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PuTTY User Manual

PuTTY is a free (MIT-licensed) Windows Telnet and SSH client. This manual documents PuTTY, and its companion utilities PSCP, PSFTP, Plink, Pageant and PuTTYgen.

Note to Unix users: this manual currently primarily documents the Windows versions of the PuTTY utilities. Some options are therefore mentioned that are absent from the Unix version; the Unix version has features not described here; and the pterm and command-line puttygen and pageant utilities are not described at all. The only Unix-specific documentation that currently exists is the man pages.

This manual is copyright 1997-2025 Simon Tatham. All rights reserved. You may distribute this documentation under the MIT licence. See appendix D for the licence text in full.

• Chapter 1: Introduction to PuTTY
  • 1.1 What are SSH, Telnet, Rlogin, and SUPDUP?
  • 1.2 How do SSH, Telnet, Rlogin, and SUPDUP differ?
• Chapter 2: Getting started with PuTTY
  • 2.1 Starting a session
  • 2.2 Verifying the host key (SSH only)
  • 2.3 Logging in
  • 2.4 After logging in
  • 2.5 Logging out
• Chapter 3: Using PuTTY
  • 3.1 During your session
  • 3.2 Creating a log file of your session
  • 3.3 Altering your character set configuration
  • 3.4 Using X11 forwarding in SSH
  • 3.5 Using port forwarding in SSH
  • 3.6 Connecting to a local serial line
  • 3.7 Making raw TCP connections
  • 3.8 Connecting using the Telnet protocol
  • 3.9 Connecting using the Rlogin protocol
  • 3.10 Connecting using the SUPDUP protocol
  • 3.11 The PuTTY command line
• Chapter 4: Configuring PuTTY
  • 4.1 The Session panel
  • 4.2 The Logging panel
  • 4.3 The Terminal panel
  • 4.4 The Keyboard panel
  • 4.5 The Bell panel
  • 4.6 The Features panel
  • 4.7 The Window panel
  • 4.8 The Appearance panel
  • 4.9 The Behaviour panel
  • 4.10 The Translation panel
  • 4.11 The Selection panel
  • 4.12 The Copy panel
  • 4.13 The Colours panel
  • 4.14 The Connection panel
  • 4.15 The Data panel
  • 4.16 The Proxy panel
  • 4.17 The SSH panel
  • 4.18 The Kex panel
  • 4.19 The Host Keys panel
  • 4.20 The Cipher panel
  • 4.21 The Auth panel
  • 4.22 The Credentials panel
  • 4.23 The GSSAPI panel
  • 4.24 The TTY panel
  • 4.25 The X11 panel
  • 4.26 The Tunnels panel
  • 4.27 The Bugs and More Bugs panels
  • 4.28 The ‘Bare ssh-connection’ protocol
  • 4.29 The Serial panel
  • 4.30 The Telnet panel
  • 4.31 The Rlogin panel
  • 4.32 The SUPDUP panel
  • 4.33 Storing configuration in a file
• Chapter 5: Using PSCP to transfer files securely
  • 5.1 Starting PSCP
  • 5.2 PSCP Usage
• Chapter 6: Using PSFTP to transfer files securely
  • 6.1 Starting PSFTP
  • 6.2 Running PSFTP
  • 6.3 Using public key authentication with PSFTP
• Chapter 7: Using the command-line connection tool Plink
  • 7.1 Starting Plink
  • 7.2 Using Plink
  • 7.3 Using Plink in batch files and scripts
  • 7.4 Using Plink with Git
  • 7.5 Using Plink with CVS
  • 7.6 Using Plink with WinCVS
• Chapter 8: Using public keys for SSH authentication
  • 8.1 Public key authentication - an introduction
  • 8.2 Using PuTTYgen, the PuTTY key generator
  • 8.3 Getting ready for public key authentication
• Chapter 9: Using Pageant for authentication
  • 9.1 Getting started with Pageant
  • 9.2 The Pageant main window
  • 9.3 The Pageant command line
  • 9.4 Using agent forwarding
  • 9.5 Loading keys without decrypting them
  • 9.6 Security considerations
• Chapter 10: Common error messages
  • 10.1 ‘The host key is not cached for this server’
  • 10.2 ‘WARNING - POTENTIAL SECURITY BREACH!’
