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TomOnTime
Asked: 2012-02-22 19:16:51 +0800 CST

A script that updates interfaces if /etc/network/interfaces changes

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[This is for Debian Squeeze, but applies to Ubuntu and other Linux distros.]

I have a rather complex /etc/network/interfaces file which is generated based on various factors (number of interfaces, are bridges needed, vlans, etc). After the new file is generated, I need to ifup any new interfaces and ifdown any obsolete interfaces; and I might have to reboot if the primary interface changes (for example, it changes from eth0 or br0).

Right now I figure out what to ifup/ifdown manually.

Is there a script that will do this for me?

ubuntu debian

3 Answers

  1. I don't know how you currently modify/generate your /etc/network/interfaces. Probably the best solution would be to use a configuration management tool (such as Puppet, Chef or Cfengine) to do this task, and have it call ifup when the file is modified. Such tools are tailored for tasks like this one. You could even benefit from Puppet's templating capabilities or the Augeas provider to modify your file.

    Another solution would be to use inotify. For examople, you could set up incron to call ifup every time /etc/network/interfaces is modified.

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  2. I don't know of any readily available script for this use-case, but hacking together a simple shell script for this task shouldn't be too hard.

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  3. This is how I manage ifcfg files with puppet. I create a directory under files/ for each host, e.g.:

    modules/network/files/foohostname/
modules/network/files/someotherhostname/

    Then in modules/network/manifests/init.pp I do the following:

    1. Copy all files in modules/network/files/hostname/ to the network scripts directory on the host.
    2. Run service network start or /etc/init.d/network start when any files are added/changed. I've found that service network start will bring up any interfaces that are not up yet, but won't kill my existing network connections. 
    class network {
  # copy all ifcfg files from files/hostname/ directory to network-scripts/ 
  # other files in network-scripts/ will not be touched.
  file { '/etc/sysconfig/network-scripts/':
      recurse => true,
      purge   => false,
      owner   => root,
      group   => root,
      ignore  => '\.svn', # this is specific to me as I use svn.
      source  => "puppet:///modules/network/${hostname}/",
  }

  # if anything changes with the above File resource, then fire network start to bring them up.
  # this won't restart the network, only bring up any ifaces that are not up yet.
  exec{ 'network-ifup':
      command     => 'service network start',       
      refreshonly => true,
      subscribe   => File['/etc/sysconfig/network-scripts/'],
  }        
}

    FYI some of the above may be a little CentOS/RHEL-specific.

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