A few questions from a Debain user...

[bobby21]

Hi all,

I am new to the RPM/CentOS world, but have used Debain based distros for a while. I've come across a couple of questions recently that I have been unable to find the answers to...

I have an old laptop that I use as a NAS/Server and am currently playing with the idea of changing it to CentOS from Debain. I use Avahi to facilitate local discovery of CUPS printers and make them available to all devices. I noticed that the version of Avahi that is in the EL6 repos is 0.6.25, whereas I would like to use 0.6.31 (or at least something higher than 0.6.25 to start) because my printers aren't showing up automagically with 0.6.25. I added the EPEL repo hoping a newer version might be in there but when I type 'yum info avahi' I am still presented with version 0.6.25, I also added the REMI repo, but no luck. I imagine that getting a higher version installed won't be too easy due to dependencies, but can someone give me some advice/pointers?

Also, In Debian, I have been used to 'apt-get install avahi' and the service is installed, started and pre-configured with basic settings. In CentOS, I have to 'yum install avahi' then 'chkconfig avahi-daemon on' then edit avahi's conf file, then finally 'service avahi-daemon start'. This might seem like a dumb question - but is the world of RH/CentOS usually this 'manual'? I mean, I don't mind tinkering in the terminal or anything but it's just a gear change from Debian is all.

[Super Jamie]

Enterprise Linux (so RHEL, and then CentOS which is compiled from the RHEL source) is built from a snapshot of Fedora at a point in time. In the case of EL6, this snapshot was taken around late 2009.

Red Hat then stabilise on the versions of software, and promise their customers they will maintain ABI compatibility until the next EL major version. This means they usually stick to the same version number of packages, and backport specific features as-required. Over time, the EL version of a package becomes a mix of the old upstream version with new upstream bits added in.

I'm not sure of the details of avahi-daemon specifically, but either it is not possible to backport 0.6.31 to EL6, or simply nobody has asked Red Hat to do it.

However, note that the version in EL6 is actually avahi-0.6.25-12.el6 the important part is the -12. This means there have been at least 12 changes between upstream 0.6.25 and the package supplied in EL6. You can view the changelog with rpm -q --changelog avahi to see what these changes are.

I couldn't find anyone who packages a later avahi for EL6. If you really do need 0.6.31, you could try compiling the latest avahi-daemon from the upstream source.

If you need the latest and greatest packages, EL is probably not the distro for you. Much like Debian gets really old after a few years, because none of the packages can have major features compared to their latest upstream versions in Ubuntu/Fedora, EL can suffer the same old-version-syndrome.

Generally yes, a service won't be automatically started and enabled at boot just because you have installed that service. That's an awful idea. Most services come with a sane default config so they start and work, which you can edit if you have special needs.

[TrevorH]

Not being able to discover printers also sounds like it might be an iptables problem.

[bobby21]

Thank you both for your replies.

I will take a look at the changelog for Avahi and see if there is anything in there that stands out.

I also considered that it could be an iptables issue, so I disabled the firewall completely to test using: '/etc/init.d/iptables save' then '/etc/init.d/iptables stop' then 'chkconfig iptables off' to keep it off but the printers still do not show. Is there anything else I am missing?

[Super Jamie]

'/etc/init.d/iptables save' then '/etc/init.d/iptables stop' then 'chkconfig iptables off'

Just a little sysadmin tip, you are better to run service iptables blah instead of /etc/init.d/iptables blah. If you run the script directly, your current environment variables might interfere. When you use the service command, the initscript is run in a "clean" shell environment. chkconfig is used to list services, and manage service start at boot, it won't have any effect on a currently running service. Personally I find service management a lot easier on CentOS than Debian, chkconfig and service provide really easy wrappers, I'm never sure what update-rc.d does and doesn't do, and chkconfig is much easier than ls on runlevel folders

[bobby21]

Thanks for that. I think i'll put CentOS on another less critical system and have a play before I commit to replacing my Debian system. Thanks both for the help and advice.