Enable SNMP on Ubuntu Server

On the agent and manager server:

apt update

apt install snmp snmp-mibs-downloader

On the agent server:

vim /etc/snmp/snmp.conf  

/etc/snmp/snmp.conf

# As the snmp packages come without MIB files due to license reasons, loading # of MIBs is disabled by default. If you added the MIBs you can reenable # loading them by commenting out the following line.  

#mibs :

vim /etc/snmp/snmpd.conf

Comment the following lines: 

 #  Listen for connections from the local system only
#agentAddress  udp:127.0.0.1:161
#  Listen for connections on all interfaces (both IPv4 *and* IPv6)
agentAddress udp:161,udp6:[::1]:161

vim /etc/snmp/snmpd.conf

Add these lines: 

createUser bootstrap MD5 temp_password DES

rwuser bootstrap priv
rwuser demo priv 

systemctl restart snmpd

On the Manager server:

Verify with snmpget 

snmpget -u bootstrap -l authPriv -a MD5 -x DES -A temp_password -X temp_password agent_server_ip_address 1.3.6.1.2.1.1.1.0 

Output
SNMPv2-MIB::sysDescr.0 = STRING: Linux agent 4.15.0-66-generic #75-Ubuntu SMP Tue Oct 1 05:24:09 UTC 2019 x86_64 

Create a user based on bootstrap 

snmpusm -u bootstrap -l authPriv -a MD5 -x DES -A temp_password -X temp_password agent_server_ip_address create demo bootstrap 

 Change the password

snmpusm -u demo -l authPriv -a MD5 -x DES -A temp_password -X temp_password agent_server_ip_address passwd temp_password new_password 

On the Agent server:

Remove the bootstrap

vim /etc/snmp/snmpd.conf 

Comment the following lines:

...
#createUser bootstrap MD5 temp_password DES
#rwuser bootstrap priv
...

On the Manager server:

snmpusm -u bootstrap -l authPriv -a MD5 -x DES -A temp_password -X temp_password 100.90.8.48 delete bootstrap
User successfully deleted.

 
On the Agent server: 

systemctl restart snmpd