sudo service smbd restart
Job for smbd.service failed because the control process exited with error code.
See "systemctl status smbd.service" and "journalctl -xe" for details.

重启失败，查看详细情况

systemctl status smbd.service
● smbd.service - Samba SMB Daemon
     Loaded: loaded (/lib/systemd/system/smbd.service; enabled; vendor preset: enabled)
     Active: failed (Result: exit-code) since Thu 2021-09-30 09:07:59 CST; 37s ago
       Docs: man:smbd(8)
             man:samba(7)
             man:smb.conf(5)
    Process: 32088 ExecStartPre=/usr/share/samba/update-apparmor-samba-profile (code=exited, status=0/SUCCESS)
    Process: 32097 ExecStart=/usr/sbin/smbd --foreground --no-process-group $SMBDOPTIONS (code=exited, status=1/FAILURE)
   Main PID: 32097 (code=exited, status=1/FAILURE)

Sep 30 09:07:59 ubuntu systemd[1]: Starting Samba SMB Daemon...
Sep 30 09:07:59 ubuntu systemd[1]: smbd.service: Main process exited, code=exited, status=1/FAILURE
Sep 30 09:07:59 ubuntu systemd[1]: smbd.service: Failed with result 'exit-code'.
Sep 30 09:07:59 ubuntu systemd[1]: Failed to start Samba SMB Daemon.

journalctl -xe
-- The job identifier is 9729 and the job result is failed.
Sep 30 09:09:01 ubuntu CRON[32100]: pam_unix(cron:session): session opened for user root by (uid=0)
Sep 30 09:09:01 ubuntu CRON[32101]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && if [ ! -d /run/systemd/system ]; then /usr/lib/php>
Sep 30 09:09:01 ubuntu CRON[32100]: pam_unix(cron:session): session closed for user root
Sep 30 09:09:22 ubuntu systemd[1]: Starting Clean php session files...
-- Subject: A start job for unit phpsessionclean.service has begun execution
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- A start job for unit phpsessionclean.service has begun execution.
-- 
-- The job identifier is 9796.
Sep 30 09:09:22 ubuntu sessionclean[32118]: PHP Warning:  PHP Startup: Unable to load dynamic library 'php_curl.so' (tried: /usr/lib/php>
Sep 30 09:09:22 ubuntu sessionclean[32118]: PHP Warning:  PHP Startup: Unable to load dynamic library 'php_mysql.so' (tried: /usr/lib/ph>
Sep 30 09:09:22 ubuntu sessionclean[32118]: PHP Warning:  PHP Startup: Unable to load dynamic library 'php_mysqli.so' (tried: /usr/lib/p>
Sep 30 09:09:22 ubuntu systemd[1]: phpsessionclean.service: Succeeded.
-- Subject: Unit succeeded
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- The unit phpsessionclean.service has successfully entered the 'dead' state.
Sep 30 09:09:22 ubuntu systemd[1]: Finished Clean php session files.
-- Subject: A start job for unit phpsessionclean.service has finished successfully
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- A start job for unit phpsessionclean.service has finished successfully.
-- 
-- The job identifier is 9796.

看不出错误情况，打印samba日志

tail -f /var/log/samba/log.smbd
[2021/09/30 09:01:02.693433,  0] ../../source3/smbd/server.c:1775(main)
  smbd version 4.11.6-Ubuntu started.
  Copyright Andrew Tridgell and the Samba Team 1992-2019
[2021/09/30 09:01:02.704827,  0] ../../lib/util/util.c:427(directory_create_or_exist_strict)
  invalid permissions on directory '/var/lib/samba/private/msg.sock': has 0777 should be 0700
[2021/09/30 09:07:59.966661,  0] ../../source3/smbd/server.c:1775(main)
  smbd version 4.11.6-Ubuntu started.
  Copyright Andrew Tridgell and the Samba Team 1992-2019
[2021/09/30 09:07:59.966945,  0] ../../lib/util/util.c:427(directory_create_or_exist_strict)
  invalid permissions on directory '/var/lib/samba/private/msg.sock': has 0777 should be 0700

msg.sock文件权限问题，修改文件权限

sudo chmod 700 /var/lib/samba/private/msg.sock

再次重启samba

sudo service smbd restart