2023-08-18

Annoyed by named pouring out messages about unreachable IPv6 addresses, e.g. 
   named[3556893]: network unreachable resolving 'nn.uninett.no/A/IN': 2001:502:ad09::12#53
wanted to pass it "-4" parameter on start-up, to limit it to IPv4.

This used to be easy by a file in /etc/sysconfig/  (or was it /etc/default ?).
Now (RHEL 9) it's complicated, thanks to elaborate systemd. 

There's an 'edit' option for the systemctl command:
 # systemctl edit named 

This copies a default config and allows editing: see below for an example.

It's of course a little more complicated than that. 
It was necessary to include the heading "[Service]" (very reasonable). 
But it then failed:
  # systemctl restart  named
   Failed to restart named.service: Unit named.service has a bad unit file setting.
   ..date..host.. systemd[1]: named.service: Service has more than one ExecStart= setting, which is only allowed for Type=oneshot services. Refusing.

It turns out that the ExecStart has to be cleared first!  See below.

----------------------------- example of the edited file in 'systemctl edit named' -----------------------------
### Editing /etc/systemd/system/named.service.d/override.conf
### Anything between here and the comment below will become the new contents of the file

[Service]
ExecStart=
ExecStart=/usr/sbin/named -4 -u named -c ${NAMEDCONF} $OPTIONS

### Lines below this comment will be discarded
### /usr/lib/systemd/system/named.service

# [Unit]
# Description=Berkeley Internet Name Domain (DNS)
# Wants=nss-lookup.target
# Wants=named-setup-rndc.service
# Before=nss-lookup.target
# After=named-setup-rndc.service
# After=network.target
# 
# [Service]
# Type=forking
# Environment=NAMEDCONF=/etc/named.conf
# EnvironmentFile=-/etc/sysconfig/named
# Environment=KRB5_KTNAME=/etc/named.keytab
# PIDFile=/run/named/named.pid
# 
# ExecStartPre=/bin/bash -c 'if [ ! "$DISABLE_ZONE_CHECKING" == "yes" ]; then /usr/sbin/named-checkconf -z "$NAMEDCONF"; else echo "Checking of zone files is disabled"; fi'
# ExecStart=/usr/sbin/named -u named -c ${NAMEDCONF} $OPTIONS
# ExecReload=/bin/sh -c 'if /usr/sbin/rndc null > /dev/null 2>&1; then /usr/sbin/rndc reload; else /bin/kill -HUP $MAINPID; fi'
# 
# ExecStop=/bin/sh -c '/usr/sbin/rndc stop > /dev/null 2>&1 || /bin/kill -TERM $MAINPID'
# 
# PrivateTmp=true
# 
# [Install]
# WantedBy=multi-user.target

----------------------------- end -----------------------------