I had a boring default ubuntu start up sound : P so I was thinking of changing it to some pleasing music, so here is place of my ubuntu sounds.
There will be a file with name system-ready.ogg
Replace this file with your .ogg file kep the name ‘system-ready.ogg’ same . You need have sudo permissions for this 😉
Actually I have an mp3 song so I took that song and cut the clip I want using ONLINE MP3 CUTTER and then I convert to .ogg format using command line converter mpg321.
First install mpg321
$ apt-get install mpg321 vorbis-tools
then convert .mp3 track to .ogg track,
$mpg321 input.mp3 -w - | oggenc -o output.ogg -