Bug#767891: apt: Provide ability to manually mark packages as "essential"

[Johannes Schauer]

Hi,

On Mon, 3 Nov 2014 20:37:26 +1000 Anthony Towns  wrote:
> On 3 November 2014 20:30, Anthony Towns  wrote:
> > On 3 November 2014 20:22, Julian Andres Klode  wrote:
> >> A simple way to achieve what you want is to create a local dummy
> >> package that depends on the packages you want and is
> >> "Essential: yes" or "Important: yes". Important being preferred, since
> >> it has less restrictions on installation ordering.

I actually like aj's proposed solution for another reason that is not
achievable via a local dummy package: currently apt hardcodes that it treats
itself as Essential:yes and the proposed solution allows the user to influence
this behaviour.

So instead of seeing aj's patch as a way to add more package names to what apt
treats as Essential:yes (something which can certainly be achieved via a local
dummy package), I see it as a way to make currently hardcoded apt behaviour
(apt treating itself as Essential:yes) configurable by the user.

Not having apt treat itself as Essential:yes is important for the following
scenarios:

 - use the EDSP interface to generate installation sets similar to what can
   already be done with tools like dose3. Currently these sets will always
   include apt which makes the solution less useful.

 - use multistrap to create a very minimal chroot (i.e. without apt). Currently
   multistrap is unable to create a chroot that does not contain apt due to
   this limitation of apt.

> > Yeah, I've done that before (and the equivs package is helpful there).  But
> > it's two somewhat complicated steps (build a package, install a local
> > package), for something that seems more like it should be a simple
> > configuration step ("these packages are important to me: ...").
> 
> Alternatively, it might make sense (from a user/admin's POV) to do it
> via 'apt-mark', ie:
> 
>   apt-mark important xmonad
>   apt-mark essential sysvinit-core
> 
> (I'm not really familiar with apt-mark though, particular if it's something
> people should feel comfortable relying on)

I'm also not very familiar with apt-mark but above two scenarios would be much
more complicated to achieve if one had to go through apt-mark first. Using the
apt configuration would make both of the above two scenarios very simple to
implement, so I think a configuration variable similar to the one proposed by
aj might be a good way forward.

Thanks!

cheers, josch


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Bug#767891: apt: Provide ability to manually mark packages as essential

[Anthony Towns]

Package: apt
Version: 1.0.9.3
Severity: wishlist
Tags: patch

Hi,

It would be useful to be able to locally mark certain packages as
Essential:yes so that they are never uninstalled. Trivial example: mark
sysvinit-core as essential on systems you don't want to have upgraded
to systemd as init.

I'm including a patch that allows you to do this by:

$ sudo apt-get -o pkgCacheGen::ForceEssential=systemd-sysv,apt update
...
$ sudo apt-get install sysvinit-core
Reading package lists... Done
Building dependency tree   
Reading state information... Done
The following packages will be REMOVED:
  systemd-sysv
The following NEW packages will be installed:
  sysvinit-core
WARNING: The following essential packages will be removed.
This should NOT be done unless you know exactly what you are doing!
  systemd-sysv
0 upgraded, 1 newly installed, 1 to remove and 304 not upgraded.
Need to get 0 B/130 kB of archives.
After this operation, 179 kB of additional disk space will be used.
You are about to do something potentially harmful.
To continue type in the phrase 'Yes, do as I say!'
 ?] no
Abort.

versus:

$ sudo apt-get -o pkgCacheGen::ForceEssential=apt update
...
$ sudo apt-get install sysvinit-core
Reading package lists... Done
Building dependency tree   
Reading state information... Done
The following packages will be REMOVED:
  systemd-sysv
The following NEW packages will be installed:
  sysvinit-core
0 upgraded, 1 newly installed, 1 to remove and 304 not upgraded.
Need to get 0 B/130 kB of archives.
After this operation, 179 kB of additional disk space will be used.
Do you want to continue? [Y/n] n
Abort.


