[Buildmaster] - SshException: Unable to send channel request

[Anthony]

Hello Inedo, the community, everyone,

One of our scripts is running into an issue in buildmaster.
This script is involved in a deployment pipeline that has been used with success for a long time.

Basically, it consists in an Otterscript dealing with a build variable by sending it as an argument to a subsequent Shell script invoked with SHCall.

When this argument exceeds 34632 characters, or when multiple passed arguments exceed together 34632 characters, the execution fails with :

Unable to send channel request
Unhandled exception: Inedo.Agents.Ssh.SshException: Unable to send channel request
   at Inedo.Agents.Ssh.Libssh2.Libssh2Session.HandleError(Int32 res, IntPtr sftp)
   at Inedo.Agents.Ssh.Libssh2.Libssh2Session.WithSocketAsync[T](Func`1 run, Func`2 getError, IntPtr sftp, CancellationToken cancellationToken)
   at Inedo.Agents.Ssh.SshProcess.StartInternalAsync(CancellationToken cancellationToken)
   at Inedo.Agents.Ssh.SshProcess.StartInternalAsync(CancellationToken cancellationToken)
   at Inedo.Extensions.Scripting.Operations.Shell.SHUtil.ExecuteShellScriptAsync(IShellOperation operation, ShellStartInfo startInfo, IOperationExecutionContext context) in C:\Users\builds\AppData\Local\Temp\InedoAgent\BuildMaster\192.168.44.60\Temp\_E573257\Src\Scripting\InedoExtension\Operations\Shell\SHUtil.cs:line 264
   at Inedo.Extensions.Scripting.Operations.Shell.SHUtil.ExecuteShellScriptAhAsync[TOperation](TOperation operation, IOperationExecutionContext context, String execMode) in C:\Users\builds\AppData\Local\Temp\InedoAgent\BuildMaster\192.168.44.60\Temp\_E573257\Src\Scripting\InedoExtension\Operations\Shell\SHUtil.cs:line 389
   at Inedo.Extensions.Scripting.Operations.Shell.SHCallOperation.ExecuteAsync(IOperationExecutionContext context) in C:\Users\builds\AppData\Local\Temp\InedoAgent\BuildMaster\192.168.44.60\Temp\_E573257\Src\Scripting\InedoExtension\Operations\Shell\SHCallOperation.cs:line 81
   at Inedo.BuildMaster.Windows.ServiceApplication.Executions.PlanExecuter.OtterScriptExecuter.Inedo.ExecutionEngine.Executer.IExecutionHostEnvironment.ExecuteActionAsync(ActionStatement actionStatement, IExecuterContext context) in C:\Users\builds\AppData\Local\Temp\InedoAgent\BuildMaster\192.168.44.60\Temp\_E574178\Src\BuildMasterSolution\BuildMaster.Service\Executions\PlanExecuter\OtterScriptExecuter.cs:line 350

The pipeline looks like :

{
  "Name": "pipeline",
  "Stages": [
    {
      "Name": "test",
      "Targets": [
        {
          "ScriptId": "global::OtterScript",
          "EnvironmentName": "test",
          "ServerNames": [
            "server"
          ],
  

The server which the Shell script is submitted on is Linux like and the used credentials are SSHKeyPair.
I suspect that some SSH agent is implemented by Buildmaster.

The Otterscript looks like :

##AH:UseTextMode

set $arg="<more than 34632 characters>";
# Test Otterscript
{   
        {
        # # SHcall
            {
                SHCall Test_SSH
                (
                Arguments: $arg,

Our instance runs Buildmaster 7.0.23 but I am able to reproduce the issue in Buildmaster 2024.8

Could you please help ?

Thank you.

[atripp]

Hi @Anthony ,

When you use SHCall, it's translated into a remote SSH command that includes all arguments inline on the shell. Basically something like ssh user@host bash -c '...'

However, there is an OS-enforced limit on how long this can be, which is typically between ~32K and ~64K characters. It looks like you're there exactly, and you may be able to see this limit with getconf ARG_MAX. Note that you would also get this error if you did ssh user@host bash -c 'echo "Really long....."'.

So bottom line -- this is an OS/SSH limit. To work-around it, you can just write out $arg to a file, and have your script read in that file.

Thanks,
Alana