diff --git a/tools/genpw.py b/tools/genpw.py
index b840251..ca0266a 100755
--- a/tools/genpw.py
+++ b/tools/genpw.py
@@ -18,18 +18,23 @@ parser.add_argument('--password', '-p',
                     required=False)
 parser.add_argument('--username', '-u',
                     help='Username',
-                    required=True)
+                    required=False)
 parser.add_argument('--topic', '-t',
                     help='Initially granted topic',
-                    required=True)
+                    required=False)
 parser.add_argument('--acl', '-a',
                     help='ACL value for topic, Bit0=read, Bit1=write, Bit2=subscribe',
-                    required=True)
+                    required=False)
+parser.add_argument('--printonly', '-p',
+                    help='Just print the password hash, do not write to database',
+                    action='store_true')
 
 args = parser.parse_args()
 length = args.length
 password = args.password
 
+print_only = args.printonly
+
 alphabet = string.ascii_letters + string.digits
 iterations = 100000
 
@@ -47,28 +52,37 @@ pw = f"PBKDF2$sha512${iterations}${salt_b64}${hash}"
 print(f"{password=}")
 print(f"hash={pw}")
 
+if not print_only:
+    login = args.username
+    if (not login):
+        raise Exception("For writing to database a username must be given")
+    topic = args.topic
+    acl = int(args.acl)
 
-login = args.username
-topic = args.topic
-acl = int(args.acl)
+    conn = psycopg2.connect()
+    conn.autocommit = False
 
-conn = psycopg2.connect()
-conn.autocommit = False
-
-try:
-    with conn:
-        with conn.cursor() as cur:
-            cur.execute('insert into users_t (username, pw) values(%(username)s, %(pw)s) returning id', 
-                        { 'username': login, 'pw': pw })
-            res = cur.fetchone()
-            if res is None:
-                raise Exception("Unable to add user to database")
-            id = res[0]
-            print("User added to database")
-        with conn.cursor() as cur:
-            cur.execute('insert into acls_t ("user", topic, rw) values(%(user)s, %(topic)s, %(rw)s)',
-                        { 'user': id, 'topic': topic, 'rw': acl })
-            print("ACL added to database")
-finally:
-    if conn:
-        conn.close()
+    try:
+        with conn:
+            with conn.cursor() as cur:
+                cur.execute("""
+                            insert into users_t (username, pw) 
+                                values(%(username)s, %(pw)s) 
+                                on conflict do update
+                                    set pw = %(pw)s
+                                returning id 
+                            """,
+                            { 'username': login, 'pw': pw })
+                res = cur.fetchone()
+                if res is None:
+                    raise Exception("Unable to add user to database")
+                id = res[0]
+                print("User added to database")
+            if (topic and acl):
+                with conn.cursor() as cur:
+                    cur.execute('insert into acls_t ("user", topic, rw) values(%(user)s, %(topic)s, %(rw)s)',
+                                { 'user': id, 'topic': topic, 'rw': acl })
+                    print("ACL added to database")
+    finally:
+        if conn:
+            conn.close()