RAR stands for Roshal ARchive. It is a proprietary archive file format that supports data compression, error recovery, and file spanning. It was developed by a Russian software engineer, Eugene Roshal (the first letter of his surname contributing to the name of the archive format), and is currently licensed by win.rar GmbH.

The filename extension used by RAR is .rar for the data volume set and .rev for the recovery volume set. In previous versions, if a RAR-archive was broken into many smaller files (a “multi-volume archive”), then the smaller files used the extensions .rar, .r00, .r01, .r02 etc.

Install unrar command

To extract RAR files under Linux system, you need to install unrar command. There are some ways to install unrar command. Under Ubuntu/Debian Linux, type the following command

# apt-get install unrar

If you are using Fedora core Linux then type the following command

# yum install unrar

If any of above, methods is not working, download binary package from official rarlab site, enter

# wget http://www.rarlab.com/rar/rarlinux-4.0.1b1.tar.gz

To Extract rarlinux-4.0.1b1.tar.gz, type the following command

# tar zxvf rarlinux-4.0.1b1.tar.gz

Sample output

rar/
rar/readme.txt
rar/default.sfx
rar/whatsnew.txt
rar/license.txt
rar/order.htm
rar/rar
rar/unrar
rar/rar_static
rar/technote.txt
rar/rarfiles.lst
rar/makefile
rar/rar.txt

Now copy rar and unrar commands to /bin directory, type the following command

# cd rar
# cp rar unrar /bin

How to use unrar

To extract rar file in current directory, type the following command

$ unrar e file.rar

To list file inside rar archive, type the following command

$ unrar l file.rar

To extract file with full path, type the following command

$ unrar x file.rar

To test integrity of archive file, type the following command

$ unrar t file.rar

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You can apply kernel updates using “yum” command or “apt-get” command line options. After each upgrade you need to reboot the server. How to skip reboot step and apply hotfixes to kernel without rebooting the server ?

What is Ksplice Uptrack?

Ksplice Uptrack is a subscription service that lets you apply 100% of the important kernel security updates released by your Linux vendor without rebooting.

Install Ksplice

First, you’ll need an access key. If you don’t have one, request a free trial.
Download the Ksplice Uptrack repository installation RPM package

[root@lifelinux ~]# wget https://www.ksplice.com/yum/uptrack/centos/ksplice-uptrack-release.noarch.rpm

To install, type the following command as root

[root@lifelinux ~]# rpm -ivh ksplice-uptrack-release.noarch.rpm
[root@lifelinux ~]# yum -y install uptrack

Edit /etc/uptrack/uptrack.conf, enter

[root@lifelinux ~]# vi /etc/uptrack/uptrack.conf

Sample outputs

[Auth]
accesskey = [ACCESS KEY HERE]

[Network]
# Proxy to use when accessing the Uptrack server, of the form
# [protocol://][:port]

# The proxy must support making HTTPS connections. If this is unset,
# Uptrack will look for the https_proxy, HTTPS_PROXY, and http_proxy
# environment variables in that order, and then finally look for a
# proxy setting in the system-wide GConf database, if available.
https_proxy =

[Settings]
# Automatically install updates at boot time. If this is set, on
# reboot into the same kernel, Uptrack will re-install the same set of
# updates that were present before the reboot.
install_on_reboot = yes

# Options configuring the Uptrack cron job.
#
# GUI users will get all notices via the GUI and likely want to set
# the following cron options to "no".

# Cron job will install updates automatically
autoinstall = no

# Cron job will print a message when new updates are installed.
# This option is only relevant if autoinstall = yes
cron_output_install = no

# Cron job will print a message when new updates are available
cron_output_available = no

# Cron job will print a message when it encounters errors
cron_output_error = no

Insert your access key. Please use the same access key for all of your systems. If you would like Uptrack to automatically install rebootless kernel updates as they become available, set autoinstall = yes.

When you are done with your Uptrack configuration, please run the following command as root to bring your kernel up to date:

uptrack-upgrade -y

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What is Ksplice Uptrack?

