User Accounts and Groups

Question 1

/etc/passwd

Answer 1

• Most account features are defined
• Contains a list of comma-delineated lines
• Each line has a record defining a single user account
• Must be readable by all users

Question 2

Information in an /etc/passwd entry

Answer 2

• Username/Password
  *UID (user identification, machine readable Username)
• GID (Group ID)
• Comment field
• Home directory
• Default shell (/bin/bash)

Question 3

/etc/shadow file

Answer 3

• Contains actual password
• Uses salted hash (on way mathematical process)
• Only readable by root

Question 4

Information in /etc/shadow file entry

Answer 4

• Username (no UID)
• Password as slated hash
• • or ! denotes an account is locked
• Last password change (stored as a number of days since 1/1/1970)
• Days until a change is allowed
• Days until a change is required
• Days of warning before password expiration
• Days between expiration and deactivation
• Expiration date (stored as a number of days since 1/1/1970)
• Special flag (reserved for future use)

Question 5

/etc/group

Answer 5

Defines collection of account called groups

Question 6

Information in an /etc/group entry

Answer 6

• Group name
• Password (maybe)
• GID (Group ID)
• User list (member accounts)

Question 7

Ways to define a users group membership

Answer 7

• Specifying the GID in users /etc/passwd entry (only one group can be assigned this way. Default group)
• Specifying usernames in the user list of the /etc/group file

Question 8

newgrp groupname command

Answer 8

Changes active group

Question 9

whoami command

Answer 9

Display currently logged in user

Question 10

id command

Answer 10

• Current user
• UID
• Active GID
• Group memberships

Question 11

who command

Answer 11

• shows who is logged on
• Username
• Terminal identifier (0 means local login)
• PTS or TTY
• Login date and time (when person logged in)
• Remote host (login source)

Question 12

w command

Answer 12

• shows who is logged on and what they are doing in the system
• More verbose version of who
• Idle time
• JCPU (total amount of CPU time associated with that session)
• PCPU (amount of CPU time of the processes running inside that session)
• WHAT (what session is running and doing)

Question 13

useradd -m command

Answer 13

• Create a user without a home directory

Question 14

passwd command

Answer 14

Used to change the password of a user’s account. This command runs as the root user using SUID

Question 15

useradd -d command

Answer 15

• (useradd -d /path/to/directory username)
• specify the user’s home directory location instead of using the default directory

Question 16

/etc/skel

Answer 16

Automatically copied over to a new user’s home directory when the account is first created

Question 17

UID 0

Answer 17

Represents root user

Question 18

last command

Answer 18

Displays the entries of successful login attempts made by users in the past