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"Snap" question

Robert Heller
I just installed xv under snap using the instructions here:

https://snapcraft.io/install/xv/ubuntu

And I am encountering a "weirdness" (at least to me).  I can only access and
view images that are under $HOME.  Images located elsewhere yield a file not
found error (the files are in fact there and I was able to view them with xv
installed under CentOS 6 (from a standard RPM).

Background: I needed to jump from CentOS 6 to Ubuntu 18.04 on my laptop, so I
installed Ubuntu 18.04 on a separate LVM volume on my laptop. I use LVM on my
laptop and have a number of LVM volumes:

Filesystem                        Size  Used Avail Use% Mounted on
udev                              1.9G     0  1.9G   0% /dev
tmpfs                             385M  1.8M  383M   1% /run
/dev/mapper/vg_newgollum-UB1804    12G  7.1G  4.1G  64% /
tmpfs                             1.9G  115M  1.8G   6% /dev/shm
tmpfs                             5.0M  4.0K  5.0M   1% /run/lock
tmpfs                             1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/loop1                         98M   98M     0 100% /snap/core/10444
/dev/loop2                         36M   36M     0 100% /snap/gtk-common-themes/1198
/dev/loop3                        141M  141M     0 100% /snap/gnome-3-26-1604/82
/dev/loop4                        2.3M  2.3M     0 100% /snap/gnome-calculator/260
/dev/loop5                         15M   15M     0 100% /snap/gnome-logs/45
/dev/loop6                         92M   92M     0 100% /snap/core/6531
/dev/loop8                         13M   13M     0 100% /snap/gnome-characters/139
/dev/loop10                       3.8M  3.8M     0 100% /snap/gnome-system-monitor/57
/dev/loop12                        87M   87M     0 100% /snap/core/4486
/dev/loop14                        56M   56M     0 100% /snap/core18/1932
/dev/mapper/vg_newgollum-mp3s      19G   14G  4.4G  76% /mp3s
/dev/mapper/vg_newgollum-scratch   40G   36G  1.7G  96% /scratch
/dev/mapper/vg_newgollum-lv_home   30G   27G  974M  97% /home
/dev/sda1                         477M  316M  132M  71% /boot
tmpfs                             385M   16K  385M   1% /run/user/120
tmpfs                             385M   40K  385M   1% /run/user/5125
/dev/mapper/vg_newgollum-lv_root   20G   14G  4.9G  74% /mnt
/dev/loop15                       384K  384K     0 100% /snap/gnome-characters/570
/dev/loop16                       1.0M  1.0M     0 100% /snap/gnome-logs/100
/dev/loop17                       2.3M  2.3M     0 100% /snap/gnome-system-monitor/148
/dev/loop18                       2.5M  2.5M     0 100% /snap/gnome-calculator/826
/dev/loop19                       141M  141M     0 100% /snap/gnome-3-26-1604/100
/dev/loop0                         65M   65M     0 100% /snap/gtk-common-themes/1514
/dev/loop20                       218M  218M     0 100% /snap/gnome-3-34-1804/60
/dev/loop7                        4.4M  4.4M     0 100% /snap/xv/9

Is there some "magic" to allow xv to view files anywhere on any file system
(permissions permitting)?

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Re: "Snap" question

Oliver Grawert
hi,
Am Donnerstag, den 10.12.2020, 18:13 -0500 schrieb Robert Heller:

> I just installed xv under snap using the instructions here:
>
> https://snapcraft.io/install/xv/ubuntu
>
> And I am encountering a "weirdness" (at least to me).  I can only
> access and
> view images that are under $HOME.  Images located elsewhere yield a
> file not
> found error (the files are in fact there and I was able to view them
> with xv
> installed under CentOS 6 (from a standard RPM).
this is pretty normal behavior for confined snaps, they access the
outside world of their confinement vi interfaces, typically desktop
apps have the home interface auto-connected (as you found) that enables
you to access all iles in ~/ with the exception of any hidden dirs (so
we can guarantee that a snapped app can not access any information of
any other app unless you allow it to explicitly)

often apps also have the removable-media interface available, that
allows access to /mnt and /media ... so the easiest to give apps access
to your additional disks would be to mount them there ...

