tmpfs is a temporary file system that resides in memory and/or swap partition(s).
tmpfs is commonly used for
/tmp. By default, a tmpfs has its maximum size set to half the total of RAM. Note that the actual memory/swap consumption depends on how much you fill it up, as tmpfs partitions do not consume any memory until it is actually needed.
Problem example: You want to build an Android development lab in a VM. You set VM RAM to 2GB. So by default,
/tmp size will be 1GB. You begin to install Android Studio but an error occured, telling you that there is not enough space on the disk. That's because
/tmp is too small to contain all temporary downloads of Android Studio during the install process.
For a problem like the prvious example, we don't want to do a permanent change as that's just a punctual need. So to fix the problem we'll temporarily increase the size of
/tmp. It is posible because in our example the VM has 2GB RAM + 4GB SWAP, so we can increase a tmpfs partition up to 6GB.
Before the resizing:
$ df /tmp
mount -o remount,size=4G,noatime /tmp
After the resizing:
$ df /tmp