Bug#619820: either bash or dash should be enough

[Jonathan Nieder]

Hi again,

Harald Dunkel wrote:

> I _do_ have to deal with minimal systems.

Ok, that makes more sense.  (Keep in mind that you're talking about
97284 bytes on i386 here, plus 15199 bytes of control files and an
entry in dpkg's "status" file.  Manpages and documentation can be
excluded with a dpkg filter.)

Thanks for explaining.

[...]
> About the removal path: AFAICS that is the job of update-
> alternatives.

Unfortunately the current implementation of update-alternatives is
not robust enough for that: when switching between alternatives,
there is a window of time when the symlink points nowhere.

It is also not clear that making /bin/sh point to another symlink in
/etc is worth the indirection.  But I could be convinced about that,
especially if update-alternatives is polished into good enough shape
to support it.

Hope that helps,
Jonathan



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Bug#619820: either bash or dash should be enough

[Harald Dunkel]

On 06/21/12 21:29, Jonathan Nieder wrote:
> 
> I guess I'm confused about why you filed this bug report and not a
> different one, especially given the subject line. Perhaps this is a
> request to make bash the default shell by removing dash altogether?
> 

I _do_ have to deal with minimal systems.

If dash would be sufficient to run such a system, then I
would be fine. But it is not. Today some developers (in Debian
or upstream) "still" work with bash, even though they create
system shell scripts for Wheezy and beyond. Debian doesn't
dare to drop the essential flag for bash, because it is in
afraid of bashisms in existing code (if I got other postings/
bug reports correctly).

If I could setup a bash-only system, then I would be fine,
too. But dash is marked essential. It was consensus to make
it the system shell for Squeeze (or was it Lenny?).

My request is to make a choice which shell we _really_
need for running a Debian host, and to drop the essential
flag for the other. Of course this choice implies balancing
risk, performance, work needed, etc.

About the removal path: AFAICS that is the job of update-
alternatives.


Regards

Harri



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Bug#619820: either bash or dash should be enough

[Jonathan Nieder]

Harald Dunkel wrote:
> On 06/21/12 13:49, Jonathan Nieder wrote:

>> Is the size of dash a problem for you?
>
> I am more interested in compatibility and efficiency.

Thanks for clarifying. Is your concern then about what the default
shell is, rather than whether dash should be optional?

I guess I'm confused about why you filed this bug report and not a
different one, especially given the subject line. Perhaps this is a
request to make bash the default shell by removing dash altogether?



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Bug#619820: either bash or dash should be enough

[Harald Dunkel]

On 06/21/12 13:49, Jonathan Nieder wrote:
> 
> Is the size of dash a problem for you?
> 

I am more interested in compatibility and efficiency.

Surely I don't want to argue about which shell is better.
I understand that dash has a much smaller working set
and a significant speed advantage at boot time, while
bash is widely accepted as the default when it comes
to user scripts.

But is the boot time performance argument still relevant,
when it comes to systemd and startup programs written
in C?


Regards

Harri



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Bug#619820: either bash or dash should be enough

[Jonathan Nieder]

reassign 619820 dash
affects 619820 + bash
severity 619820 wishlist
quit

Hi Harri,

Harald Dunkel wrote:

> Are there any system shell scripts in Debian that do
> _not_ work with bash? Would such an incompatibility be
> seen as a bug?

If a packaged shell script uses #!/bin/sh and doesn't work with bash,
that is a bug.  You can experience such bugs when they exist by
reconfiguring dash to make /bin/sh point to bash.

If a packaged shell script uses #!/bin/dash and the package doesn't
declare a dependency on dash, that is arguably a bug.  Anyway, it's
easy to search for.

I don't think these are what is blocking making dash and bash
optional.  A harder problem is making sure the removal path is safe.
If you have a set of patches that takes care of that, we'd be happy to
look at it.

Is the size of dash a problem for you?

Hope that helps,
Jonathan



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Bug#619820: either bash or dash should be enough

[Harald Dunkel]

Any news about this?

I learned from the messages in this report that dash is
essential for "good style" system scripts, while bash
is essential for user scripts, login, etc., and as a last
resort for the scripts with bashisms.

Are there any system shell scripts in Debian that do
_not_ work with bash? Would such an incompatibility be
seen as a bug?

Regards

Harri



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Bug#619820: either bash or dash should be enough

[Harald Dunkel]

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Just a short remark: I tried to install Websphere 7 on
Squeeze. IBM's installer silently got stuck. After moving
the /bin/sh symlink from dash to bash the installation went
fine. This problem took me a lot of time :-(.

