What does errno 3 (ESRCH) mean?

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: The selected process or process group did not exist when the API resolved the supplied identifier.

Could be also:
Constant	Type	OS
ERROR_PATH_NOT_FOUND	Win32 error	Windows
STATUS_WAIT_3	NTSTATUS	Windows
KERN_NO_SPACE	Kern return	Mac
ippStsSqrtNegArg	Intel Ipp Status	Any
INVALID_AFFINITY_SET	BugCheck Code	Windows

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ENOENT	EINTR

ESRCH

Process identity is time-sensitive

ESRCH is most familiar from kill(): the supplied process ID or process-group ID did not identify a target at the time the kernel handled the request. The same condition can occur after a child has already been reaped, or when Linux pidfd_open() is asked to obtain a descriptor for a process that has already disappeared.

This is different from EPERM. EPERM means a target was found but the caller was not allowed to signal it; ESRCH means the lookup found no target. A preliminary kill(pid, 0) check can test a PID without sending a signal, but it cannot make a later operation race-free because the process may exit after the check.

What to record and how to handle it

Log the exact operation, PID or process-group ID, requested signal, and the relevant PID-namespace or service-manager context.
For a managed child, inspect waitpid() and SIGCHLD handling: an earlier wait in another code path may already have consumed the child state.
Decide explicitly whether a missing target means an expected “already stopped” outcome or a control-plane error. Retrying an unchanged raw PID does not recreate the original process.
On Linux, use a PID file descriptor for long-lived process management when available. pidfd_send_signal() addresses a stable process reference and reports ESRCH after that referenced process has terminated, avoiding accidental signaling after PID reuse.

References

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