Acho que meu tema é minha pergunta.
quando eu uso o sudo apt-get update no meu Ubuntu (15.10).
Eu recebo o aviso abaixo, eu não sou bom no Ubuntu, alguém pode explicar e me dar uma lição.
Hit http://in.archive.ubuntu.com wily-backports/main Sources
Hit http://in.archive.ubuntu.com wily-backports/restricted Sources
Hit http://in.archive.ubuntu.com wily-backports/universe Sources
Hit http://in.archive.ubuntu.com wily-backports/multiverse Sources
Hit http://in.archive.ubuntu.com wily-backports/main amd64 Packages
Hit http://in.archive.ubuntu.com wily-backports/restricted amd64 Packages
Hit http://in.archive.ubuntu.com wily-backports/universe amd64 Packages
Hit http://in.archive.ubuntu.com wily-backports/multiverse amd64 Packages
Hit http://in.archive.ubuntu.com wily-backports/main i386 Packages
Hit http://in.archive.ubuntu.com wily-backports/restricted i386 Packages
Hit http://in.archive.ubuntu.com wily-backports/universe i386 Packages
Hit http://in.archive.ubuntu.com wily-backports/multiverse i386 Packages
Hit http://in.archive.ubuntu.com wily-backports/main Translation-en
Hit http://in.archive.ubuntu.com wily-backports/multiverse Translation-en
Hit http://in.archive.ubuntu.com wily-backports/restricted Translation-en
Hit http://in.archive.ubuntu.com wily-backports/universe Translation-en
Fetched 1,015 kB in 29s (34.7 kB/s)
Reading package lists... Done
W: There is no public key available for the following key IDs:
1397BC53640DB551