FTP Reply Codes
FTP 421 — Service not available, closing control connection
In FTP Reply Codes, code 421. The official source describes it as “Service not available, closing control connection”. Its concrete cause depends on the operation and surrounding message.
Code421
Symbol—
Source confidencehigh
Official definition
Service not available, closing control connection
In plain language
In FTP Reply Codes, code 421. The official source describes it as “Service not available, closing control connection”. Its concrete cause depends on the operation and surrounding message.
Context to inspect
- The surrounding operation, version and subsystem determine the actual cause.
- The same numeric value can mean something different in another namespace.
Safe first checks
- Confirm which product, protocol or subsystem produced the code.
- Read the full surrounding error message and inspect relevant logs.
- Compare the code with the linked authoritative documentation before changing configuration.
Important context
The surrounding operation, version and subsystem determine the actual cause.