What do I need to modify in the Makefile.linux file for my Ubuntu system?
short answer: to whatever YOUR system, and your interests, need
i don't use ubuntu, so can't help you specifically i strongly suggest you look at the defaults, and modify path accordingly for your ubu sys; if you're building from src & installing, you should know your tools & path paths fwiw, mine, for *my* fedoral install, which i do NOT recommend you blindly copy/use, is milter-regex-2.7/Makefile.my_linux CFLAGS+= LDFLAGS= -L/usr/lib64 -lmilter -lpthread -lbsd all: milter-regex milter-regex.cat8 milter-regex: milter-regex.o eval.o y.tab.o gcc -o milter-regex milter-regex.o eval.o y.tab.o $(LDFLAGS) milter-regex.o: milter-regex.c eval.h gcc $(CFLAGS) -c milter-regex.c eval.o: eval.c eval.h gcc $(CFLAGS) -c eval.c y.tab.o: y.tab.c gcc $(CFLAGS) -c y.tab.c y.tab.c: parse.y yacc -d parse.y milter-regex.cat8: milter-regex.8 nroff -Tascii -mandoc milter-regex.8 > milter-regex.cat8 clean: rm -f *.core milter-regex y.tab.* *.o *.cat8 install: rm -rf /usr/local/milter-regex mkdir -p /usr/local/milter-regex/{share/man/man8,sbin} cp ./milter-regex /usr/local/milter-regex/sbin cp milter-regex.8 milter-regex.cat8 /usr/local/milter-regex/share/man/man8/ uninstall: rm -rf /usr/local/milter-regex