tmpfs is not a ramdisk (was: delimiters with more than one character? ...)

From	Nicolas George <george@nsup.org>
Newsgroups	linux.debian.user
Subject	tmpfs is not a ramdisk (was: delimiters with more than one character? ...)
Date	2020-07-17 13:30 +0200
Message-ID	<AtwIV-3Ur-5@gated-at.bofh.it> (permalink)
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rhkramer@gmail.com (12020-07-17):
> I'm not the op, but, in what sense do you say that?

tmpfs is FILESYSTEM backed in memory. A ramdisk is a kind of DISK, i.e.
a block device, backed in memory and in which you can store a filesystem
if you want.

There are significant differences, like the fact that a file removed
from a tmpfs will really free the memory and make it available for the
system, while a file removed from a filesystem stored on ramdisk will
just have its data marked as available for the same filesystem.
(Nowadays, a ramdisk could implement the trim features, but that's
piling hacks on top of hacks.)

There are also performance differences, because filesystems are designed
to ensure consistency over catastrophic interruptions, which is
completely useless if the data itself does not survive catastrophic
interruptions.

> I use tmpfs filesystems for files that either I want fast access to (ram speed) 
> or want to make sure they disappear on reboot / power loss.
> 
> I have tried to do a little reading since I saw this, I see some references 
> that say it is stored on RAM, some others that say it is stored in virtual 
> memory and could be on swap.

I am pretty sure it can be on swap. If you want to be sure, just test:
create a tmpfs larger than your physical memory, and fill it with a big
file.

> Among other things, should I be worried that it won't disappear on power loss 
> / reboot?

Depends on what kind of disappear you want. If all you want is not to
have to worry about cleaning up, then you are good with tmpfs.

If you are worried that sensitive data may end up on disk, then encrypt
your swap with an ephemeral key.

Regards,

-- 
  Nicolas George

Thread

delimiters with more than one character? ... Albretch Mueller <lbrtchx@gmail.com> - 2020-07-14 15:00 +0200
  Re: delimiters with more than one character? ... Alex Mestiashvili <amestia@rsh2.donotuse.de> - 2020-07-14 15:00 +0200
    Re: delimiters with more than one character? ... Greg Wooledge <wooledg@eeg.ccf.org> - 2020-07-14 15:10 +0200
      Re: delimiters with more than one character? ... Nicolas George <george@nsup.org> - 2020-07-14 15:10 +0200
      Re: delimiters with more than one character? ... Alex Mestiashvili <amestia@rsh2.donotuse.de> - 2020-07-14 15:20 +0200
  Re: delimiters with more than one character? ... Greg Wooledge <wooledg@eeg.ccf.org> - 2020-07-14 15:10 +0200
  Re: delimiters with more than one character? ... Nicolas George <george@nsup.org> - 2020-07-14 15:20 +0200
  Re: delimiters with more than one character? ... Nicolas George <george@nsup.org> - 2020-07-14 17:30 +0200
    Re: delimiters with more than one character? ... Albretch Mueller <lbrtchx@gmail.com> - 2020-07-15 12:30 +0200
      Re: delimiters with more than one character? ... Greg Wooledge <wooledg@eeg.ccf.org> - 2020-07-15 14:00 +0200
      Re: delimiters with more than one character? ... David Wright <deblis@lionunicorn.co.uk> - 2020-07-15 14:30 +0200
      Re: delimiters with more than one character? ... Bob Weber <bobrweber@gmail.com> - 2020-07-15 14:40 +0200
        Re: delimiters with more than one character? ... Greg Wooledge <wooledg@eeg.ccf.org> - 2020-07-15 14:50 +0200
          Re: delimiters with more than one character? ... Bob Weber <bobrweber@gmail.com> - 2020-07-15 16:20 +0200
            Re: delimiters with more than one character? ... Greg Wooledge <wooledg@eeg.ccf.org> - 2020-07-15 16:30 +0200
            Re: delimiters with more than one character? ... The Wanderer <wanderer@fastmail.fm> - 2020-07-15 16:30 +0200
            Re: delimiters with more than one character? ... Nicolas George <george@nsup.org> - 2020-07-15 17:50 +0200
        Re: delimiters with more than one character? ... Nicolas George <george@nsup.org> - 2020-07-15 15:10 +0200
  Re: delimiters with more than one character? ... Bob Weber <bobrweber@gmail.com> - 2020-07-14 17:30 +0200
  Re: delimiters with more than one character? ... Alessandro Baggi <alessandro.baggi@gmail.com> - 2020-07-15 17:30 +0200
  Re: delimiters with more than one character? ... Eric S Fraga <e.fraga@ucl.ac.uk> - 2020-07-16 12:10 +0200
    Re: delimiters with more than one character? ... "Thomas Schmitt" <scdbackup@gmx.net> - 2020-07-16 13:40 +0200
      Re: delimiters with more than one character? ... Greg Wooledge <wooledg@eeg.ccf.org> - 2020-07-16 14:00 +0200
        Re: delimiters with more than one character? ... Greg Wooledge <wooledg@eeg.ccf.org> - 2020-07-16 16:00 +0200
          Re: delimiters with more than one character? ... Zenaan Harkness <zenaan@freedbms.net> - 2020-07-17 04:50 +0200
            Re: delimiters with more than one character? ... Nicolas George <george@nsup.org> - 2020-07-17 10:50 +0200
              Re: delimiters with more than one character? ... rhkramer@gmail.com - 2020-07-17 13:20 +0200
                tmpfs is not a ramdisk (was: delimiters with more than one  character? ...) Nicolas George <george@nsup.org> - 2020-07-17 13:30 +0200
                Re: tmpfs is not a ramdisk (was: delimiters with more than one  character? ...) David Wright <deblis@lionunicorn.co.uk> - 2020-07-17 18:20 +0200
                Re: tmpfs is not a ramdisk (was: delimiters with more than one character? ...) rhkramer@gmail.com - 2020-07-17 20:30 +0200
                Re: tmpfs is not a ramdisk (was: delimiters with more than one  character? ...) Zenaan Harkness <zenaan@freedbms.net> - 2020-07-18 07:20 +0200
                Re: tmpfs is not a ramdisk (was: delimiters with more than one  character? ...) <tomas@tuxteam.de> - 2020-07-18 10:40 +0200
                Re: delimiters with more than one character? ... Greg Wooledge <wooledg@eeg.ccf.org> - 2020-07-17 13:40 +0200
        Re: delimiters with more than one character? ... "Thomas Schmitt" <scdbackup@gmx.net> - 2020-07-16 16:00 +0200
        Re: delimiters with more than one character? ... Zenaan Harkness <zenaan@freedbms.net> - 2020-07-17 04:50 +0200
      Re: delimiters with more than one character? ... Eric S Fraga <e.fraga@ucl.ac.uk> - 2020-07-16 15:00 +0200
  Re: delimiters with more than one character? ... John Crawley <john@bunsenlabs.org> - 2020-08-05 08:30 +0200
    Re: delimiters with more than one character? ... Greg Wooledge <wooledg@eeg.ccf.org> - 2020-08-05 15:10 +0200
      Re: delimiters with more than one character? ... John Crawley <john@bunsenlabs.org> - 2020-08-06 05:00 +0200
        Re: delimiters with more than one character? ... Greg Wooledge <wooledg@eeg.ccf.org> - 2020-08-06 13:40 +0200
          Re: delimiters with more than one character? ... John Crawley <john@bunsenlabs.org> - 2020-08-07 03:10 +0200

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