Linux User Administration

User Administration

Only root (i.e. system administrator) can use adduser command to create new users. It is not allow to other users.

Adduser is symlink of Useradd which is binary in /usr/sbin. We (root) can customize adduser by using another word (rocky) & make it  symlink of useradd.  Let's see

Main File of useradd

[root@localhost Desktop]# ls -l /usr/sbin/adduser

lrwxrwxrwx. 1 root root 7 Jun 20  2015 /usr/sbin/adduser -> useradd

[root@localhost Desktop]# which useradd   -to check file location

/usr/sbin/useradd    ----------------------main file of useradd command

#useradd   ---main file (/usr/sbin/useradd)

#ln –s /usr/sbin/useradd   /user/sbin/u    ---create links or short cut file

Now “ u” is symlink of useradd.

#u rocky --- create user

[root@localhost Desktop]# ln -s /usr/sbin/useradd /usr/sbin/T

Now “T” is symlink of useradd.

[root@localhost Desktop]# T mouse

[root@localhost Desktop]# ls /home

rocky  lalit  mouse  olx  rajesh  paytm  test

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                             There are 3 types of users

            ________________________|________________________      

            |                                              |                                               |

 Super user                              System user                            Normal user

 <1> Superuser : At the time of linux installation it is create.  He has right to make other users & his`userid' & `groupid' is zero in `/etc/Passwd' file. 

<2> Systemuser: These users create by System. They can't login  becoz their shell `sbin/noloin' is default in  seventh field in `/etc/passwd' file.  

<3> Normaluser: These users create by superuser.(root user)

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Let's see how superuser make normaluser :

[root@localhost root]$ adduser john 

[root@localhost root]$ passwd john 

New password :( user password)

Retype new password:(user password)

Passwd: all authentication tokens updated successfully.

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[root@localhost root]$ userdel john ---> `userdel' command delete only name of the user from /home directory but it's data remain there. It's  /usr/sbin/userdel  

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[root@localhost root]$ userdel -r john  ---->userdel -r delete name of user as well as data.

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[root@localhost root]$ usermod -G groupname username 

i.e.  [root@localhost root]$ usermod -G sales vikas  

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usermod –G   ----  Secondary Group

usermod –g   ------Primary Group

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 ---->`usermod -G' command makes the user vikas member of the group sales. /usr/sbin/usermod.   

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su ----> with the help of this command root can work as  substitute user. 

su -r ---->with the help of this command root come out from  substitute user.

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[root@localhost root]$  adduser  john 

# useradd  mouse    --- after create user, created the below details

i)                    UID   -----------------------------------------User ID

ii)                  GID   -----------------------------------------Group ID

iii)                cd /home/mouse/ ---------------------------Create Home Directory

iv)                Owner Group  Permission 700 --------- Set Default permission to group

v)                  Owner Group (John) ----------------------create owner group same as user name.

vi)                /etc/skel ----------------------Copied all file from /etc/skel to user home directory.

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[root@localhost Desktop]# id---------------------- with the help of this command to check user id

uid=0(root) gid=0(root) groups=0(root)

[root@localhost ~]# id john  --------------------------- with the help of this command to check user id

uid=514(john) gid=514(john) groups=514(john)

[root@localhost ~]# id tushar --------------------------- with the help of this command to check user id

uid=515(tushar) gid=515(tushar) groups=515(tushar)

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 [root@tushar ~]# T -G sales lalit   -----user create and group added as a secondary

[root@tushar ~]# id lalit

uid=3003(lalit) gid=3005(lalit) groups=3005(lalit),3003(sales)

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[root@tushar ~]# T -g maket sohel    ---user create and group added as a primary

[root@tushar ~]# id sohel

uid=3004(sohel) gid=3004(maket) groups=3004(maket)

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# useradd file ---- Refers 2 files &  update  4 files

The information of adduser refers 2 files & updates 4 files.  

Refers 2 Files

|----ls /etc/login.defs

|

|----ls /etc/default/useradd  

Updates 4 files    ------user all information updated in below files.

