Using Bitvise SSH Client unattended

Bitvise SSH Client comes with several command line SSH clients that can be run unattended from other programs, or from the Windows Task Scheduler:

  • Use sftpc for unattended file transfers.
  • Use sexec for remote command execution.
  • Use stnlc for unattended port forwarding/tunneling. See also our page about running stnlc as a service.

In addition, the following clients also offer a command line interface, but are usually used interactively:

  • stermc provides a console-based terminal shell.
  • spksc allows command-line management of client authentication keypairs configured for a user at an SSH server. (Requires an SSH server that supports the SSH Public Key Subsystem; e.g. Bitvise SSH Server.)

Each of the above clients supports a large variety of command line parameters. For help, run each of the clients as follows:

sftpc -?

Or like this:

sftpc -? | more

retry and log utilities

Bitvise SSH Client also includes utilities retry and log:

  • Use the retry utility to repeat an SSH client session, another program, or a command script.
  • Use the log utility to record the output of an SSH client session, another program, or a command script.

For help, run either of these commands without parameters. For example:

retry

The commands can be chained. For example:

log -tcx C:\Dir\Log retry -f=100,101 sftpc -profile=C:\Dir\Profile.bscp cd /dir; put *.txt

This will retry an upload a default number of times, or until it succeeds; and record all output with timestamps, in log files of the form C:\Dir\Log-(...).log.

Host Key Verification

The most common issue when using Bitvise SSH Client non-interactively occurs when the client is run under a different Windows account than was previously used interactively, and the client has no way to verify the server's host key.

Verification of the server's host key is essential to the security of the SSH session, so this step cannot be skipped. There are a number of ways in which the SSH Client can be told what host keys the server might use that the Client can accept:

  • When you connect to the server interactively using the graphical SSH Client, and manually verify the server's host key, the SSH Client will store the host key in the Windows registry, but only for the currently logged on Windows user. All aspects of the SSH Client will then be able to connect to that server and trust that host key, as long as they are run in a Windows logon session belonging to the same Windows user.
     
  • A host key can also be stored in a Bitvise SSH Client profile, and will then be trusted for the server connected to with that profile, regardless of the Windows logon session in which the connection occurs. If you have a host key that is trusted in the Windows registry, and you want to copy it to a profile:
     
    1. Open the profile using the graphical Bitvise SSH Client.
    2. Open the Host key manager interface from the Login tab of the SSH Client.
    3. Find the host key, right click it, and select Copy to profile.
     
  • A host key or its fingerprint can be passed to any instance of the SSH Client - graphical or command line - using the following command line parameters:
     
    • -hostKeyFile=...: Specifies a file in which one or more host keys are stored.
    • -hostKeyFp=...: Specifies a SHA-256, Bubble-Babble, or MD5 fingerprint of a host key to trust.

If the server has multiple host keys, make sure that the unattended client has access to information about all of the host keys that the server might present. Otherwise, if the unattended client negotiates a different host key algorithm than the graphical client, host key verification may fail because the server will be presenting a different host key.

Public Key Authentication

Like with host key verification, when the SSH Client is run unattended under a different Windows account than when the Client is used interactively, it cannot access authentication keypairs that are stored in a different Windows user's registry.

There are a number of ways an authentication keypair can be passed to the SSH Client when it's running under a different account:

  • In the graphical SSH Client that has access to the keypair, use the Client key manager to export the full keypair into a file. Then, log into the other Windows account, run the graphical SSH Client, and use the Client key manager to import the keypair. This will allow you to use the keypair under that account using the -pk=... parameter.

  • Instead of importing the keypair using the other Windows account, you can also pass it directly to a command line SSH client using the -keypairFile=... parameter. For example:

    sftpc user@host:port -hostKeyFile=... -keypairFile=... cd /dir; put *.txt

  • A client authentication keypair can also be stored in a Bitvise SSH Client profile. To prepare a profile so that it will contain a keypair, open the graphical SSH Client that has access to the keypair. Configure host settings and use Save profile as to save the profile. Then, use the Client key manager, right click on the keypair, and select Copy to profile. If you do the same for the host key, using instructions in the previous section, you can then use the profile as follows:

    sftpc -profile=C:\Path\Profile.bscp cd /dir; put *.txt