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TMPFS Available space does not equal size

rated 0 times [ 1] [ 0] / answers: 1 / hits: 1240 / 1 Year ago, mon, december 5, 2022, 1:07:10

I have a quick question. I have a 64bit Ubuntu 10.04 server with 24GB of RAM and is used as a VMWare Workstation 7.1 host. I would like to use an in-memory drive for the VM Memory location, which I setup as the following:

tmpfs /mnt/vmware tmpfs defaults,size=100% 0 0

That all works. Next I want to allocate 16GB of RAM to the VM, I know its a lot but we do a lot of processing that needs a lot of RAM.

After the VM is started and I run df -h, I get the following for that drive:

Filesystem             Size  Used  Avail Use% Mounted On

tmpfs                  24G   11G   14G  44% /mnt/vmware

Why is it that the Available (14GB) size does not equal the Size (24GB) of the drive? And why wouldn't the whole 16GB get allocated to the memory space, which is what i set in the vmware guest .vmx file? Is there a limit to the space that can be allocated to a tmpfs file system?

Thanks for your time.

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ibuteking

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4 Years ago

answered 1 Year ago serveeel · Accepted Answer

Available space does not have to equal size. What you're seeing in the case of /dev/shm is the fact that the system uses very little or zero space for this filesystem (Used = 0), so in this case available = size.

I'm not sure why df doesn't show 16G of used space, but, generally speaking, when a process asks the kernel for allocation of space, the request might be granted, but the kernel can in fact allocate smaller space and later (in case more memory is needed) expand it.