README.systemd

README.systemd
--------------
Net-SNMP provides two daemons, which support systemd system manager. 
See http://www.freedesktop.org/wiki/Software/systemd to learn how
systemd works. Both socket activation and notification is supported by these
daemons.

To enable systemd support, the sources must be compiled with
--with-systemd configure option.

snmpd - The SNMP agent
----------------------
Socket activation od snmpd daemon is implemented, but it's discouraged.
The reason is simple - snmpd not only listens and processes SNMP requests
from network, but also gathers system statistics counters, sends traps and
communicates with subagents. It even opens few netlink sockets.

In other words, snmpd should run from system start to properly work.
This can be done in two ways:
1) either as snmpd service unit with 'Type=notification' and without a socket
   unit
2) or as snmpd service unit with 'Type=simple', appropriate socket socket unit
   and the snmpd service enabled. This way systemd creates the snmpd listening
   socket early during boot and passes the sockets to snmpd slightly later
   (but still during machine boot). This way systemd can paralelize start of
   services, which depend on snmpd. Admins must adjust the socket file manually,
   depending if the snmpd support AgentX, IPv6, SMUX etc.

snmpd should be started with '-f' command line parameter to disable forking -
systemd does that for us automatically.


snmptrapd - The trap processing daemon
--------------------------------------
snmptrapd supports full socket activation and also notification (if needed).
Both 'Type=simple' (with appropriate socket unit) and 'Type=notify' services
will work. Again, '-f' parameter should be provided on snmptrapd command line.

If integration with SNMP agent using AgentX protocol is enabled, snmptrapd should
start during boot and not after first SNMP trap arrives. Same rules as for snmpd
applies then.