Patch is (git diff -b, ignoring whitespace-only changes):

--- a/apt-pkg/deb/deblistparser.cc
+++ b/apt-pkg/deb/deblistparser.cc
@@ -277,13 +277,20 @@ bool debListParser::UsePackage(pkgCache::PkgIterator Pkg,
if (Section.FindFlag(Important,Pkg-Flags,pkgCache::Flag::Important) == 
false)
   return false;
 
-   if (strcmp(Pkg.Name(),apt) == 0)
+   std::vectorstd::string force_essential = 
_config-FindVector(pkgCacheGen::ForceEssential,apt);
+   for (std::vectorstd::string::const_iterator p = force_essential.begin(); 
p != force_essential.end(); ++p)
+   {
+  if (strcmp(p-c_str(), Pkg.Name()) == 0)
   {
  if ((essential == native  Pkg-Arch != 0  myArch == Pkg.Arch()) 
||
  essential == all)
 Pkg-Flags |= pkgCache::Flag::Essential | 
pkgCache::Flag::Important;
  else
 Pkg-Flags |= pkgCache::Flag::Important;
+
+ _error-Notice(Marking package as essential: %s,p-c_str());
+
+  }
}
 
if (ParseStatus(Pkg,Ver) == false)

Cheers,
aj


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Bug#767891: apt: Provide ability to manually mark packages as essential

[Julian Andres Klode]

On Mon, Nov 3, 2014 at 10:26 AM, Anthony Towns a...@erisian.com.au wrote:
 Package: apt
 Version: 1.0.9.3
 Severity: wishlist
 Tags: patch

 Hi,

 It would be useful to be able to locally mark certain packages as
 Essential:yes so that they are never uninstalled. Trivial example: mark
 sysvinit-core as essential on systems you don't want to have upgraded
 to systemd as init.

A simple way to achieve what you want is to create a local dummy
package that depends on the packages you want and is
Essential: yes or Important: yes. Important being preferred, since
it has less restrictions on installation ordering.

It's what I do on all my machines: Create one metapackage per machine
that is Important: yes, and install that. Works nicely.

-- 
Julian Andres Klode  - Debian Developer, Ubuntu Member

See http://wiki.debian.org/JulianAndresKlode and http://jak-linux.org/.


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Bug#767891: apt: Provide ability to manually mark packages as essential

[Anthony Towns]

On 3 November 2014 20:22, Julian Andres Klode j...@debian.org wrote:
 A simple way to achieve what you want is to create a local dummy
 package that depends on the packages you want and is
 Essential: yes or Important: yes. Important being preferred, since
 it has less restrictions on installation ordering.

Yeah, I've done that before (and the equivs package is helpful there).
But it's two somewhat complicated steps (build a package, install a
local package), for something that seems more like it should be a
simple configuration step (these packages are important to me: ...).

Cheers,
aj


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Bug#767891: apt: Provide ability to manually mark packages as essential

[Anthony Towns]

On 3 November 2014 20:30, Anthony Towns a...@erisian.com.au wrote:
 On 3 November 2014 20:22, Julian Andres Klode j...@debian.org wrote:
 A simple way to achieve what you want is to create a local dummy
 package that depends on the packages you want and is
 Essential: yes or Important: yes. Important being preferred, since
 it has less restrictions on installation ordering.

 Yeah, I've done that before (and the equivs package is helpful there).
 But it's two somewhat complicated steps (build a package, install a
 local package), for something that seems more like it should be a
 simple configuration step (these packages are important to me: ...).

Alternatively, it might make sense (from a user/admin's POV) to do it
via 'apt-mark', ie:

  apt-mark important xmonad
  apt-mark essential sysvinit-core

(I'm not really familiar with apt-mark though, particular if it's
something people should feel comfortable relying on)

Cheers,
aj

-- 
Anthony Towns a...@erisian.com.au


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