Tramp hang waiting for prompts from remote shell

[Zhongwei Yao]

Hi, all,
when I open /ssh:ser03: in emacs, it hangs with prompt: Waiting for prompts
from remote shell...

My setup is 1. start emacs by emacs -Q, 2. remove server ser03's .bashrc
and .bash_profile is cleared. and emacs is version 26.2, tramp version is
2.3.5.26.2.

I set the tramp-verbose to 10 and get the following log:

15:44:14.206923 tramp-set-connection-property (7) # process-buffer nil
15:44:14.207182 tramp-maybe-open-connection (3) # Opening connection for
ser03 using ssh...
15:44:14.207512 tramp-get-connection-property (7) # login-args undef
15:44:14.207592 tramp-get-connection-property (7) # login-args undef
15:44:14.207683 tramp-get-connection-property (7) # process-name nil
15:44:14.207745 tramp-get-connection-property (7) # process-buffer nil
15:44:14.208550 tramp-set-connection-property (7) # vector (tramp-file-name
ssh nil nil ser03 nil /mnt/ssd/user01/ nil)
15:44:14.208636 tramp-maybe-open-connection (6) # /bin/sh -i
15:44:14.208698 tramp-get-connection-property (7) # vector (tramp-file-name
ssh nil nil ser03 nil /mnt/ssd/user01/ nil)
15:44:14.208769 tramp-get-connection-property (7) # check-remote-echo nil
15:44:14.208825 tramp-get-connection-property (7) # check-remote-echo nil
15:44:14.209513 tramp-accept-process-output (10) # *tramp/ssh ser03* run t
#$
15:44:14.209580 tramp-get-connection-property (7) # check-remote-echo nil
15:44:14.209637 tramp-get-connection-property (7) # check-remote-echo nil
15:44:14.209702 tramp-wait-for-regexp (6) #
#$
15:44:14.209770 tramp-get-connection-property (7) # login-program undef
15:44:14.209838 tramp-get-connection-property (7) # login-args undef
15:44:14.209903 tramp-get-connection-property (7) # login-env undef
15:44:14.209968 tramp-get-connection-property (7) # async-args undef
15:44:14.210030 tramp-get-connection-property (7) # connection-timeout undef
15:44:14.210090 tramp-get-connection-property (7) # temp-file undef
15:44:14.210201 tramp-set-connection-property (7) # temp-file
/tmp/tramp.Retqm2
15:44:14.210691 tramp-maybe-open-connection (3) # Sending command ‘exec ssh
  -o ControlMaster=auto -o ControlPath='tramp.%C' -o ControlPersist=no -e
none ser03’
15:44:14.210773 tramp-get-connection-property (7) # process-name nil
15:44:14.210838 tramp-get-connection-property (7) # remote-echo nil
15:44:14.210896 tramp-send-command (6) # exec ssh   -o ControlMaster=auto
-o ControlPath='tramp.%C' -o ControlPersist=no -e none ser03
15:44:14.210958 tramp-get-connection-property (7) # process-name nil
15:44:14.211018 tramp-get-connection-property (7) # chunksize nil
15:44:14.211077 tramp-set-connection-property (7) # last-cmd-time (24005
7374 211060 426000)
15:44:14.211139 tramp-send-string (10) # exec ssh   -o ControlMaster=auto
-o ControlPath='tramp.%C' -o ControlPersist=no -e none ser03
15:44:14.211199 tramp-get-connection-property (7) # process-buffer nil
15:44:14.211281 tramp-set-connection-property (7) # first-password-request
nil
15:44:14.211480 tramp-process-actions (3) # Waiting for prompts from remote
shell...
15:44:15.212739 tramp-accept-process-output (10) # *tramp/ssh ser03* run nil
15:44:15.212812 tramp-process-one-action (5) # Looking for regexp
"\(.*\(user\|login\)\( .*\)?: *\)\'" from remote shell
15:44:15.212878 tramp-get-connection-property (7) # check-remote-echo nil
15:44:15.212935 tramp-get-connection-property (7) # check-remote-echo nil

I notice the remote shell doesn't have any output at the following line:
15:44:15.212739 tramp-accept-process-output (10) # *tramp/ssh ser03* run nil

But when I try to run the command:
  exec ssh   -o ControlMaster=auto -o ControlPath='tramp.%C' -o
ControlPersist=no -e none ser03
it give the following output:
  Welcome to Ubuntu 16.04.6 LTS (GNU/Linux 4.15.0-47-generic x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

0 packages can be updated.
0 updates are security updates.

New release '18.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.


Last login: Fri Nov  8 15:42:10 2019 from 192.168.1.1

What can I do to solve it?

--
Best regards,
Zhongwei