RHEL7: Configure automatic updates.

Presentation

The yum-cron package provides a convenient way to check for, download and apply updates automatically.

Installation procedure

Install the yum-cron package:

# yum install -y yum-cron

Start the yum-cron service:

# systemctl start yum-cron

By default, the configuration of the yum-cron service is done through two files following exactly the same syntax:

• /etc/yum/yum-cron.conf defines what is done once every day,
• /etc/yum/yum-cron-hourly.conf defines what is done once every hour.

Still by default, no action in defined in the /etc/yum/yum-cron-hourly.conf file. Conversely, in the /etc/yum/yum-cron.conf file associated with daily actions, instructions are given to send a message on stdio (which means written into the /var/log/cron file) when any update is available (see update categories below), to download it without applying it.

Configuration syntax

In any of the two configuration files, configuration is defined through the following directives:

• update_cmd = value specifies the category of upgrade where value can take:
  • default for yum upgrade,
  • security for yum –security upgrade,
  • security-severity:Critical for yum –sec-severity=Critical upgrade,
  • minimal for yum –bugfix upgrade-minimal,
  • minimal-security for yum –security upgrade-minimal,
  • minimal-security-severity:Critical for yum –sec-severity=Critical upgrade-minimal.
• update_messages = yes/no defines whether a mail is sent when updates from the previously specified category are available.
  
• download_updates = yes/no specifies whether these available updates need to be downloaded.
  
• apply_updates = yes/no defines whether these available updates need to be applied.
  
• random_sleep = 15 specifies the maximum time in minutes to randomly sleep preserving bandwidth and avoiding download storms.
• emit_via = stdio/email/none defines what kind of message is used: stdio means written into the /var/log/cron file, email causes a mail to be sent, none doesn’t do anything.
• email_from = root@localhost, email_to = root, email_host = localhost defines respectively when the message is a mail the originator’s email address, the recipient’s email address and the host to which the mail is sent.
  

Note: As the official CentOS repositories don’t provide any security metadata, update_cmd = default is the only option that works (see here for details). To get these security metadata, you will have to get them through this website. It is also possible to get CentOS security updates through the procedure provided by Casey Labs.

Source: Linuxaria’s website.

Additional Resources

Rackspace wrote a similar tool called Auter available through EPEL:

• Auter installation procedure,
• Auter github,
• Auter presentation (22min/2018).

You can also read a Centmin Mod article about Setting up automatic updates.

Vladimir Smitka wrote an article about Enhancing your CentOS security for $1 a month with autoupdates.