场景
# sudo apt-get install gdb
Reading package lists... Done
Building dependency tree      
Reading state information... Done
Package gdb is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'gdb' has no installation candidate

网上的方案是更新源apt-get update，但是目前没有更好的源地址

解决
1）安装termcap
wget https://ftp.gnu.org/gnu/termcap/termcap-1.3.1.tar.gz
./configure
make
make install
2） 安装gdb
wget http://ftp.gnu.org/gnu/gdb/gdb-7.8.tar.xz
tar -xf gdb-7.8.tar.xz    
cd gdb-7.8/    
./configure
make

sudo cp gdb/gdb /usr/local/bin/gdb

注意
gdb使用源码安装的时候遇到错误：no termcap library found，安装termcap