どうやら ntpdate が deprecated となっていて、いれちゃマズイようだ
astroberry@astroberry:~ $ apt search ntp
Sorting... Done
Full Text Search... Done
adjtimex/stable 1.29-10 armhf
....
中略
....
ntp/stable,now 1:4.2.8p12+dfsg-4 armhf [residual-config]
Network Time Protocol daemon and utility programs
ntp-doc/stable 1:4.2.8p12+dfsg-4 all
Network Time Protocol documentation
ntpdate/stable 1:4.2.8p12+dfsg-4 armhf
client for setting system time from NTP servers (deprecated)
...
以下略
チラホラ見かける chrony が後継の仕組みらしい