IT’S CALL THE LINUX USER DATABASE

|----/etc/passwd

|

|----/etc/group

|

|----/etc/shadow

|

|----/etc/gshadow

l.   ----------------------------to see hidden file

ls –a ------------------------- to see hidden file

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[root@localhost ~]# vi /etc/login.defs   -  (.defs –Defaults )

# Min/max values for automatic uid selection in useradd

#

UID_MIN                   500 ------------------ TAG---------500  -----create only 100 user

UID_MAX                 60000-----------------TAG---------600   u can change this value

#

# Min/max values for automatic gid selection in groupadd

#

UID_MIN                   500 --------------------  TAG-------500  -- create only 200 groups

UID_MAX                 60000-----------------TAG---------700   u can change this value

#

# If useradd should create home directories for users by default

# On RH systems, we do. This option is overridden with the -m flag on

# useradd command line.

#

CREATE_HOME     yes   ------if should be not create home DIR  so u can just type no

You can manage and change home directory name.

How money user create in Linux

User and group = 59500  - by default user created

Answer: its depends on the /etc/login.defs file

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# passwd ------to change current user password

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/etc/login.defs

<1> /etc/login.defs : It keep the information of directory where mailboxes  reside or name of file relative to the home directory,  Password duration & how many users can login. 

"Passwd file" & "Group file" get the information of userid & groupid from this file. 

"shadow file" & "Gshadow file" get the information of user login & password duration of user from this file.   

Min/max values for automatic uid selection in useradd.   

UID-MIN 500 

UID-MAX 60000  

The id of user start from 500 & max it is 60000 which is default according to REDHAT but we can customize it.  

If there are two department ACCOUNTANT & MARKETING in one office then I can start userid to ACCOUNTANT from 1000 & to MARKETING from 2000 which is reliable.

Similar way to Groupid 

GID-MIN 500 

GID-MAX 60000

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Umask

Default value of umask is:

For root 022

For user 002

777                      777        

022                      002       

------                  ------          

755                      775  

Umask 077 is default permissions

MAIL_DIR        /var/spool/mail    --------------------  TAG  - user mails server indox in /var/spool/mail

_______________________________________________________________________________

/etc/default/useradd

<2> /etc/default/useradd : It has information of no. of groups, directory of users & user using which shell in following way.

1. Group=100 ----> It's default no. of groups according to Redhat which can customise.

2. Home=/home ----> It's default dir of user as Redhat say to which we can give any name i.e. we can make `ghar'instead of `home' by making directory under /

3. Inactive ----> It's number of days after account expire of user.

4. Expire ----> It's number of days for the password of user will expire.

5. Shell=/bin/bash --> It's path of user shell.

6. Skel=/etc/skel ---> When user create there is zero dir or file but when give command `l.' it shows some hidden files which comes from /etc/skel.

[root@localhost ~]# vi /etc/default/useradd

# useradd defaults file

GROUP=100   ------------------------------------------------------------------query

HOME=/home     (wallet)----------------------u can manage home dir and u can change the /home sir name

INACTIVE=-1   ------------------------------------10 account expire day select (-1 ----no value or its depends of       

                                                                                 the other files)

EXPIRE=    ---------------------------------------------IF you set 7 days the password will be expire after 7 days  

SHELL=/bin/bash  -----------------------------------if you want to change folder eg . /bin/sh  ---The shell of the user will be /bin/sh for feture

SKEL=/etc/skel  --------------------------------------If you want to change this pasth /etc/opt  u can manage that ,  Then opt folder all file copied to home dir

IF you want to share common file to every new joiner get this file so u can copy file in /etc/skel  folder

CREATE_MAIL_SPOOL=yes

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[root@localhost /]# mkdir   wallet  ---------------wallet dir create in / locaton

[root@localhost /]# T paresh  ------------------------create user

 [root@localhost jacky]# cd /wallet/paresh/   --------change home dir name

[root@localhost paresh]# l.   or   ls -a

.  ..  .bash_logout  .bash_profile  .bashrc  .gnome2  .mozilla

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[root@localhost ~]# cd /home/jacky/

[root@localhost jacky]# l.

.  ..  .bash_logout  .bash_profile  .bashrc  .gnome2  .mozilla

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LINUX USER DATABASE

Update 4 files  

i)                    /etc/passwd

ii)                  /etc/shadow

iii)                /etc/group

iv)                /etc/gshadow

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1)                   /etc/passwd

<3> /etc/passwd : * It keeps the record of new user when create by superuser. Each line is entry of new user. It is text file & has details of all system users.

* It has 7 fields for each user in each line so

it is called `system passwd database' & each field is separated : (colon) also called "Internal field Separator".

