Remember password after `sudo -i`

Question

If I do sudo <command> and enter the password, my Debian Squeeze remembers the fact I passed the password and never asks for it for i.e. 15 minutes.

But if I do sudo -i and then exit, the system does not remembers the password and asks for it all over again every time I use sudo -i. Doing just once sudo <command> makes the system not ask for password even for a next sudo -i.

Here are the scenarios I've described above:

First one:

1. login (by SSH),
2. sudo <command>: system's asking for the password,
3. sudo -i: system is not asking for the password.

Second one:

1. login (by SSH),
2. sudo -i: system's asking for the password,
3. exit
4. sudo -i: system's again asking for the password.

Doing something beetween 2. and 3. makes the system remember the password.

What is the reason of such a behaviour? Is it possible to make the system remember the password (fact I passed it) also after using sudo -i?

Answer 1

From the sudoers(5) man page:

As a special case, if sudo's -i option (initial login) is specified, sudoers will initialize the environment regardless of the value of env_reset. The DISPLAY, PATH and TERM variables remain unchanged; HOME, MAIL, SHELL, USER, and LOGNAME are set based on the target user. On Linux and AIX systems the contents of /etc/environment are also included. All other environment variables are removed

The fact that USER is being set, would likely mean that regardless of your passwd success, that counter is getting reset.

There are other knowledge points in that documentation you should be aware of as well.