Andrea Dell'Amico wrote:

Don't do that, neither. Assign the group "backup" to the amanda user,
chown root /usr/local/sbin/amcheck, and then rerun it as amanda.

I've done what Gene Heskett said:

# cat /etc/group
...
backup::303:amanda
...
# cat /etc/passwd
...
amanda:x:400:303:Amanda Operator:/Disk2/amanda:/bin/bash
...

As user amanda:
bash-2.00$ tar zxvf amanda-2.4.4p1.tar.gz
...
bash-2.00$ export LDFLAGS="-L/usr/local/lib -R/usr/local/lib"
bash-2.00$ cd amanda-2.4.4p1
bash-2.00$ ./configure --with-user=amanda --with-group=backup
...
bash-2.00$ make
...
bash-2.00$ su
# make install
...
bash-2.00$ id amanda
uid=400(amanda) gid=303(backup)

bash-2.00$ amcheck daily
bash: /usr/local/sbin/amcheck: Permission denied

I've tried diverse suggestions from other posters (thanks!),
but so far can't get anything other than a verboten, or the usual
'port not secure' shinola.

Thanks, I'll keep trying.