Ubuntu systems at Google are upgraded every LTS release. The entire process of upgrading can take as much as 4 months and it is also quite expensive as one reboot or a small change can cost them as much as 1 million dollars.
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"And do you think (fop that I am) that I could be the Scarlet Pumpernickel?" -- Looney Tunes, The Scarlet Pumpernickel (1950, Chuck Jones)