Description of problem:

post script of systemd forcily append of `systemd` in following databases

- passwd
- group

While the behavior make sense for initial installation, but not necessary for upgrade. Some customers need to use their own nsswitch.conf, and would not want it to be modified by systemd upgrade script.


Quote Pavel Březina from https://bugzilla.redhat.com/show_bug.cgi?id=1577250#c7

> Do you actually need to run it during upgrade?
> Wouldn't it be sufficient to run it only during first installation?


Version-Release number of selected component (if applicable):

systemd-250-12.el9_1.1.x86_64

How reproducible:

always


Steps to Reproduce:
1. Edit /etc/nsswitch.conf, and make the passwd line become: 
 
   passwd: sss files
2. Upgrade systemd
3. grep passwd /etc/nsswitch.conf

Actual results:

systemd is forcibly appended 

passwd: sss files systemd

Expected results:

the passwd line is untouched

passwd: sss files

Additional info:

Work around:

Instead of removing systemd keywords, comment them out like

 
passwd:     files sss # systemd
group:      files sss # systemd


================ systemd post script
# rpm -q --scripts systemd-libs
postinstall scriptlet (using /bin/sh):


function mod_nss() {
    if [ -f "$1" ] ; then
        # Add nss-systemd to passwd and group
        grep -E -q '^(passwd|group):.* systemd' "$1" ||
        sed -i.bak -r -e '
                s/^(passwd|group):(.*)/\1:\2 systemd/
                ' "$1" &>/dev/null || :
    fi
}

FILE="$(readlink /etc/nsswitch.conf || echo /etc/nsswitch.conf)"
if [ "$FILE" = "/etc/authselect/nsswitch.conf" ] && authselect check &>/dev/null; then
        mod_nss "/etc/authselect/user-nsswitch.conf"
        authselect apply-changes &> /dev/null || :
else
        mod_nss "$FILE"
        # also apply the same changes to user-nsswitch.conf to affect
        # possible future authselect configuration
        mod_nss "/etc/authselect/user-nsswitch.conf"
fi
...