WinSCP : Cannot initialize SFTP protocol. Is the host running an SFTP server?

Question

I can edit all the files using WinSCP on my server using root, but for security, I disabled root on my Ubuntu server and now have a problem using an admin user or sudo <user> to edit files/folders via chmod 755.

• I changed WinSCP's Protocol Option (Advanced... 🠆 Environment 🠆 SFTP server ) to the following and received the below error:

  sudo su -c /bin/sftp-server
  

   Cannot initialize SFTP protocol. Is the host running an SFTP server?
  

Is there any way to resolve this problem or do I have to enable/disable root every time in my server?

• Log:

  16:41:33.348 --------------------------------------------------------------------------
  16:41:33.348 WinSCP Version 5.17.6 (Build 10516) (OS 10.0.17763 - Windows 10 Enterprise LTSC 2019)
  16:41:33.348 Configuration: HKCU\Software\Martin Prikryl\WinSCP 2\
  16:41:33.348 Log level: Normal
  16:41:33.348 Local account: DESKTOP-LDVV9BM\Ehsan
  16:41:33.348 Working directory: C:\Program Files (x86)\WinSCP
  16:41:33.348 Process ID: 2672
  16:41:33.348 Command-line: "C:\Program Files (x86)\WinSCP\WinSCP.exe"
  16:41:33.348 Time zone: Current: GMT+4:30, Standard: GMT+3:30 (Iran Standard Time), DST: GMT+4:30 (Iran Daylight Time), DST Start: 3/21/2020, DST End: 9/20/2020
  16:41:33.348 Login time: Monday, June 22, 2020 4:41:33 PM
  16:41:33.348 --------------------------------------------------------------------------
  16:41:33.348 Session name: [email protected] (Site)
  16:41:33.348 Host name: 192.168.67.134 (Port: 22)
  16:41:33.348 User name: ehsan1362 (Password: No, Key file: No, Passphrase: No)
  16:41:33.348 Tunnel: No
  16:41:33.348 Transfer Protocol: SFTP
  16:41:33.348 Ping type: Off, Ping interval: 30 sec; Timeout: 15 sec
  16:41:33.348 Disable Nagle: No
  16:41:33.348 Proxy: None
  16:41:33.352 Send buffer: 262144
  16:41:33.352 SSH protocol version: 2; Compression: No
  16:41:33.352 Bypass authentication: No
  16:41:33.352 Try agent: Yes; Agent forwarding: No; TIS/CryptoCard: No; KI: Yes; GSSAPI: Yes
  16:41:33.352 GSSAPI: Forwarding: No; Libs: gssapi32,sspi,custom; Custom:
  16:41:33.352 Ciphers: aes,chacha20,blowfish,3des,WARN,arcfour,des; Ssh2DES: No
  16:41:33.352 KEX: ecdh,dh-gex-sha1,dh-group14-sha1,rsa,WARN,dh-group1-sha1
  16:41:33.352 SSH Bugs: Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto
  16:41:33.352 Simple channel: Yes
  16:41:33.352 Return code variable: Autodetect; Lookup user groups: Auto
  16:41:33.352 Shell: sudo su -
  16:41:33.352 EOL: LF, UTF: Auto
  16:41:33.352 Clear aliases: Yes, Unset nat.vars: Yes, Resolve symlinks: Yes; Follow directory symlinks: No
  16:41:33.352 LS: ls -la, Ign LS warn: Yes, Scp1 Comp: No; Exit code 1 is error: No
  16:41:33.352 SFTP Bugs: Auto,Auto
  16:41:33.352 SFTP Server: sudo su -c /bin/sftp-server
  16:41:33.352 Local directory: C:\Users\Ehsan\Desktop, Remote directory: /, Update: Yes, Cache: Yes
  16:41:33.352 Cache directory changes: Yes, Permanent: Yes
  16:41:33.352 Recycle bin: Delete to: No, Overwritten to: No, Bin path:
  16:41:33.352 DST mode: Win
  16:41:33.352 --------------------------------------------------------------------------
  16:41:33.412 Looking up host "192.168.67.134" for SSH connection
  16:41:33.412 Connecting to 192.168.67.134 port 22
  16:41:33.436 We claim version: SSH-2.0-WinSCP_release_5.17.6
  16:41:33.436 Remote version: SSH-2.0-OpenSSH_8.2p1 Ubuntu-4