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[root@localhost paresh]# vi /etc/passwd

: (colon) is separated by filed

How many filed in passwd file = 7

Paresh  :x    :517  : 517   :    :/wallet/paresh     :/bin/bash

\_____/\__/\____/\____/|__|\______________/\__________/

      |         |       |          |       |               |                         |        

     1        2      3         4      5             6                       7

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Champu :x :500 :500  :   :/home/champu     :/bin/bash

\_____/\__/\___/\___/|_|\______________/\________/

      |         |      |        |     |              |                        |     

     1        2     3       4   5              6                       7

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1   ---   It is username

2   ---- X means your password reside in shadow files

 It contain user password which is somewhere else if exist.

If we put * in place of x then user can't login.

If we keep second field blank then user can login without password.

i.e. (x) --- password somewhere else or its store in shadow file

(*) --- user can't login.

( ) --- user can login without passwd.

3   ----   UID ------User id

4   ------ GID-------Group id 

It contains groupid which is always same as userid.  It's group of users.

5   ------It is comment field or GECOS(General electric compressive

operating system) Finger Information’s ( blank filed )

user can keep his information by using command

Name []:   office []:  office phone []:  Home phone []:

6  ------- field (/home/champu) : It's home of champu. /home is directory where

all users store. ( Home directory of the user )

7 ----- field (/bin/bash) : shell of the user

It contain the full path of shell used by user.

Through shell we can convert shell script into binary format &

Whatever get from kernel convert into text format.

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 2)               /etc/shadow   ---passwd policy

: (colon) is separated by filed: How many filed in passwd file = 9

John   : $1$eEfpbdwf$PyPoi0   :16792 : 0  : 99999 : 7  :   :   :

\___/\_____________________/\______/\_/\_______/\_/|_|_|_|__|

     1                      2                            3        4      5       6    7  8  9

man shadow -------all the detain get in man shadow files.

The meanings of each field are:

1  ---------User Name  (sp_namp - pointer to null-terminated user name)

2   ------- Password is in MD5 clear text encryption   ( IMP ) (sp_pwdp-password)

3   ------- sp_lstchg - days since Jan1,1970 password was last changed Unix Time is called epoch time (u can used time conversion) Last password change record

4  --------- sp_min – 10 days before which password may not be changed

                User may not change before 10 day his passwd                 

5  --------- sp_max – 65 days after which password must be changed

                                           User must be change password after 65 days (forcefully change)

6 ---------- sp_warn – 30 days before password is to expire that user

       is warned of pending password expiration

7  ----------- sp_inact – 55 days after password expires that account is

                   considered inactive and disabled

8  ------------ sp_expire – 4 days since Jan 1,1970 when account will be disabled

9  -------------- sp_flag - reserved for future use

root:$1$Z.8vsNYS$/cSeo0Sx/5aQlQdR4oF6M.:16793:0:99999:7:::

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3)                      /etc/group

Group contain 4 fields

line in this field like follow

groupadd  maket

tushar:x:3001:

maket:x:3004:

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vi /etc/group

tushar    :x     :3001   : --------user own group

maket    :x     :3004    :  ---------create group

\_____/\___/\_____/\_/

 1        2     3     4

1  ---- Group Name

2  ---- Group Password

3  ---- group ID

4  ---- Members of the group

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$ usermod -G groupname username

[root@localhost ~]# usermod -G sales lalit  -----add users to in group

sales:x:3003:lalit -  add lalit to sales group as secondary

[root@tushar rajeshj]# id lalit

uid=3003(lalit) gid=3005(lalit) groups=3005(lalit),3003(sales)

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 [root@localhost ~]# usermod -g maket sohel

[root@tushar ~]# id sohel

uid=3004(sohel) gid=3004(maket) groups=3004(maket) ---add as primary

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Diferance between primary and secondary group

usermod –G   ----  Secondary Group

usermod –g   ------Primary Group

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Group Password Set

#gpasswd sales– set group passwd

User can change this own primary group

[root@localhost ~]# su vikas

[vikas@localhost root]$ newgrp PUR

Password:

[vikas@localhost root]$ id

uid=513(vikas) gid=519(PUR) groups=513(vikas),505(sales),519(PUR) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

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 [root@tushar ~]# su - rajeshj

[rajeshj@tushar ~]$ id

uid=3007(rajeshj) gid=3008(rajeshj) groups=3008(rajeshj) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

[rajeshj@tushar ~]$ newgrp sales   ---user self-change group

Password:

[rajeshj@tushar ~]$ id

uid=3007(rajeshj) gid=3003(sales) groups=3008(rajeshj),3003(sales) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

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<4> /etc/group : This file keep the information of group. It has four field of each group of each line so it is called `system group database'.

