Keeping the Linux systems updated

Spend some time perusing the Common Vulnerabilities and Exposures database, and you’ll soon see why it’s so important to keep your systems updated. Yes, indeed, you’ll even find that there have been security flaws with our beloved Linux, as you can see here:

Figure 1.18: Common Vulnerabilities and Exposures

Updating a Linux system only requires one or two simple commands, and it’s generally faster and less painful than updating a Windows system.

Next, let’s look at updating the Debian-based systems, which include Ubuntu.

Updating Debian-based systems

Let’s take a look at how to update Debian-based systems:

1. On Debian and its many children, including Ubuntu, run two commands, as shown here:

   sudo apt update
   sudo apt dist-upgrade
   

2. Occasionally, you’ll also need to remove some old packages that are no longer needed. How will you know? Easy. When you log in to the system, a message will appear on the command line. To remove these old packages, just run this command:

   sudo apt auto-remove
   

Next, we will configure auto updates for Ubuntu.

Configuring auto updates for Ubuntu

When you first install Ubuntu 22.04, automatic updates are turned on by default. To verify that, you’ll first check the status of the unattended-upgrades service, like so:

donnie@ubuntu2204-packt:~$ systemctl status unattended-upgrades
● unattended-upgrades.service - Unattended Upgrades Shutdown
     Loaded: loaded (/lib/systemd/system/unattended-upgrades.service; enabled; vendor preset: enabled)
     Active: active (running) since Sat 2022-10-08 19:25:54 UTC; 52min ago
. . .
. . .
donnie@ubuntu2204-packt:~$

Then, look in the /etc/apt/apt.conf.d/20auto-upgrades file. If auto-updating is enabled, you’ll see this:

APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Unattended-Upgrade "1";

I must confess, though, that I have mixed feelings about this. I mean, it’s nice that the security updates get installed without me having to do anything, but a lot of those updates require that the system be rebooted before they can take effect. By default, Ubuntu systems don’t automatically reboot after an update is installed. If you keep it that way, you’ll see a message about it when you log into the system. But if you prefer, you can set Ubuntu to automatically reboot after it automatically updates itself. Here’s how to do it:

1. Go into the /etc/apt/apt.conf.d directory and open the 50unattended-upgrades file in your favorite text editor. In the vicinity of line 67, you’ll see a line that says:

   //Unattended-Upgrade::Automatic-Reboot "false";
   

2. Uncomment the line by removing the leading slashes, and change false to true, like so:

   Unattended-Upgrade::Automatic-Reboot "true";
   

3. With this new configuration, Ubuntu will now reboot itself immediately after the automatic update process has completed. If you’d rather have the machine reboot at a specific time, scroll down to about line 103, where you’ll see this:

   //Unattended-Upgrade::Automatic-Reboot-Time "02:00";
   

4. Since this line is commented out with its pair of leading slashes, it currently has no effect. To have the machine reboot at 2:00 A.M., just uncomment this line. To have it reboot at, say, 10:00 P.M., uncomment the line and change the time to 22:00, like so:

   Unattended-Upgrade::Automatic-Reboot-Time "22:00";
   

5. To disable automatic updates, just go into the /etc/apt/apt.conf.d directory and open the 20auto-upgrades file in your favorite text editor. Here’s what you’ll see:

   APT::Periodic::Update-Package-Lists "1";
   APT::Periodic::Unattended-Upgrade "1";
   

6. Change the parameter for that second line to 0, so that the file will now look like this:

   APT::Periodic::Update-Package-Lists "1";
   APT::Periodic::Unattended-Upgrade "0";
   

7. If you want to see if there are any security-related updates available, but don’t want to see any non-security updates, use the unattended-upgrade command, like so:

   sudo unattended-upgrade --dry-run -d
   

8. To manually install the security-related updates without installing non-security updates, just run:

   sudo unattended-upgrade -d
   

sudo apt install unattended-upgrades

You can also use the apt command to install only the security updates, but it would require piping the apt output into a convoluted set of text filters in order to mask the non-security updates. Using the unattended-upgrade command is much easier.

Next, let’s look at updating the RHEL 7 systems.

Updating Red Hat 7-based systems

With Red Hat-based systems, which include CentOS and Oracle Linux, there’s no automatic update mechanism that you can set up during installation. So, with the default configuration, you’ll need to perform updates yourself:

1. To update a Red Hat 7-based system, just run this one command:

   sudo yum upgrade
   

2. Sometimes, you might just want to see if there are any security-related updates that are ready to be installed. Do that by running this command:

   sudo yum updateinfo list updates security
   

3. If any security updates are available, you’ll see them at the end of the command output. On the system that I just tested, there was only one security update available, which looks like this:

   FEDORA-EPEL-2019-d661b588d2 Low/Sec. nagios-common-4.4.3-1.el7.x86_64
   updateinfo list done
   

4. If the only thing you want to install is the security updates, run this command:

   sudo yum upgrade --security
   

5. Now, let’s say that you need a CentOS system to automatically update itself. You’re in luck because there’s a package for that. Install and enable it, and start it by running these two commands:

   sudo yum install yum-cron
   sudo systemctl enable --now yum-cron
   

6. To configure it, go into the /etc/yum directory, and edit the yum-cron.conf file. At the top of the file, you’ll see this:

   [commands]
   # What kind of update to use:
   # default = yum upgrade
   # security = yum --security upgrade
   # security-severity:Critical = yum --sec-severity=Critical upgrade
   # minimal = yum --bugfix update-minimal
   # minimal-security = yum --security update-minimal
   # minimal-security-severity:Critical = --sec-severity=Critical update-minimal
   update_cmd = default
   

This lists the various types of upgrades we can do. The last line shows that we’re set to update everything.

