Command to purge and reinstall package

Solution 1:

It's not advisable, but you can undercut apt and go directly to dpkg.

For example, taking postfix and postfix-dev:

$ sudo apt-get purge postfix
Reading package lists... Done
Building dependency tree
Reading state information... Done.
The following packages will be REMOVED:
  postfix* postfix-dev*
0 upgraded, 0 newly installed, 2 to remove and 99 not upgraded.
After this operation, 4449 kB disk space will be freed.
Do you want to continue? [Y/n] n
Abort.

Now we use dpkg to purge postfix without removing dependents:

$ sudo dpkg --purge --force-depends postfix
dpkg: postfix: dependency problems, but removing anyway as you requested:
 postfix-dev depends on postfix (>= 3.1.0-0).
 postfix-dev depends on postfix (<< 3.1.0.0-0).
 postfix-dev depends on postfix (>= 3.1.0-0).
 postfix-dev depends on postfix (<< 3.1.0.0-0).

(Reading database ... 293223 files and directories currently installed.)
Removing postfix (3.1.0-3) ...
Purging configuration files for postfix (3.1.0-3) ...
Processing triggers for libc-bin (2.23-0ubuntu5) ...
Processing triggers for man-db (2.7.5-1) ...

And now re-install postfix:

$ sudo apt-get install postfix
Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
  procmail postfix-mysql postfix-pgsql postfix-ldap postfix-pcre sasl2-bin dovecot-common postfix-cdb postfix-doc
The following NEW packages will be installed:
  postfix
0 upgraded, 1 newly installed, 0 to remove and 99 not upgraded.
Need to get 0 B/1152 kB of archives.
After this operation, 3697 kB of additional disk space will be used.
Preconfiguring packages ...
Selecting previously unselected package postfix.
(Reading database ... 293035 files and directories currently installed.)
Preparing to unpack .../postfix_3.1.0-3_amd64.deb ...
Unpacking postfix (3.1.0-3) ...
...