Member of group has right to enter other member's of system who is member of same group.

line in this field like follow

 Accounts:x:500:

    |            |    |    |

    1          2   3   4

1. field (accounts) : It contain name of group which is always same as the first member username.

2. field (x) : It contain group password which is somewhere else if exist & it's password is same of first member of group.

3. field (500) : It contain group id which is same of first member's id of group.

4. field : It contains list of members of group. By default Redhat it is blank but user can fill it by put the name of members of group.

One user can makes members of his group by using command

 `usermod -G' which

is run by only root.

$usermod -G groupname username

when system admin first time creates users he can send message like

`Thanku for using redhat linux' through this & user get this mail whenever

he login.

[root@tushar ~]# T -G sales lalit

[root@tushar ~]# id lalit

uid=3003(lalit) gid=3005(lalit) groups=3005(lalit),3003(sales)

[root@tushar ~]# T -g maket sohel

[root@tushar ~]# id sohel

uid=3004(sohel) gid=3004(maket) groups=3004(maket)

[root@tushar ~]# ls -l /home/

-rw-r--r--. 2 root   root     47 Dec 18 22:44 harry.txt

drwx------. 4 lalit  lalit  4096 Dec 28 02:07 lalit

drwx------. 4 ls     ls     4096 Dec 15 23:13 ls

drwx------. 4 rakesh rakesh 4096 Dec 28 02:03 rakesh

drwx------. 4 sohel  maket  4096 Dec 28 02:07 sohel

-rw-r--r--. 1 root   root     32 Dec 18 20:23 test1.txt

drwx------. 4 tushar tushar 4096 Dec 28 02:03 tushar

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CREATE ANY USER WITHOUT EXECUTE ANY COMMADS

Fist refers 2 files and updates 4 files

1) /etc/login.defs
2) /etc/default/useradd


3) /etc/passwd
4) /etc/shadow/
5) /etc/group
6) /etc/gshadow

Create user home DIR as same user name
chmod 700 /home/samy/
su – samy
copy skel form home dir

cp /etc/skel/.bash* /home/samy/

chown –Rv samy : samy /home/samy

[root@localhost ~]# mkdir /hiome/samy

[root@localhost home]# chmod 700 /home/samy/

[root@localhost home]# ls -l

drwx------. 2 root root 4096 Dec 24 00:13 samy
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3 # vi /etc/shadow

Ms5-crypt -------you can set encrypted passed to user

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PASSWORD AGING CONTROLS:

1. PASS-MAX-DAYS 99999 : The maximum number of days a password can be used.

i.e max 99999 days.

2. PASS-MIN-DAYS 0 : The minimum number of days allowed between password

can change.

3. PASS-MIN-LEN 5 : The minimum length of the password. i.e. 5 character.

4. PASS-WARN-AGE 7 : Specifies the number of days warning given to user

before the password expire. ie 7 days.

The above PASSWORD AGING information is default according to REDHAT which we can customize it.

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# /etc/passwd   ------User details for UID and GID

Whenever we create second user then system can refer /etc/passwd file 

 How to delete user account

# userdel  champu   ------User can delete but user home DIR not delete.

Advantage of userdel command ----Database delete only but home DIR not delete.

# userdel  -r champu   ( -r -----recursive)  delete USER as well as HOME DIR

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How to check user is created or not

You can check user name or to search in below files

[root@localhost home]# less /etc/passwd

OR

[root@localhost home]# grep tushar /etc/passwd

tushar:x:515:515::/home/tushar:/bin/bash

paresh   :x   :517 :517  :   :/wallet/paresh  :/bin/bash

\______/\_/\___/\____/|_|\_____________/\__________/

      |         |      |        |      |            |                         |

     1         2    3      4      5           6                       7

1   ---   It is username

2   ---- X means your password reside in shadow files

If we put * in place of x then user can't login.

If we keep second field blank then user can login without password.

i.e. (x) --- password somewhere else or its store in shadow file

(*) --- user can't login.

( ) --- user can login without passwd.

3   ----   UID ------User id

4   ------ GID-------Group id It contains groupid which is always same as userid.

5   ------It is comment field or GECOS(General electric compressive

operating system) Finger Information’s ( blank filed )

user can keep his information by using command

Name []:   office []:  office phone []:  Home phone []:

6  ------- field (/home/champu) : It's home of champu. /home is directory where

all users store. ( Home directory of the user )

7 ----- field (/bin/bash) : shell of the user

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How to user modification

Usermod ---------to modify user

How to change UID

-u   ---------- UID    ------- to change UID

-s ------------ Shell ------- to change Shell

-c ------------- add comment   ----------to add comments eg . Thane mob no , add , location off add

-d --------------home DIR   ------------------ to change home DIR name.