Of course this is not a failure of dash. Point is, that
you can find bashisms everywhere. On RedHat Enterprise
and on Suse Websphere installed fine without any tweaks.

BTW, I found this highly interesting page listing a lot of
bashisms, and how to replace them:

http://mywiki.wooledge.org/Bashism


Regards

Harri
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Bug#619820: Fwd: Re: Bug#619820: either bash or dash should be enough

[Holger Levsen]

this should be saved in the bug log.


cheers!
--- Begin Message ---
Ben Finney  writes:
> Luk Claes  writes:

>> Well, by making dash the default *system* shell. bash is still the
>> default user shell.

> So, does that mean ‘bash’ and ‘dash’ should both remain essential?

Practically speaking, I think bash is going to have to remain essential.
There are innumerable scripts, package build rules, maintainer scripts,
and other things in Debian referencing /bin/bash without declaring a
dependency, particularly since that was one of the common solutions to
bashisms in scripts when we did the cleanup to be able to support dash as
/bin/sh.  I don't think there's much to be gained by going through all of
those and requiring them to declare a dependency, particularly given how
much third-party Linux stuff also assumes that /bin/bash is always
available.

So, I think this reduces to whether or not dash needs to remain essential.
I personally think that our default /bin/sh shell should be essential, and
the reasons why we switched to dash for that still apply, so I'm
comfortable keeping it essential.

The problem with instead making "sh" essential is that we'd have to be
very careful about what was allowed to Provide sh.  Other people have
discovered, for example, that zsh as /bin/sh has interesting and
surprising issues that can break software that otherwise works with more
common /bin/sh shells.  If someone sets up their /bin/sh symlink manually
to point to some other shell, more power to them, but allowing those
shells to Provide sh the way that various awk implementations Provide awk
promises somewhat more interoperability and testing than I think we can
promise.

-- 
Russ Allbery (r...@debian.org)   


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Bug#619820: either bash or dash should be enough

[Ben Finney]

Luk Claes  writes:

> On 03/28/2011 12:05 PM, Holger Levsen wrote:
> > On Sonntag, 27. März 2011, Jonathan Nieder wrote:
> >> # which packages are essential affects the entire distribution
> >> reassign 619820 general
> > 
> > For the distro we have solved^wdecided this by making dash the default 
> > shell. 
>
> Well, by making dash the default *system* shell. bash is still the
> default user shell.

So, does that mean ‘bash’ and ‘dash’ should both remain essential?

-- 
 \“There was a point to this story, but it has temporarily |
  `\escaped the chronicler's mind.” —Douglas Adams |
_o__)  |
Ben Finney 



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Bug#619820: either bash or dash should be enough

[Luk Claes]

On 03/28/2011 12:05 PM, Holger Levsen wrote:
> reassign 619820 dash,bash
> block 619820 by 540512
> thanks
> 
> On Sonntag, 27. März 2011, Jonathan Nieder wrote:
>> # which packages are essential affects the entire distribution
>> reassign 619820 general
> 
> For the distro we have solved^wdecided this by making dash the default shell. 

Well, by making dash the default *system* shell. bash is still the
default user shell.

Cheers

Luk



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Bug#619820: either bash or dash should be enough

[Holger Levsen]

reassign 619820 dash,bash
block 619820 by 540512
thanks

On Sonntag, 27. März 2011, Jonathan Nieder wrote:
> # which packages are essential affects the entire distribution
> reassign 619820 general

For the distro we have solved^wdecided this by making dash the default shell. 


cheers,
Holger


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Bug#619820: either bash or dash should be enough

[Jonathan Nieder]

# which packages are essential affects the entire distribution
reassign 619820 general
quit

Hi,

Harald Dunkel wrote:

> I cannot remove dash nor bash. Both are marked as essential packages.
> One shell should be enough for a minimal system.

That's a good point.  Raphael, do you remember why dash is essential?
Once we have a good mechanism for safely switching between arbitrary
policy-compliant shells (Bug#540512), would it be possible to make
"sh" essential instead?



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Bug#619820: either bash or dash should be enough

[Harald Dunkel]

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Package: dash
Version: 0.5.5.1-7.4

I cannot remove dash nor bash. Both are marked as essential packages.
One shell should be enough for a minimal system.

Please reassign, if necessary


Regards

Harri
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