Using qemu agent to run code inside VM?

[Dunuin]

Hi,

I want to monitor a VMs RAM usage from the host so I can dynamically adjust the "minimum RAM" by script so ballooning won't remove more RAM than the guest got free or available and caching isn't wasting that much RAM. My idea was to run free -b inside the guest and monitor total RAM and available RAM because the "qm monitor" command is only reporting "free" and "used" RAM but not "avaialbe" or "cache/buffer" (so you can't see how much is used for caching).
Is there a way to do that using the qemu guest agent? I've seen its possible to read/write from/to files inside the guest using the agent. Or do I need to use SSH for that?
Would be a bit annoying to add a monitor user with RSA key for that to each of the VMs.

 

[aaron]

Check out qm guest exec.

For example:

qm guest exec 501 -- "/bin/bash" "-c" "/usr/bin/free" "-b"

If you want to do that via the API you need to do some escaping: https://forum.proxmox.com/threads/proxmox-api-agent-exec-escape-chars.84833/

 

[Dunuin]

Thanks!

Needed to change the "-b" but now it works:

root@Hypervisor:/# qm guest exec 107 -- "/bin/bash" "-c" "/usr/bin/free -b"
{
   "exitcode" : 0,
   "exited" : 1,
   "out-data" : "               total        used        free      shared  buff/cache   available\nMem:      1550704640   875958272    79859712    24952832   594886656   500973568\nSwap:     2145382400      262144  2145120256\n"
}

 

[UdoB]

Hello,

just for curiosity and possibly for saving innocent resources: has the invocation of an initial bash plus forking "free" any advantages?

Without bash I can get the exact same result

root@pved:/etc/pve# qm guest exec 1901 -- "/bin/bash" "-c" "/usr/bin/free -b"
{
   "exitcode" : 0,
   "exited" : 1,
   "out-data" : "              total        used        free      shared  buff/cache   available\nMem:     2091909120   861155328   182390784    27033600  1048363008  1013248000\nSwap:    1070592000   107479040   963112960\n"
}
root@pved:/etc/pve# qm guest exec 1901 -- "/usr/bin/free" "-b"
{
   "exitcode" : 0,
   "exited" : 1,
   "out-data" : "              total        used        free      shared  buff/cache   available\nMem:     2091909120   860831744   182714368    27033600  1048363008  1013579776\nSwap:    1070592000   107479040   963112960\n"
}

Best regards

 

[aaron]

AFAIU this should not make much of a difference in this use case. Depending on what you want to run, it can help to do it in the context of a shell. For example, if you need any of the shell features, like globbing.