errno 109 (ETOOMANYREFS): meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: too many file descriptors are in flight through a UNIX domain socket.

Could be also:
Constant	Type	OS
ERROR_BROKEN_PIPE	Win32 error	Windows
EDESTADDRREQ	errno	Windows
SESSION1_INITIALIZATION_FAILED	BugCheck Code	Windows

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ETOOMANYREFS

ETOOMANYREFS has a very concrete Linux diagnostic use with UNIX domain sockets. The unix(7) page documents it for sendmsg(2) when sending file descriptors with SCM_RIGHTS: the number of in-flight descriptors exceeds the process limit and the caller lacks CAP_SYS_RESOURCE.

It is therefore not a normal network saturation error. It often means that descriptor-passing backpressure is missing: the sender keeps transferring rights faster than the receiver consumes and closes them. Retrying without draining the receiver can increase the in-flight count again.

Check these first

How many descriptors are sent per message and whether they are acknowledged by the receiver.
The sender and receiver RLIMIT_NOFILE values.
Whether the receiver closes descriptors after importing them.
Whether the sender has CAP_SYS_RESOURCE and whether relying on it would hide a leak.

Linux unix(7) · Linux sendmsg(2) · Linux errno(3) · Linux UAPI errno definitions

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