so) not found.

yum install libpng-devel.x86_64

configure: error: freetype.h not found.

yum install freetype-devel.x86_64

configure: error: Please reinstall the iconv library.

"--with-iconv" \

configure: error: mcrypt.h not found. Please reinstall libmcrypt.

yum install libmcrypt.x86_64 libmcrypt-devel.x86_64

configure: error: Please reinstall libmhash – I cannot find mhash.h

yum install mhash.x86_64 mhash-devel.x86_64

Note that the MySQL client library is not bundled anymore!

yum install php-mysql.x86_64 mysql-devel.x86_64

configure: error: Please reinstall the BZip2 distribution

yum install bzip2-devel.x86_64

configure: error: utf8_mime2text() has new signature, but U8T_CANONICAL is missing. This should not happen. Check config.log for additional information.
DISABLE IMAP
configure: error: Cannot find pspell

yum install aspell-devel.x86_64

configure: error: Cannot find libtidy

yum install libtidy.x86_64 libtidy-devel.x86_64

error: xslt-config not found. Please reinstall the libxslt >= 1.1.0 distribution

yum install libxslt.x86_64 libxslt-devel.x86_64

collect2: ld returned 1 exit status

yum install glibc-utils.x86_64 libtool-ltdl-devel.x86_64

Step by step to guide PHP Compile

Step 1: Update & Install Development Tools & Libraries

yum update
yum group install "Development Tools"
yum group install "Development Libraries"

Step 2: Run the bellow bash script

#!/bin/sh
"./configure" \
"--prefix=/usr/local/php5" \
"--enable-force-cgi-redirect" \
"--enable-fastcgi" \
"--with-bz2" \
"--with-config-file-path=/usr/local/etc" \
"--with-config-file-scan-dir=/usr/local/etc/php.d" \
"--with-curl=/usr/local/lib" \
"--with-gd" \
"--with-gettext" \
"--with-jpeg-dir=/usr/local/lib" \
"--with-freetype-dir=/usr/local/lib" \
"--with-kerberos" \
"--with-mcrypt" \
"--with-mhash" \
"--with-mime-magic" \
"--with-mysql" \
"--with-mysqli" \
"--with-pcre-regex=/usr" \
"--with-pdo-mysql=shared" \
"--with-pdo-sqlite=shared" \
"--with-pear=/usr/local/lib/php" \
"--with-png-dir=/usr/local/lib" \
"--with-pspell" \
"--with-sqlite=shared" \
"--with-tidy" \
"--with-ttf" \
"--with-xmlrpc" \
"--with-xsl" \
"--with-zlib" \
"--with-zlib-dir=/usr/local/lib" \
"--with-openssl" \
"--with-iconv" \
"--with-libdir=lib64" \
"--enable-bcmath" \
"--enable-calendar" \
"--enable-exif" \
"--enable-ftp" \
"--enable-gd-native-ttf" \
"--enable-libxml" \
"--enable-magic-quotes" \
"--enable-soap" \
"--enable-sockets" \
"--enable-mbstring" \
"--enable-zip" \
"--enable-wddx"

The post Error compiling PHP on CentOS x64 appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

Load balancing helps provide redundancy to your website. However, one often asked question is how to keep your content synchronized on each server. If you put a new web page on one server, how does it get copied over to the second server? In this article, i’ll explain how to use rsync command to synchronize data between a specific directory on each server.

Install rsync

On Centos Linux type the following command:

yum install rsync

Using rsync command with password authentication

For example, i have two servers using for load balanced and called server1(192.168.1.101) and server2(192.168.1.102). I wanted to keep data in /var/www/html sync between to servers. Type the following command on server1:

rsync -avr --progress --links --rsh='/usr/bin/ssh' 192.168.1.102:/var/www/html /var/www/html

With:
-avr : archive mode (a), verbose (v), recurse into directories (r).
–progress: Show progress.
–links: copy symlinks as symlinks.
–rsh: use to specify the remote shell ssh to use.
192.168.1.102:/var/www/html: IP address of server2 and path to synchronize to server1
/var/www/html: Server1 path

Using rsync command with SSH certificate

Replace above command with following command:

rsync -avr --progress --links --rsh='/usr/bin/ssh -i /path_to_private_key' 192.168.1.102:/var/www/html /var/www/html

A sample shell script

#!/bin/bash
SOURCEPATH='source'
DESTPATH='destination'
SOURCEHOST='ip_address'
PRIVATEKEY='private_key'
LOGFILE='log_file'
SSH='/usr/bin/ssh'
rsync -avr --progress --links --rsh="'$SSH -i $PRIVATEKEY'" $SOURCEHOST:$SOURCEPATH $DESTPATH 2>&1 >> $LOGFILE

The post How To Keep Data Sync’d Between Two Load Balanced Servers appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

To check avilable memory in Linux type free -m command. free displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel.

free -m
free -h
free -b

Output:

             total       used       free     shared    buffers     cached
Mem:          2025       1961         64          0        172       1035
-/  buffers/cache:        753       1272
Swap:         1906          0       1906

1. The -b switch displays the amount of memory in bytes
2. The -k switch (set by default) displays it in kilobytes
3. The -m switch displays it in megabytes
4. The -g switch displays it in gigabytes.

vmstat

Output:

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 0  0      0  63316 176624 1062340    0    0    25    18   39  592  5  1 94  0

1. swpd: the amount of virtual memory used.
2. free: the amount of idle memory.
3. buff: the amount of memory used as buffers.
4. cache: the amount of memory used as cache.

The post Check Available Memory On Linux appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

The yum command is used to install and update software under Centos, RedHat and Fedora. In this topic, i will use yum command to update Centos and configure yum to update automatically with Crontab.

Create file yum_update.sh

vi /etc/cron.daily/yum_update.sh

With following content :

#!/bin/bash

/usr/bin/yum -y -R 120 -d 0 -e 0 update yum

/usr/bin/yum -y -R 10 -e 0 -d 0 update

-e 0 -d 0 are to only show critical errors.
-R adds random delay between command execution.

Make it executable

chmod 755 /etc/cron.daily/yum_update.sh

The post Auto Update CentOS Server With yum Command appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

The find utility on linux allows you to pass in a bunch of interesting arguments, including one to execute another command on each file. We’ll use this in order to figure out what files are older than a certain number of days, and then use the rm command to delete them.

Command Syntax:

find /path/to/files* -mtime  x -exec rm {} ;

Note that there are spaces between rm, {}, and ;

Example:

find /path/to/files* -mtime +7 -exec rm {} ;

Explanation:

• The first argument is the path to the files. This can be a path, a directory, or a wildcard as in the example above. I would recommend using the full path, and make sure that you run the command without the exec rm to make sure you are getting the right results.
• The second argument, -mtime, is used to specify the number of days old that the file is. If you enter +7, it will find files older than 7 days.
• The third argument, -exec, allows you to pass in a command such as rm. The {} ; at the end is required to end the command.

This should work on Ubuntu, Suse, Redhat, CentOS or pretty much any version of linux.

More:

If you happen to get an error:

/usr/bin/find argument list too long

You try again with the following command:

find /path/to/files* -type f -mtime +7 -print 0 | xargs -0 -rm

The post Delete Files Older Than x Days appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.