FreeBSD: syslog-ng: I/O error occurred while writing; fd='xx', error='No buffer space available (yy)'

Mark Blackman mark at
Thu Mar 22 09:52:18 UTC 2012

On 22 Mar 2012, at 09:00, Traiano Welcome wrote:

> My question is: What does this error mean, and how can I resolve it?

From a very casual inspection of the problem, I'd say you're pushing out
syslog messages faster than the kernel can get them out the interface.
How many syslog messages are going in (per second) and what kind of
network interface are you trying to send them out through?

> I have tried to frame this as an operating system kernel resource issue,
> and experimented with increasing the freebsd kernel sysctls for UDP
> performance:

I think you can push nmbclusters up to about 600k, but if your input is
running faster than your output, no amount of buffering will permanently
stave off this problem.

- Mark

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