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N0rbert
Asked: 2020-08-02 10:00:32 +0800 CST

How to allow snap applications to access /tmp folder?

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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?

permissions tmp tmpfs snap

2 Answers

  1. Best Answer

    It seems you may be looking for the "proper" way to solve the issue caused with snaps...

    but if you were looking for a workaround so you can use your tmp directory, you could:

    mkdir /home/you/tmp
sudo mount --bind /tmp /home/you/tmp/

    mdl will have full access to the /tmp directory via the /home/you/tmp mountpoint:

    echo "# header" > /home/you/tmp/test.md
mdl /home/you/tmp/test.md

    To make it permanent you can add this line to the /etc/fstab:

     # <file system> <mount point>   <type>  <options>       <dump>  <pass>
/tmp        /home/you/tmp   auto    bind    0   3

    and rebuild the initrd with sudo update-initramfs -u -k all .

    • 10

  2. I'm usually very supportive of change and of Ubuntu, but if, like me, you find this really annoying, the fix I came up with is to add a directory to my home:

    mkdir /home/mlissner/tmp

    And to add a crontab to nuke it on reboot:

    sudo crontab -e

    Then add:

    @reboot rm -rf /home/mlissner/tmp/*

    Having to do this is really dumb.

    I'm all for sandboxing and security. I'm all for change, but this removes an important use case of "Save this file here, and then delete it later without me thinking about it."

    It's also really buggy from a user perspective. You can save something from Firefox into /tmp, no errors. But then when you try to find that thing in the file browser, it doesn't exist. WTF.

    Count me very annoyed.

    • 3