User and Group Management
1. USER:- All linux user have a
used ID and a unique numeric identification number called User Id (UID).
Every
user of the system is assigned a unique User ID number. User’s name and UID are
stored in /etc/passwd. User are assigned
a home directory and a program that is run when they log in (usually called
shell). Users can not read, write or execute
each other files and directory without permission.
Types of User User ID
1.
Superuser 0
2.
System User 1-499
3.
Normal User 500-60000
2. GROUP:- All Linux users have
a group ID and a unique numeric identification number called Group Id (GID).
Users are assigned to group with unique Group ID number. GID are stored in
/etc/group file. Each user is given their own private group, they can also be
added to other groups to gain the additional access of a particular file or directory. All users
in a group can share files that belong to the same group.
When
a user is get created in linux its entry is recorded in the following files.
1.
/home
2.
/etc/passwd
3.
/etc/shadow
4.
/etc/group
5.
/etc/default/useradd
6.
/etc/login.defs
1. /home :- this is a user
default home directory except root user and the command to view the users from
home directory is :-
[root@server1~]#
cd /home
[root@server1 home]# ll or ls
2. /etc/passwd :- user account information is store in this file
and it contains 7 filed. And the command
to view the user account information is :-
[root@server1~]#
cd /etc
[root@server1 etc]# cat
passwd
1.linus = username
2. x = password ( its indicate that
password is set for a user)
3. 501 = uid
4. 501 = gid
5. : : = user information
(GECOS = General Electronics
COmprehensive System)
6. /home/linus = user’s home
directory
7. /bin/bash =
user’s default log in shell or shell
type
To
add user information in GECOS filed the command is :-
[root@server1~]#
chfn username
Name
[] : Linus Torvald
Office
[] : Vashi Plaza, Navi Mumbai , Setcor-17.
Office
Phone [] : 022-323646569/70
Home
Phone [] : 022-12345678
Figure
information changed.
[root@server1~]#cat passwd
Linus:x:501:501:Linus
Torvald, Vashi Plaza,Navi
Mumbai,Sector-17,022-323646569/70,022-12345678:/home/linus:/bin/bash
3. /etc/shadow :- Secure user account
information is stored in this file and it contains 9 filed. And the command to
view the secure user account information is :-
[root@server1~]#
cd /etc
[root@server1 etc]# cat
shadow
1. linus = username
2. $78$xgfyryioruo$/df0 = user password in
encrypted form (MD5 – Message Daigest)
3. 14763 = Date of last password
change
4. 0 = minimum password age
5. 99999 = maximum password
age
6. 7= worning before password is
expired
7. : : =password inactivity
period
8. : : = account expiration
date
9. : : = reserved filed
4. /etc/group :- User group account
information is stored in this file and it contains 4 filed. Andthe command to
view the user group account information is :-
[root@server1~]#
cd /etc
[root@server1 etc]# cat
group
1. linus = username or group
name log in with
2. x = password ( its
indicate that password is set for a user and if it is black no password has
been set)
3. 501 = group GID
4.:: = members of the group,
if it is blank no member has been added to the group
5. /etc/default/useradd :- Default value or a
default log in shell script is store in this file for a new user. You can
change the value from it and while changing the value from this file existing
users value will not be change. And the command to view the this script is :-
[root@server1~]#
cd /etc
[root@server1 etc]# cd /default
[root@server1
default]# cat useradd
#
useradd defaults file
GROUP=100
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
CREATE_MAIL_SPOOL=yes
1.
GROUP=100 = this indicate the user type
2.
HOME=/home = defines the directory where
user's home directory is created by default.
3.
INACTIVE=-1 = active user account and allow to user login,
if it is 1 user will not able to log in
4.
EXPIRE= user account expires days can be
set
5.
SHELL=/bin/bash = default user bash
shell
6.
