What does errno 121 (ESOCKTNOSUPPORT) mean?

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: Socket type not supported

Could be also:
Constant	Type	OS
ERROR_SEM_TIMEOUT	Win32 error	Windows
EREMOTEIO	errno	Linux
ENOLINK	errno	Windows
MISMATCHED_HAL	BugCheck Code	Windows

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EREMOTEIO	ENOLINK

ESOCKTNOSUPPORT

Socket type controls communication semantics

ESOCKTNOSUPPORT is about the requested socket type. Solaris says support for the type is not configured or implemented. POSIX defines types such as SOCK_STREAM, SOCK_DGRAM, and SOCK_SEQPACKET, and notes that support is implementation- and address-family-dependent.

The failure is different from EPROTONOSUPPORT: a system can know the family yet not provide the requested communication semantics. POSIX also documents historical variation where implementations may report EPROTONOSUPPORT or EPROTOTYPE for some unsupported-type cases, so the complete socket argument tuple matters.

What to record

Capture domain, type including any type flags, and protocol from the exact socket() call.
Verify the requested type is supported by the selected address family on Solaris rather than assuming another UNIX implementation's matrix.
If a wrapper adds SOCK_NONBLOCK or close-on-exec flags, log the final type value seen by the syscall.

References

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