  • 10.3 ‘This server presented a certified host key which was signed by a different certification authority ...’
  • 10.4 ‘SSH protocol version 2 required by our configuration but remote only provides (old, insecure) SSH-1’
  • 10.5 ‘The first cipher supported by the server is ... below the configured warning threshold’
  • 10.6 ‘Remote side sent disconnect message type 2 (protocol error): "Too many authentication failures for root"’
  • 10.7 ‘Out of memory’
  • 10.8 ‘Internal error’, ‘Internal fault’, ‘Assertion failed’
  • 10.9 ‘Unable to use key file’, ‘Couldn't load private key’, ‘Couldn't load this key’
  • 10.10 ‘Server refused our key’, ‘Server refused our public key’, ‘Key refused’
  • 10.11 ‘Access denied’, ‘Authentication refused’
  • 10.12 ‘No supported authentication methods available’
  • 10.13 ‘Incorrect MAC received on packet’ or ‘Incorrect CRC received on packet’
  • 10.14 ‘Incoming packet was garbled on decryption’
  • 10.15 ‘PuTTY X11 proxy: various errors’
  • 10.16 ‘Network error: Software caused connection abort’
  • 10.17 ‘Network error: Connection reset by peer’
  • 10.18 ‘Network error: Connection refused’
  • 10.19 ‘Network error: Connection timed out’
  • 10.20 ‘Network error: Cannot assign requested address’
• Appendix A: PuTTY FAQ
  • A.1 Introduction
  • A.2 Features supported in PuTTY
  • A.3 Ports to other operating systems
  • A.4 Embedding PuTTY in other programs
  • A.5 Details of PuTTY's operation
  • A.6 HOWTO questions
  • A.7 Troubleshooting
  • A.8 Security questions
  • A.9 Administrative questions
  • A.10 Miscellaneous questions
• Appendix B: Feedback and bug reporting
  • B.1 General guidelines
  • B.2 Reporting bugs
  • B.3 Reporting security vulnerabilities
  • B.4 Requesting extra features
  • B.5 Requesting features that have already been requested
  • B.6 Workarounds for SSH server bugs
  • B.7 Support requests
  • B.8 Web server administration
  • B.9 Asking permission for things
  • B.10 Mirroring the PuTTY web site
  • B.11 Praise and compliments
  • B.12 E-mail address
• Appendix C: PPK file format
  • C.1 Overview
  • C.2 Outer layer
  • C.3 Private key encodings
  • C.4 Key derivation
  • C.5 Older versions of the PPK format
• Appendix D: PuTTY Licence
• Appendix E: PuTTY hacking guide
  • E.1 Cross-OS portability
  • E.2 Multiple backends treated equally
  • E.3 Multiple sessions per process on some platforms
  • E.4 C, not C++
  • E.5 Security-conscious coding
  • E.6 Independence of specific compiler
  • E.7 Small code size
  • E.8 Single-threaded code
  • E.9 Keystrokes sent to the server wherever possible
  • E.10 640×480 friendliness in configuration panels
  • E.11 Coroutines in protocol code
  • E.12 Explicit vtable structures to implement traits
  • E.13 Do as we say, not as we do
• Appendix F: PuTTY download keys and signatures
  • F.1 Public keys
  • F.2 Security details
  • F.3 Key rollover
• Appendix G: SSH-2 names specified for PuTTY
  • G.1 Connection protocol channel request names
  • G.2 Key exchange method names
  • G.3 Encryption algorithm names
  • G.4 Agent extension request names
• Appendix H: PuTTY authentication plugin protocol
  • H.1 Requirements
  • H.2 Transport and configuration
  • H.3 Data formats and marshalling
  • H.4 Protocol versioning
  • H.5 Overview and sequence of events
  • H.6 Message formats
  • H.7 References
• Appendix I: PuTTY privacy considerations
  • I.1 Information that PuTTY stores locally
  • I.2 Sending information over the network
  • I.3 Configuration
  • I.4 Modified versions of PuTTY
• Index

If you want to provide feedback on this manual or on the PuTTY tools themselves, see the Feedback page.