SKEL=/etc/skel = defines the path of the director which contains the files and
directories which are copied to the users home directory when the user login is
created. Here you can place additional files and directories, which you want to
be copied to users home directory, when user is created.
7.
CREATE_MAIL_SPOOL=yes = define the
directory where user’s mails will get stored by default.
6. /etc/login.defs :- This file defines user
password details, uid, gid, and mail
directory location. And the command to view the this script is :-
[root@server1~]#
cd /etc
[root@server1 etc]# cat login.defs
User and Group
Management Tutorial.
1. To create a user.
[root@server1~]#
useradd username
[root@server1~]#cd
/etc
[root@server1
etc]#cat passwd
2. To set password for new and
existing user.
[root@server1~]#
passwd username
Changing
password for user username.
New
password: * * * * *
BAD
PASSWORD: it is based on a directory word
BAD
PASSWORD: is too simple
Retype
new password:
passwd:
all authentication token updated successfully.
3. To create a group.
[root@server1~]#
groupadd groupname
[root@server1~]#cd
/etc
[root@server1
etc]#cat group
4. To add existing user to a group.
[root@server1~]#
usermod -G groupname username
[root@server1~]#cd
/etc
[root@server1
etc]#cat group
5. To add new user to a Secodary group.
[root@server1~]#
useradd -G groupname username
[root@server1~]#cd
/etc
[root@server1
etc]#cat group
6. To add newly created user to a Primary group.
[root@server1~]#
useradd -g groupname username
[root@server1~]#cd
/etc
[root@server1
etc]#cat group
7. To remove user from a group.
[root@server1~]#
gpasswd -d username
groupname
Removing
user username from group groupname
8. To remove user password.
[root@server1~]#
passwd -d username
Now
login with that user in another console
Press
CTRL+ALT+F2
Server1
Login: username
username@server1~]$
username@server1~]$
9. To create user without
password.
[root@server1~]#
useradd username
[root@server1~]#
passwd -d username
Now
login with that user in another console
Press
CTRL+ALT+F2
Server1
Login: username
[username@server1~]$
10. To delete a user.
[root@server1~]#
userdel username
root@server1~]#cd
/etc
[root@server1
etc]#cat passwd
11. To delete a user along with
its files forcefully.
[root@server1~]#
userdel –rf username
root@server1~]#cd
/etc
[root@server1
etc]#cat passwd
[root@server1
etc]#cd /home
[root@server1
home]#ll
[root@server1
home]#cd /var/spool/mail
[root@server1
var]#ll
12. To delete a group.
[root@server1~]#
groupdel groupname
root@server1~]#cd
/etc
[root@server1
etc]#cat group
13. To lock user.
[root@server1~]#
usermod -L username
Now
login with hat user from another console
Server1
Login : username
Password:
******
Login
incorrect
14. To unlock user.
[root@server1~]#
usermod -U username
Now
login with hat user from another console
Server1
Login : username
Password:
******
[username@server1~]$
15. To change username.
[root@server1~]#
cd /etc
[root@server1
etc]# cat passwd
[root@server1
etc]#usermod -l oldusername
[root@server1
etc]# cat passwd
[root@server1
etc]# cat group
[root@server1
etc]#id username
uid= username gid=
groupname groups=
groupname
16. To change user UID.
[root@server1~]#
cd /etc
[root@server1
etc]# cat passwd
[root@server1
etc]#usermod -u
username
[root@server1
etc]# cat passwd
[root@server1
etc]# cat group
[root@server1
etc]#id username
uid= username gid=
groupname groups=
groupname
17. To change groupname.
[root@server1~]#
cd /etc
[root@server1
etc]# cat group
[root@server1
etc]#groupmod -n newgroupnmae
oldgroupname
[root@server1
etc]# cat group
18. To change group GID.
[root@server1~]#
cd /etc
[root@server1
etc]# cat group
[root@server1
etc]#groupmod -g
groupname
[root@server1
etc]# cat group
[root@server1
etc]# cat passwd
