sudo apt-get install sendmail
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
  liblockfile-bin liblockfile1 make procmail sendmail-base sendmail-bin
  sendmail-cf sensible-mda
Suggested packages:
  make-doc sendmail-doc rmail logcheck resolvconf sasl2-bin
Recommended packages:
  default-mta mail-transport-agent fetchmail
The following NEW packages will be installed:
      liblockfile-bin liblockfile1 make procmail sendmail sendmail-base
      sendmail-bin sendmail-cf sensible-mda
0 upgraded,9 newly installed,0 to remove and 0 not upgraded.
Need to get 2256 kB of archives.
After this operation,5263 kB of additional disk space will be used.
Do you want to continue? [Y/n] y

所以我们安装了sendmail – 9个新软件包和5.2MB.
几分钟后,我改变主意,想要卸载它.没问题,apt-get让我受到了保护,对吧？我清除(删除包和包配置文件)：

sudo apt-get purge sendmail
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  procmail sensible-mda
Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
  sendmail*
0 upgraded,0 newly installed,1 to remove and 0 not upgraded.
After this operation,219 kB disk space will be freed.
Do you want to continue? [Y/n] y

然后autoremove(删除自动安装的包依赖项)

sudo apt-get autoremove sendmail
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package 'sendmail' is not installed,so not removed
The following packages will be REMOVED:
  procmail sensible-mda
0 upgraded,2 to remove and 0 not upgraded.
After this operation,550 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 24702 files and directories currently installed.)
Removing sensible-mda (8.14.4-8+deb8u1) ...
Removing procmail (3.22-24) ...
Processing triggers for man-db (2.7.0.2-5) ...

这是219 550 = 769KB恢复！我刚刚松开了4.something MB的空间吗？为了什么？

仔细观察输出后,apt-get似乎只删除了之前自动安装的3个包.例如,sendmail-base包仍然是：

sudo apt-get remove sendmail-base
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
  sendmail-base sendmail-bin
0 upgraded,2464 kB disk space will be freed.
Do you want to continue? [Y/n]

所以我浪费了一些空间.
但为什么仍然安装这些自动安装的依赖项？