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Note: Note: Red Hat versions 5.1 and earlier used the BIND 4.x package,which used a slightly different format for its configuration file. BIND8.x offers more functionality over that offered by BIND 4.x, and as 4.x isno longer being developed, you should probably consider upgrading yourBIND package to the latest version. Simply install the BIND RPM package(see for details on using the RPM utility),then convert your configuration file to the new format.Fortunately, converting your existing BIND 4.x configuration file tobe compliant with BIND 8.x is easy! In the documentation directoryprovided as part of BIND (for example,`` /usr/doc/bind-8.1.2/' for BINDversion 8.1.2), there exists a file called`` named-bootconf.pl', which is anexecutable Perl program. Assuming you have Perl installed on your system,you can use this program to convert your configuration file. To do so,type the following commands (as root): cd /usr/doc/bind-8.1.2./named-bootconf.pl /etc/named.conf mv /etc/named.boot /etc/named.boot-obsoleteYou should now have an`` /etc/named.conf' file whichshould work with BIND 8.x 'out-of-the-box'. Tip: Tip: Make note of the allow-transferoptions above, which restricts DNS zone transfers to a given IP address.In our example, we are allowing the host at 123.12.41.40 (probably a slaveDNS server in our domain) to request zone transfers.

If you omit thisoption, anyone on the Internet will be able to request such transfers.As the information provided is often used by spammers and IP spoofers, Istrongly recommend you restrict zone transfers except to your slave DNSserver(s), or use the loopback address, `` 127.0.0.1'instead.Now you can set up your DNS tables in the`` var/named/' directory asconfigured in the`` /etc/named.conf' file in stepthree. Configuring DNS database files for the first time is a majorundertaking, and is beyond the scope of this document. There are severalguides, online and in printed form that should be referred to.

However,several examples are provided below.Sample entries in the`` /var/named/mydomainname.db'forward lookup file:; This is the Start of Authority (SOA) record. Contains contact; & other information about the name server. The serial number; must be changed whenever the file is updated (to inform secondary; servers that zone information has changed).@ IN SOA mydomain.name. (19990811; Serial number3600; 1 hour refresh300; 5 minutes retry172800; 2 days expiry43200 ); 12 hours minimum; List the name servers in use.

Unresolved (entries in other zones); will go to our ISP's name server isp.domain.name.comIN NS mydomain.name.IN NS isp.domain.name.com.; This is the mail-exchanger. You can list more than one (if; applicable), with the integer field indicating priority (lowest; being a higher priority)IN MX mail.mydomain.name.; Provides optional information on the machine type & operating system; used for the serverIN HINFOPentium/350LINUX; A list of machine names & addressesspock.mydomain.name. IN A 123.12.41.40; OpenVMS Alphamail.mydomain.name.

IN A 123.12.41.41; Linux (main server)kirk.mydomain.name. IN A 123.12.41.42; Windows NT (blech!); Including any in our other class C'stwixel.mydomain.name. IN A 126.27.18.161; Linux test machinefoxone.mydomain.name. IN A 126.27.18.162; Linux devel. Kernel; Alias (canonical) namesgopherIN CNAMEmail.mydomain.name.ftp IN CNAMEmail.mydomain.name.www IN CNAMEmail.mydomain.name.Sample entries in the`` /var/named/12312.rev' reverselookup file:; This is the Start of Authority record. Same as in forward lookup table.@ IN SOA mydomain.name.

(19990811; Serial number3600; 1 hour refresh300; 5 minutes retry172800; 2 days expiry43200 ); 12 hours minimum; Name servers listed as in forward lookup tableIN NS mail.mydomain.name.IN NS isp.domain.name.com.; A list of machine names & addresses, in reverse.

Contribute on GitHub This guide presents a collection of common issues and useful tips for Linux system administration. Whether you’re new to system administration or have been maintaining systems for some time, we hope this collection of basic Linux commands will help you manage your system from the command line.Basic ConfigurationThese tips cover some of the basic steps and issues encountered during the beginning of system configuration. We provide a general for your convenience if you’re new to Linode and basic Linux system administration.

Additionally, you may find our useful. Set the HostnamePlease follow our instructions for. You can use the following commands to make sure it is set properly: hostnamehostname -fThe first command should show your short hostname, and the second should show your fully qualified domain name (FQDN). Set the Time ZoneWhen setting the time zone of your server, it may be best to use the time zone of the majority of your users. If you’re not sure which time zone would be best, consider using Universal Coordinated Time or UTC (i.e., Greenwich Mean Time).By default, Linodes are set to UTC.

