YUM is a package management system for Red Hat Enterprise Linux (RHEL), CentOS, Fedora, and other Red Hat-based Linux operating systems. It is command-line driven and is an easy tool you can use to keep your server updated and install any new software you need.

Normally, when you perform updates, YUM will search the distribution’s online repository and select any newly updated packages for download and installation. These may include everything from Apache web server to the Linux kernel itself.

Most of the time, it is a general good practice to update all of the available packages, but there are times when this may not be ideal. For example, if you know for certain that a new version of a particular package that you have installed will not work with a version of one of your web applications, you may want to delay updating until you have patched your application. Another possible scenario is that you may want to update most of your other packages now but wait until later to update the kernel, which will require a reboot.

YUM has a built-in feature that allows you to exclude a package or group of packages of your choosing. You can either use the exclude function on a long-term basis or for one particular update. To make a long-term change, you should edit your repository file (usually yum.conf). Find the [main] section and add the following line:

Continue reading: How to Force YUM to Exclude Certain Packages

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By default, FTP servers require the user to login in order to upload or download files. Many web hosts, however, additionally offer the ability to use anonymous FTP. It basically gives you the ability to allow users to login to the FTP server without providing a username or a password.

What it really does is give users access to a username called anonymous, which does not require a password. They can then perform whatever tasks that are allowed for that user. For example, the anonymous use may be allowed to download public files but probably will not be allowed to upload. Downloading with FTP takes load off of the web server and usually offers more connections so more users can access the files at once.

Despite its name, anonymous FTP is not completely anonymous. As a website owner, you can still track IP addresses and host name, in case someone attempts to compromise your system. If you do not offer public downloads of any sort, it is usually a good idea to disable anonymous FTP.

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As I have been reiterating all week, an open relay is a bad idea. If your mail server is left open, anyone can use your SMTP service to send mail, and spammers will use it. This can result in your server being blacklisted and extraneous use of system resources that neither benefit you nor your users.
To secure Postfix, there are a number of functions you can add the configuration file /etc/mail/main.cf. Edit the file and add the following lines:

smtpd_helo_required = yes
smtpd_delay_reject = no
disable_vrfy_command = yes

smtpd_helo_restrictions = permit_mynetworks,
reject_invalid_hostname,
reject_unknown_hostname,
reject_non_fqdn_hostname

This will force incoming requests to pause and identify themselves before proceeding, and will allow properly authenticated users to pass through and send mail. To finish, save the file and restart Postfix:

/etc/init.d/postfix restart

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Microsoft has formed an alliance with Dell, HP, and Fujitsu to sell pre-configured Microsoft Azure-powered cloud servers. By pre-configured, they mean that the servers should be ready to go without any further configuration required. As such, they call them “appliances” rather than servers.

These appliances will allow companies to take advantage of the “private cloud”, with which they run their own applications and storing them in their own data centers. This differs from the “public cloud”, in which the applications are on servers in third-party data centers.

Potential customers are expected to be larger businesses with scalable enterprise server needs. The first in line is the auction super site Ebay.com. The Azure software itself, however, will be more widely available. Microsoft is joining numerous other big IT companies that are now offering cloud services, including IBM, Google, and Amazon.

Source: The China Post
Photo: Flickr

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Question: One of my Linux system log files has suddenly become very large (several hundred megabytes). What should I do?

Answer: The first thing to find out is what exactly is happening in the log files. To see the latest log activity for your web server error log, for example, you would run:

tail -f /var/log/httpd/error.log

If the file is expanding, you should see errors popping up. When you are finished looking at it, press CTRL-C.

The next step is to fix whatever error you are receiving. If it is enough to fill up several megabytes or even a gigabyte of log space, it is a recurring error that should be fixed. For a web server, repeated failed connections could be some type of denial of service (DoS) attack. For a mail server, numerous open connections could mean that someone is using your server to send spam. The key is to find out exactly what the root cause is and then fix it. If you want to clear the log file, run:

> /var/log/httpd/error.og

Your logs will be back to normal size once your server is running normally again.