  16:41:33.436 Using SSH protocol version 2
  16:41:33.436 Have a known host key of type ssh-ed25519
  16:41:33.440 Doing ECDH key exchange with curve Curve25519 and hash SHA-256
  16:41:33.514 Server also has ecdsa-sha2-nistp256/ssh-rsa host keys, but we don't know any of them
  16:41:33.514 Host key fingerprint is:
  16:41:33.514 ssh-ed25519 255 b9:6f:37:38:99:fc:e4:f6:84:3c:88:64:20:cf:43:36 qtGAL1C/LIGDwsC/YoXlDtU/7VxgnuQTLPXT4lwj6fE=
  16:41:33.542 Host key matches cached key
  16:41:33.542 Initialised AES-256 SDCTR (AES-NI accelerated) outbound encryption
  16:41:33.542 Initialised HMAC-SHA-256 outbound MAC algorithm
  16:41:33.542 Initialised AES-256 SDCTR (AES-NI accelerated) inbound encryption
  16:41:33.542 Initialised HMAC-SHA-256 inbound MAC algorithm
  16:41:33.542 Using username "ehsan1362".
  16:41:33.572 Server offered these authentication methods: publickey,password
  16:41:33.572 Prompt (password, "SSH password", <no instructions>, "&Password: ")
  16:41:36.915 Sent password
  16:41:36.926 Access granted
  16:41:36.926 Opening main session channel
  16:41:37.297 Opened main channel
  16:41:37.297 Started a shell/command
  16:41:37.332 --------------------------------------------------------------------------
  16:41:37.332 Using SFTP protocol.
  16:41:37.332 Doing startup conversation with host.
  16:41:37.348 Type: SSH_FXP_INIT, Size: 5, Number: -1
  16:41:37.348 sudo: a terminal is required to read the password; either use the -S option to read from standard input or configure an askpass helper
  16:41:37.348 Session sent command exit status 1
  16:41:37.348 Main session channel closed
  16:41:37.348 All channels closed
  16:41:37.348 Attempt to close connection due to fatal exception:
  16:41:37.348 **Connection has been unexpectedly closed.** Server sent command exit status 1.
  16:41:37.348 Closing connection.
  16:41:37.375 (EFatal) **Connection has been unexpectedly closed.** Server sent command exit status 1.
  16:41:37.375 Cannot initialize SFTP protocol. Is the host running an SFTP server?
  

Solution

Your log file says:

sudo: a terminal is required to read the password; either use the -S option to read from standard input or configure an askpass helper

WinSCP cannot prompt you for a sudo password. That's technically nearly impossible with SFTP protocol (or SCP).

If you want to use sudo with WinSCP, you cannot require password prompt.

See WinSCP FAQ How do I change user after login?

Comments

[JW0914]

@ehsan_kabiri_33 Have you tried the connection via SCP (Session 🠆 File Protocol), which does support sudo passphrase support IIRC? To piggyback on Martin's answer, SSH is most efficient and secure when using keys (preferably passphrase protected), adding the public key to the remote user's ~/.ssh/authorized_keys. (Also, please don't direct link files, instead placing their content within a code box; if the content exceeds the character limit, please use PasteBin and link to that.)

[Martin Prikryl]

@JW0914 SCP won't work either with sudo with a password.

[JW0914]

@ehsan_kabiri_33 Since SCP doesn't support sudo in the manner it's meant to be utilized, a workaround would be to use a normal terminal (PuTTY, Win32-OpenSSH, etc.) when needing to execute sudo commands. WinSCP natively supports this via CTRL+P (Commands → Open in PuTTY) , which will open the session in PuTTY as well

[Charles Kenyon]

Please give more information than a link.