Automatic installation using a package repository, e.g. http://fon.rogue.be/lafonera
note: ipkgs must be for MIPS (Atheros, big endian)

let ipkg know, where to get it:

/etc/ipkg.conf
#src fon http://download.fon.com/release/fonera/0.7/packages
src whiterussian http://fon.rogue.be/lafonera
dest root /
dest ram /tmp

# then do:
root@OpenWrt:~# ipkg update
Downloading http://fon.rogue.be/lafonera
Updated list of available packages in /usr/lib/ipkg/lists/whiterussian
Done.


# ckeck if desired package is available:
root@OpenWrt:~# ipkg list|grep openntpd
openntpd - 3.7p1-1 - OpenNTPD is a FREE, easy to use implementation of NTP


# and finally, install it:
root@OpenWrt:~# ipkg install openntpd

#######################
Let's try manual:

root@OpenWrt:~# wget http://downloads.openwrt.org/whiterussian/packages/openntpd_3.7p1-1_mipsel.ipk
Connecting to downloads.openwrt.org[195.56.146.238]:80
openntpd_3.7p1-1_mip 100% |*****************************| 20684       00:00 ETA
root@OpenWrt:~# tar xzf openntpd_3.7p1-1_mipsel.ipk
root@OpenWrt:~# tar xzf data.tar.gz
root@OpenWrt:~# cd usr/sbin/
root@OpenWrt:~/usr/sbin# ls
ntpd



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Also check
http://fon.rogue.be/wiki/index.php/Main_Page