Configuring SNMP Traps

I’ve got an Ubuntu LTS 16.04 Server that I want to act as a Manager. There will be a few hundred Multiplexer devices which need to forward traps to the Manager’s IP.
I can’t seem to find any SNMP configuration guides that were able to answer all of my questions due to most of them being created with two linux servers in mind.
On my multiplexers, the SNMP configuration is only 1 line.

Manager[3] > 192.168.40.26

One of the ubuntu config guides I read said that the only thing the Manager needs is:

sudo apt-get install snmp snmp-mibs-downloader

and to comment out the #mibs line in

/etc/snmp/snmp.conf

However when I start:

root@alarmux:/home/abdmin# /usr/sbin/snmpd -f
Turning on AgentX master support.
Error opening specified endpoint "udp:161"
Server Exiting with code 1

UFW is not enabled.
Here is my config file:

###############################################################################
#
# EXAMPLE.conf:
#   An example configuration file for configuring the Net-SNMP agent ('snmpd')
#   See the 'snmpd.conf(5)' man page for details
#
#  Some entries are deliberately commented out, and will need to be explicitly activated
#
###############################################################################
#
#  AGENT BEHAVIOUR
#

#  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



###############################################################################
#
#  SNMPv3 AUTHENTICATION
#
#  Note that these particular settings don't actually belong here.
#  They should be copied to the file /var/lib/snmp/snmpd.conf
#     and the passwords changed, before being uncommented in that file *only*.
#  Then restart the agent

#  createUser authOnlyUser  MD5 "remember to change this password"
#  createUser authPrivUser  SHA "remember to change this one too"  DES
#  createUser internalUser  MD5 "this is only ever used internally, but still change the password"

#  If you also change the usernames (which might be sensible),
#  then remember to update the other occurances in this example config file to match.



###############################################################################
#
#  ACCESS CONTROL
#

                                                 #  system + hrSystem groups only
view   systemonly  included   .1.3.6.1.2.1.1
view   systemonly  included   .1.3.6.1.2.1.25.1

                                                 #  Full access from the local host
#rocommunity public  localhost
                                                 #  Default access to basic system info
 rocommunity public  default    -V systemonly
                                                 #  rocommunity6 is for IPv6
 rocommunity6 public  default   -V systemonly

                                                 #  Full access from an example network
                                                 #     Adjust this network address to match your local
                                                 #     settings, change the community string,
                                                 #     and check the 'agentAddress' setting above
#rocommunity secret  10.0.0.0/16

                                                 #  Full read-only access for SNMPv3
 rouser   authOnlyUser
                                                 #  Full write access for encrypted requests
                                                  #     Remember to activate the 'createUser' lines above
rwuser demo priv
#rwuser   authPrivUser   priv

#  It's no longer typically necessary to use the full 'com2sec/group/access' configuration
#  r[ow]user and r[ow]community, together with suitable views, should cover most requirements



###############################################################################
#
#  SYSTEM INFORMATION
#  

#  Note that setting these values here, results in the corresponding MIB objects being 'read-only'
#  See snmpd.conf(5) for more details
sysLocation    Sitting on the Dock of the Bay
sysContact     Me <[email protected]>
                                                 # Application + End-to-End layers
sysServices    72


#
#  Process Monitoring
#  
                               # At least one  'mountd' process               
proc  mountd             
                               # No more than 4 'ntalkd' processes - 0 is OK
proc  ntalkd    4
                               # At least one 'sendmail' process, but no more than 10
proc  sendmail 10 1

#  Walk the UCD-SNMP-MIB::prTable to see the resulting output 
#  Note that this table will be empty if there are no "proc" entries in the snmpd.conf file


#
#  Disk Monitoring
#
                               # 10MBs required on root disk, 5% free on /var, 10% free on all other disks
disk       /     10000
disk       /var  5%
includeAllDisks  10%

#  Walk the UCD-SNMP-MIB::dskTable to see the resulting output
#  Note that this table will be empty if there are no "disk" entries in the snmpd.conf file


#
#  System Load
#
                               # Unacceptable 1-, 5-, and 15-minute load averages
load   12 10 5

#  Walk the UCD-SNMP-MIB::laTable to see the resulting output
#  Note that this table *will* be populated, even without a "load" entry in the snmpd.conf file



###############################################################################     
#
#  ACTIVE MONITORING
#
                                    #   send SNMPv1  traps
 trapsink     localhost public
                                    #   send SNMPv2c traps
#trap2sink    localhost public
                                    #   send SNMPv2c INFORMs
#informsink   localhost public

#  Note that you typically only want *one* of these three lines                
#  Uncommenting two (or all three) will result in multiple copies of each notification.


#
#  Event MIB - automatically generate alerts
#  
                                   # Remember to activate the 'createUser' lines above
iquerySecName   internalUser      
rouser          internalUser
                                   # generate traps on UCD error conditions
defaultMonitors          yes
                                   # generate traps on linkUp/Down
linkUpDownNotifications  yes



###############################################################################
#
#  EXTENDING THE AGENT
#

#
#  Arbitrary extension commands
#  
 extend    test1   /bin/echo  Hello, world!
 extend-sh test2   echo Hello, world! ; echo Hi there ; exit 35
#extend-sh test3   /bin/sh /tmp/shtest

#  Note that this last entry requires the script '/tmp/shtest' to be created first,
#    containing the same three shell commands, before the line is uncommented

#  Walk the NET-SNMP-EXTEND-MIB tables (nsExtendConfigTable, nsExtendOutput1Table
#     and nsExtendOutput2Table) to see the resulting output

#  Note that the "extend" directive supercedes the previous "exec" and "sh" directives
#  However, walking the UCD-SNMP-MIB::extTable should still returns the same output,       
#     as well as the fuller results in the above tables.


#             
#  "Pass-through" MIB extension command
#
#pass .1.3.6.1.4.1.8072.2.255  /bin/sh       PREFIX/local/passtest
#pass .1.3.6.1.4.1.8072.2.255  /usr/bin/perl PREFIX/local/passtest.pl

# Note that this requires one of the two 'passtest' scripts to be installed first,             
#    before the appropriate line is uncommented.
# These scripts can be found in the 'local' directory of the source distribution,
#     and are not installed automatically.

#  Walk the NET-SNMP-PASS-MIB::netSnmpPassExamples subtree to see the resulting output

#
#  AgentX Sub-agents
#
                                           #  Run as an AgentX master agent
 master          agentx       
                                           #  Listen for network connections (from localhost)
                                           #    rather than the default named socket /var/agentx/master
#agentXSocket    tcp:localhost:705

snmpd 6083 root 8u IPv4 1309634 0t0 UDP *:snmp
snmpd 6083 root 10u IPv6 1309635 0t0 UDP localhost:snmp