Ksplice Uptrack is a subscription service that lets you apply 100% of the important kernel security updates released by your Linux vendor without rebooting.

Update Linux Kernel With Ksplice Uptrack

Ksplice updates are the same security and bugfix updates you would get from your Linux vendor, packaged in a special rebootless form. Type the following to apply updates (note it may take a few hours to get ksplice update as they upgrade their system after RHN releases kernel upgrades):

[root@lifelinux ~]# uptrack-upgrade

The post How To Update Linux Kernel With Ksplice Uptrack appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

rpm is a powerful Package Manager, which can be used to build, install, query, verify, update, and erase individual software packages. A package consists of an archive of files and meta-data used to install and erase the archive files. The meta-data includes helper scripts, file attributes, and descriptive information about the package. Packages come in two varieties: binary packages, used to encapsulate software to be installed, and source packages, containing the source code and recipe necessary to produce binary packages.

Install RPM File

To install an rpm file, open a terminal and then type the following command:

[root@server2 ~]# rpm -ivh file.rpm

Note:
-i: Installs a new package
-v: Print verbose information – normally routine progress messages will be displayed.
-h: Print 50 hash marks as the package archive is unpacked. Use with -v|–verbose for a nicer display.

Upgrade RPM File

[root@server2 ~]# rpm -Uvh file.rpm

Note:
-U: Upgrades or installs the package currently installed to a newer version. This is the same as install, except all other version(s) of the package are removed after the new package is installed.

Erase RPM File

[root@server2 ~]# rpm -ev ile.rpm

Note:
-e: Erase command
The following options may also be used:

--nodeps

Don’t check dependencies before uninstalling the packages.

List of all install packages

Type the following command:

[root@server2 ~]# rpm -qa 

Sample outputs:

...
libxslt-devel-1.1.17-2.el5_2.2
perl-libwww-perl-5.805-1.1.1
libc-client-devel-2004g-2.2.1
libidn-devel-0.6.5-1.1
libjpeg-devel-6b-37
gmp-devel-4.1.4-10.el5
libmcrypt-devel-2.5.8-4.el5.centos
libtidy-0.99.0-12.20070228.el5.centos
libtool-ltdl-1.5.22-7.el5_4
gpg-pubkey-1aa78495-3eb24301
openssl-0.9.8e-12.el5_5.7
NetworkManager-glib-0.7.0-10.el5_5.2
perl-XML-NamespaceSupport-1.09-1.2.1
perl-XML-Filter-BufferText-1.01-1.2.el5.rf
perl-XML-Simple-2.14-4.fc6
rsnapshot-1.3.1-1.el5.rf

List the files and state the installed version of the package called package. Example

[root@server2 ~]# rpm -ql mysql-5.0.77-4.el5_5.5

Sample outputs:

/etc/ld.so.conf.d/mysql-i386.conf
/etc/my.cnf
/usr/bin/msql2mysql
/usr/bin/my_print_defaults
/usr/bin/mysql
/usr/bin/mysql_config
/usr/bin/mysql_find_rows
/usr/bin/mysql_tableinfo
/usr/bin/mysql_waitpid
/usr/bin/mysqlaccess
/usr/bin/mysqladmin
/usr/bin/mysqlbinlog
/usr/bin/mysqlcheck
/usr/bin/mysqldump
/usr/bin/mysqlimport
/usr/bin/mysqlshow
/usr/lib/mysql

Read the man page

[root@server2 ~]# man rpm

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yum is an interactive, automated update program which can be used for maintaining systems using rpm.

Synopsis

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

The following is a list of the most commonly used yum commands:

Install a package

yum install [package name]

Used to install the latest version of a package or group of packages. If no package matches the specified package name(s), they are assumed to be a shell glob, and any matches are then installed.

Update the specified packages

yum update [package name]

Used to update the specified packages to the latest available version. If no package name/s are specified, then yum will attempt to update all installed packages.

Check update

yum check-update

This command allows you to determine whether any updates are available for your installed packages. yum returns a list of all package updates from all repositories if any are available.

