Embedded Files
There are 3 type of user
Super user /admin ---> root
Normal user
System user
To Create new user (Normal)
#adduser username
#useradd username
to change passwd for normal user
#passwd username
to change root password.
#passwd
/etc/passwd (File for user password and user name information)
file with 7 field .
1 : 2 : 3 : 4 :5: 6 : 7
xyz : X : 501 : 501 : : /home/xyz :/bin/bash
username:password:userid:groupid:finger information:home dir :shell
whenever we create user /etc/defaults/useradd file has read by system
/etc/defaults/useradd
to give a special permission
/etc/defalts/useradd
group = 100
* disallow the user
home = /home
inactive = -1
Expire = !! disallow the user
Shell = /bin/bash
Skel = /etc/skel
To clear Password.
#vi /etc/passwd
2nd field of this file is :x: password information :x: does means user having password.
If we remove :x: (x) password will be null (blank)
---------------------------------------------------------------------
Password reset for Root User.
If we have current password then simple process
#passwd
Enter new password :
Conform new Password :
If we haven’t password for Root:
Stat system ----> Press E (edit Grub file’s line by edit it may ask grub password )put password and edit line
Put single --------> in spite of : RO
Press b (For boot)
System start with Single user:
It will prompt #
Put command #passwd (And change password).
If we haven’t password for Grub:
Start your system----------> with 1st disk of installed os. (it could be Centos,redhat ,any Linux flavors which is installed)
After booting from CD linux installation prompt will come
:linux rescue ( type this to rescue password)
mount file system:
hit command # passwd
Password Group and user related Configuration files.
/etc/passwd
/etc/gshadow
/etc/login.defs
/etc/group
/etc/skel
/etc/defaults/useradd
/etc/shadow
/etc/shells
#useradd username
#useradd –u 555 username (to give special UID)
# useradd –s /bin/sh username (to assign special Shell)
# useradd –e 2007-7-29 username (Assigning Expiry date)
# useradd –f 10 username (de active after certain day)
# useradd –G group1,group2,group3 username (add in multi group)
#mkdir ghar
#useradd –d /ghar/newusername newusername
(to assign particular home directory for user)
# useradd –d badman username
(not tested above command please verify command by testing)
# useradd –l newuser exiting username
(to change login name)
# useradd –c “user is for testing” username
(to add comment on user)
to Edit exiting User use all above commands with
#usermod (page no 11,12 commands)
#usermod –L username (to lock user)
#usermod –U username (to unlock user)
#chsh username (to change shell)
#chfn username (to change finger information)
#finger username (display finger information of user)
#useradd –u 707 –c “all field” –e 2007.10-29 –s /bin/sh –G g1,g2,g3
(add user name with particular uid (707),comment ,time ,shell and multi group)
# Add root user
#useradd –u 0 –o –g 0 username
(To add root user 0 (zero) is uid for root)
#who am I (to know which user login)
SUDO User
# /etc/sudoers
To make other user to limited administrator or full administrator.
#visudo
To give command in sudo user
#sudo command path
#visudo
(we can add sudo user in this file , also can add wheel (root) group and edit user.
#allow
b1 ALL=(ALL) ALL
# % wheel ALL
Adding Alias for SUDO
#user_alias U=nl
Cmmd_Alias C= /usr/sbin/useradd , more commands if required
#common Alias
cmnd_Aliasc=/usr/sbin/useradd
U ALL = C
Also can Add more alias like “Network”
U ALL = NETWORKING
#useradd –G groupname
User_Alias U = n1
Cmnd_alias C= /usr/sbin/useradd
U ALL = C
Group
To Create group and assign different login IDs
#vi /etc/login.defs
#id –u username (to know about particular user ID)
#groupadd newgroupname
/etc/group
#useradd –G groupname newusername
#groupdel groupname
#usermod –G groupname existing username
/etc/shadows
to know password information
(Linux use MD5 protection for encryption )
/etc/shadows has 8 field .
fields
username : username (root)
encryption :$d7748jj%&^fb (add ! before $ to inactive user)
days remaining : Remaining days before expire
change password :(after how many day user has to change passwd)
password must change :(after how many day passwd must change)
warning : password expiry warning
inactive :user will inactive after days
days counting : since user created
/etc/skel
Whatever file stored in this folder are automatically added for new user creation.
#vi /etc/group
Groupname:password:groupid
/etc/gshadows
to know about group password
groupname: password: users
#gpasswd (to change group password)
#groupadd group name
#groupadd –u gid
(group add with special gid. means particular gid no {I.E 1000} )
#groupdel groupname
#grupmod (with all about switch for exiting group)
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