This Issue

When using Veeam if you use Pre/Post freeze scripts for application aware processing, these scripts must reside on the VBR server, which uploads to the virtual machine you are protecting.

I hit an issue when running a job that I received the error;

Error: Script finished execution with unexpected exit code: 126

The Cause

I reviewed the task logs on the VBR server;

• C:\ProgramData\Veeam\Backup\{Job_Name}\task_{VMName}.txt

You are looking for the sections [ScriptInvoker] for troubleshooting. And I found that my script was uploaded successfully, however when it was ran the Guest OS was throwing an error;

[ScriptInvoker] Failed to execute script in lin guest machine over SSH. Script path: C:\Backup\Scripts\stop-vra.sh.

bash: /tmp/d6791b89-e0b8-4cce-acec-45d682ce1f2c_stop-vra.sh: /bin/bash^M: bad interpreter: No such file or directory

I also connected to the linux machine and ran “journalctl -xe -f” whilst running the backup job and seen the same error flash up too.

The script indicates that it must be executed by a shell located at /bin/bash^M. 
There is no such file: it's called /bin/bash. The ^M is a carriage return character. 
Linux uses the line feed character to mark the end of a line, whereas Windows uses the two-character sequence CR LF. Your file has Windows line endings, which is confusing Linux. 
(Source)

You can see the full part of the task logs relating to this below.

[ScriptInvoker] Scripting mode is FailJobOnError.
[ScriptInvoker] Script enabled
[ScriptInvoker] Creating Linux invoker.
[ScriptInvoker] Starting pre-freeze script execution 
[ScriptInvoker] Running Linux script (SSH) 'C:\Backup\Scripts\stop-vra.sh'
[Ssh] SSH connection ae2f5df0-1d28-4dfc-a8a5-7ceb952af2a9 to server 192.168.200.39 created successfully
...
[ScriptInvoker] SSH connection is established (192.168.200.39).
[ScriptInvoker] Exception thrown during script execution (SSH).
[Ssh] Connection ae2f5df0-1d28-4dfc-a8a5-7ceb952af2a9 - [host: '192.168.200.39', port: 22, elevation to root: 'no', autoSudo: no, use su if sudo fails: no, host name: sc-dc1-vra001.simon.local, IPs: [192.168.200.39], AuthenticationData: [UserName: root, AuthTypes: [KeyboardInteractive, Password]]] is disposing.
[ScriptInvoker] Failed to execute script in lin guest machine over SSH. Script path: C:\Backup\Scripts\stop-vra.sh.
bash: /tmp/d6791b89-e0b8-4cce-acec-45d682ce1f2c_stop-vra.sh: /bin/bash^M: bad interpreter: No such file or directory
(System.Exception)
at Veeam.Backup.SSH.CSshCommandResult.GetAnswer(Boolean trimAnswer, String failText, Boolean checkStdErr)
at Veeam.Backup.Core.CSshScriptInvoker.RunScript(CSshScriptFile scriptFile, TimeSpan timeout, Boolean collectLogs, String stdOutFilePath, String stdErrFilePath, Boolean checkStdErr, Int32& exitCode)
at Veeam.Backup.Core.CSshScriptInvoker.ExecScriptInner(String localPath, TimeSpan timeout, Boolean collectLogs, String stdOutFilePath, String stdErrFilePath, Boolean checkStdErr, Int32& exitCode)

[ScriptInvoker] Failed to execute script over SSH, failing over to VIX.
bash: /tmp/d6791b89-e0b8-4cce-acec-45d682ce1f2c_stop-vra.sh: /bin/bash^M: bad interpreter: No such file or directory

...
[ScriptInvoker] Running Linux script (VIX) 'C:\Backup\Scripts\stop-vra.sh'
[ScriptInvoker] Linux script exit code = '126'

The Fix

The fix is quite easy, either change your text editor to show the correct line endings.

Or create the script on a Linux machine and copy it to your VBR Server.

To fix this issue in your text editor

Notepad++ 
Edit --> EOL Conversion --> UNIX/OSX Format

Eclipse  
File > Convert Line Delimiters To > Unix (LF, \n, 0Α, ¶)

Or change the New text file line delimiter to Other: Unix on Window > Preferences > General > Workspace

Sublime Text Editor
View > Line Endings > Unix 

Atom
See this guide. 

(Source)

Regards

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