Many operating systems provide built-in, interactive methods for changing time zones: Set the Time Zone in Debian or UbuntuIssue the following command and answer the questions as prompted on the screen: dpkg-reconfigure tzdataSet the Time Zone in CentOS 7 or Arch Linux.View the list of available time zones: timedatectl list-timezonesUse the Up, Down, Page Up and Page Down keys to navigate to the correct zone. Remember it, write it down or copy it as a mouse selection.

Then press q to exit the list.Set the time zone (change America/NewYork to the correct zone): timedatectl set-timezone 'America/NewYork'Set the Time Zone Manually on a Linux SystemFind the appropriate zone file in /usr/share/zoneinfo/ and link that file to /etc/localtime. See the examples below for possibilities:Universal Coordinated Time: ln -sf /usr/share/zoneinfo/UTC /etc/localtimeEastern Standard Time: ln -sf /usr/share/zoneinfo/EST /etc/localtimeAmerican Central Time (including Daylight Savings Time): ln -sf /usr/share/zoneinfo/US/Central /etc/localtimeAmerican Eastern Time (including Daylight Savings Time): ln -sf /usr/share/zoneinfo/US/Eastern /etc/localtimeConfigure the /etc/hosts FileThe /etc/hosts file provides a list of IP addresses with corresponding hostnames. This allows you to specify hostnames for an IP address in one place on the local machine, and then have multiple applications connect to external resources via their hostnames.

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Dns Server Configuration In Linux 6 Step By Step Pdf To Jpg File

The system of host files precedes, and hosts files are always checked before DNS is queried. As a result, /etc/hosts can be useful for maintaining small “internal” networks, for development purposes, and for managing clusters.Some applications require that the machine properly identify itself in the /etc/hosts file. As a result, we recommend configuring the /etc/hosts file shortly after deployment. Here is an example file: /etc/hosts. 100.30 example. ComIn this example, all requests for the example.com hostname or domain will resolve to the IP address 198.51.100.30, which bypasses the DNS records for example.com and returns an alternate website.The second entry tells the system to look to 192.168.1.1 for the domain stick.example.com.

These kinds of host entries are useful for using “private” or “back channel” networks to access other servers in a cluster without needing to send traffic on the public network. Network DiagnosticsIn this section, we’ll review some basic Linux commands that will help you assess and diagnose network problems. If you suspect connectivity issues, adding the output from the relevant commands to your can help our staff diagnose your issue. This is particularly helpful in cases where networking issues are intermittent. The ping CommandThe ping command tests the connection between the local machine and a remote address or machine. The following commands “ping” google.com and 216.58.217.110: ping google.comping 216.58.217.110These commands send a small amount of data (an ICMP packet) to the remote host and wait for a response.

If the system is able to make a connection, it will report on the “round trip time” for every packet. Here is the sample output of four pings to google.com: PING google.com (216.58.217.110): 56 data bytes64 bytes from 216.58.217.110: icmpseq=0 ttl=54 time=14.852 ms64 bytes from 216.58.217.110: icmpseq=1 ttl=54 time=16.574 ms64 bytes from 216.58.217.110: icmpseq=2 ttl=54 time=16.558 ms64 bytes from 216.58.217.110: icmpseq=3 ttl=54 time=18.695 ms64 bytes from 216.58.217.110: icmpseq=4 ttl=54 time=25.885 msThe time field specifies in milliseconds the duration of the round trip for an individual packet. When you’ve gathered the amount of information you need, use Control+C to interrupt the process. You’ll be presented with some statistics once the process is stopped.

This will resemble: - google.com ping statistics -4 packets transmitted, 4 received, 0% packet loss, time 3007msrtt min/avg/max/mdev = 33.890/40.175/53.280/7.679 msThere are several important data points to notice:. Packet Loss, or the discrepancy between the number of packets sent and the number of packets that return successfully. This number shows the percentage of packets that are dropped. Round Trip Time (rtt) statistics on the final line report information about all the ping responses. For this ping we see that the fastest packet round trip (min) took 33.89 milliseconds.

The average round trip (avg) took 40.175 milliseconds. The longest packet (max) took 53.28 milliseconds. A single standard deviation unit (mdev) for these four packets is 7.67 milliseconds.The ping command is useful as an informal diagnostic tool to measure point-to-point network latency, and as a tool to simply ensure you are able to make a connection to a remote server. The traceroute CommandThe traceroute command expands on the functionality of the command. It provides a report on the path that the packets take to get from the local machine to the remote machine. Each step (intermediate server) in the path is called a hop.

