在Retrofit 1 时，会在onError中返回并抛出HttpException，但是在2中，不会再回调onError了，而是会在onNext中，这个任务就需要客户端自己处理。
https://futurestud.io/tutorials/retrofit-2-simple-error-handling
参考如下：
Error Handler in Action
etrofit 2 has a different concept of handling "succe[......]
apt-get update时出现错误，如下：
W: GPG error: http://ftp.us.debian.org lenny-proposed-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AED4B06F473041FA
这个是由于PGP证书的问题，如下解决：
gpg --keyserve[......]
Problem
With the latest version of qemu-kvm, I can't successfully compile with error below:
#make && make install
kvm-all.o: In function `kvm_run':
/home/liheyuan/code/qemu-kvm-0.13.0/qemu-kvm.c:675: undefined reference to `kvm_handle_int[......]
现象
最新版本的qemu-kvm-0.13.0居然编译出错。。现象如下：
[shell]
#出错信息
kvm-all.o: In function `kvm_run':
/home/liheyuan/code/qemu-kvm-0.13.0/qemu-kvm.c:675: undefined reference to `kvm_handle_internal_error'
collect2: ld returned 1 exit status
[/shell]
原因
经[......]