Showing posts with label Linux Password. Show all posts
Showing posts with label Linux Password. Show all posts

Friday, December 19, 2014

Linux Password file explained in detail



/etc/passwd file stores essential information, which is required during login i.e. user account information. /etc/passwd is a text file, that contains a list of the system's accounts, giving for each account some useful information like user ID, group ID, home directory, shell, etc. It should have general read permission as many utilities, like ls use it to map user IDs to user names, but write access only for the superuser (root).

Password file format
account:password:UID:GID:GECOS:directory:shell 

  1. Username: It is used when user logs in. It should be between 1 and 32 characters in length. Shows what is the Login Id for a user.
  2. Password: An x character indicates that encrypted password is stored in /etc/shadow file.
  3. User ID (UID): Each user must be assigned a user ID (UID). UID 0 (zero) is reserved for root and UIDs 1-99 are reserved for other predefined accounts. Further UID 100-999 are reserved by system for administrative and system accounts/groups.
  4. Group ID (GID): The primary group ID (stored in /etc/group file)
  5. User ID Info: The comment field. It allow you to add extra information about the users such as user's full name, phone number etc. This field use by finger command.
  6. Home directory: The absolute path to the directory the user will be in when they log in. If this directory does not exists then users directory becomes /
  7. Command/shell: The absolute path of a command or shell (/bin/bash). Typically, this is a shell. Please note that it does not have to be a shell.

See User List

/etc/passwd is only used for local users only. To see list of all users, enter:
$ cat /etc/passwd

To search for a username called tom, enter:
$ grep tom /etc/passwd

/etc/passwd file permission
The permission on the /etc/passwd file should be read only to users (-rw-r--r--) and the owner must be root:
$ ls -l /etc/passwd

Output:
-rw-r--r-- 1 root root 2659 Sep 17 01:46 /etc/passwd

Your password is stored in /etc/shadow file

Your encrpted password is not stored in /etc/passwd file. It is stored in /etc/shadow file



Monday, November 24, 2014

How to increase Password Expire date without resetting the password


It is commonly used that when we have to increase the password expire date of any user we simply reset the password of that user .
But we can increase the Password Expire date of user without resetting the password.
Here is the below scenario –

[root@server ~]# chage -l linux
Last password change : Nov 22, 2010
Password expires : Feb 20, 2011
Password inactive : never
Account expires : never
Minimum number of days between password change : 0
Maximum number of days between password change : 90
Number of days of warning before password expires : 7
[root@server ~]#

In above sentence  Last password change,Password expires & Maximum number of days between password change is important fields.
Here the “Maximum number of days between password change” has value 90 days.
So on the basis of this we will increase the Password Expire date.
for above scenario use the command :
chage -d 2011-02-20 linux
Here in above command we have changed the “last password change” value .
So by doing this it will automatically add 90 days and give new value in “Password Expires
Check the below result
[root@server ~]# chage -l linux
Last password change : Feb 20, 2011
Password expires : May 20, 2011
Password inactive : never
Account expires : never
Minimum number of days between password change : 0
Maximum number of days between password change : 90
Number of days of warning before password expires : 7
[root@server ~]#