Rsync error: error starting client-server Protocol (Code 5) at main.c(1648) [Receiver=3.1.2]
1. Try to close the firewall test

[root@sm ~]# systemctl stop firewalld

2. Check whether the confidential file attribute is 600

[root@sm ~]# ls -l /etc/rsyncd.secrets 
-rw------- 1 root root 26 Nov 29 22:00 /etc/rsyncd.secrets

3, check the configuration file for formatting errors, including command comments cannot be peer

[share]
comment = user share
path = /share
ignore errors
#exclude = lost+found/  
auth users = bob,maray

4, command syntax formatting error
rsync command syntax formatting error.