What does errno 512 (ERESTARTSYS) mean?

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: the kernel selected signal-dependent restart handling for an interrupted syscall.

Could be also:
Constant	Type	OS
ECVPERORR	errno	Mac

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ECVCERORR	ECVPERORR

ERESTARTSYS

ERESTARTSYS is a Linux kernel restart code. Current Linux kernel comments state that ERESTART* codes should not be left for normal user programs; ptrace can observe them at syscall-exit tracing while the kernel is still converting the interrupted syscall into a restart or into EINTR.

The key detail is signal policy. ERESTARTSYS is the restart path that depends on whether the signal handler allows restart, commonly through SA_RESTART. It should be diagnosed at the syscall/signal boundary, not handled like a regular portable errno in application logic.

What to inspect

The interrupted syscall and whether it has restart semantics.
The delivered signal and handler flags.
Whether the observation comes from ptrace, strace, seccomp, or kernel instrumentation.
Whether user-space ultimately receives EINTR or a successful restarted syscall result.

Linux restart_syscall(2) · Linux internal errno definitions

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