[ns] ns compilation problem

["\"TSANG Chi Man Estella\"" <c7609080@comp.polyu.edu.hk>]

Hi, I received this error when trying to compile ns-2.1b6. Can anyone let
me know what has gone wrong and what error 1 means :

In file included from scheduler.cc:49:
mem-trace.h: In method `void MemInfo::checkpoint()':
mem-trace.h:67: implicit declaration of function `int getrusage(...)'
make: *** [scheduler.o] Error 1

Here are the version of the programs that I am using : 
Version of ns : ns-2.1b6
Version of TCL : 8.0.4
Version of TK : 8.0
Version of otcl : 1.0a5
Version of tclcl : 1.0b9


Thanks in advance.

Regards
Estella