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Context: I'm porting an opensource server software (and writing associated documentation) from Debian/Ubuntu to CentOS/RHEL.

For the software to run correctly, I need to add a dozen of specific parameters to Mysql configuration (example: increase max_allowed_packet).

From a Debian point of view, I known I can override Mysql's my.cnf by adding a file to /etc/mysql.d, say /etc/mysql.d/my-software.cnf.

My question is: how to do the same correctly on CentOS/RHEL ?

Other infos:

  • I know where mysqld looks for its configuration file thanks to https://dev.mysql.com/doc/refman/5.7/en/option-files.html. But, for CentOS, I don't understand:
    • how NOT to directly edit /etc/my.cnf (that may not be package-update-proof)
    • where to add my specific Mysql parameters
  • Reading the CentOS Mysql init script (/etc/init.d/mysql), I've seen that a /etc/sysconfig/mysqld is sourced, but I don't know how to add configuration parameters.
  • I've search for combinations of override / my.cnf / centos on ServerFault, StackOverflow and also DBA.StackExchange, but found nothing relevant.
  • I make all the tests within a "centos:6" Docker container
  • the software is Asqatasun https://github.com/Asqatasun/Asqatasun
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    Why are you using centos 6 rather than centos 7? This is just going to add three and a half years of technical debt instantly. – Michael Hampton Sep 22 '16 at 6:14
  • @MichaelHampton to widen the audience, some users still have conservative upgrade policies. But as our base is Debian/Ubuntu, if centos6 is not feasible, we will certainly switch to centos7 – Matthieu FAURE Sep 22 '16 at 6:22
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    On CentOS 7, you would just stick everything in /etc/my.cnf.d like you do now. This wasn't set up on 6. – Michael Hampton Sep 22 '16 at 6:24
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    And as for conservative, EL 6 is past the end of Production 1, which is about the time you should stop deploying it for new projects. Doing anything greenfield on EL 6 right now is steadily moving away from "conservative" and toward "insane". – Michael Hampton Sep 22 '16 at 6:27
  • @MichaelHampton I didn't know that Redhat document, really interesting, thanks! I have arguments now, we will switch to 7. – Matthieu FAURE Sep 22 '16 at 6:47
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Using strace -e open /some/prog/name, e.g. strace -e open mysql would reveal what places are checked for configuration directives and in what order for each particular OS and a program version. Different programs use different location and sections within a configuration.

As to overriding, you can only be sure that CentOS/RHEL installs and uses /etc/my.cnf. If software your are porting uses libmysqlclient, you may take the path of overriding MYSQL_HOME environmental variable. If not, adding !include /some/location.cnf to [client] section of /etc/my.cnf is still an option.

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