one part of file access confinement is managed by the kernels apparmor
security mechanism, apparmor does not allow you to follow links t
outside areas of teh defined confinement *but* it allows access to
mounts, so another option to gain access to your disks is to simply set
up a bind mount between their mount points and an accessible place
(/home/mydisk-foo ... /media/mydisk-bar ... )


> Is there some "magic" to allow xv to view files anywhere on any file
> system
> (permissions permitting)?

all that above said, the xv snap is clearly only available in the edge
channel *and* only installable by defining --devmode ...

the first one here tells you that this snap is not really done yet,
typically things in edge are under development, untested, buggy etc

second, if you install it with the --devmode option (as installing it
from comandline will suggest to you) you turn off all confinement and
as such, you should be able to access any place on the filesystem.

did you use --jailmode instead of -devmode when installing it ?

ciao
        oli

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Re: "Snap" question

Robert Heller
At Fri, 11 Dec 2020 00:33:38 +0100 "Ubuntu user technical support,  not for general discussions" <[hidden email]> wrote:

>
> hi,
> Am Donnerstag, den 10.12.2020, 18:13 -0500 schrieb Robert Heller:
> > I just installed xv under snap using the instructions here:
> >
> > https://snapcraft.io/install/xv/ubuntu
> >
> > And I am encountering a "weirdness" (at least to me).  I can only
> > access and
> > view images that are under $HOME.  Images located elsewhere yield a
> > file not
> > found error (the files are in fact there and I was able to view them
> > with xv
> > installed under CentOS 6 (from a standard RPM).
>
> this is pretty normal behavior for confined snaps, they access the
> outside world of their confinement vi interfaces, typically desktop
> apps have the home interface auto-connected (as you found) that enables
> you to access all iles in ~/ with the exception of any hidden dirs (so
> we can guarantee that a snapped app can not access any information of
> any other app unless you allow it to explicitly)
>
> often apps also have the removable-media interface available, that
> allows access to /mnt and /media ... so the easiest to give apps access
> to your additional disks would be to mount them there ...
>
> one part of file access confinement is managed by the kernels apparmor
> security mechanism, apparmor does not allow you to follow links t
> outside areas of teh defined confinement *but* it allows access to
> mounts, so another option to gain access to your disks is to simply set
> up a bind mount between their mount points and an accessible place
> (/home/mydisk-foo ... /media/mydisk-bar ... )
>
>
> > Is there some "magic" to allow xv to view files anywhere on any file
> > system
> > (permissions permitting)?
>
> all that above said, the xv snap is clearly only available in the edge
> channel *and* only installable by defining --devmode ...
>
> the first one here tells you that this snap is not really done yet,
> typically things in edge are under development, untested, buggy etc
>
> second, if you install it with the --devmode option (as installing it
> from comandline will suggest to you) you turn off all confinement and
> as such, you should be able to access any place on the filesystem.
>
> did you use --jailmode instead of -devmode when installing it ?
>

I used -edge and -devmode.  Was that the mistake?

> ciao
> oli
>

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http://www.deepsoft.com/  -- Linux Administration Services
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Re: "Snap" question

Oliver Grawert
hi,
Am Donnerstag, den 10.12.2020, 20:38 -0500 schrieb Robert Heller:

> > did you use --jailmode instead of -devmode when installing it ?
> >
> I used -edge and -devmode.  Was that the mistake?
>
nope, for this snap --devmode is the best you can do, one thing you can
try is to simply prefix your path (i.e. navigate
to) /var/lib/snapd/hostfs, this is where a devmode snap is able to see
a copy of the rootfs ... i.e.
try /var/lib/snapd/hostfs/usr/share/pixmaps

i took a look at the snap and it seems really not completely ready yet
(i.e. it only provides the home interface by default while it should
also offer removable-media, btw "snap connections xv" shows you the
possible interfaces the snap packager has allowed and if they are
connected) so you will have to work around some shortcomings ...

ciao
        oli
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Re: "Snap" question

Robert Heller
At Fri, 11 Dec 2020 09:31:51 +0100 "Ubuntu user technical support,  not for general discussions" <[hidden email]> wrote:

