[CentOS] Does devtmps and tmpfs use underlying hard disk storage or Physical Memory (RAM)

Sat Apr 20 08:23:28 UTC 2019
Pete Biggs <pete at biggs.org.uk>

On Sat, 2019-04-20 at 06:21 +0530, Kaushal Shriyan wrote:
> Hi,
> 
> I am running the below command on CentOS Linux release 7.6.1810 (Core)
> 
> # df -hT --total
> Filesystem     Type      Size  Used Avail Use% Mounted on
> /dev/xvda1     xfs       150G  8.0G  143G   6% /
> devtmpfs       devtmpfs  7.8G     0  7.8G   0% /dev
> tmpfs          tmpfs     7.8G     0  7.8G   0% /dev/shm
> tmpfs          tmpfs     7.8G  817M  7.0G  11% /run
> tmpfs          tmpfs     7.8G     0  7.8G   0% /sys/fs/cgroup
> tmpfs          tmpfs     1.6G     0  1.6G   0% /run/user/995
> tmpfs          tmpfs     1.6G     0  1.6G   0% /run/user/1000
> total          -         185G  8.8G  176G   5% -
> #
> 
> Does devtmpfs and tmpfs use underlying hard disk storage or does it uses
> Physical Memory (RAM).

It uses RAM, that's what 'tmpfs' is, a temporary RAM filesystem.

>  What is the purpose of devtmpfs which is mounted on
> /dev, tmpfs mounted on /dev/shm and so on and so forth. What is the
> difference between devtmpfs and tmpfs?

devtmpfs is a kernel maintained filesystem of automated device nodes.  

tmpfs is a RAM disk.

> 
> I will appreciate if anyone can help me understand the above output.

Google really is your friend here. 

P.