How to Resolve SFTPError: Permission denied: File Permissions and Ownership Problems in Paramiko

Paramiko’s SFTP client may raise SFTPError: Permission denied when attempting file operations on remote systems. This comprehensive guide explains Unix file permissions, ownership, umask, ACLs, and Python-based workarounds to diagnose and fix permission issues in SFTP workflows.

1. Understand Unix File Permissions

Unix permissions consist of three bits for user, group, and others (read, write, execute). Check permissions with:

$ ls -l /remote/path/file.txt
-rw-r--r-- 1 alice staff 1024 Aug 21 10:00 file.txt
  

• Owner (alice) can read/write.
• Group (staff) can read.
• Others can read.

2. Verify Ownership and Group

Mismatched ownership can block access. Identify user and group of the SFTP session:

stdin, stdout, _ = ssh.exec_command('id')
print(stdout.read().decode())
# uid=1001(alice) gid=50(staff) groups=50(staff),... 
  

3. Adjust Remote File Permissions with chmod

Use chmod to grant necessary access:

# Grant owner write and group write
ssh.exec_command('chmod 664 /remote/path/file.txt')
# To allow all users write (use carefully)
ssh.exec_command('chmod 666 /remote/path/file.txt')
  

4. Change Ownership with chown

If you have sudo privileges, change file owner or group:

ssh.exec_command('sudo chown alice:staff /remote/path/file.txt')
  

5. Check and Configure umask

umask defines default permissions for new files. A restrictive umask can block group/other write access:

stdin, stdout, _ = ssh.exec_command('umask')
print(stdout.read().decode())  # e.g., 0022
# umask 0022 yields 644 default perms; use 0002 for 664
ssh.exec_command('umask 0002')
  

6. Handle ACLs (Access Control Lists)

Some systems use ACLs for fine-grained permissions. Check with:

$ getfacl /remote/path/file.txt
  

Modify ACLs via setfacl:

ssh.exec_command('setfacl -m u:alice:rw /remote/path/file.txt')
  

7. Use Paramiko SFTP chmod/chown Methods

Paramiko exposes chmod and chown directly on SFTP:

sftp = ssh.open_sftp()
# Change permissions
sftp.chmod('/remote/path/file.txt', 0o664)
# Change ownership (if server permits over SFTP)
sftp.chown('/remote/path/file.txt', uid=1001, gid=50)
  

8. Retry Logic and Error Handling

Implement retries for transient permission changes:

import time

def safe_put(local, remote, retries=3):
    for i in range(retries):
        try:
            sftp.put(local, remote)
            return
        except IOError as e:
            if 'Permission denied' in str(e) and i < retries-1:
                time.sleep(1)
            else:
                raise
  

9. Summary Checklist

1. Check remote file permissions with ls -l.
2. Verify SFTP user’s id matches file owner or group.
3. Adjust permissions with chmod or SFTP chmod().
4. Change ownership via chown or SFTP chown() if permitted.
5. Review umask to ensure correct defaults for new files.
6. Inspect and modify ACLs with getfacl/setfacl.
7. Wrap file operations in retry logic for resilience.