excerpt from 'man sudo'
SUDO(8)                    MAINTENANCE COMMANDS                    SUDO(8)

NAME
       sudo, sudoedit - execute a command as another user

SYNOPSIS
       sudo -K | -L | -V | -h | -k | -l | -v

       sudo [-HPSb] [-a auth_type] [-c class|-] [-p prompt] [-u user-
       name|#uid] {-e file [...] | -i | -s | command}

       sudoedit [-S] [-a auth_type] [-p prompt] [-u username|#uid] file
       [...]

DESCRIPTION
       sudo allows a permitted user to execute a command as the superuser
       or another user, as specified in the sudoers file.  The real and
       effective uid and gid are set to match those of the target user as
       specified in the passwd file and the group vector is initialized
       based on the group file (unless the -P option was specified).  If
       the invoking user is root or if the target user is the same as the
       invoking user, no password is required.  Otherwise, sudo requires
       that users authenticate themselves with a password by default
 (NOTE: in the default configuration this is the user's password,
       not the root password).  Once a user has been authenticated, a
       timestamp is updated and the user may then use sudo without a pass-
       word for a short period of time (5 minutes unless overridden in
       sudoers).

       When invoked as sudoedit, the -e option (described below), is
       implied.

       sudo determines who is an authorized user by consulting the file
       /etc/sudoers.  By giving sudo the -v flag a user can update the
       time stamp without running a command. The password prompt itself
       will also time out if the user's password is not entered within 5
       minutes (unless overridden via sudoers).

       If a user who is not listed in the sudoers file tries to run a com-
       mand via sudo, mail is sent to the proper authorities, as defined
       at configure time or in the sudoers file (defaults to root).  Note
       that the mail will not be sent if an unauthorized user tries to run
       sudo with the -l or -v flags.  This allows users to determine for
       themselves whether or not they are allowed to use sudo.

       If sudo is run by root and the SUDO_USER environment variable is
       set, sudo will use this value to determine who the actual user is.
       This can be used by a user to log commands through sudo even when a
       root shell has been invoked.  It also allows the -e flag to remain
       useful even when being run via a sudo-run script or program.  Note
       however, that the sudoers lookup is still done for root, not the
       user specified by SUDO_USER.

       sudo can log both successful and unsuccessful attempts (as well as
       errors) to syslog(3), a log file, or both.  By default sudo will
       log via syslog(3) but this is changeable at configure time or via
       the sudoers file.

excerpt 'man sudoers';

SUDOERS(5)                 MAINTENANCE COMMANDS                 SUDOERS(5)

NAME
       sudoers - list of which users may execute what

DESCRIPTION
       The sudoers file is composed of two types of entries: aliases
       (basically variables) and user specifications (which specify who
       may run what).

       When multiple entries match for a user, they are applied in order.
       Where there are conflicting values, the last match is used (which
       is not necessarily the most specific match).

 excerpt from 'man sudo'
-i  The -i (simulate initial login) option runs the shell specified
           in the passwd(5) entry of the user that the command is being
           run as.  The command name argument given to the shell begins
           with a - to tell the shell to run as a login shell.  sudo
           attempts to change to that user's home directory before running
           the shell.  It also initializes the environment, leaving TERM
           unchanged, setting HOME, SHELL, USER, LOGNAME, and PATH, and
           unsetting all other environment variables.  Note that because
           the shell to use is determined before the sudoers file is
           parsed, a runas_default setting in sudoers will specify the
           user to run the shell as but will not affect which shell is
           actually run.