Apparently `-lkvm` is needed for swap on FreeBSD Thanks to Micheal Buch and Jason Smith (See thread https://lists.suckless.org/dev/1907/33594.html)
@@ -15,6 +15,7 @@ CPPFLAGS = -I$(X11INC) -D_DEFAULT_SOURCE
CFLAGS = -std=c99 -pedantic -Wall -Wextra -Os
LDFLAGS = -L$(X11LIB) -s
# OpenBSD: add -lsndio
+# FreeBSD: add -lkvm
LDLIBS = -lX11
# compiler and linker