vim /etc/apt/sources.list

Debian for v6(Squeeze) to v7(Wheezy)

deb wheezy main
deb-src wheezy main

deb wheezy/updates main
deb-src wheezy/updates main

# wheezy-updates, previously known as 'volatile'
deb wheezy-updates main
deb-src wheezy-updates main

Debian for v7(Wheezy) to v8(Jessie)

deb jessie main
deb-src jessie main

deb jessie/updates main contrib
deb-src jessie/updates main contrib

# wheezy-updates, previously known as 'volatile'
deb jessie-updates main contrib
deb-src jessie-updates main contrib

upgrade debian

apt-get update
apt-get upgrade -y
apt-get dist-upgrade -y

#if error “There is no public key available for the following key IDs”
#fix by



#after reboot
cat /etc/debian_release
lsb_release -a
uname -a

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