Specify location of netstat binary as a constant

letsencrypt/client/constants.py

@@ -66,3 +66,7 @@ IConfig.work_dir. Used for easy revocation."""
 REC_TOKEN_DIR = "recovery_tokens"
 """Directory where all recovery tokens are saved (relative to
 IConfig.work_dir)."""
+
+NETSTAT = "/bin/netstat"
+"""Location of netstat binary for checking whether a listener is already
+running on the specified port (Linux-specific)."""

letsencrypt/client/standalone_authenticator.py

@@ -275,7 +275,7 @@ class StandaloneAuthenticator(object):
 
         try:
             proc = subprocess.Popen(
-                ["/bin/netstat", "-nta", "--program"],
+                [constants.NETSTAT, "-nta", "--program"],
                 stdout=subprocess.PIPE, stderr=subprocess.PIPE)
             stdout, _ = proc.communicate()
             if proc.wait() != 0: