Managing Packages on RedHat/CentOS Systems

First, we'll clean the existing YUM metadata and cache, and create a fresh one:

yum clean all
yum makecache

Next, let's list the available updates:

yum list updates

Finally, we need to update the software packages on the system:

yum -y update

This may take a little while, since we're downloading updates for everything currently installed on the system.

Use the yum command to search for any packages with apache or http in their names:

yum search 'apache http'

The Apache server comes with an httpd file. Knowing this, we can use yum to find which package includes (provides) such a file:

yum provides httpd

Now that we know the name of the actual package we need to install, we can do it:

yum -y install httpd

Use the systemctl command to start the httpd.service, and enable it to start when the system boots. This will do both:

systemctl enable httpd --now

Now check the status of the httpd.service, and would should see active and running in the output:

systemctl status httpd.service

After installing a package like httpd, we can use rpm to query for its configuration details, documentation, and other information. Using rpm -qa can provide information about all the packages installed on the system.

Let's look at any documentation files belonging to the package:

rpm -qd httpd

Show configuration files:

rpm -qc httpd

Show which package owns a file (in this case /sbin/httpd):

rpm -qf /sbin/httpd

Show all packages installed on the system:

rpm -qa | wc

We piped this command into wc, just so our screen wouldn't be inundated with information, but we can see that there are several hundred packages installed on the system. To look at them in order of install time, from oldest to newest:

rpm -qa --last | tac

At least this way, what's down near our new command prompt is the most recently installed packages.

Now if we just want to see packages that start with httpd, we'd run:

rpm -qa 'httpd*'

Let's first make sure that the elinks package isn't installed:

rpm -q elinks

Now we should make sure the development team did in fact download the correct elinks package:

ls /tmp/elinks*.rpm

Using the rpm command, we can query that elinks package and get some information about it:

rpm -qp /tmp/elinks-0.12-0.37.pre6.el7.0.1.x86_64.rpm

Now let's see what scripts will execute when the package is installed:

rpm -qp --scripts /tmp/elinks-0.12-0.37.pre6.el7.0.1.x86_64.rpm

This is good information to have. If the package files are potentially not from a trusted source, we're going to want to know what scripts will run during the install process, and what they do.

We can try to install the package with this:

rpm -ivh /tmp/elinks-0.12-0.37.pre6.el7.0.1.x86_64.rpm

Alas, we will probably have unmet dependencies. And when we try to install the packages in these error messages, we may find that those have unmet dependencies. It can be a mess. Let's try this with yum instead:

yum localinstall /tmp/elinks-0.12-0.37.pre6.el7.0.1.x86_64.rpm

Answer y at the prompt.

Finally, let's use the elinks command to make sure that the package installed correctly, and browse the http://localhost website:

elinks http://localhost

If we land at the CentOS Apache welcome page, we're all set.