>
> hi,
> Am Donnerstag, den 10.12.2020, 20:38 -0500 schrieb Robert Heller:
> > 
> > > did you use --jailmode instead of -devmode when installing it ?
> > >
> > I used -edge and -devmode.  Was that the mistake?
> >
> nope, for this snap --devmode is the best you can do, one thing you can
> try is to simply prefix your path (i.e. navigate
> to) /var/lib/snapd/hostfs, this is where a devmode snap is able to see
> a copy of the rootfs ... i.e.
> try /var/lib/snapd/hostfs/usr/share/pixmaps
>
> i took a look at the snap and it seems really not completely ready yet
> (i.e. it only provides the home interface by default while it should
> also offer removable-media, btw "snap connections xv" shows you the
> possible interfaces the snap packager has allowed and if they are
> connected) so you will have to work around some shortcomings ...
OK, this will not do. I have used xv as my "standard" image viewer application
and have used it to view images all over the various file systems mounted on
my system. I will have to find a "real" (eg .deb) install of xv or else I'll
have to find the source and build it that way.

>
> ciao
> oli

--
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Deepwoods Software        -- Custom Software Services
http://www.deepsoft.com/  -- Linux Administration Services
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Re: "Snap" question

Oliver Grawert
hi,
Am Freitag, den 11.12.2020, 09:44 -0500 schrieb Robert Heller:
>
> OK, this will not do. I have used xv as my "standard" image viewer
> application
> and have used it to view images all over the various file systems
> mounted on
> my system. I will have to find a "real" (eg .deb) install of xv or
> else I'll
> have to find the source and build it that way.

luckily rebuilding a snap (if you know where the snapcraft.yaml source
file is [1]) is a trivial task of a few minutes ... i made a --classic
version [2] of the snap in the store (classic snaps are running
completely without confinement, while they are hard o get into the
store (security review etc), they are easy to build):

https://people.canonical.com/~ogra/snaps/xv_3.10a+dg20180618_amd64.snap

download it, install it with:

sudo snap install --dangerous --classic xv_3.10a+dg20180618_amd64.snap

that should get you a fully functional xv ...

note though that this is completely illegal, xv upsream denies any
distribution of modified (including self built) binaries of the app via
its license ... (which is likely also the reason it was removed from
debian (and thus from ubuntu, as it only came from there as a sync))

indeed snaps from locally installed .snap files do not get updated etc
but i doubt xv gets updated a lot anyway :)

ciao
        oli

[1] https://github.com/cmatsuoka/xv/tree/xv
[2] https://paste.ubuntu.com/p/TGHHpCvKGP/

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Re: "Snap" question

Robert Heller
At Sat, 12 Dec 2020 15:54:28 +0100 "Ubuntu user technical support,  not for general discussions" <[hidden email]> wrote:

>
> hi,
> Am Freitag, den 11.12.2020, 09:44 -0500 schrieb Robert Heller:
> >
> > OK, this will not do. I have used xv as my "standard" image viewer
> > application
> > and have used it to view images all over the various file systems
> > mounted on
> > my system. I will have to find a "real" (eg .deb) install of xv or
> > else I'll
> > have to find the source and build it that way.
>
> luckily rebuilding a snap (if you know where the snapcraft.yaml source
> file is [1]) is a trivial task of a few minutes ... i made a --classic
> version [2] of the snap in the store (classic snaps are running
> completely without confinement, while they are hard o get into the
> store (security review etc), they are easy to build):
>
> https://people.canonical.com/~ogra/snaps/xv_3.10a+dg20180618_amd64.snap
>
> download it, install it with:
>
> sudo snap install --dangerous --classic xv_3.10a+dg20180618_amd64.snap
>
> that should get you a fully functional xv ...
>
> note though that this is completely illegal, xv upsream denies any
> distribution of modified (including self built) binaries of the app via
> its license ... (which is likely also the reason it was removed from
> debian (and thus from ubuntu, as it only came from there as a sync))
>
> indeed snaps from locally installed .snap files do not get updated etc
> but i doubt xv gets updated a lot anyway :)

I found a site with step-by-step instructions for building xv from source as a
normal executable, complete with the RPMFusion and Jumbo patches.

>
> ciao
> oli
>
> [1] https://github.com/cmatsuoka/xv/tree/xv
> [2] https://paste.ubuntu.com/p/TGHHpCvKGP/
>

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Deepwoods Software        -- Custom Software Services
http://www.deepsoft.com/  -- Linux Administration Services
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