昨天我在 vagrant box（几周来一直没变）中运行了这段代码，没有出现问题。今天就失败了：
add-apt-repository ppa:adiscon/v8-stable && apt-get update
Contains the latest RSyslog V8-Stable packages and dependencies.
More info: https://launchpad.net/~adiscon/+archive/ubuntu/v8-stable
Press [ENTER] to continue or ctrl-c to cancel adding it
gpg: keyring `/tmp/tmpxudrwwvh/secring.gpg' created
gpg: keyring `/tmp/tmpxudrwwvh/pubring.gpg' created
gpg: requesting key 5234BF2B from hkp server keyserver.ubuntu.com
gpg: /tmp/tmpxudrwwvh/trustdb.gpg: trustdb created
gpg: key 5234BF2B: public key "Launchpad PPA for Adiscon" imported
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)
OK
root@hcf-vagrant:/home/vagrant# apt-get install rsyslog rsyslog-relp rsyslog-mmjsonparse rsyslog-gnutls -y
Reading package lists... Done
Building dependency tree
Reading state information... Done
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:
rsyslog-gnutls : Depends: rsyslog (= 8.18.0-0adisconatrusty1) but 7.4.4-1ubuntu2.6 is to be installed
rsyslog-mmjsonparse : Depends: rsyslog (= 8.18.0-0adisconatrusty1) but 7.4.4-1ubuntu2.6 is to be installed
rsyslog-relp : Depends: rsyslog (= 8.18.0-0adisconatrusty1) but 7.4.4-1ubuntu2.6 is to be installed
E: Unable to correct problems, you have held broken packages.
root@hcf-vagrant:/home/vagrant#
看着https://launchpad.net/~adiscon/+archive/ubuntu/v8-stablelibfastjson我可以看到该仓库是在 2016-05-06 11:00:00 UTC 左右更新的。一位同事认为问题在于仓库中没有 的库ubuntu/trusty，只有 的库xenial。
我不是今天唯一遇到这种情况的人：
https://twitter.com/jaymzcampbell/status/728612402984521732
有人有解决方法吗？用 替换 是否可行ppa:adiscon/v8-stable（ppa:adiscon/v7-stable这实际上是一个繁琐的修复，因为我们的构建系统设置方式，但我会尝试一下）？