Managing Users and Groups

Question 1

Content of /etc/passwd

Answer 1

user_name:password:uid:gid:comment:full_path_to_home_dir:/shell
root:x:0:0:root:/root:/bin/bash

Question 2

Content of /etc/shadow

Answer 2

user_name:encr_passd:days password_changed_since_01.01.1970:min_days_between_passwd_changes:max_days_passwd_valid:warning_days_expiration_of_passwd:days_to_lock_account_when_passwd_is_expired:date_days_since_01.01.01_account_will_expire
root:$1$***$...:17618:0:99999:7::
dbus:!!:17618::::::
$1$=MD5
$2$,$2y$=Blowfish
$5$=sha-256
$6$=sha-512
$***-salt
$...-hashed passed
!-account is locked
*-account is locked and passed was never set

Question 3

Add user

Answer 3

useradd -m [home dir] -c[comment] “Adam Vance” -u [uid] 1002 -g[gid] 25 -G wheel -s [shell] /bin/tcsh

Question 4

Set password to a user

Set a password for yourself

Answer 4

passwd avance

passwd without any params

Question 5

Force expiration of password and make a user to set up a new password after the login

Answer 5

passwd -e avance

chage -d 0 avance

Question 6

Remove user’s account keeping home folder

The same and remove user’s home folder

Answer 6

userdel avance

userdel -r avance

Question 7

Create system account

Answer 7

useradd -r my_service -s /sbin/nologin

Question 8

Check groups current user belongs to

Check groups a user belongs to

Answer 8

groups

groups avance

Question 9

Create new group

Delete a group

Answer 9

groupadd [-g[gid] 501] my_group

groupdel my_group

Question 10

Conf file with default settings set by useradd command

Answer 10

/etc/default/useradd
common settings:
GROUP=100
HOME=/home
SHELL=/bin/bash
SKEL=
EXPIRE=date the account will expire
INACTIVE=-1 (account will not be disabled when password is expired) if =0- disable account when passwd expired

Question 11

Query db content of specified group id

Answer 11

getent group 100

Question 12

Conf file that changes the behaviour of /etc/default/useradd file
and should be used by admins to set up vars

Answer 12

/etc/login.defs
GID_MIN=1000
this will override min value of GROUP var
UID_MIN=1000-this will setup starting uid

Question 13

Modify a user account

Answer 13

usermod
usermod -a -G finance avance -append avance to suppl group finance
usermod -d /opt/projectx my_project -change home dir from /home/my_project
usermod -e 1 - accoutn will expire in 1 day
usermod -l -change user_login name from to new
usermod -p -passwd
usermod -u -uid
usermod -L- lock user’s password
usermod -U - unlock account

Question 14

Modify a group

Answer 14

groupmod
groupmod -g 1002 engineering
groupmod -n Engineers engineering

Question 15

File to create for displaying a message, when a user has /sbin/nologin as shell

Answer 15

/etc/nologin

Question 16

Change aging params of a user’s account

Set expiration date of account

Answer 16

chage
k=date -d+'15 days' +%Y-%d-%d
chage -E $k avance
chage -E 2020-01-01 avance -set expiration date of account

Question 17

Set no expiration to account

Answer 17

chage -E -1 avance

chage -l user -list account aging info

Question 18

Change warning period before password expires

Answer 18

chage -W 15 avance

Question 19

Change password expiration date 15 days from now

Answer 19

chage -M 15 avance

Question 20

Lock the account that will be inactive after 5 days when the password is expired

Answer 20

chage -I 5 avance

Question 21

Log in into new group

Answer 21

newgrp
newgrp finance - (use the dash to initiate entering a user to finance suppl group)
so when creating new files and dirs, group ownship would be finance and not user’s primary group