errno 56 (EBADRQC) in Linux: meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: EBADRQC is a legacy Linux errno meaning invalid legacy request code.

Could be also:
Constant	Type	OS
ERROR_TOO_MANY_CMDS	Win32 error	Windows
EISCONN	errno	Mac
EDEADLOCK	errno	Solaris
SERIAL_DRIVER_INTERNAL	BugCheck Code	Windows

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EBADSLT	EISCONN

EBADRQC

EBADRQC: Linux legacy errno

EBADRQC (errno 3) reports that the legacy request channel does not accept the supplied request-code value. These names come from historical System V/XENIX compatibility interfaces; on modern Linux they usually point to a driver, STREAMS-compatibility layer, or legacy IPC contract rather than a general filesystem error.

Evidence to capture

Record request code, ioctl/API entry point, driver version, and accepted command namespace.

Focused test

issue one documented request code through the same channel and compare the first errno.

Correction

use a request code supported by the deployed driver/interface version.

Verification

Repeat the original system call and confirm it passes the former EBADRQC boundary with the same object identity.

Technical references

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