SCP复制时出现 “subsystem request failed on channel 0”

By | 2025-09-10
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The error message “subsystem request failed on channel 0 scp: Connection closed” indicates a problem during the file transfer process using SCP, often related to the underlying SSH/SFTP subsystem on the server.

Here’s a breakdown of potential causes and solutions:

1. OpenSSH 9.0 and SFTP Protocol:

  • Cause:
    Starting with OpenSSH 9.0, the scp command defaults to using the SFTP protocol for file transfers. If the server does not fully support SFTP or has an older, incompatible SFTP implementation, this can lead to the error.
  • Solution:
    Force scp to use the legacy SCP protocol by adding the -O option to your scp command.

代码
    scp -O <source_file> <user>@<server>:<destination_path>
2. Server-Side Configuration Issues:

  • Cause:
    The SSH server configuration on the remote machine might be incorrectly set up, particularly regarding the SFTP subsystem.
  • Solutions:
    • Verify sshd_config: Check the /etc/ssh/sshd_config file on the server. Ensure the Subsystem sftp line is present and correctly configured, typically pointing to the sftp-server binary (e.g., /usr/libexec/sftp-server or /usr/lib/openssh/sftp-server).
    • Check sftp-server binary: Confirm that the sftp-server binary exists at the path specified in sshd_config and has the correct permissions.
    • Restart SSH service: After making any changes to sshd_config, restart the SSH service on the server (e.g., sudo systemctl restart sshd).
3. Firewall or Network Issues:

  • Cause:
    A firewall on either the client or server side might be blocking the connection or specific ports required for the SFTP/SCP transfer.
  • Solution:
    Temporarily disable firewalls (if safe to do so for testing) or ensure that the necessary ports (typically port 22 for SSH/SFTP) are open.

4. User Permissions or Resource Limits:

  • Cause:
    The user attempting the SCP transfer might have insufficient permissions on the destination path, or the server might be hitting resource limits (e.g., number of processes).
  • Solutions:
    • Check permissions: Verify that the user has write permissions to the target directory on the server.
    • Increase resource limits: If resource limits are suspected, consult server documentation on adjusting limits for processes or other resources.
5. Debugging Information:

  • Solution: Run your scp command with the verbose flag (-vvv) to get more detailed output, which can help pinpoint the exact point of failure.
代码
    scp -vvv <source_file> <user>@<server>:<destination_path>
Review the output for clues about the connection closure or subsystem request failure.



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