有很多关于"add-apt-repository"的帖子，但我觉得我已经看过并尝试了大部分的解决方案。
我正在尝试在Ubuntu Server 12.04上安装Java。一些搜索结果指向了下面最常见的解决方案：
sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java7-installer
然而，当我运行
sudo add-apt-repository ppa:webupd8team/java
我遇到了以下错误：
sudo: add-apt-repository: command not found
所以，经过更多的搜索和故障排除，我得出了以下结论：
sudo apt-get install software-properties-common
这给了我（现在至少 - 第一次，它实际上安装了软件包）：
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
其他建议指出可能需要以下内容：
sudo apt-get install python-software-properties
出现以下错误：
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
python-software-properties : Depends: python-pycurl but it is not installable
E: Unable to correct problems, you have held broken packages.
所以我尝试了：
sudo apt-get install python-pycur
而且还有这个：
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'python-pycurl' has no installation candidate
有点困住了。有什么想法下一步去哪里吗？
根据Thomas W.的建议，这是/etc/apt/sources.list的内容：
# deb cdrom:[Ubuntu-Server 12.04.5 LTS _Precise Pangolin_ - Release i386 (20140806.1)]/ precise main restricted
#deb cdrom:[Ubuntu-Server 12.04.5 LTS _Precise Pangolin_ - Release i386 (20140806.1)]/ precise main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.archive.ubuntu.com/ubuntu/ precise main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ precise main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ precise-updates main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-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 http://us.archive.ubuntu.com/ubuntu/ precise universe
deb-src http://us.archive.ubuntu.com/ubuntu/ precise universe
deb http://us.archive.ubuntu.com/ubuntu/ precise-updates universe
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-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 http://us.archive.ubuntu.com/ubuntu/ precise multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise multiverse
deb http://us.archive.ubuntu.com/ubuntu/ precise-updates multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-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 http://us.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu precise-security main restricted
deb-src http://security.ubuntu.com/ubuntu precise-security main restricted
此外，sudo apt-get update 的结果可能也会有所帮助。
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/main/source/Sources Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/restricted/source/Sources Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/universe/source/Sources Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/multiverse/source/Sources Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/main/binary-i386/Packages Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/restricted/binary-i386/Packages Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/universe/binary-i386/Packages Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/multiverse/binary-i386/Packages Hash Sum mismatch
E: Some index files failed to download. They have been ignored, or old ones used instead.
/etc/apt/sources.list文件的内容吗？ - Thomas Wardnslookup us.archive.ubuntu.com来验证你的系统正在尝试使用哪些服务器。 - Thomas Ward