[scl.org] Idea: Software Collections Daemons Made System-wide

Honza Horak hhorak at redhat.com
Tue Mar 21 17:17:34 UTC 2017

On 03/21/2017 06:04 PM, Vacelet, Manuel wrote:
> On Tue, Mar 21, 2017 at 4:05 PM, Honza Horak <hhorak at redhat.com
> <mailto:hhorak at redhat.com>> wrote:
>     This is basically a kick-off for getting more feedback for an idea
>     shared at
>     http://www.themindiseverything.eu/2017/03/software-collections-daemons-made.html
>     <http://www.themindiseverything.eu/2017/03/software-collections-daemons-made.html>.
>     Shortly, SCL has worked nicely for several years and people love
>     them. But even the beloved ones have some issues. And what we hear
>     from users, the issues with Software Collections concept currently
>     are basically those:
>     * we need to use scl enable, which changes $PATH and other
>     environment variables, so the binaries placed in different location
>     are visible by the system
>     * scripts originally written for "normal" MySQL use full paths (like
>     /usr/bin/mysql) which does not work when we only have the Software
>     Collection installed
>     * Data directory, config files and log files are on different
>     location than it is common
>     The blog post tries to summarize possible solution, which I'm
>     looking for feedback now, ideally by replying to this mail..
> Hi Honza,
> I do love SCLs and I share most of the pitfalls you raised about using
> them (I would have loved not to write tons of custom scripts to manage
> my various parallel PHP / Nginx versions on my systems).
> Do you foresee a way to deal with package dependencies ?
> I might be wrong but when I'm installing packages that requires
> php(language>=5.3) it doesn't see rh-php56 or rh-php70 scls
> It's a bit cumbersome because I end-up having the default package
> installed whereas I'm only using the ones that come from SCLs

Interesting point. In case php(language) is common in php world, then 
someone might expect php from base is installed when asking for such 
requirement and thus adding the same virtual name into rh-php56 or 
rh-php70 scls might make troubles. Or maybe more important issue -- if 
modules are meant to work with php 5.5, then they might break with 5.6, 
especially in case of binary extensions. That's why the original idea 
was concerning the daemon SCLs like databases only.

> Last, as an alternative to wrapper package, I find useful the
> "update-alternative" from debian.
> It's pretty much the same thing (links AFAIK) but switch is done with a
> command rather than a package install.

Yeah, it would be nice, although I'm not sure entirely how this concept 
works with tens of binaries (requiring to run alternative command for 
every binary would not be very nice). Also, alternatives require all of 
the alternatives to support this method, which we are not able to do in 
RHEL-7/CentOS-7, because it would mean to change packages from the base 


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