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.
Thanks in Advance and i look forward to hearing from you.
Best Regards,
Kaushal
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.
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.
On Fri, Apr 19, 2019 at 8:51 PM Kaushal Shriyan kaushalshriyan@gmail.com wrote:
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?
tmpfs *tries* not to use disk. /dev/shm is great to use as *fast* large scratch space.
Have used /dev/shm to greatly speed up a daily process to parse web server logs. Didn’t /seem/ like the process was IO or disk bound. . . Until I threw the logs in /dev/shm and a multi hour process completed in 1/4 the time.
Have used /dev/shm for other “things”.
There is /dev/ram# which should never be written to disk, but has the problem of being much much smaller (4MB iirc) and no filesystem access. So you’d have to `mkfs /dev/ram#` and then `mount /dev/ram# /somewhere`.
Once used /dev/ram# for USB camera “security system”. The camera gave large-ish files and couldn’t figure out how to get the camera app to output to stdOut to then shrink the file to a tiny jpeg with pipes. So had the camera write to /dev/ram and then read the file from /dev/ram through `convert` or something to jpeg-ify the image. Greatly sped up (like 2-3x) how often that could save images.
Happy learning how to Linux. (:
-
Kaushal Shriyan -
Pete Biggs -
Steven Tardy -
Yamaban