howto-schedule-cron-jobs-to-download-rpm-packages-after-hours.md

HowTo Schedule a Nightly YUM or DNF Downloud of RPM Packages After Hours

Scenario:
Fedora Linux machine that has a daily influx of RPM packages (patches).

Problem:
I have bandwidth constraints from 8am to 10pm every day in my region.

Solution:
Set up a cronjob (a job scheduler) to download all those RPMs after hours.

RPM based linux machines are patched with RPM packages downloaded from the internet. Sometimes these RPMs can be relatively large. Management of these RPMs is down using a utility called DNF on newer linux distributions (Fedora Linux, SUSE, etc) and YUM on older linuxes (namely CentOS 7 and RHEL 7).

If you are on a desktop machine running GNOME, there is a GUI software manager that can also install these RPMs. It is essentially a wrapper around DNF.

Let's solve our problem. You can do it one of two ways...

Assumptions:

• You have to perform these actions as the root user directly or indirectly via sudo. My examples use sudo.
• You know how to use the vi editor. That's what the commands assume.
• crontab -e is how you schedule things. The process is...
  Edit crontab ⟶ Save ⟶ Exit ⟶ Changes applied
• Read more about crontab here: https://github.com/taw00/howto/blob/master/howto-schedule-cron-jobs-to-run-at-random-intervals.md

CentOS 7 or RHEL 7 Linux - Extra step

Install the yum downloader plugin:

sudo yum install yum-plugin-downloadonly

Method1: Download the RPM packages after hours. Install them later.

• Edit crontab:

  sudo crontab -e
  

• Set a schedule for 2:30am every day to download all available packages. Remember the format for crontab entries is...
  mins hours day-of-month month day-of-week command-or-script

  # I'm a Fedora Linux machine...
  30 2 * * * /usr/bin/dnf upgrade --downloadonly -y --refresh
  # I'm a CentOS 7 or RHEL 7 machine...
  #30 2 * * * /usr/bin/yum update --downloadonly -y --refresh
  

  Save that and exit...

  :w
  :q
  

  You are scheduled! List your work...

  sudo crontab -l
  

• Install at your convenience (the next day, for example)...
  There may have potentially been additional packages made available between the time you downloaded them an when you trigger the actual update, but the difference should be much smaller. There are ways to offline update, but I leave figuring that out as an exercise for the reader.

  # I'm a Fedora Linux machine...
  sudo dnf upgrade
  # I'm a CentOS 7 or RHEL 7 machine...
  #sudo yum update
  

  If you just want to list what you have available...

  sudo dnf list
  # Or for CentOS/RHEL...
  #sudo yum list
  

Method2: Download and install the RPM packages after hours.

Just do the same thing, but remove the --downloadonly option from the commandline.

Troubleshooting

You can see your cron activity in the logs via...

sudo journalctl /usr/sbin/crond | tail -n 100

That is one example. I leave it up to the reader to figure out more ways to look at the Journaling logs and how CentOS and RHEL probably do it differently.