Route information is useful when troubleshooting a networking issue: if there is packet loss in one of the first few hops the problem is often related to the user’s local area network (LAN) or Internet service provider (ISP). If you are giving other users access to upload files to your server, consider the of all additional access that you grant to third parties. Upload Files to a Remote ServerIf you’re used to using an FTP client, OpenSSH (which is included and active with all of the Linode distribution images) allows you to use an FTP-like interface over the SSH protocol.

Known as “SFTP,” many clients support this protocol, including for Windows, for Mac OS X, and for Linux, OS X, and Windows desktops.If you are accustomed to FTP, SFTP will be very familiar to you. By default, whatever access a user has to a file system at the command line, that user will also have over SFTP. Consider the implications of when configuring user access.You can also use Unix utilities including scp and to securely transfer files to your Linode. On a local machine, a command to copy team-info.tar.gz would look like: scp team-info.tar.gz username@hostname.example.com:/home/username/backups/The command, scp, is followed by the path of the file on the local file system to be transferred. Next, the username and hostname of the remote machine follow, separated by an “at” sign ( @). Follow the hostname with a colon (:) and the path on the remote server to where the file should be uploaded.

Using a more generalized example: scp /path/to/local/file remote-username@remote-hostname:/path/to/remote/fileThis command is available by default on OS X and Linux machines. You can use it to copy files to a Linode, as well as between remote servers. If you use SSH keys, you can use the scp command without entering a password for every transfer.The syntax of scp follows the form scp source destination.

You can copy files from a remote host to the local machine by reversing the order of the paths in the above example. Protect Files on a Remote ServerBecause Linode servers are network accessible and often have a number of distinct users, maintaining the security of files is often an important concern. We recommend you familiarize yourself with our. Our guide on may provide additional insight.We suggest the following best practices for maintaining security:. Only give users the permission to do what they need to. This includes application-specific users.

Only run services on public interfaces that you are actively using. One common source of security vulnerabilities is in unused daemons that are left running. This includes database servers, HTTP development servers, and FTP servers. Use SSH connections whenever possible to secure and encrypt the transfer of sensitive information.Symbolic LinksSymbolic linking, colloquially “symlinking”, allows you to create an object in your filesystem that points to another object on your filesystem. This is useful when you need to provide users and applications access to specific files and directories without reorganizing your folders.

This way you can provide restricted users access to your web-accessible directories without moving your DocumentRoot into their home directories.To create a symbolic link, issue a command in the following format: ln -s /home/username/config-git/etc-hosts /etc/hostsThis creates a link of the file etc-hosts at the location of the system’s /etc/hosts file. More generically: ln -s /path/to/target/file /path/to/location/of/sym/linkNote the following features of the link command:. The final term, the location of the link, is optional. If you omit the link destination, a link will be created in the current directory with the same name as the file you’re linking to.

When specifying the location of the link, ensure that path does not have a final trailing slash. You can create a sym link that targets a directory, but sym links cannot terminate with slashes. You may remove a symbolic link without affecting the target file.

You can use relative or absolute paths when creating a link.Manage Files on a Linux SystemIf you’re new to using Linux and manipulating files on the terminal interface we encourage you to consider our guide on. This section provides a list of basic commands to manage the contents of your filesystem.To copy files: cp /home/username/todo.txt /home/username/archive/todo.01.txtThis copies todo.txt to an archive folder, and adds a number to the file name. If you want to recursively copy all of the files and subdirectories in a directory to another directory, use the -R option.

This command looks like: cp -R /home/username/archive/ /srv/backup/username.01/To move a file or directory: mv /home/username/archive/ /srv/backup/username.02/You can also use the mv command to rename a file.To delete a file: rm scratch.txtThis will delete the scratch.txt file from the current directory.For more information about file system navigation and manipulation, please consider our documentation of. Package ManagementMost Linux systems use package management tools to facilitate the installation and maintenance of all software on your system. For more in-depth coverage of this topic, please reference our guide.While these tools provide a number of powerful features, it is easy to look past the benefits of package management. If you install software manually without package management tools, it becomes difficult to keep your system up to date and to manage dependencies. For these reasons, we recommend installing all software through package management tools unless other means are absolutely necessary. The following tips outline a couple of basic package management tasks.

Find Packages Installed on Your SystemBecause packages are so easy to install, and often pull in a number of dependencies, it can be easy to lose track of what software is installed on your system. 1ErrorLog /var/www//html/example.com/logs/error.log CustomLog /var/www/html/example.com/logs/access.log combinedWhere example.com represents the name of your virtual host and the location of its resources.

These directives make Apache create two log files that contain logging information specific to that virtual host. This allows you to easily troubleshoot errors on specific virtual hosts. To track or tail the error log: tail -F /var/www/html/example.com/logs/error.logThis will allow you to see new error messages as they appear. Problems can be diagnosed by using specific parts of an error message from an Apache log as a term in web search. Common errors to look for include:.

