errno 99 (ENOPROTOOPT): meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: Protocol not available

Could be also:
Constant	Type	OS
EADDRNOTAVAIL	errno	Linux
ENOSTR	errno	Mac
SECURITY1_INITIALIZATION_FAILED	BugCheck Code	Windows

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ENOSTR	ENETDOWN

ENOPROTOOPT

Option name and option level form a pair

ENOPROTOOPT points to protocol option selection. Solaris states that a bad option or level was specified when getting or setting protocol options. POSIX socket option APIs likewise take both a level and an option_name; the same numeric option name can only be interpreted within its level.

This is not equivalent to an unsupported socket operation. EOPNOTSUPP concerns an operation on an endpoint, whereas ENOPROTOOPT directs attention to getsockopt()/setsockopt() arguments and the protocol that owns the option namespace.

Option-level diagnostics

Log level, option name, socket family/type, and protocol before any wrapper translates constants.
Confirm the option is documented for that protocol and Solaris release; options are not automatically portable across UNIX implementations.
Check conditional compilation around IPv4, IPv6, TCP, and socket-level options to catch a constant used with the wrong level.

References

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