Month: August 2019

The Network Time Protocol (NTP) defines a set of algorithms for the dissemination of time across the Internet. The NTP protocol can be used to synchronise the system time on your Linux Server with a highly accurate Internet time reference.

This article describes how to configure the Network Time Protocol (NTP) daemon on your Linux server to synchronise with an Internet based NTP server. It also provides a list of well-know public Internet time references.

Obtaining the NTP Source Code Distribution

The Linux NTP source code distribution is publicly available open source’ software. The distribution can be freely downloaded from the NTP web site ntp.org’. The latest NTP version for Linux is 2.4.2. A port is also available for Windows platforms, but the primary development platform for NTP is the Linux operating system. A number of Linux based operating systems such as Mandrake and Redhat offer NTP as an installable RPM package.

Once download is complete, the NTP distribution should be configured and compiled on the host computer.

Configuration of the NTP Daemon

The NTP daemon is configured through entries in the primary NTP configuration file ntp.conf’. The NTP configuration file contains a list of commands that instruct the daemon to synchronise with a specified NTP server. NTP servers are specified using the server’ command followed by the domain name of the server thus:

server ntp2c.mcc.ac.uk
server ntp.cis.strath.ac.uk

A number of access control options are also available to restrict the use of your NTP server by network time clients. To only allow machines on your own network to synchronize with the server use:

restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap

Alternatively, you can restrict all access to your NTP server with the following command:

restrict default ignore

Multiple directives can be specified to restrict access to a specified range of computers.

Using NTP Authentication

NTP authentication is used by time clients to authenticate the time server to prevent rogue server intervention. NTP authentication is based on encrypted keys. A key is encrypted and sent to the client by the server, where it is unencrypted and checked against the client key to ensure a match.

NTP keys are stored in the ntp.keys’ file in the following format:

Key-number M Key (The M stands for MD5 encryption), e.g.:

1 M secret
5 M RaBBit
7 M TiMeLy
10 M MYKEY

The NTP configuration file ntp.conf’ specifies which of the keys are trusted. Any keys specified in the keys file but not trusted will not be used for authentication, e.g.:

trustedkey 1 7 10

NTP Client Authentication Configuration

The NTP client also needs to be configured with similar authentication information as the server. The client may use a subset of the keys specified on the server. A different subset of keys can also be used on different clients, e.g.:

Client A) Client B)
1 M secret 1 M secret
7 M TiMeLy 5 M RaBBit

trustedkey 1 7 trustedkey 1

Controlling the NTP Server Daemon

Once configured, the NTP daemon can be controlled using the commands: ntpd start’; ntpd stop’ and ntpd restart’.

Querying the NTP Server Daemon

The NTP server daemon can be queried using the ntpq p’ command. The ntpq command queries the NTP server for synchronisation status and provides a list of servers with synchronisation information for each server.

Public Internet NTP Servers

Public NTP servers provide subscription free, highly accurate, timing references for computer time synchronisation. Below is a list of popular public NTP time servers.

Stratum 1 Public NTP Servers
chronos.csr.net – 194.35.252.7 – Computing Systems Research Ltd. United Kingdom – NTP V4 primary (Odetics GPS), Sun/Sparc Solaris 2.6
ntp.my-inbox.co.uk – 81.168.77.149 – Falmouth, Cornwall, UK – NTP V4.2.0 primary (MSF Radio Clock Receiver), Trustix Linux

Stratum 2 Public NTP Servers
ntp2.sandvika.net – 194.164.127.6 – Telehouse Europe, London E14 – NTP V4 secondary Sun UltraSPARC Solaris 8
ntp2d.mcc.ac.uk – 130.88.203.12 – University of Manchester, Manchester, England – NTP secondary (S2), SGI/Irix
ntp2c.mcc.ac.uk – 130.88.200.4 – University of Manchester, Manchester, England – NTP secondary (S2), PC/FreeBSD
ntp.exnet.com – 194.207.34.9 – ExNet Ltd, London, UK – NTP secondary (stratum 2), Sun-4/Unix
audaxsystems.co.uk – 193.201.200.83 – Interhouse London E14 – NTP V4, SuSE 9.0 (Stratum 1)
ntp1.sandvika.net – 194.164.127.5 – Telehouse Europe, London E14 – NTP V4 secondary Sun UltraSPARC Solaris 8
ntp.cis.strath.ac.uk – University of Strathclyde, Glasgow, Scotland – NTP V4 secondary
ntp0.sandvika.net – 194.164.127.4 – Telehouse Europe, London E14 – NTP V4 secondary Sun UltraSPARC Solaris 8

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Linux

Linux is an open source operating system based on the model of UNIX operating system. Linux is a leading server operating system. It can be installed in a wide range of computer hardware’s, mobile phones, video game consoles to mainframe and super computers. Linux is very cheap when compared to windows. In the case of web hosting servers Linux is an obvious preference due to its stability and durable approach.

