User management under Linux (i)

There are three types of users under Linux:

1. Superuser: Root has all the privileges of the operating system, the UID value is 0 is the super user

2. Normal User: Only has limited operating system permissions, UID is from 500 to 6000 range

3. Pseudo-User: is to facilitate system management, to meet the corresponding system process file owner requirements, can not login, UID is from 1 to 499

passwd because all users have access to the/etc/passwd file, only the account number defined in this file does not define the password.

Each row in the/etc/passwd file represents a user, each line has 6 colons, and a row of records is divided into 7 parts

The first part: the name of the account.

The second part: password. X

Part III: User identifiers (user IDs)

Part IV: Identifier of the group in which the user is located (user group ID)

Part V: Information about the user (comment function)

Part VI: User home directory

Part VII: The user's environment (that is, the user's shell interpretation environment, such as the part is/bin/bash, is to use/bin/bash to explain the user action)

/etc/shadow is a file that holds the user's password, which can only be read by the root user.

Each line has 8 colons, spaced into 9 parts, followed by:

User name

Password (storing encrypted password, MD5 encryption) if the first character of the string is! , it indicates that the user cannot log on

Time Last modified: number of seconds from 1970 to the last modified time

Maximum time interval: 0 can be changed at any time, and if not, it will need to wait until the number of seconds to change.

Minimum time interval: 10 days, for example, indicates that 10 days must be changed. If it is 99999, it means that you can never change

Time of warning: the notification time for the password change. The default is one week

Inactivity Time: If it expires, there is still no change, the time of the delay.

Expiry time: From 1970 onwards

User management under Linux (i)