Puppet : get mountpoint using facter filter - hash

Question

I am trying to get a root partition (mountpoint => "/") name using Puppet facter. When I run "facter mountpoints", it shows multiple partitions. I would like to get the variable "/dev/md3" from the result.
{
/ => {
available => "893.71 GiB",
available_bytes => 959608590336,
capacity => "1.86%",
device => "/dev/md3",
filesystem => "ext4",
options => [
"rw",
"errors=remount-ro"
],
size => "910.69 GiB",
size_bytes => 977843884032,
used => "16.98 GiB",
used_bytes => 18235293696
},
/run => {
available => "794.91 MiB",
available_bytes => 833527808,
capacity => "0.07%",
device => "tmpfs",
filesystem => "tmpfs",
options => [
"rw",
"noexec",
"nosuid",
"size=10%",
"mode=0755"
],
size => "795.48 MiB",
size_bytes => 834125824,
used => "584.00 KiB",
used_bytes => 598016
},
/tmp => {
available => "1.78 GiB",
available_bytes => 1909157888,
capacity => "1.21%",
device => "/dev/md1",
filesystem => "ext4",
options => [
"rw"
],
size => "1.80 GiB",
size_bytes => 1932533760,
used => "22.29 MiB",
used_bytes => 23375872
}
}
I tried to use filter, but I was not able to filter "/" device.
$root_mount = $facts['mountpoints'].filter |$mountpoint| { $mountpoint == '/' } Do you guys have any idea?

Answer 1

You can access this fact directly via hash notation. Since your question heavily implies you are using Facter 3/Puppet 4, I will work with that syntax.
You just directly traverse the keys in the Facter hash to arrive at the /dev/md3 value. If we minimize the hash to the relevant portion from facter mountpoints:
{
/ => {
device => "/dev/md3"
}
}
then we see that the keys are mountpoints (you accessed that key directly when you did facter mountpoints from the CLI), /, and device. Therefore, using standard hash notation in Puppet with the $facts hash, we can access that value with:
$facts['mountpoints']['/']['device'] # /dev/md3
Check here for more info: https://docs.puppet.com/puppet/4.9/lang_facts_and_builtin_vars.html#the-factsfactname-hash