Linux Server Hosting

Before hiring a company for hosting service, there is an important thing that you need to consider. The scripting language used in your website is the first thing that you need to consider. If your website is using languages like PHP, MySQL or Pearl, you must go for Linux server hosting. Linux Hosting India offers web hosting on Linux platform. Linux is basically an open source software product and thus is not bound by any high licensing fees. Thus it can be freely downloaded from the website.

Linux server can be easily converted into a windows server. But the same cannot be said about windows as it is very complicated. Linux is an operating system which is very much adaptive and flexible. Businesses run in a vibrant environment and many changes has to be made time and again. Linux is modifiable. You can make changes according to your requirements. The programmers and expert staff of Linux Hosting India provide state of the art service in web hosting.

One of the plus points of Linux server is that it is capable of handling large volumes of traffic to the website. It is also capable of hosting multiple sites. With Linux Hosting India customization can be done in real time. Linux works with some of the most popular scripting languages like PHP, MySQL and Pearl. Linux web hosting is the most economical form of hosting your website. The host or owner has to only bear the cost of distribution. Linux hosting is deemed to be the most secure form of web hosting. Linux gives us innumerable advantages when compared to other platforms used for web hosting. It provides compatibility, stability, security and very easy Linux conversion process.

Hosting your website on a Linux sever can be very exciting for several reasons. One of them is the emergence of several Linux server management services. Such services make it simple to manage huge websites since many services are taken care of by the company that is in charge of the server management. The fact that you are backed up by 24×7 server management services gives you the confidence that no website problem will seem too huge for you to handle and hence you can stay in touch with your clients on a regular basis.

The online world is increasing its hold on our lives. Whether it is to know about a restaurant in our neighborhood or a university in another part of the world, we have begun trusting the internet to feed us all information. While all such useful information is present out there, there are also several harmful viruses that make the rounds and hence your website could be vulnerable to threats from such harmful programs. A 24×7 server management system ensures that your website is monitored and all vulnerabilities are checked from time to time to make sure the website is free of threats. The Linux server management system also does its best to strengthen your website so as to reduce the chances of attack by malicious programs.

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It is a fact that Linux server management services have proved to be true blessings to business that aim to catapult to success. Ensure you place you trust in the best 24×7 server management company and you will have nothing stopping you from climbing the stairs of success. You can know more about companies that offer the services and also the prices for each of them through the internet. Compare the quotes and select the services that will benefit your company.

Of all the open source operating systems, LINUX heralded an era of freedom from licensed softwares and signalled the end of the road for monopoly softwares from the giant Microsoft. With the arrival of LINUX and its many versions, users got themselves liberated from the shackles of Windows operating systems and soon found that they could edit and tinker with LINUX to generate new versions of the famous OS. Linux has gained an unexpectedly large amount of interest in the home market over the past two years. This could be due to any number of reasons including, it’s both free and open source, almost all applications are free and open source, the stability is unsurpassed, the code is constantly revised, updated and added to by a numerous amount of programmers across the world. Linux is undisputable a giant in the OS world, with just the name Linux being a symbol of stability and security. With the interest in Linux growing, many new distributions have surfaced offering easy installation and configuration. Well-established distributions such as Redhat are also striving to meet the same goals.

Linux is an operating system and therefore is the basic set of programs and utilities that make the computer run. Some other common operating systems are Unix (and its variants BSD, AIX, Solaris, HPUX, and others); DOS; Microsoft Windows; Amiga; and Mac OS.Linux is Free Software. In a nutshell, software that is free in the sense that Linux is distributed along with its source code so that anyone who receives it is free to make changes and redistribute it. Users are free to make copies of Linux and give them to friends, it’s also fine to tweak a few lines of the source code.The only catch is that the user who modifies it has to necessarily make available the source code to all users. Linux is not owned by anyone. One misconception many first-time Linux.com readers have is that this site, Linux.com, is similar to Microsoft.com, which is owned and controlled by the company that produces the Windows operating system. No one company or individual “owns” Linux, which was developed, and is still being improved, by thousands of corporate-supported and volunteer programmers all over the world.