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Question: My database server is timing out because MySQL seems to hang once it has used up 4GB of RAM, even though the server is equipped with 6GB. How can I make MySQL take advantage of the full 6GB available?

Answer: If your current server setup involves a 32-bit architecture or even just a 32-bit version of your operating system, the short answer is: you cannot. By design MySQL will not be able to use more than 4GB unless it is running on a 64-bit OS.

If you are running Linux, type ” uname -m ” from the command line to see whether or not you are using a 64-bit version. If you know for a fact that your server actually has 64-bit processors, you can reinstall Linux with a 64-bit kernel.

The other less-drastic measure you may be able to take is to install a PAE (Physical Address Extension) kernel, which will allow your server to access physical address space larger than 4 GB. Some distributions, such as CentOS offer PAE kernel packages that you can easily install.

Source: Webhostingtalk.com
Photo: Flickr

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Intel processors have a variety of names, and there is no shortage in the number of variations. When you are looking to lease or purchase a server, this can be confusing. On the current market, you may find servers with Intel’s Core 2, Celeron, Xeon, and the newer Core i7.

The first distinction that you should make is between processors designed for servers and those that are not. Generally speaking, Core 2 and Celeron processors are for workstations and not servers. The Xeon processors may, in some cases, even have identical architecture to the Core 2 models but will be packaged and sold for servers. Similarly, there are Core i7 chips with similar architecture to high-end Xeon CPUs, but the former is for desktops, while the latter is for servers.

What you truly want to avoid, however, is getting a server with a Celeron processor. While there may be little difference between a high-powered i7 and a similar Xeon, a Celeron processor of the same clock speed will often have less cache and slower FSB. If a server company is trying to market Celeron servers to you, they are actually selling you an inferior product.

Photo Source: Flickr

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When MySQL works correctly, it can be a thing of beauty, but when something goes wrong, it can drive you mad. Here are a few things you can do to troubleshoot connection problems:

1. Make sure your username and password are correct.
2. Double-check the hostname. Although “localhost” works on most servers, it may not on yours.
3. Test the connection string (if you wrote the code yourself). You may have a simple typo.
4. If you have your own server, check the mysql server to see if it is running and running without errors.
5. Does the database you are trying to connect to actually exist? Sometimes automatic database creation fails, and you are left wondering why you cannot connect to it.
6. If you can connect locally but cannot connect remotely, check your firewall settings to see if port 3306 (or whichever port you use for mysql) is open.
7. Finally, be sure your mysql user has the necessary privileges to perform whatever task you are trying to accomplish.

Photo Source: Flickr

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As I mentioned in a previous MySQL post, knowing how to quickly perform database tasks from the command line is a good idea if you are a Linux system administrator. Sometimes, it is the easier way to get things done, especially if you are helping another user and need root access to his or her database.

To delete a table, first login to MySQL:

mysql -u root -p

Enter your password and then switch to the database you want to edit by typing the following at the mysql> prompt:

mysql> use [db name];

Finally, drop the table:

mysql> drop table [table name];

Replace [table name] with the actual name of the table you want to remove.

To remove a row, type:

mysql> DELETE from [table name] where [field name] = 'whatever';

When you are finished, type “quit” to exit.

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With your own dedicated server, many of the configuration tasks fall squarely on your shoulders. PHP is no exception. Most of the PHP configuration settings are found in the php.ini file, which is often located in /etc/php.ini on Linux servers. You must edit the file as root, and any configuration changes will only take effect after you restart your web server.

For example, a common setting that system administrators might want to change is the memory limit, which is generally too low for many web applications. Edit php.ini and find:

memory_limit = 16M

You can then change it to something like:

memory_limit = 64M

Save the file and then restart Apache:

service httpd restart

To see if changes have come into effect and to look at any other configuration settings you might want to change, you can create a phpinfo.php file in a regular document root of one your websites. Edit the file and add the following code:

<?php

?>

Save it and then load that file from your web browser. It will print out a list of all PHP configuration settings.

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