root@sonic:~# systemctl stop serial-getty@ttyS1.service
root@sonic:~# systemctl status serial-getty@ttyS1.service
● serial-getty@ttyS1.service - Serial Getty on ttyS1
     Loaded: loaded (/lib/systemd/system/serial-getty@.service; enabled-runtime; vendor preset: enabled)
     Active: inactive (dead) since Mon 2021-08-02 05:37:43 UTC; 10s ago
       Docs: man:agetty(8)
             man:systemd-getty-generator(8)
             http://0pointer.de/blog/projects/serial-console.html
    Process: 6404 ExecStart=/sbin/agetty -o -p -- \u 9600 ttyS1 $TERM (code=killed, signal=TERM)
   Main PID: 6404 (code=killed, signal=TERM)

Aug 02 05:33:16 sonic /container[486266]: read_data: config:True feature:pmon fields:[('set_owner', 'local'), ('no_fallback_to_local', False)] val:['local',
Aug 02 05:33:16 sonic /container[486266]: read_data: config:False feature:pmon fields:[('current_owner', 'none'), ('remote_state', 'none'), ('container_id',
Aug 02 05:33:16 sonic /container[486266]: container_stop: pmon: set_owner:local current_owner:none remote_state:none docker_id:pmon
Aug 02 05:33:20 sonic /container[486266]: docker cmd: stop for pmon
Aug 02 05:33:20 sonic /container[486266]: container_stop: END
Aug 02 05:37:19 sonic passwd[487639]: pam_unix(passwd:chauthtok): password changed for admin
Aug 02 05:37:43 sonic systemd[1]: Stopping Serial Getty on ttyS1...
Aug 02 05:37:43 sonic sudo[486141]: pam_unix(sudo:session): session closed for user root
Aug 02 05:37:43 sonic systemd[1]: serial-getty@ttyS1.service: Succeeded.
root@sonic:~# monit status serial-getty
Monit 5.20.0 uptime: 6d 22h 45m

Process 'serial-getty'
  status                       Running
  monitoring status            Monitored
  monitoring mode              active
  on reboot                    start
  pid                          487705
  parent pid                   487651
  uid                          0
  effective uid                0
  gid                          0
  uptime                       0m
  threads                      1
  children                     1
  cpu                          0.0%
  cpu total                    0.0%
  memory                       0.1% [4.0 MB]
  memory total                 0.1% [5.0 MB]
  data collected               Mon, 02 Aug 2021 05:38:34

root@sonic:~# systemctl status serial-getty@ttyS1.service
● serial-getty@ttyS1.service - Serial Getty on ttyS1
     Loaded: loaded (/lib/systemd/system/serial-getty@.service; enabled-runtime; vendor preset: enabled)
     Active: active (running) since Mon 2021-08-02 05:39:34 UTC; 27s ago
       Docs: man:agetty(8)
             man:systemd-getty-generator(8)
             http://0pointer.de/blog/projects/serial-console.html
   Main PID: 487793 (login)
      Tasks: 4 (limit: 9517)
     Memory: 5.2M
     CGroup: /system.slice/system-serial\x2dgetty.slice/serial-getty@ttyS1.service
             ├─487793 /bin/login -p --
             ├─487811 -bash
             ├─487816 sudo -i
             └─487817 -bash

Aug 02 05:39:34 sonic systemd[1]: Started Serial Getty on ttyS1.
Aug 02 05:39:43 sonic login[487793]: pam_unix(login:session): session opened for user admin by LOGIN(uid=0)
Aug 02 05:39:45 sonic sudo[487816]:    admin : TTY=ttyS1 ; PWD=/home/admin ; USER=root ; COMMAND=/bin/bash
root@sonic:~#