Gow to set / add CAP_NET_ADMIN in linux?

Check your script again. There should be two backquotes (`) around the which command. Backquotes denote a sub-shell command, the output of which is inserted into the invoking command. In your case which hcitool probably returns /usr/bin/hcitool, so setcap 'cap_net_admin' `which hcitool` is equivalent to setcap 'cap_net_admin' /usr/bin/hcitool Note that if you're using bash, then sub-shells are more often called using the $( ) usage rather than the backquotes. There are a few reasons for this. Firstly, depending on the font used, backqoutes and single quotes can be hard to distinguish, leading to scripting errors. They're also quite small and easy to miss when reading an example. But mostly, the $( ) usage can be nested, whereas backquotes cannot. This means that with $( ) you can do

$ cmd1  c1arg1 $(cmd2 $(cmd3 c3arg1 c3arg2) c2arg1 c2arg2) c1arg2

If you were to try this with backquotes you get the following:

$ cmd1 c1arg1 `cmd2 `cmd3 c3arg1 c3arg2 `c2arg1 c2arg2` c1arg2

In this case, cmd2 gets called in a sub-shell with no arguments, we try to create a sub-shell with the command c2arg1 (which probably fails).