Lecture

1
Lecture Users and groups

• Unix account management

2
User management

• Adding/Removing Users
• UNIX Traditionally, user account details are
  stored in the /etc/passwd file (/etc/group,
  /etc/shadow)
• This file has the format
• usernamepassworduidgidcommenthome dirshell
• one way to get a list of usernames on a system
• cut d -f1 /etc/passwd
• Do not edit this file directly, use
• useradd / userdel / groupadd / groupdel commands

3
useradd (linux)

• Create a new user or update default new user
  information
• useradd -c comment -d home_dir
• -e expire_date -f
  inactive_time
• -g initial_group -G
  group,...
• -m -k skeleton_dir -M -n
  -o -p passwd -r
• -s shell -u uid login
• useradd -D -g default_group -b default_home
• -e default_expire_date -f
  default_inactive
• -s default_shell
• The D option causes system defaults specified in
  /etc/login.defs to be used for this account
  creation

4
userdel

• Delete a user account and related files
• userdel -r login
• The userdel command modifies the system
  account files, deleting all entries that refer to
  login. The named user must exist. The options
  which apply to the userdel command are
• -r Files in the users home directory will
  be removed along with the home directory itself
  and the users mail spool. Files located
  in other file systems will have to be searched
  for and deleted manually.

5
groupadd (linux)

• Create a new group
• groupadd -g gid -o -r -f group
• Creates a new group account using the values
  specified on the command line and the default
  values from the system.
• The new group will be entered into the system
  files as needed.
• Options
• -g gid The numerical value of the groups ID.
  This value must be unique, unless the -o option
  is used. The value must be non-negative. The
  default is to use the smallest ID value greater
  than 500 and greater than every other group.
  Values between 0 and 499 are typically reserved
  for system accounts.

6
groupadd (linux)

• -r instructs groupadd to add a system
  account. The first available gid lower than 499
  will be automatically selected unless the -g
  option is also given on the command line.
• -f the force flag. This will cause groupadd
  to exit with an error when the group about to
  be added already exists on the system. If that is
  the case, the group wont be altered (or
  added again).
• Also modifies the way -g option works. When you
  request a gid that it is not unique and you dont
  specify the o option too, the group creation
  will fall back to the standard behavior (adding a
  group as if neither -g or o options were
  specified).

7
groupdel (linux)

• Delete a group
• groupdel group
• The groupdel command modifies the system
  account files, deleting all entries that refer to
  group. The named group must exist.
• You must manually check all filesystems to insure
  that no files remain with the named group as the
  file group ID.

8
groupdel (linux)

• Delete a group
• groupdel group
• The groupdel command modifies the system
  account files, deleting all entries that refer to
  group. The named group must exist.
• You must manually check all filesystems to insure
  that no files remain with the named group as the
  file group ID.

9
Managing Users

• Whether in the UNIX or Windows (or other)
  environment, it is best practice to manage users,
  where possible, on a per-group basis
• Wherever possible, settings and configurations
  should be managed on a per-group basis
• For this reason, the management of group settings
  is as important in any multi-user environment as
  is the management of individual settings

10
Managing Groups

• One approach to the management of groups is a
  hierarchical approach, whereby the user community
  is divided into a number of groups based on roles
  within the organisation
• In this way, an individual may belong to several
  groups, each of which may have a different
  combination of security settings etc.
• If we can be assured users have only setting
  which are assigned on a per-group basis, it
  becomes easier for us to ensure that all users
  with similar or identical roles are subject to
  the same rules

11
Managing Users and Groups in the Windows
Environment

• Microsoft provides a network server platform
  based on the SMB (Server Message Block) protocol
• The management tools and the features of these
  server platforms have changed somewhat over the
  years, but remain broadly the same
• This module includes emulation of SMB on UNIX
  using SaMBa