What does errno 91 (ERESTART) mean?

ERESTART

Internal syscall restart state

On Solaris, ERESTART is errno value 91. The base message is Restartable system call, but the useful diagnostic context is narrower than the short message: Solaris uses this not-externally-visible value when an interrupted system call should be restarted.

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

What to check

• Ordinary application code should normally see EINTR or a restarted call rather than this result.
• If tracing shows this result, inspect signal handling and syscall restart flags.
• Do not expose it as a stable application-level protocol error.

References

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

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