How to Handle SFTPError: Failure: Generic SFTP Errors and Server-Side Issues in Paramiko

Paramiko’s SFTPError: Failure is a catch-all for server-side SFTP problems. To resolve it, diagnose directory existence, protocol support, server restrictions, and timeout/configuration mismatches. This guide synthesizes insights from server and SSH protocol PDFs to systematically troubleshoot and handle generic SFTP failures.

1. Verify Remote Directory Exists

Attempting operations in non-existent directories triggers generic failures.

try:
    sftp.chdir('/remote/target/path')
except IOError:
    print("Directory not found. Creating it...")
    sftp.mkdir('/remote/target/path')

Tip: Use posixpath to build and normalize paths: posixpath.normpath().

2. Check SFTP Protocol Version Support

Some servers only support SFTP v3. Paramiko defaults to v3 but verify:

transport = ssh.get_transport()
sftp = transport.open_sftp_client()
print("SFTP version:", sftp.proto)

Note: Mismatched protocol versions can cause generic failures. Upgrade server or client accordingly.

3. Inspect Server-Side Disk Quotas and Restrictions

Disk quotas or chroot jails may block file creation:

# Check free space via SSH
stdin, stdout, _ = ssh.exec_command('df -h /remote/target/path')
print(stdout.read().decode())

Tip: For chrooted users, ensure SFTP root directory has necessary write permissions and subdirectories exist.

4. Increase Timeout and Adjust Buffer Sizes

Large transfers may time out, resulting in ambiguous failures.

transport = ssh.get_transport()
transport.set_keepalive(30)
sftp = ssh.open_sftp()
sftp.sock.settimeout(60)

Note: Use set_keepalive() on transport and settimeout() on socket.

5. Enable Detailed Logging

Activate Paramiko logging to capture SFTP packet exchanges and error codes:

import logging
logging.basicConfig(level=logging.DEBUG)
paramiko.util.log_to_file('paramiko_sftp.log')

6. Wrap Operations in Retry Logic

Implement retries for transient server issues:

import time

def safe_sftp_put(local, remote, retries=3):
    for i in range(retries):
        try:
            sftp.put(local, remote)
            return
        except IOError as e:
            if i < retries - 1:
                time.sleep(2 ** i)
            else:
                raise

7. Validate Server SFTP Configuration

Ensure SSH server’s sshd_config allows SFTP and correct subsystem:

# /etc/ssh/sshd_config
Subsystem sftp /usr/lib/openssh/sftp-server
AllowTcpForwarding yes

Tip: Restart SSH service after changes: sudo systemctl restart sshd.

8. Summary Checklist

Ensure remote directory exists and create if needed.
Confirm SFTP protocol version compatibility.
Check disk quotas, chroot, and directory permissions.
Increase keepalive and socket timeouts for long transfers.
Enable Paramiko DEBUG logging to trace low-level errors.
Wrap transfers in exponential-backoff retry logic.
Verify SSHD SFTP subsystem configuration on the server.