503
FTP
503 Bad Sequence
Bad sequence of commands. The command is valid but was sent in the wrong order relative to other commands.
On this page
When You See This Code
When you skip a required step, like sending PASS before USER, or RNTO without first sending RNFR.
How to Fix
Follow the correct command sequence. Common sequences: USER then PASS for login, RNFR then RNTO for rename, PASV then RETR for transfer.
Specification
Compare With
Guides
FTP Reply Codes: Understanding File Transfer Responses
DNS & Networking
TCP Three-Way Handshake and Connection Lifecycle
DNS & Networking
Essential Network Debugging Tools: ping, traceroute, mtr, and tcpdump
DNS & Networking
RFC 959: FTP Protocol Deep Dive
Protocol Deep Dives
TLS 1.3: Faster, Simpler, More Secure
Protocol Deep Dives
Migrating from FTP to SFTP: A Complete Transition Guide
Migration & Upgrades
HTTP Access Log Management: Rotation, Parsing, and Analysis
Production Infrastructure
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FTP over TLS (RFC 4217)
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Frequently Asked Questions
What is FTP 503 Bad Sequence?
Bad sequence of commands. The command is valid but was sent in the wrong order relative to other commands.
When do you see FTP 503 Bad Sequence?
When you skip a required step, like sending PASS before USER, or RNTO without first sending RNFR.
How to fix FTP 503 Bad Sequence?
Follow the correct command sequence. Common sequences: USER then PASS for login, RNFR then RNTO for rename, PASV then RETR for transfer.