...is a permission issue.

The specified file could not be read by user "_apt" so Apt elevated itself to root user - as it's a warning not an error (W: not E:), it means the action (install) probably still succeeded, but there's a reason Apt runs as its own user, so possibly there are security implications.

The fix depends on which file/directory is causing the complaint - i.e. why can't _apt access it.

In some instances, the solution can be to fix ownership, e.g. chown --changes --recursive _apt:root TARGET

In other instances, it may involve granting read permissions, e.g. chmod --changes --recursive a+r TARGET

And sometimes the above have no effect because the filesystem was mounted with an over-restrictive umask - in which case remount it with, e.g. mount -o umask=022 DEVICE MOUNTPOINT

Alternatively, for the Synaptic-related errors here, see if Synaptic can be configured to put temporary files in a better location (i.e. not inside root user's home dir).

W: Download is performed unsandboxed as root as file '/root/.synaptic/tmp//tmp_sh' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)

I've been randomly getting exactly the same message inside the console log in synaptic when installing packages. I don't know when it happens or when it doesn't. I'm starting synaptic from the usual launcher in the menu. When it's shows up in the expanded console then it will also throw this actual error dialog after closing the installation dialog:

I'm using XFCE on Chimaera.

 The package description says "interface::commandline" so that might explain why it's not in the menu.

I had not noticed this and it explains a lot.

and I did not know about

ls /usr/bin/dvb*

so thanks for the education.

I was hoping for a dvb app that has a GUI, so it's back to searching for me.

the machine responds with

 /home/mine# apt install dvb-apps
Reading package lists... Done
Building dependency tree       
Reading state information... Done
dvb-apps is already the newest version (1.1.1+rev1500-1.1+b1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

and

dpkg -L dvb-apps

THe machine responds with as a user

 $ dpkg -L dvd-apps
dpkg-query: package 'dvd-apps' is not installed
Use dpkg --info (= dpkg-deb --info) to examine archive files,
and dpkg --contents (= dpkg-deb --contents) to list their contents.

as su the command dpkg -L dvb-apps

lists about 100 dvb-apps  files from a list of several hundred.

most appear to be in the /usr/share/doc/dvb-apps/examples/test/       folder

Neither as su or a user is there a man page.

W: Download is performed unsandboxed as root as file '/root/.synaptic/tmp//tmp_sh' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)

That's the message you get when you download a package as root. Download as ordinary user instead.

What message do you get when you run

apt install dvb-apps

If it's already installed, apt will tell you that. Look in /usr/share/doc/dvb-apps for information. The package description says "interface::commandline" so that might explain why it's not in the menu.

dpkg -L dvb-apps

will give you a list of the files in the package. That will include a list of any commands. There will probably be man pages for those commands.

I've tried to install, several times, dvb-apps, through both the command line and synaptic package manager, and though apparently sucessful it does not appear on any menu.

During the install dvb-scan-tables is also installed.

During one install attempt I got an error message stating

W: Download is performed unsandboxed as root as file '/root/.synaptic/tmp//tmp_sh' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)

Which I do not understand, but has me thinking dvb-apps is sandboxed. But I am probably wrong.

So what have I got to do to get dvb-apps working correctly for a normal user?

I've thought about installing from source, but the instruction-

cd dvb-apps

does not make sense. Should it be cd /user/share/dvb-apps?

As a secondary interest I'd like to know how to unsandbox an app.

thanks