The munin async daemon connects to a munin node periodically, and requests plugin configuration and data.
This is stored in a spool directory, which is read by munin-async.
| -s <spooldir>¶
Directory for spooled data [/var/lib/munin/spool]
Connect a munin node running on this host name and port [localhost:4949]
Set default interval size [86400 (one day)]
Number of interval files to retain 
Disable automated spool dir cleanup
Fork one thread per plugin available on the node. [no forking]
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See munin for an overview over munin.
See also Asynchronous proxy node for more information and examples of how to configure munin-asyncd.