diff --git a/spug_api/apps/host/views.py b/spug_api/apps/host/views.py
index 3b0e76e..7fd6fdb 100644
--- a/spug_api/apps/host/views.py
+++ b/spug_api/apps/host/views.py
@@ -66,11 +66,11 @@ def valid_ssh(hostname, port, username, password):
         AppSetting.set('public_key', public_key, 'ssh public key')
     if password:
         cli = SSH(hostname, port, username, password=password)
-        code, stdout, stderr = cli.exec_command('mkdir -p -m 700 ~/.ssh && \
+        code, out = cli.exec_command('mkdir -p -m 700 ~/.ssh && \
                 echo %r >> ~/.ssh/authorized_keys && \
                 chmod 600 ~/.ssh/authorized_keys' % public_key)
         if code != 0:
-            raise Exception('add public key error: ' + ''.join(x for x in stderr))
+            raise Exception(f'add public key error: {out!r}')
     else:
         cli = SSH(hostname, port, username, private_key)