[CentOS] About mysql upgrade

[Lamar Owen]

On 04/28/2016 08:45 AM, Sergio Belkin wrote:
> I've found some issues upgrading mysql, some people recommends run
> mysql_upgrade. I wonder why such a script is not run from scriptlet of
> mysql-server rpm.
Back in the Dark Ages of the PostgreSQL RPMset (PostgreSQL 6.5), early 
in my time as RPM maintainer for the community PostgreSQL.org RPMset, I 
asked a very similar question of some folks, and I got a canonical 
answer from Mr. RPM himself, Jeff Johnson.

The answer is not very complex, but it was spread across a several 
message private e-mail thread.  The gist of it is that the RPM 
scriptlets are very very limited in what they can do.  Trying to do 
something clever inside an RPM scriptlet is almost never wise.  The key 
thing to remember is that the scriptlet has to be able to be run during 
the OS install phase (back when upgrades were actually supported by the 
OS installer that is now known as anaconda). Quoting this introductory 
section:

On August 18, 1999, Jeff Johnson wrote:
 > The Red Hat install environment is a chroot. That means no daemons,
 > no network, no devices, nothing. Even sniffing /proc can be problematic
 > in certain cases.

Now, I realize that that is OLD information; however, anaconda is still 
doing the same basic chrooted install, just with a prettier face.  You 
cannot start a daemon in the chroot, since many things are simply not 
available to the scriptlets when installed/upgraded by anaconda.  
Scriptlets have to work in an environment other than 'yum update.'  And 
also note that this is a very different situation than Debian packages 
live in; RPM scriptlets are essentially forbidden from interactivity 
with the user; Debian's equivalent are not so hindered.  At least that 
was the rule as long as I was an active packager.

Further reference a WayBack Machine archive of a page I wrote long ago:
https://web.archive.org/web/20010122090200/http://www.ramifordistat.net/postgres/rpm_upgrade.html

And leaving you with this thought, again from Jeff Johnson:

On August 18, 1999, Jeff Johnson wrote:
 > Good. Now you're starting to think like a packager  Avoiding MUD is
 > *much* more important than attempting magic.
....

 > The bottom line is you shouldn't attempt a database conversion as
 > part of the package install. The package, however, should contain 
programs
 > and procedures necessary to do the job.