rajivmars@rajivmars-desktop:~$ sudo apt update -y
[sudo] password for rajivmars:
Hit:1 http://download.nus.edu.sg/mirror/ubuntu xenial InRelease
Ign:2 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:3 http://dl.google.com/linux/chrome/deb stable Release
Get:4 http://download.nus.edu.sg/mirror/ubuntu xenial-updates InRelease [102 kB]
Get:6 http://download.nus.edu.sg/mirror/ubuntu xenial-backports InRelease [102 kB]
Hit:7 http://download.nus.edu.sg/mirror/ubuntu xenial-security InRelease
Ign:8 http://download.nus.edu.sg/mirror/ubuntu xenial-updates/main amd64 Packages
Ign:9 http://download.nus.edu.sg/mirror/ubuntu xenial-updates/main i386 Packages
Ign:10 http://download.nus.edu.sg/mirror/ubuntu xenial-updates/universe amd64 Packages
Ign:11 http://download.nus.edu.sg/mirror/ubuntu xenial-updates/universe i386 Packages
Ign:12 http://download.nus.edu.sg/mirror/ubuntu xenial-backports/main Sources
Ign:13 http://download.nus.edu.sg/mirror/ubuntu xenial-backports/main amd64 Packages
Ign:14 http://download.nus.edu.sg/mirror/ubuntu xenial-backports/main i386 Packages
Ign:15 http://download.nus.edu.sg/mirror/ubuntu xenial-backports/main Translation-en
Ign:16 http://download.nus.edu.sg/mirror/ubuntu xenial-backports/universe amd64 Packages
Ign:17 http://download.nus.edu.sg/mirror/ubuntu xenial-backports/universe i386 Packages
Get:8 http://download.nus.edu.sg/mirror/ubuntu xenial-updates/main amd64 Packages [460 kB]
Err:8 http://download.nus.edu.sg/mirror/ubuntu xenial-updates/main amd64 Packages
Hash Sum mismatch
Get:12 http://download.nus.edu.sg/mirror/ubuntu xenial-backports/main Sources [3,176 B]
Err:12 http://download.nus.edu.sg/mirror/ubuntu xenial-backports/main Sources
Hash Sum mismatch
Get:15 http://download.nus.edu.sg/mirror/ubuntu xenial-backports/main Translation-en [3,200 B]
Fetched 463 kB in 3s (135 kB/s)
Reading package lists... Done
E: Failed to fetch http://download.nus.edu.sg/mirror/ubuntu/dists/xenial-updates/main/binary-amd64/Packages.xz Hash Sum mismatch
E: Failed to fetch http://download.nus.edu.sg/mirror/ubuntu/dists/xenial-updates/main/binary-i386/Packages.xz 404 Not Found
E: Failed to fetch http://download.nus.edu.sg/mirror/ubuntu/dists/xenial-updates/universe/binary-amd64/Packages.xz 404 Not Found
E: Failed to fetch http://download.nus.edu.sg/mirror/ubuntu/dists/xenial-updates/universe/binary-i386/Packages.xz 404 Not Found
E: Failed to fetch http://download.nus.edu.sg/mirror/ubuntu/dists/xenial-backports/main/source/Sources.xz Hash Sum mismatch
E: Failed to fetch http://download.nus.edu.sg/mirror/ubuntu/dists/xenial-backports/main/binary-amd64/Packages.xz 404 Not Found
E: Failed to fetch http://download.nus.edu.sg/mirror/ubuntu/dists/xenial-backports/main/binary-i386/Packages.xz 404 Not Found
E: Failed to fetch http://download.nus.edu.sg/mirror/ubuntu/dists/xenial-backports/universe/binary-amd64/Packages.xz 404 Not Found
E: Failed to fetch http://download.nus.edu.sg/mirror/ubuntu/dists/xenial-backports/universe/binary-i386/Packages.xz 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
rajivmars@rajivmars-desktop:~$