Move an SFTP Server's Files to the Cloud Without a Local Download

How to connect an SFTP server to CloudsLinker

SFTP is a server-parameter connection. There is no OAuth screen; you type the same details you would give WinSCP or FileZilla, and CloudsLinker keeps them for its transfer workers.

Before you start

• A reachable host and port. The server must accept SSH connections from the public internet on the SFTP port (22 unless you moved it). Test from outside your own network first with sftp -P 22 user@host; if that hangs, a firewall or NAT rule is in the way and CloudsLinker will hang too.
• A password-authenticated account. The dialog has no SSH key field, so the account must allow password login. Rather than loosening your admin account, add a dedicated user and restrict it in /etc/ssh/sshd_config:

Match User cloudslinker
    PasswordAuthentication yes
    ForceCommand internal-sftp
    ChrootDirectory /srv/export
    AllowTcpForwarding no
    X11Forwarding no

OpenSSH requires the ChrootDirectory itself to be owned by root and not writable by the group or others; put the files in a subdirectory such as /srv/export/data. Reload sshd after editing.

• Modern ciphers on the server. Any OpenSSH from 6.5 (2014) onward is fine out of the box. Appliances that only offer aes128-cbc, 3des-cbc or diffie-hellman-group-exchange-sha1 will be refused; enable aes256-ctr or [email protected] and curve25519-sha256 on them first.
• The start path, if you want CloudsLinker confined to one directory. For a chrooted user the path is relative to the chroot, for example /data.

Connection steps

1. Sign in at app.cloudslinker.com, open Add Cloud and choose SFTP.
2. Display name is pre-filled with “SFTP”. Rename it to something you will recognise in the task list, such as “Hetzner VPS – backups”.
3. Host: the hostname or IP address, without sftp:// and without a port.
4. Username: the SFTP account.
5. Port: pre-filled with 22; change it only if the server listens elsewhere.
6. Password: the account password.
7. Access Path (optional): leave empty to start at the account’s root, or enter a directory such as /var/backups.
8. Click I got it, Authorize Now SFTP. CloudsLinker connects immediately. On success the page reloads and the server appears under My Linkers; on failure the error is shown and nothing is saved, so re-check the port, the password and the cipher note above.

Creating the first transfer task

Open Transfer, choose a folder on the SFTP server as the source and a folder in the destination cloud as the target. Optional filters let you include only certain extensions and set minimum or maximum file sizes in MB. Run the task once, or open the schedule and pick weekly or monthly execution. The task page lists every file with its status, so a failed file can be retried without touching the ones that succeeded.

Revoke access

Delete the SFTP entry under My Linkers to remove the stored credentials from CloudsLinker. To be certain on the server side, change the account password or lock the account with usermod -L cloudslinker; either action makes the stored connection unusable immediately.

SFTP limits and behaviours you should know

SFTP is a protocol rather than a hosted service, so most ceilings come from your server. These are the ones the CloudsLinker connector itself sets or depends on:

• Authentication: username and password only. SSH keys, passphrases and agent forwarding are not available in the dialog.
• Port: any TCP port; 22 by default.
• Request size: 32 KiB per read or write, up to 64 requests outstanding per file; concurrent reads and writes enabled.
• Ciphers and key exchange refused: aes128-cbc, aes192-cbc, aes256-cbc, 3des-cbc, diffie-hellman-group-exchange-sha1, diffie-hellman-group-exchange-sha256.
• Host key: accepted on first use; not pinned against a known-hosts list.
• Integrity check: md5sum / sha1sum executed on the server when the account has a shell; otherwise size plus modification time.
• Modification time: preserved in both directions with 1-second precision.
• Idle connection timeout: 60 seconds, after which pooled sessions are closed.
• Maximum file size: none imposed by the connector. Limits come from the server filesystem (ext4 16 TiB per file) and the destination: OneDrive 250 GB, Google Drive 5 TB, Amazon S3 5 TB per object.
• Scheduling: run once, weekly, or on selected days each month.
• Filters: file extension include list, minimum and maximum size in MB.
• Traffic allowance: free account 10 GB per month for testing; Lite 800 GB per month with rollover at $3.33 per month on yearly billing; Unlimited at $5.83 per month on yearly billing; Lifetime Unlimited $138.80 one-time.

Sources: OpenSSH release notes (10.0: DSA removed, post-quantum default key exchange), OpenSSH sshd_config manual: ChrootDirectory, ForceCommand, Match, IETF draft-ietf-secsh-filexfer: SSH File Transfer Protocol, ArchWiki: SFTP chroot, CloudsLinker pricing.