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Ubuntu sysctl chaos, /etc/systcl.conf not read / ignored

Explanation: https://serverfault.com/questions/355520/after-reboot-debian-box-ignore-sysctl-conf-values

  • /etc/sysctl.conf is not used, or the values are overriden by other sysctl configs like in /etc/sysctl.d or ufw (se below)

  • If you use ufw (uncomplicated firewall) you really need to change the values in /etc/ufw/sysctl.conf as the configuration here overrides /etc/sysctl.conf one!!!

    • net/ipv4/... directives

  • The problem seems to exist for many years, even in Ubuntu 20.04

Solution:

  • Use /etc/sysctl.d/99-sysctl.conf or separate files in /etc/sysctl.d