There are several extremely useful commands that I frequent.  These include, tar, find, and rsync. On the QNAP, these are much older versions and or dumbed down which negative impacts the capabilities of each of these tools.  There is a cure, Entware_1.03std.qpkg.  This article is a basic overview of how to install the desired tools.

Download

Go to qnapclub and search for Entware-3x-Std.

Install QNAP Package

From your QNAP, go to App Center to  install  manually.

Install Utility

Go to the bin.

cd /share/CACHEDEV1_DATA/.qpkg/Entware/bin

Type in command to install iPerf3 or desired app.

./opkg install iperf3
./opkg install find
./opkg install tar