man 2 ktrace says that the following header files need to be included:

#include <sys/types.h>
#include <sys/uio.h>
#include <sys/ktrace.h>

But during compile, I get:

[stathis@netbsd ~]$ gcc fktrace.c -Wall -W -Wextra -ansi -pedantic
In file included from fktrace.c:9:
/usr/include/sys/ktrace.h:65: error: 'MAXCOMLEN' undeclared here (not  
in a function)
/usr/include/sys/ktrace.h:142: error: expected  
specifier-qualifier-list before 'sig_t'

It seems that the <sys/param.h> file needs to be included in <sys/ktrace.h>

Kind regards,
Stathis K