What does errno 48 (ENOTSUP) mean?

ENOTSUP

Unsupported feature or operation

On Solaris, ENOTSUP is errno value 48. The base message is Operation not supported, but the useful diagnostic context is narrower than the short message: solaris does not support the requested feature or operation in this system version or object context.

For ENOTSUP, use the Solaris-specific errno table first, then compare with POSIX only for portable behavior. For ENOTSUP, some Solaris values share names with other UNIX systems but have different numbers or more specific historical meanings.

What to check for ENOTSUP

• Check whether the failure is system-wide support, filesystem support, socket option support, or device capability.
• Use feature detection and alternate code paths rather than retry loops.
• Do not assume it means invalid syntax; EINVAL is a different contract violation.

References for ENOTSUP

• Oracle Solaris intro(2): error numbers
• illumos errno.h definitions
• POSIX errno.h

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