On Sat, 20 Apr 2019 02:51, 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). 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?
>
> I will appreciate if anyone can help me understand the above output.
"Per Principa" are both, - devtmpfs and tmpfs - RAM based, BUT, pages
of RAM can be stored on disk/ssd via use of swap, same as any other
RAM usage.
Whats the difference between devtmpfs and tmpfs?
For the normal user none.
Original toughts for devtmpfs where based where based around reducing
the needed memory per entry, because /dev {excluding /dev/shm}
should only contain device-nodes, or links witch both are stored as
directory-entries without data-inodes-entries, later direcories where
included.
While tmpfs is similar to other on-disk-filesystems capable of storing
files with a size greater than zero. "/dev/shm" was the first in-ram-fs
available to the casual user without extra work.
What is the difference with the actual kernels?
I would have to look into the kernel source, as my detail knowlegde
of the matter is dated.
- Yamaban.