Information about /etc/shadow file in Linux/Unix

The /etc/shadow file contains the password in encrypted format. It contains the information about user password.

Here, we will need to notice that /etc/passwd file contains the information about the user and /etc/shadow file contains the information about the user password.

This file contains the username, user password in encrypted format, last password change, etc.

The /etc/passwd file contains the information as shown below

[root@SOC01 ~]# cat /etc/shadow

root:x:0:0:root:/root:/bin/bash

bin:x:1:1:bin:/bin:/sbin/nologin

daemon:x:2:2:daemon:/sbin:/sbin/nologin

adm:x:3:4:adm:/var/adm:/sbin/nologinlp:*:14789:0:99999:7:::

sync:*:14789:0:99999:7:::

shutdown:*:14789:0:99999:7:::

halt:*:14789:0:99999:7:::

mail:*:14789:0:99999:7:::

uucp:*:14789:0:99999:7:::

operator:*:14789:0:99999:7:::

games:*:14789:0:99999:7:::

gopher:*:14789:0:99999:7:::

ftp:*:14789:0:99999:7:::

nobody:*:14789:0:99999:7:::

usbmuxd:!!:15582::::::

shashank:$6$8ExtOSsV$fMEDgsIA5dIyFE56cbBfLkePl.udw7LDMY68jj912VqAwvz/gs7h3rU1s6Y

ldap:!!:15654:0:99999:7:::
ldapuser:$6$P/kWJv9S$v3XhBrO9nSf9Cu05yW4QmfA7s26mSuMHyGRg05f5Bp.MReKjnzFlqLIf3pp

This file contains 8 fields separated by colon (:)

1st field:           Contains the username

2nd field:          This field contains the password in encrypted format

3rd field:           It contains the last password change since 1 Jan 1970

4th field:           The minimum number of days before the password change

5th field:           The maximum number of days before the password change

6th field:           This field contains the warning message before password expires. The user is requested to change the password.

7th field:           The number of days after password expires
8th field:           This field contains when the user account disables and user can no longer be used.

chage command is used to modify the filed in /etc/shadow file.

!! means password never set
! In second column if first word is ! which means that account is locked

Information about /etc/passwd file in linux/unix

The /etc/passwd file contains the list of all the users in Linux/Unix. It also contains some information related to the user. 

For example, the uid (user id) and gid (group id) of the user, home directory of the user, comment and login shell of the user.

The /etc/passwd file contains the information as shown below

 

This file contains 7 columns separated by colon (:)

1^st column: Contains the list of the user.

2^nd column: Contains x which means that password is stored in encrypted format in /etc/shadow file.

3^rd column: Contains the user id

4^th column: Contains the group id

5^th column: It contains the information related to the user

6^th column: It contains the home directory of the user

7^th column: The last column contains the login shell of the user.

Note:  

root user having 0 uid and gid. 1-499 uid is reserved for system user and 500 and more contains the uid or gid for normal users. 

usermod command is used to modify the fields in /etc/passwd file.