Ubuntu 16.10 will be supported for 9 months until July 2017.
Release date: October 13, 2016
End of Life date: July 20, 2017
https://wiki.ubuntu.com/Releases
$ sudo apt-get update
Ign:1 http://kr.archive.ubuntu.com/ubuntu yakkety InRelease
Ign:2 http://kr.archive.ubuntu.com/ubuntu yakkety-updates InRelease
Ign:3 http://kr.archive.ubuntu.com/ubuntu yakkety-backports InRelease
Err:4 http://kr.archive.ubuntu.com/ubuntu yakkety Release
404 Not Found
Err:5 http://kr.archive.ubuntu.com/ubuntu yakkety-updates Release
404 Not Found
Err:6 http://kr.archive.ubuntu.com/ubuntu yakkety-backports Release 404 Not Found
Get:7 https://apt.dockerproject.org/repo ubuntu-xenial InRelease [48.7 kB]
Ign:8 http://security.ubuntu.com/ubuntu yakkety-security InRelease
Ign:7 https://apt.dockerproject.org/repo ubuntu-xenial InRelease
Err:9 http://security.ubuntu.com/ubuntu yakkety-security Release
404 Not Found [IP: 91.189.88.149 80]
Reading package lists... Done
E: The repository 'http://kr.archive.ubuntu.com/ubuntu yakkety Release' does no longer have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://kr.archive.ubuntu.com/ubuntu yakkety-updates Release' does no longer have a Release file.
...
[Solution]
Add below old releases repository of yakkety (16.10) to '/etc/apt/sources.list'.
# old release
# ----------------------------------------------
deb http://old-releases.ubuntu.com/ubuntu/ yakkety main restricted
deb-src http://old-releases.ubuntu.com/ubuntu/ yakkety main restricted
deb http://old-releases.ubuntu.com/ubuntu/ yakkety-updates main restricted
deb-src http://old-releases.ubuntu.com/ubuntu/ yakkety-updates main restricted
#
deb http://old-releases.ubuntu.com/ubuntu/ yakkety universe
deb-src http://old-releases.ubuntu.com/ubuntu/ yakkety universe
deb http://old-releases.ubuntu.com/ubuntu/ yakkety-updates universe
deb-src http://old-releases.ubuntu.com/ubuntu/ yakkety-updates universe
#
deb http://old-releases.ubuntu.com/ubuntu/ yakkety multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ yakkety multiverse
deb http://old-releases.ubuntu.com/ubuntu/ yakkety-updates multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ yakkety-updates multiverse
#
deb http://old-releases.ubuntu.com/ubuntu/ yakkety-backports main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ yakkety-backports main restricted universe multiverse
# ----------------------------------------------
-----
cheers,
June
