B4X

Flush an SFTP File to Stable Storage (Fsync)

Demonstrates the Chilkat SFtp.Fsync method, which requests that the server flush pending data for an open file to stable storage. The only argument is the handle. It uses the OpenSSH fsync@openssh.com extension and succeeds only when the server supports it.

Background: A successful write does not guarantee the data has reached disk — it may still sit in the server's write cache, where a crash or power loss would lose it. Fsync forces it to durable storage, which matters for transactional or journal-style files where a committed record must survive a failure. Because it relies on a non-standard OpenSSH extension, expect it to fail against servers that do not implement it, and treat that as a capability check rather than a hard error where appropriate.

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Dim success As Boolean = False

'  Demonstrates the SFtp.Fsync method, which requests that the server flush pending data for an
'  open file to stable storage.  The only argument is the handle.

Dim sftp As ChilkatSFtp
sftp.Initialize("sftp")

'  Connect, authenticate, and initialize the SFTP subsystem.
Dim port As Int = 22
success = sftp.Connect("sftp.example.com", port)
If success = False Then
    Log(sftp.LastErrorText)
    Return
End If


'  Normally you would not hard-code the password in source.  You should instead obtain it
'  from an interactive prompt, environment variable, or a secrets vault.
Dim password As String = "mySshPassword"

success = sftp.AuthenticatePw("mySshLogin", password)
If success = False Then
    Log(sftp.LastErrorText)
    Return
End If


success = sftp.InitializeSftp
If success = False Then
    Log(sftp.LastErrorText)
    Return
End If


Dim handle As String = sftp.OpenFile("subdir/journal.log", "writeOnly", "openOrCreate,appendData")
If sftp.LastMethodSuccess = False Then
    Log(sftp.LastErrorText)
    Return
End If


'  Write a critical record.
success = sftp.WriteFileText(handle, "utf-8", "2026-07-23 transaction committed" & Chr(10))
If success = False Then
    Log(sftp.LastErrorText)
    Return
End If


'  Ask the server to flush the data to durable storage before continuing.  Fsync uses the
'  OpenSSH fsync@openssh.com extension and succeeds only when the server supports it.
success = sftp.Fsync(handle)
If success = False Then
    Log(sftp.LastErrorText)
    Return
End If


success = sftp.CloseHandle(handle)
If success = False Then
    Log(sftp.LastErrorText)
    Return
End If

Log("Data flushed to stable storage.")

sftp.Disconnect