Remove a package

yum remove [package name]

Used to remove specified packages, along with any other packages dependent on the packages being removed.

Determine which packages provide a specific file or feature

yum provides [file name]

Find any packages containing the specified keyword

yum search [keyword]

This command is used to find any packages containing the specified keyword in the description, summary, packager and package name fields of RPMs in all repositories.

For a complete list of available yum commands, refer to man yum.

man yum

Sample outputs:

NAME
       yum - Yellowdog Updater Modified

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

DESCRIPTION
       yum  is an interactive, rpm based, package manager. It can automatically perform system updates, including dependency analysis and obsolete pro-
       cessing based on "repository" metadata. It can also perform installation of new packages, removal of old packages and  perform  queries  on  the
       installed  and/or  available  packages  among many other commands/services (see below). yum is similar to other high level package managers like
       apt-get and smart.

       While there are some graphical interfaces directly to the yum code, more recent graphical interface development is happening with PackageKit and
       the gnome-packagekit application.

       command is one of:
        * install package1 [package2] [...]
        * update [package1] [package2] [...]
        * check-update
        * upgrade [package1] [package2] [...]
        * remove | erase package1 [package2] [...]
        * list [...]
        * info [...]
        * provides | whatprovides feature1 [feature2] [...]
        * clean [ packages | headers | metadata | dbcache | all ]
        * makecache
        * groupinstall group1 [group2] [...]
        * groupupdate group1 [group2] [...]
        * grouplist [hidden] [groupwildcard] [...]
        * groupremove group1 [group2] [...]
        * groupinfo group1 [...]
        * search string1 [string2] [...]
        * shell [filename]
        * resolvedep dep1 [dep2] [...]
        * localinstall rpmfile1 [rpmfile2] [...]
        * localupdate rpmfile1 [rpmfile2] [...]
...

Example: Install LAMP with single command by yum

Enter the following command:

yum install httpd mysql mysql-server php 

The post Using yum command on CentOS / RedHat appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

iptables is a user space application program that allows a system administrator to configure the tables provided by the Linux kernel firewall (implemented as different Netfilter modules) and the chains and rules it stores. Different kernel modules and programs are currently used for different protocols; iptables applies to IPv4, ip6tables to IPv6, arptables to ARP, and ebtables for Ethernet frames.
Iptables requires elevated privileges to operate and must be executed by user root, otherwise it fails to function. On most Linux systems, iptables is installed as /usr/sbin/iptables and documented in its man page,[2] which can be opened using man iptables when installed. It may also be found in /sbin/iptables, but since iptables is not an “essential binary”, but more like a service, the preferred location remains /usr/sbin.
iptables is also commonly used to inclusively refer to the kernel-level components. x_tables is the name of the kernel module carrying the shared code portion used by all four modules that also provides the API used for extensions; subsequently, Xtables is more or less used to refer to the entire firewall (v4,v6,arp,eb) architecture.
Source: http://en.wikipedia.org/wiki/Iptables

In most Linux distros including Redhat / CentOS Linux installs iptables by default. You can use the following procedure to verify that iptables has been installed. Open terminal and type the following command:

root@longvnit:~# iptables -V

Sample outputs:

iptables v1.3.5

You can use the following command to view the status of iptables command, enter:

root@longvnit:~#yum info iptables

Sample outputs:

Installed Packages
Name       : iptables
Arch       : i386
Version    : 1.3.5
Release    : 5.3.el5_4.1
Size       : 552 k
Repo       : installed
Summary    : Tools for managing Linux kernel packet filtering capabilities.
URL        : http://www.netfilter.org/
License    : GPL
Description: The iptables utility controls the network packet filtering code in
           : the Linux kernel. If you need to set up firewalls and/or IP
           : masquerading, you should install this package.

If the above message does not appear, then type the following command to install iptables

root@longvnit:~#yum install iptables

You can use the following command to view rules in all chains:

root@longvnit:~#iptables -L -n

Sample outputs:

Chain INPUT (policy DROP)
target     prot opt source               destination         
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED 
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

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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

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