systemctl disable apt-daily.timer
systemctl disable apt-daily-upgrade.timer

apt has a daily and weekly update on Ubuntu servers. On servers with limited CPU and Memory this could pose an issue. If the servers are inside the firewall and do not require any updates, security or otherwise, it helps to disable this.

The apt configurations as at /etc/apt/apt.conf.d directory

Of particular interest is the file 10periodic

The key parameters to set to 0 are below

APT::Periodic::Update-Package-Lists "0";
APT::Periodic::Download-Upgradeable-Packages "0";
APT::Periodic::AutocleanInterval "0";

Alongside apt updates are the Ubuntu release checks that run periodically and take up values resources. To disable edit /etc/update-manager/release-upgrades and update Prompt=lts to Prompt=never

The cron jobs that cause the issue are

• /etc/cron.weekly/apt-xapian-index
• /etc/cron.weekly/update-notifier-common
• /etc/cron.daily/update-notifier-common
• /etc/cron.daily/apt
• /etc/cron.daily/apt-compat

The other option may be to disable execute on these files. Actually only this may work as the settings don't seem to limit it!

chmod -x /etc/cron.weekly/apt-xapian-index
chmod -x /etc/cron.weekly/update-notifier-common
chmod -x /etc/cron.daily/update-notifier-common
chmod -x /etc/cron.daily/apt
chmod -x /usr/lib/ubuntu-release-upgrader/release-upgrade-motd
chmod -x /etc/cron.daily/apt-compat

Automatic apt upgrades