今天打算對樹莓派安裝jdk發現jdk9後似乎已經沒有了32位版本的，樹莓派的官方鏡像是32位的，而樹莓派的cpu其實是64位的，是支持64位系統的，又發現樹莓派的ubuntu server竟然是18.04長期支持版本，而且是64位的，於是整起來……，然後安裝好後發現用官方的源更新太慢了，發現清華大學鏡像庫有這個倉庫，下面把官方源換成清華大學的源
找到/etc/apt/source.list，修改成如下即可
## Note, this file is written by cloud-init on first boot of an instance
## modifications made here will not survive a re-bundle.
## if you wish to make changes you can:
## a.) add 'apt_preserve_sources_list: true' to /etc/cloud/cloud.cfg
## or do the same in user-data
## b.) add sources in /etc/apt/sources.list.d
## c.) make changes to template file /etc/cloud/templates/sources.list.tmpl
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic main restricted
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-updates main restricted
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic universe
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic universe
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-updates universe
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-updates multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-updates multiverse
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-backports main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-security main restricted
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-security main restricted
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-security universe
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-security universe
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-security multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports bionic-security multiverse
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu bionic partner
# deb-src http://archive.canonical.com/ubuntu bionic partner
sudo apt-get update
sudo apt-get upgrade