7. Let’s say that you only want security updates to get applied automatically. Just change the last line to the following:

   update_cmd = security
   

8. On lines 15 and 20, you’ll see this:

   download_updates = yes
   apply_updates = no
   

9. This indicates that by default, yum-cron is only set to automatically download updates, but not to install them.
10. If you want the updates to get automatically installed, change the apply_updates parameter to yes.

11. Finally, let’s look at the mail settings for yum-cron, which you’ll find on lines 48 through 57 of the yum-cron.conf file, as shown here:

     [email]
    # The address to send email messages from.
    # NOTE: 'localhost' will be replaced with the value of system_name.
    email_from = root@localhost
    # List of addresses to send messages to.
    email_to = root
    # Name of the host to connect to to send email messages.
    email_host = localhost
    

As you can see, the email_to = line is set to send messages to the root user account. If you want to receive messages on your own account, just change it here.

12. To see the messages, you’ll need to install a mail reader program, if one isn’t already installed. (It hasn’t been installed if you chose Minimal installation when you installed the operating system.) Your best bet is to install mutt, like so:

    sudo yum install mutt
    

13. When you open mutt and look at a message, you’ll see something like this:

Figure 1.19: Mutt mail client

14. As with all operating systems, certain updates will require that the system be restarted. And how do you know when the system needs to be restarted? With the needs-restarting command, of course. First, though, you need to make sure that needs-restarting is installed on your system. Do that with this command:

    sudo yum install yum-utils
    

Once the package is installed, there are three ways to use needs-restarting. If you just run the command without any option switches, you’ll see the services that need to be restarted and the packages that require you to reboot the machine. You can also use the -s or -r options, as shown here:

Next, we will be updating Red Hat 8/9-based systems.

Updating Red Hat 8/9-based systems

The old yum utility has been around for practically forever, and it’s been a good, hard-working utility. But it does have its occasional quirks, and at times it can be excruciatingly slow. But, not to worry. Our heroes at Red Hat have finally done something about that, by replacing yum with dnf. So, when you work with your AlmaLinux 8/9 virtual machines, you’ll use dnf instead of yum. Let’s see how to do this:

1. For the most part, you use dnf the same way that you’d use yum, with the same arguments and options. For example, to do a system upgrade, just do:

   sudo dnf upgrade
   

2. The main functional difference between yum and dnf is that dnf has a different automatic update mechanism. Instead of installing the yum-cron package, you’ll now install the dnf-automatic package, like so:

   sudo dnf install dnf-automatic
   

3. In the /etc/dnf directory, you’ll see the automatic.conf file, which you’ll configure the same way as you did the yum-cron.conf file for CentOS 7. Instead of working as a cron job, as the old yum-cron did, dnf-automatic works with a systemd timer. When you first install dnf-automatic, the timer is disabled. Enable it and start it by running this command:

   sudo systemctl enable --now dnf-automatic.timer
   

4. Verify that it’s running with this command:

   sudo systemctl status dnf-automatic.timer
   

5. If it started successfully, you should see something like this when you check the status:

   [donnie@redhat-8 ~]$ sudo systemctl status dnf-automatic.timer
    dnf-automatic.timer - dnf-automatic timer
      Loaded: loaded (/usr/lib/systemd/system/dnf-automatic.timer; enabled; vendor preset: disabled)
      Active: active (waiting) since Sun 2019-07-07 19:17:14 EDT; 13s ago
     Trigger: Sun 2019-07-07 19:54:49 EDT; 37min left
   Jul 07 19:17:14 redhat-8 systemd[1]: Started dnf-automatic timer.
   [donnie@redhat-8 ~]$
   

man dnf-automatic

And that’s all there is to it.

There are special considerations about doing updates in an enterprise environment. Let’s look at them next.

Managing updates in an enterprise

When you first install any Linux distro, it will be configured to access its own package repositories. This allows the user to install software packages and updates directly from these normal distro repositories. This is great for home or small business use, but not so great for the enterprise.

In an enterprise setting, there are two additional considerations:

• You want to restrict what packages the end users are allowed to install.
• You always want to test updates on a separate test network before allowing them to be installed on a production network.

For these reasons, enterprises will often set up their own repository servers that only have approved packages and approved updates. All other machines on the network will be configured to pull their packages and updates from them, rather than from the normal distro repository. (We won’t go into how to set up on-premises repository servers here, because that topic is better suited for a Linux administration book.)

I think that that’s about it for our introductory chapter. Let’s wrap things up in a summary, shall we?