The sibRNAfold package needs to be downloaded, and then unpacked and compiled using:
tar -zxvf sibRNAfold-1.0.tar.gz
cd sibRNAfold-1.0
./configure
make
make install (optional, requires root privileges)
Important note:
The options -p (calculation of partition functions), -d3 and -circ are not available in this release of sibRNAfold.