Users are generally provided with Linux distribution that contains not only the basic Linux operating system, but also programs that enhance it in many ways. Anyone who wants to put together his or her own Linux distribution is free to do so, and we know of more than 200 different Linux distributions that fill special “niche” purposes. But we advise new users to stick with one of the five or six most popular general-purpose Linux distributions until they know a little about what Linux can and can’t do. You can get Linux from a number of online software repositories, including the official Web sites for each distribution. It helps to have a fast connection and a CD burner so you can quickly download an .ISO image of the distribution and burn it onto a CD. You then can load the bootable installation programs that lead you, step by step, through the process of getting Linux on your computer.

The more popular distributions are available in many computer stores and directly from each distribution’s publisher. The convenience of a distribution on CDs, including manuals, generally makes your first installation so much easier that it is well worth the money.

Linux boasts of some of the best free online support for its operating system.Take advantage of some free, expert technical support: the Linux Users Group, or LUG. The heartbeat of Linux support, and of Linux itself, is the LUG. There are LUGs in almost every country in the world, where you can get Linux advice and help from people who live near you, speak your language, and are willing to donate their time so that new users can learn about Linux without going through any more head-scratching than necessary.Each LUG operates independently and has its own style and meeting schedule. Note that if there is no LUG close enough for you to conveniently attend meetings, most LUGs maintain email lists you can join and use to get answers to any Linux questions you have.

The best-known corporate GNU/Linux distribution is REDHAT. Mandrake Linux was the first Linux distribution that worked hard to make Linux easy for ordinary desktop users. Freely downloadable version available; commercial versions have pre-integrated sofware packages and are easier for first-timers to set up than the download edition. There are other distributions like Fedora, Debia, Knoppix,Suse, Slackware, MEPIS, Gentoo and so on.

The EXT3 file system in Linux is divided into various block groups. Each block group further contains a data structure called group descriptors that contains critical information about the block. Corruption in group descriptors primarily occurs due to operating system malfunctioning, file system damage, malicious software like virus and more. Two major outcomes of corrupted group descriptors are unbootable system and inaccessible data. To successfully recover the lost data, restore it from the latest backup. In case, no recent backup is available or is invalid, you need to go for advanced Linux Recovery software.

Consider a practical scenario, where you encounter the below error message when you attempt to boot your system:

Uncompressing Linux:…Ok booting kernel

audit(xxx.x….x..:0) : initialized

EXT3-fs error (device hda3):ext3_check_descriptors:Block bitmap for grade 38 not int grade ( block 34799616)

EXt3-fs:group descriptors corrupted.

Mount: error 22 mounting ext3

pivot root ivot_root (/sysroot, /sysroot/initrd) failed: 2

unmount/initrd/proc_failed:2

kernel panic: No init found: Try passing init=0 to kernel

You encounter the same error message each time you attempt to boot your system. As a result of the above error, all your critical data becomes inaccessible.

Cause:

The above error message is encountered when group descriptors are corrupted.

Resolution:

To resolve the above issue and access the data, you need to use FSCK command. This command is mainly used to repair the EXT3 file system. But, if the file system has been badly corrupted, then this command fails to repair. In such circumstances, you need to recreate the file system again by formatting and reinstalling Linux. A clean reinstall of Linux will completely erase all data from the selected Linux volume. For complete and orderly recovery of data after reinstalling Linux, you will need to use powerful Linux Recovery software.

These Linux Data Recovery applications ensure comprehensive scanning of formatted Linux volumes by using powerful scanning algorithms. These recovery tools can recover and restore data after problems like group descriptors faults, Inode table damage and superblock corruption. They are built with highly graphical and interactive user interface that makes them easily understandable without prior technical skills.

Stellar Phoenix Linux Data Recovery is the most efficient and trust worthy Linux Recovery tool. It supports Ext2, Ext3 and ReiserFS file systems based Linux volumes. This read only Data Recovery Linux application gets installed on Windows (Vista, XP, 2003 and 2000) and the affected Linux drive should be connected as slave.