PREIN

/bin/sh

getent group docker > /dev/null || /usr/sbin/groupadd -r docker
exit 0

PREUN

/bin/sh

 
if [ $1 -eq 0 ] && [ -x "/usr/lib/systemd/systemd-update-helper" ]; then 
    # Package removal, not upgrade 
    /usr/lib/systemd/systemd-update-helper remove-system-units docker || : 
fi

POSTIN

/bin/sh

 
if [ $1 -eq 1 ] && [ -x "/usr/lib/systemd/systemd-update-helper" ]; then 
    # Initial installation 
    /usr/lib/systemd/systemd-update-helper install-system-units docker || : 
fi

POSTUN

/bin/sh

 
if [ $1 -ge 1 ] && [ -x "/usr/lib/systemd/systemd-update-helper" ]; then 
    # Package upgrade, not uninstall 
    /usr/lib/systemd/systemd-update-helper mark-restart-system-units docker || : 
fi