PuTTY is a free and open-source software client designed for secure remote access to servers and systems. It functions as an SSH, Telnet, and Rlogin client, allowing users to establish encrypted connections to Unix, Linux, and other remote machines. The software is maintained by Simon Tatham and a group of volunteers. It is available for Windows, with compatibility extended to Unix systems and macOS through wrappers or Wine. The primary purpose of PuTTY is to provide a terminal emulator that enables users to interact with remote command-line interfaces as if they were physically present at the machine's console. This functionality is essential for developers, system administrators, and power users who need to manage servers, transfer files, or execute commands remotely. The software is distributed under an open-source licence, and its source code is publicly available for review and modification.
What is PuTTY?
PuTTY is a terminal emulator and network file transfer application. It is specifically designed to run on the Windows platform but has been ported to other operating systems. The software implements the client end of a remote session, meaning it displays the session on the local machine while the actual processes run on the remote server. In practical terms, a user runs PuTTY on their Windows computer, enters the IP address or hostname of a remote Unix machine, and PuTTY opens a window. Any text typed into this window is transmitted directly to the remote machine, and all responses from the remote machine are displayed within the same window. This creates a seamless command-line interface for remote administration.
The core protocols supported by PuTTY are SSH (Secure Shell), Telnet, and Rlogin. SSH is the most widely used protocol due to its strong encryption, which protects credentials, commands, and data transfers from interception. Telnet and Rlogin are older protocols that transmit data in plain text and are generally considered less secure, though they may still be used in specific, controlled environments. PuTTY also includes a suite of companion utilities: PSCP for secure file transfer, PSFTP for SFTP file transfer, Plink for command-line use, Pageant for SSH authentication agent management, and PuTTYgen for generating SSH key pairs.
PuTTY is known for its stability and lightweight design. It is described as having no bloat or delays, loading quickly even on older systems. It can handle long-running SSH sessions without interruption, making it suitable for extended administrative or development tasks. While originally built for Windows, its functionality has been extended to Unix systems and macOS, though the latter may require additional software like Wine or specific wrappers to run.
How to Download and Install PuTTY
PuTTY is distributed as free software, and the latest version can be downloaded from the official project website or its designated mirrors. The current stable release version is 0.83, as of the provided information. The software is provided as a single executable file for Windows, with separate downloads available for different architectures. For Windows 95, 98, ME, NT, and 2000 on Intel x86 systems, the download includes putty.exe (the main client), puttytel.exe (a Telnet-only version), pSCP.exe, plink.exe, pageant.exe, and puttygen.exe. For Windows NT on Alpha architecture, corresponding files with an -alpha suffix are provided. The source code for all platforms is available in a zip file.
The download process involves selecting the appropriate file for your system. The files offered are cryptographically signed to verify their authenticity and integrity. The project also supplies signed lists of MD5 checksums, which users can compare against downloaded files to ensure they have not been tampered with. To download the public keys and understand the signature policy, users are directed to a dedicated "Keys" page on the official website. It is noted that release version 0.51 was not signed, as the signing procedure was introduced after its release, but all subsequent versions are signed.
For users who encounter issues with the stable release, the development snapshot is available. This snapshot is built automatically every day from the current development code and may contain fixes for specific bugs before they are incorporated into the stable version. Users are advised to try the snapshot if they experience a problem with the release version, before reporting the issue.
Legal Considerations for UK Users
A legal warning is provided regarding the use of encryption software. The use of PuTTY, PSCP, PSFTP, and Plink may be illegal in countries where encryption is outlawed. The project states that it is believed to be legal to use this software in England and many other countries. However, the disclaimer clarifies that the maintainer is not a lawyer, and users should seek legal advice if in doubt before downloading the software. It is important to note that the Telnet-only binary, PuTTYtel, is not subject to cryptography laws and can be used without such restrictions.
Core Features and Functionality
PuTTY’s primary function is to facilitate secure remote access. The SSH protocol, which is the most trusted and secure method for remote server management, is fully supported. SSH creates an encrypted channel between the client and the server, safeguarding all transmitted data. This is critical for system administrators deploying updates, developers accessing application backends, or any user performing sensitive operations on remote machines.
The software offers full control and flexibility. Users can easily switch between different connection modes (SSH, Telnet, Rlogin) depending on their specific task. This is useful for managing a variety of systems, including servers, network hardware, or performing file transfers. PuTTY’s terminal emulator is an xterm-style emulator, providing a familiar command-line environment for users accustomed to Unix/Linux terminals.
Additional utilities enhance PuTTY’s capabilities: * PSCP and PSFTP: These command-line tools allow for secure file transfers between local and remote systems using the SCP (Secure Copy Protocol) and SFTP (SSH File Transfer Protocol) protocols, respectively. * Plink: This is a command-line interface to PuTTY’s core network functionality, allowing for automation of connections and command execution via scripts. * Pageant: This is an SSH authentication agent that manages private keys, allowing for passwordless logins to remote servers once a key is loaded. * PuTTYgen: This utility is used to generate public-private key pairs for SSH authentication, which is a more secure alternative to password-based logins.
Availability and Mirrors
The official PuTTY home site is hosted at chiark.greenend.org.uk. To ensure availability and download speed, the project maintains a network of HTTP and FTP mirrors. These mirrors host copies of the entire website and the PuTTY release files. Users are advised that mirrors are not updated instantly, so the latest version might not be immediately available on all mirror sites.
A list of current mirrors is provided on the official website. The project encourages users to set up their own mirrors, particularly in regions where there are fewer existing mirrors. There is no need to request permission beforehand, but the project may choose to list a new mirror if it meets certain guidelines. It is noted that the project does not promise to list every mirror and that the decision is at their discretion. As of 2007, all mirror site links on the official page use the rel="nofollow" attribute.
Alternative Software Suggestions
The official PuTTY website includes a section with suggestions for alternative SSH clients. These suggestions are independent of the PuTTY project and are not endorsements. One such alternative is the Bitvise SSH Client, which is a professional, commercially developed SSH and SFTP client for Windows. It is described as robust, easy to install and use, and supports all features of PuTTY. Bitvise also offers an SSH Server for Windows. It is important to note that the provided data includes a mention of a specific incident involving Bitvise, but this is unrelated to the software's functionality as a PuTTY alternative.
Conclusion
PuTTY is a longstanding, reliable, and free terminal emulator for Windows, primarily used for secure remote system administration via the SSH protocol. Its open-source nature, stability, and comprehensive feature set—including utilities for file transfer and key management—make it a standard tool for developers and system administrators. The software is distributed under an open-source licence, and users are provided with signed binaries and checksums to verify authenticity. While the core software is free, users should be aware of legal restrictions regarding encryption in their jurisdiction, though such restrictions are not typically applicable in the UK. For those seeking alternatives, professionally developed options like Bitvise are available, though they are not affiliated with the PuTTY project. The software can be downloaded from the official website or its network of mirrors.