Missing files, or errors in file names. Permissions errors. Configuration errors. Dynamic code execution or interpretation errorsDNS Servers and Domain NamesThe Domain Name System, or DNS, is the service that the internet uses to associate the hard to remember and manage IP addresses with more human-usable domain names. This section will address several specific DNS-related tasks. To learn more about DNS, check out our.

If you are familiar with DNS and just need to figure out how to configure your DNS server, see our guide for the. Redirect DNS Queries with CNAMEsmake it possible to redirect requests for one hostname or domain to another hostname or domain. This is useful in situations where you want to direct requests for one domain to another, but don’t want to set up the web server to handle requests.CNAMEs are only valid when pointing from one domain to another.

If you need to redirect a full URL, you will need to set up a web server and and/or virtual hosting on the server level. CNAMEs will allow you to redirect subdomains, such as team.example.com, to other subdomains or domains, such as jack.example.org.

CNAMEs must point to a valid domain that has a valid A Record, or to another CNAME.Although limited in their capabilities, CNAMEs can be quite useful in some situations. In particular, if you need to change the hostname of a machine, CNAMEs are quite useful. To learn how to set up CNAME records with the, refer to our. Set Up SubdomainsWhen, we refer to parts before the main or first-level domain as “subdomains.” For example, in the domain team.example.com, team is a subdomain for the root domain example.com.Follow these steps to:.First, create an in the DNS zone for the domain. You can do this using the. You may host the DNS for your domain with any provider you choose.Set up a server to respond to requests sent to this domain.

For web servers like, this requires configuring a new virtual host. For XMPP servers you must configure an additional host to receive the requests for this host. For more information, consult the documentation for the specific server you wish to deploy.Once configured, subdomains function almost identically to root domains on your server. If you need to, you can set up HTTP redirection for the new subdomain.SMTP Servers and Email IssuesWe provide a number of guides that cover.

In this section, we’ll explain how to choose an email setup that fits your needs and how to configure your Linode to send email. Choose an Email SolutionThere are two major components that are required for email functionality. The most important part is the SMTP server or “Mail Transfer Agent.” The MTA, as it is often called, sends mail from one server to another. The second part of an email system is a server that permits users to access and download that mail from the server to their own machine. Typically these servers use a protocol such as POP3 or IMAP to provide remote access to the mailbox.There may also be other components in the email server tool chain. These components may be optional depending on the requirements of your deployment.

Dns Server Configuration In Linux 6 Step By Step Pdf To Jpg Converter

They include filtering and delivery tools like, anti-virus filters like, mailing list managers like, and spam filters like. These components function independently of the MTA and remote mailbox server.The most prevalent SMTP servers or MTAs in the UNIX-like world are,. Sendmail has the longest history and many system administrators have extensive experience with it.

Postfix is robust and modern, and is compatible with many different configurations. Exim is the default MTA in Debian systems, and many consider it to be easier to use for basic tasks. For remote mailbox access, servers like and are popular options.If you need an easy-to-install email solution, consider the. Citadel provides an integrated “turnkey” solution that includes an SMTP server, remote mailbox access, real time collaboration tools including XMPP, and a shared calendar interface. Along similar lines, we also provide documentation for the installation of the.If, by contrast, you want a more simple and modular email stack, we urge you to consider one of our guides built around the.Finally, it’s possible to outsource email service to a third-party provider, such as. These services allows you to send and receive mail from your domain, without hosting email services on your Linode.

Send Email From Your ServerFor simple configurations, you may have no need for a complete email stack like some of those documented in our. However, applications running on that server still need to be able to send mail for notifications and other routine purposes.The configuration of applications to send notifications and alerts is beyond the scope of this guide. Most applications rely on a simple “sendmail” interface, which is accessible via several common SMTP servers including Postfix and msmtp.To install Postfix on Debian and Ubuntu systems: apt-get install postfixOn CentOS and Fedora systems: yum install postfixOnce Postfix is installed, your applications should be able to access the sendmail interface, located at /usr/sbin/sendmail.

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Most applications running on your Linode should be able to send mail normally with this configuration.If you want to use your server to send email through an external SMTP server, consider a more simple tool like msmtp. Since msmtp is packaged in most distributions, and you can install it using the appropriate command: apt-get install msmtpyum install msmtppacman -S msmtpUse the command type msmtp or which msmtp, to find the location of msmtp on your system. Typically the program is located at /usr/bin/msmtp. You can specify authentication credentials with command line arguments or by declaring SMTP credentials in a configuration file. Here is an example.msmtprc file.msmtprc example.