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')
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)
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())
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)
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
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.