how to disable tmpfs

[Dennis Kaptain]

While lurking on the list, I learned in a thread "Cannot make a copy
of video DVD with k3b" that the way fedora is configured, tmpfs will
consume 50% of my RAM and mount itself in /tmp. If you have gobs of
RAM I suppose you'd never miss it unless you are doing serious video
editing or something like that.

My system has only 3GB of RAM and it does appear that 1.5GB is now a
tmpfs. I really don't have that to spare. I do have a 5GB /tmp
partition on a physical HDD that I thought I had been using for years.
Only now did I learn that I'm not.

Rick Stevens suggested  "systemctl mask tmp.mount"  as a fix. I tried
that and then I couldn't log in. It turns out, that command will make
my / partition read only. I googled it and discovered that someone
else had the same problem. There was no answer to that thread. You can
fix this by "mount -o remount,rw /" and then issuing "systemctl unmask
tmp.mount" and rebooting again.

I tried editing the entry in /etc/fstab from

UUID=996d5f64-0745-4af7-9260-559d5c66c7bd /    ext4    defaults       1 1

to

UUID=996d5f64-0745-4af7-9260-559d5c66c7bd /    ext4    defaults,rw    1 1

but that still didn't mount / rw.

So, how do I turn off fedora's tmpfs forever so I can use my physical
/tmp partition and not consume all my valuable RAM? Or stated
otherwise, how do I disable tmpfs AND keep / read-write?

Thanks,

[Chris Adams]

Once upon a time, Dennis Kaptain  said:
> While lurking on the list, I learned in a thread "Cannot make a copy
> of video DVD with k3b" that the way fedora is configured, tmpfs will
> consume 50% of my RAM and mount itself in /tmp. If you have gobs of
> RAM I suppose you'd never miss it unless you are doing serious video
> editing or something like that.

There's a lot of misinformation about this.  The tmpfs does _not_
"consume 50% of [your] RAM".  The maximum size of a tmpfs defaults to
50% of RAM, but it only uses space as needed.  Also, space used in tmpfs
can be pushed to swap (so if you run low on RAM, files in tmpfs will be
pushed out to swap on disk to free up RAM for programs).

[Dennis Kaptain]

2014-08-08 10:46 GMT-05:00 Chris Adams :
> Once upon a time, Dennis Kaptain  said:
> > While lurking on the list, I learned in a thread "Cannot make a copy
> > of video DVD with k3b" that the way fedora is configured, tmpfs will
> > consume 50% of my RAM and mount itself in /tmp. If you have gobs of
> > RAM I suppose you'd never miss it unless you are doing serious video
> > editing or something like that.
>
> There's a lot of misinformation about this.  The tmpfs does _not_
> "consume 50% of [your] RAM".  The maximum size of a tmpfs defaults to
> 50% of RAM, but it only uses space as needed.  Also, space used in tmpfs
> can be pushed to swap (so if you run low on RAM, files in tmpfs will be
> pushed out to swap on disk to free up RAM for programs).
>
> --
> Chris Adams 
> --

Thanks for clearing that up Chris.

It still doesn't seem like an ideal way to handle /tmp when I have a
perfectly good partition and swapping is a major performance killer.
I'd rather disk access wait time is caused by accessing /tmp when I
need to rather than swapping tmpfs in and out for a program.

Is there a way to totally disable tmpfs and keep / read-write?

[Chris Adams]

Once upon a time, Dennis Kaptain  said:
> It still doesn't seem like an ideal way to handle /tmp when I have a
> perfectly good partition and swapping is a major performance killer.
> I'd rather disk access wait time is caused by accessing /tmp when I
> need to rather than swapping tmpfs in and out for a program.

Swapping tmpfs files to swap is no more of a performance killer than
writing /tmp to disk to begin with (the same data would be written to
the same disk, just in a little bit different format and location).

When a program writes data to disk, it goes through the kernel page
cache, to the filesystem layer, to the block layer, and then to disk.
The filesystem has to allocate space (which means other writes to disk,
updating block allocations, directories, etc.).  The blocks are cached
in the page cache in case they are read later.  If the kernel needs RAM,
it can throw them away.

tmpfs lives directly in the page cache.  So, when a program writes to a
tmpfs file, it goes to the page cache and stops.  Later, if the kernel
needs RAM, it can push those pages to disk (swap space).

The only difference between /tmp on disk and tmpfs is when pages get
pushed to disk.  In a system with sufficient RAM to hold the normal /tmp
contents (which aren't very big under most circumstances), they never
get pushed to disk with tmpfs, and performance is faster.

The only downside to /tmp-on-tmpfs is that it is limited in size, based
on available RAM.  Ideally, it would be based on swap size, or total
RAM+swap, but that's harder to do.  However, Fedora defaults to a root
filesystem that isn't huge (with a separate /home), so the size of /tmp
is still limited.  /tmp was never supposed to be about holding arbitrary
sized chunks of data.

[Marko Vojinovic]

On Fri, 8 Aug 2014 12:39:39 -0500
Chris Adams  wrote:
> Once upon a time, Dennis Kaptain  said:
> > It still doesn't seem like an ideal way to handle /tmp when I have a
> > perfectly good partition and swapping is a major performance killer.
> > I'd rather disk access wait time is caused by accessing /tmp when I
> > need to rather than swapping tmpfs in and out for a program.
>
> Swapping tmpfs files to swap is no more of a performance killer than
> writing /tmp to disk to begin with (the same data would be written to
> the same disk, just in a little bit different format and location).

Please, please don't start about this stuff yet again.

It has been rehashed many times over, in countless places on the net:
if your typical usecase does not involve large files in /tmp and you
have enough RAM to never hit swap, tmpfs is more efficient. Otherwise,
disk is more efficient. Everyone needs to decide for themselves, and
configure their system accordingly.

If the OP has already decided what he wants, just tell him how to
configure it, rather than trying to persuade him that your size fits
all.

HTH, :-)
Marko

[Anthony Joseph Messina]

On Friday, August 08, 2014 10:32:15 AM Dennis Kaptain wrote:
> So, how do I turn off fedora's tmpfs forever so I can use my physical
> /tmp partition and not consume all my valuable RAM? Or stated
> otherwise, how do I disable tmpfs AND keep / read-write?

systemctl mask tmp.mount

-A

[Tim]

Allegedly, on or about 08 August 2014, Dennis Kaptain sent:
> Rick Stevens suggested  "systemctl mask tmp.mount"  as a fix. I tried
> that and then I couldn't log in.

That sounds like a very old problem.  I encountered that, many years
ago, when I swapped hard drives on a PC.  Check the permissions of
your /tmp directory, the sticky bit needs to be set.

$ ll -d /tmp
drwxrwxrwt. 24 root root 12288 Aug  9 02:15 /tmp

Without that, graphical logins would fail.  But command line logins
would work, as they didn't play around with putting things in /tmp.

[Rex Dieter]

Dennis Kaptain wrote:
> Rick Stevens suggested  "systemctl mask tmp.mount"  as a fix. I tried
> that and then I couldn't log in. It turns out, that command will make
> my / partition read only.

Following 
http://fedoraproject.org/wiki/Features/tmp-on-tmpfs#Release_Notes
has always worked for me.  It shouldn't affect your / partition, odd.

-- Rex