Get rid of sudo / running as root

Makefile

@@ -45,6 +45,16 @@ install: $(BINS) $(LIBEXECS)
 	mkdir -p $(DESTDIR)$(LIBEXECDIR)
 	install $(BINS) $(DESTDIR)$(BINDIR)
 	install $(LIBEXECS) $(DESTDIR)$(LIBEXECDIR)
+	@echo
+	@echo '--------------------------------------------------------------------------------'
+	@echo 'To finish the installation, set the CAP_NET_RAW on $(LIBEXECDIR)/ethermess-backend with'
+	@echo
+	@echo '    # setcap CAP_NET_RAW=ep $(LIBEXECDIR)/ethermess-backend'
+	@echo
+	@echo 'ethermess-backend needs to be able to create a raw ethernet packet socket, which'
+	@echo 'is a privileged operation. CAP_NET_RAW allows it to be done without root'
+	@echo 'privileges.'
+	@echo '--------------------------------------------------------------------------------'
 
 uninstall:
 	cd $(DESTDIR)$(BINDIR) && rm $(BINS)

ethermess.py

@@ -516,9 +516,13 @@ def eventloop(proc):
 def main():
 	global own_nick, own_status
 
+	if len(sys.argv) != 3:
+		print("Usage: %s interface nick" % sys.argv[0], file=sys.stderr)
+		sys.exit(1)
+
 	_, interface, own_nick = sys.argv
 
-	proc = subprocess.Popen(['sudo', libexec_dir + '/ethermess-backend', interface], stdin = subprocess.PIPE, stdout = subprocess.PIPE, stderr = sys.stderr, bufsize = 0)
+	proc = subprocess.Popen([libexec_dir + '/ethermess-backend', interface], stdin = subprocess.PIPE, stdout = subprocess.PIPE, stderr = sys.stderr, bufsize = 0)
 
 	# Tell the backend the status and nick
 	own_status = statuses.available

test.sh

@@ -1,4 +1,4 @@
 #!/bin/sh
-sudo true &&
 LIBEXECDIR=. make &&
+sudo setcap CAP_NET_RAW=ep ethermess-backend &&
 ./ethermess "$@"