Questions[tmpfs](ubuntu)

Usually I'm avoiding snap-based applications, but sometime I need them.

For example - Markdown Lint Tool is shipped only as Snap named mdl.

It works great when files are in home folder -

$ echo "# header" > ~/test.md
$ /snap/bin/mdl ~/test.md ; echo $?
0

but it fails when file is located in /tmp directory:

$ echo "# header" > /tmp/test.md
$ cat /tmp/test.md
# header
$ /snap/bin/mdl /tmp/test.md
/snap/mdl/140/lib/ruby/gems/2.4.0/gems/mdl-0.9.0/lib/mdl/doc.rb:57:in `read': No such file or directory @ rb_sysopen - /tmp/test.md (Errno::ENOENT)
    from /snap/mdl/140/lib/ruby/gems/2.4.0/gems/mdl-0.9.0/lib/mdl/doc.rb:57:in `new_from_file'
    from /snap/mdl/140/lib/ruby/gems/2.4.0/gems/mdl-0.9.0/lib/mdl.rb:75:in `block in run'
    from /snap/mdl/140/lib/ruby/gems/2.4.0/gems/mdl-0.9.0/lib/mdl.rb:73:in `each'
    from /snap/mdl/140/lib/ruby/gems/2.4.0/gems/mdl-0.9.0/lib/mdl.rb:73:in `run'
    from /snap/mdl/140/lib/ruby/gems/2.4.0/gems/mdl-0.9.0/bin/mdl:10:in `<top (required)>'
    from /snap/mdl/140/bin/mdl:23:in `load'
    from /snap/mdl/140/bin/mdl:23:in `<main>'

For this particular application there are no options for snap connect:

$ snap connections | grep mdl
home                      mdl:home                             :home                                 -

Also I can't install it as classic:

$ snap install mdl --classic 
Warning: flag --classic ignored for strictly confined snap mdl

mdl 0.9.0 from Snapcrafters installed

What should I do to give Snap application full access to the /tmp folder?
Does it happen by Snap design or not?

I'd like to mount /tmp without fstab entry using tmp.mount

However on Ubuntu 20.04 LTS, it doesn't seem to work.

user@user-x1:~$ systemctl status tmp.mount 
Unit tmp.mount could not be found.
user@user-x1:~$ sudo systemctl enable tmp.mount 
Failed to enable unit: Unit file tmp.mount does not exist.
user@user-x1:~$ sudo systemctl cat tmp.mount 
No files found for tmp.mount.
user@user-x1:~$ cat /usr/share/systemd/tmp.mount 
#  SPDX-License-Identifier: LGPL-2.1+
#
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=Temporary Directory (/tmp)
Documentation=https://systemd.io/TEMPORARY_DIRECTORIES
Documentation=man:file-hierarchy(7)
Documentation=https://www.freedesktop.org/wiki/Software/systemd/APIFileSystems
ConditionPathIsSymbolicLink=!/tmp
DefaultDependencies=no
Conflicts=umount.target
Before=local-fs.target umount.target
After=swap.target

[Mount]
What=tmpfs
Where=/tmp
Type=tmpfs
Options=mode=1777,strictatime,nosuid,nodev

[Install]
WantedBy=local-fs.target
user@user-x1:~$ 

What's happening? Why does systemd say unit could not be found even though bash auto tabbing fills up tmp.mount and what's the simplest way to enable this tmpfs without any config?

I have now a laptop with Ubuntu 18.04 and i love it. i have mounted /tmp as tmpfs via /etc/fstab line as this:

tmpfs           /tmp            tmpfs   defaults,noatime,nosuid,nodev,noexec,mode=1777    0       0

now, i like to know how i can do this only with systemd, i need only to activate a new systemd service only (tmp.mount related), or i need one more thing ? how i can replace my actual /etc/fstab line with systemd in my laptop on live mode?

I'd like to change the default size of /dev/shm in Lubuntu 11.10 (also known as /run/shm now, I guess).

It doesn't seem to appear in my fstab:

# / was on /dev/sdb5 during installation
UUID=66ac63f0-45fa-4766-9d20-7c56bcd0460d /               ext3    noatime,errors=remount-ro 0       1
# /home was on /dev/sdb7 during installation
UUID=227f1b29-5d04-4c28-9c9c-ea70b1726434 /home           ext3    noatime         0       2
# swap was on /dev/sdb6 during installation
#UUID=9e13b7cc-1f75-4b4e-9e79-c0f7368de353 none            swap    sw              0       0
/dev/mapper/cryptswap1 none swap sw 0 0

tmpfs /tmp tmpfs defaults,noexec,nosuid 0 0
tmpfs /var/tmp tmpfs defaults,noexec,nosuid 0 0

How do i create RAM drive under ubuntu. And would he automounted at startup?