Need a script/batch/program that runs a command that won't be killed when the parent is killed

Question

The scenario

I use Zabbix to monitor my servers and recently I wanted to add some more metrics for the Windows ones. For security reasons, I used Zabbix's User Parameter feature, but it limits the execution of external commands to about 3 seconds. After that, the command is forcibly killed.

I want to run some long run commands, so I used the trick from Zabbix's forum: run the command in the background, write the results to a file and use Zabbix to collect them.

This is rather easy under *nix thanks to the "&" operator, but there is no such support in Windows' shell. To make things worse, when Zabbix kills forcibly kill the cmd.exe it used to evaluate the commands, all child processes die including the unfinished background tasks.

Thus I need something that can sever all the ties with its children so they won't be affected in the cascading kill.

What I've tried

• start and start /B - They do nothing as the child always die with the parent
• WScript.Shell.Run as in invis.vbs from StackOverflow - Sometimes work. If the wscript process is forcibly killed as opposed to quitting on its own, the children will die as well.
• hstart - similar results to invis.vbs
• At command - This requires you to set an absolution time for the task to run as opposed to an offset, so the code would be quite messy due to the limited shell scripting capability of Windows.
• (Edit) PsExec.exe from the SysInternals suite - It uses a service to launch the command, so it is not affected by the kill; however, it prints some banner and log info to StdErr and there's no switch to disable this. When I use 2>NUL to redirect them, Zabbix reports an error.

After trying the above in different combinations, I noticed if I call hstart from invis.vbs, the command started by the former will be left alone as a parent-less process when invis.vbs is killed.

However, since I need to redirect the output, the command I want to run is always in the form of cmd.exe /c ""command" "args"" >log. The vbs also removes all the quotes, so I have to encode the command with self-defined escape sequences. The end result involves about five levels of escaping/quoting, which is almost impossible to maintain.

Anyone know any better solutions?

Some requirements

• Any bat/vbs/js/Win32 binary is acceptable
• Better not require multiple levels of escaping
• No .Net (including PowerShell) because it is not installed

Answer 1

I'm using

start "mybatch.bat"

from within another batch file (e.g. "host.bat") and it works fine. The host.bat file can be stopped and the other file runs fine.

Answer 2

Can't you use a Windows scheduled task to run the program ?

Answer 3

Have you tried BeyondExec? It's very very similar to psexec, so I don't know if the same issue you have with psexec would apply, but it's worth a shot.

Answer 4

Suggestion 1:

Use PSEXEC, but try escaping the redirect character. I'm not familiar with Zabbix, so I'm not sure if this will help though.

psexec.exe ...args... 2^>nul

Suggestion 2:

Use a batch file containing schtasks commands.

---schedzabbixscript.cmd---

@echo off
schtasks /create /ru "NT AUTHORITY\SYSTEM" /sc once /tn zabbixtemp /tr c:\path\zabbixscript.cmd /st 23:23:59 /sd 12/31/2999
schtasks /run /tn zabbixtemp

---zabbixscript.cmd---

@echo off
...command...
...command...
...command...
schtasks /delete zabbixtemp /f

If this works for you on one server, in order to do this on multiple servers without having to log into each one, you could change the account that is used for the scheduled task to a network account, and store your zabbixscript.cmd in a central location and just edit it when you need to change something.