apt-get 更新が失敗し、ゼロエラーコードを返します。

apt-get updateの実行時に失敗した場合は、ゼロ以外のエラーコードを返す必要がありますが、私の場合はまだゼロでした。以下を参照してください。

root@ubuntu-base:/home/user# apt-get update
Err http://security.ubuntu.com trusty-security InRelease

Err http://packages.siawai.com:8085 trusty InRelease

Err http://ppa.launchpad.net trusty InRelease

Err http://ppa.launchpad.net trusty Release.gpg
  Could not resolve 'ppa.launchpad.net'
Err http://security.ubuntu.com trusty-security Release.gpg
  Could not resolve 'security.ubuntu.com'
Err http://packages.siawai.com:8085 trusty Release.gpg
  Could not resolve 'packages.siawai.com'
Err http://in.archive.ubuntu.com trusty InRelease

Err http://in.archive.ubuntu.com trusty-updates InRelease

Err http://in.archive.ubuntu.com trusty-backports InRelease

Err http://in.archive.ubuntu.com trusty Release.gpg
  Could not resolve 'in.archive.ubuntu.com'
Err http://in.archive.ubuntu.com trusty-updates Release.gpg
  Could not resolve 'in.archive.ubuntu.com'
Err http://in.archive.ubuntu.com trusty-backports Release.gpg
  Could not resolve 'in.archive.ubuntu.com'
Reading package lists... Done
W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/trusty/InRelease  

W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/trusty-updates/InRelease  

W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/trusty-backports/InRelease  

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/InRelease  

W: Failed to fetch http://ppa.launchpad.net/ondrej/php/ubuntu/dists/trusty/InRelease  

W: Failed to fetch http://packages.siawai.com:8085/repos/dists/trusty/InRelease  

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/Release.gpg  Could not resolve 'security.ubuntu.com'

W: Failed to fetch http://packages.siawai.com:8085/repos/dists/trusty/Release.gpg  Could not resolve 'packages.siawai.com'

W: Failed to fetch http://ppa.launchpad.net/ondrej/php/ubuntu/dists/trusty/Release.gpg  Could not resolve 'ppa.launchpad.net'

W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/trusty/Release.gpg  Could not resolve 'in.archive.ubuntu.com'

W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/trusty-updates/Release.gpg  Could not resolve 'in.archive.ubuntu.com'

W: Failed to fetch http://in.archive.ubuntu.com/ubuntu/dists/trusty-backports/Release.gpg  Could not resolve 'in.archive.ubuntu.com'

W: Some index files failed to download. They have been ignored, or old ones used instead.
root@ubuntu-base:/home/user# echo $?
0

何が問題なのでしょうか？私はUbuntu 14.04を実行しています。