-g --------------GID ----------first check group and decide to set GID value to user or

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 Add user to group

Usermod    –u  10   -s  /bin/sh   -c “ Thane Dombivali 989283938 98293898 “  –d /opt    champu

Practice and example    

[root@localhost home]# grep john /etc/passwd

john:x:514:514::/home/john:/bin/bash   --------------------------before modification user details

--------------------------After modification john user details in below--------------------

[root@localhost home]#  usermod -u 1000 -s /bin/sh -c " Tushar Jadhav 9892562869 dombivali thane" -d /GHAR/ john

[root@localhost home]# grep john /etc/passwd

john:x:1000:514: Tushar Jadhav 9892562869 dombivali thane:/GHAR/:/bin/sh

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[root@tushar ~]# useradd jockey

[root@tushar ~]# usermod -u 1000 -s /bin/sh -c " Tushar Jadhav 9892562869 dombivali thane" -d /GHAR/ jockey

[root@tushar ~]# id jockey

uid=1000(jockey) gid=3009(jockey) groups=3009(jockey)

[root@tushar ~]# grep jockey /etc/passwd

jockey:x:1000:3009: Tushar Jadhav 9892562869 dombivali thane:/GHAR/:/bin/sh

---------------------------Change user GID & user add in group ----------------

[root@localhost home]# usermod -u 2000 -s /bin/bash -g 519 -c " Tushar Jadhav 9892562869 dombivali thane" -d /home/ john

[root@localhost home]# grep john /etc/passwd

john:x:2000:519: Tushar Jadhav 9892562869 dombivali thane:/home/: /bin/bash

[root@localhost home]# id john

uid=2000(john) gid=519(PUR) groups=519(PUR)    ----after change GID user add in this group

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While creating user we can give specific home DIR shell,

(Create user and set permission and specific flags,)

Useradd jary -----set default value

Useradd  –d –u –s    -- if you used this fags then skip home , uid , shell tags

Practice and example    

[root@Tusharjahdav ~]#  Useradd –d  /mnt  –u 3000 –s  /bin/ksh jokey 

[root@Tusharjahdav ~]# grep jary /etc/passwd

Jokey :x: 3000: 3000  : : /mnt: /bin/sh

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[root@Tusharjahdav ~]# useradd -u 1002 -s /bin/sh jary

[root@Tusharjahdav ~]# grep jary /etc/passwd

jary:x:1002:1002::/home/jary:/bin/sh

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[root@localhost /]# useradd -u 3001 -m -c "Mr.harry power is back" pintu

useradd: cannot create directory /home:/pintu

---------------------------------------------------------------------------------------------------- [root@Tusharjahdav ~]# useradd vikey

useradd: cannot create directory /home:/vikey

Ans : if facing above error then go to /etc/default/useradd file and check home path.

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How to create 10 users in one command

# Fist create user file and run for a look

Practice and example    

[root@] ~]# vi /opt/tuss   ----- add user list in this file

[root@tushar /]# for i in  "cat /opt/users" ; do useradd $i ; done

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 How to disable user ----there are multiple way to disable user

root@tushar /]# vi /etc/passwd

jary: x : 1002:1002::/home/jary:/bin/sh  ----(user will be login)original user passwd

jary:  : 1002:1002::/home/jary:/bin/sh  -----------------black (disable)

jary:* : 1002:1002::/home/jary:/bin/sh  -------------------- * (disable)

jary: x : 1002:1002::/home/jary:/sbin/false  --- ---/sbin/false   (disable)

jary: x : 1002:1002::/home/jary:/sbin/nolgin --------- / sbin/nolgin  (disable)

root@tushar /]# vi /etc/shadow

paresh:!!:16792:0:99999:7:::9  ------ Put any value of last filed, user will be disable

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How to Lock user

Passwd –l john   ----------------lock the user

[root@tushar ~]# passwd  -l  paresh

Locking  password  for user paresh.

passwd: Success

Passwd –u john   --------------unlock the user

[root@tushar ~]# passwd -u paresh

Unlocking password for user paresh.

passwd: Warning: unlocked password would be empty.

passwd: Unsafe operation (use -f to force)

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All users will be disable if /etc/login this file is exist

Touch /etc/nologin  ----just create this file then all users will be disable

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How to Add group   ---groupadd Group Name

How to Delete group  -----groupdel   Group Name

How to modify group  ------groupmod

 How to change shell

Usermode –s --------------to change shell

[root@tushar /]# chsh paresh   -----------updated in passwd

Changing shell for paresh.

