Unwarapped topsar phsae toutorial and import export unwrap

Are there any unwrapped topsar phsae toutorial and import export unwrap cause many researchers facing problems related to this subject

http://step.esa.int/main/doc/tutorials/sentinel-1-toolbox-tutorials/

After Copy the snaphu command and paste it into the command terminal in the Linux virtual machine and run the command the result : file UnwPhase_ifg_srd_IW2_VV_08Feb2016_28Nov2015.snaphu.img is not writable whats
how to fix this problem please.