Useful howtos

Short, tested procedures for the things that come up once a year and are never where you left them.

NGINX

NGINX underscores in headers

Headers containing underscores are dropped by default. Turn them back on.

underscores_in_headers on;

Self-Signed CA

Issue a wildcard cert with mkcert and get every box on the LAN to trust it.

mkcert -install

CLI commands

Clean Linux DNS cache

systemd-resolved, nscd and dnsmasq.

resolvectl flush-caches

Clean macOS DNS cache

Flush the resolver and restart mDNSResponder.

dscacheutil -flushcache

Clean Windows DNS cache

From an elevated prompt.

ipconfig /flushdns

Linux

Linux subsystem in Windows

Enabling and installing WSL.

wsl --install

Downgrading Ansible Engine on CentOS 7

Pinning a working release when the latest breaks your playbooks.

yum downgrade ansible

SpamAssassin manual learning

Feeding ham and spam to the Bayes classifier by hand.

sa-learn --spam

Sudo nopasswd

Dropping the password prompt for a user or a group.

NOPASSWD: ALL

Perl warnings

Silencing locale warnings on a fresh install.

Networking

SYS-4-CONFIG_RESOLVE_FAILURE

What the Cisco log message means and how to stop it.

no ip domain-lookup