New shell [/bin/bash]: /bin/sh

Shell changed.

-----------------------------------------------------------------------------------------

 [root@tushar /]# chfn paresh     ----- Finger information  --change in gicos filed

Changing finger information for paresh.

Name []: paresh moon 983333883 dombivali current bangalore

Office []: ajsdadada

Office Phone []: asdasda

Home Phone []: asda

Finger information changed.

Practice and example    

[root@tushar /]# grep paresh /etc/passwd

paresh:x:517:517:paresh moon 983333883 dombivali current bangalore,ajsdadada,asdasda,asda:/wallet/paresh:/bin/sh

-----------------------------------------------------------------------------------------

[root@tushar /]# finger paresh  -------all user details

-----------------------------------------------------------------------------------------

To change the AGING  ( to change the password policy in shadow file)

[root@tushar /]# chage paresh

Changing the aging information for paresh

Enter the new value, or press ENTER for the default

3     Minimum Password Age [0]:

4    Maximum Password Age [99999]:

5     Last Password Change (YYYY-MM-DD) [2015-12-23]:

6      Password Expiration Warning [7]:

7      Password Inactive [-1]:

8       Account Expiration Date (YYYY-MM-DD) [1969-12-31]:

John : $1$eEfpbdwf$PyPoi0    :16792  : 0  : 99999  : 7   :    :   :

\___/\_____________________/\______/\__/\______/\__/|__|__|__|

     1                      2                            3       4       5        6     7   8   9

1 filed -user name , 2 filed password and last is reserved is skip

Create user and set password & user will be change password is first login.

[root@tushar /]# useradd pranay                    ------------------create user

[root@tushar /]# passwd pranay                  ----------------------set password

Changing password for user pranay.

New password:

BAD PASSWORD: it is based on a dictionary word

BAD PASSWORD: is too simple

Retype new password:

passwd: all authentication tokens updated successfully.

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 Before chage command /etc/shadow entry

pranay:$1$EmTX7J96$7Van4j3TJM.lIjFBwmryZ1:16792:0:99999:7:::

root@tushar /]# chage -d 0 pranay    ---------------------user will be prompt to change password for 1^st login

[root@tushar /]# su - pranay     ----------------------------------------switch user

[pranay@tushar root]$ su pranay

Password:

You are required to change your password immediately (root enforced)

Changing password for pranay.

(current) UNIX password:

New password:

Retype new password:

Grep prnay /etc/shadow

After chage command 3 filed value will be change

pranay:$1$EmTX7J96$7Van4j3TJM.lIjFBwmryZ1:0:0:99999:7:::

This entry goes to ( 1 jan, 1970 ) Value will be change  0

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All created users call Valid Linux Users

[root@tushar ~]#  Vi /etc/passwd 

[root@tushar ~]# vipw------------------short cut file of  vi /etc/passwd

[root@tushar ~]#  vi /etc/grouphu

[root@tushar ~]# vigr    -------------shart cut file of vi /etc/group

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How to disable shadow file

[root@tushar etc]# cd /etc/shadow  -----------------   shadow file

[root@tushar etc]# pwunconv    ----Disable command ---After this command shadow file will be disable and password will show in passwd file ..

[root@localhost Desktop]# less /etc/shadow-    disable file

passwd file user entry qiukr:$1$ml1iS2Ke$TL0UYLWoGTbIfczYwy7tL.:500:500:Centos:/home/qiukr:/bin/bash

[root@tushar etc]# less /etc/shadow ---------------------- shadow-   its menas disable

[root@tushar etc]# pwconv    ---------- Enable command-----------------shadow file will be enbale

[root@tushar etc]# less /etc/shadow    -------------------enable file

---------------------------------------------------------------------------------------------------------------------

Permission of shadow files 400

[root@tushar etc]# ls -l /etc/shadow

-r--------. 1 root root 1236 Dec 24 05:29 /etc/shadow

 passwd file will be deleted by mistake  

there is already backup file is system so just copy this file passwd

passwd-       ---------------------backup files

passwd.OLD    -------------------- old backup files

[root@localhost etc]# cp /etc/passwd-  /etc/passwd