[SOLVED] Proxmox API agent exec escape chars

[azhv]

Hello,
I'm trying to automate the VM management via scripts that will reconfigure sets of VMs. However I'm struggling with changing file content. Here's an example:

curl -sSk --header ${AUTH} -X POST --data-urlencode command="echo 1 > /path/to/file" https://IP:8006/api2/json/nodes/NODE/qemu/100/agent/exec

The agent exec works fine with everything else but when I try to echo something into file nothing happens.
I tried with all sorts of escapes I could think of but without any result.
I know I'm supposed to do this with file write instead of agent exec but further in the project I'll have to use sed substitution and I need a way to figure out the escapes.
Proxmox version is 6.2-4
Thanks. Any help will be greatly appreciated.

 

[t.lamprecht]

Hi,

The agent exec works fine with everything else but when I try to echo something into file nothing happens.

thats because you do not run the command in shell context, which handles such redirections normally.

Try: command="sh -c 'echo 1 > /path/to/file'"

Alternative, avoid the shell to handle file writes and use things like awk, sed or other such tools which can operate directly on files, not relying on a shell to handle that.

 

[azhv]

Hello and thanks for the quick reply.
I've tried that but it also doesn't seem to work.
As soon as I put some special character like > or |the command no longer works.

 

[t.lamprecht]

Ah sorry, misremembered the way command arguments need to be passed. As those arguments can contain any character we actually have only one way to encode when transferred as single string:
The API expects the command as \0 separated list, posting actual \0 bytes with the CLI version of CURL is actually impressively hard, so lets use JSON encoding instead:

curl -sSk -H 'Authorization: PVEAPIToken=TOKEN' -H "Content-Type: application/json" -X POST --data '{"command": "sh\u0000-c\u0000echo hello > /foo"}'  https://HOST:8006/api2/json/nodes/NODE/qemu/100/agent/exec

JSON uses \u0000 to encode NUL in strings, so basically you just have to insert that every time there starts a new argument for the command.

Alternatively we could just use another tool for assembling the data, as either URL-encoded or JSON, or a programming language/toolkit which can handle \0 in strings (always available a quick to prototype are perl, python, ...).

For completeness' sake: URL encoded example:

curl -sSk -H 'Authorization: PVEAPIToken=TOKEN' -X POST --data command="sh%00-c%00echo%20hello%20%3E%20%2Ffoo" https://HOST:8006/api2/json/nodes/NODE/qemu/100/agent/exec

I tested both above successfully, so just ensure token/host/node gets replaced correctly.

FYI, if you're on the same host as that VM you could go a bit simpler and just use the qm CLI tool:

qm guest exec 115 -- "/bin/bash" "-c"  "echo hello > /foo"

 

[azhv]

Hello,
I've tested it and works like a charm.
Thanks a lot.