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/ etc/passwd

Looking at the / etc/passwd file in Linux, you can see something similar to the following:

Each field has the following meanings:

User name: password: user identification number: group identification number: annotative description: home directory: login Shell

Specific meaning and description of field

1 user name of logging in to the system

2 user password information after encrypted processing

3 UID (UserID, user ID number)

1) the Linux system identifies the user by the ID number instead of using the user name. (the general user uses the user name to interact with the system, while the Linux system uses the UID number)

2) range 0-65535. 0-99 is reserved for system use.

3) root user is fixed as 0

4 user default group ID.

1) A user can belong to multiple groups

2) this group is the default group for system identification

3) the groups with smaller numbers belong to the system group

5 comment information, description of the user, such as contact number, email address, etc.

6 user home directory, usually defaults to / home/ user name

7 the default shell used by this user

/ etc/shadow

Looking at the / etc/shadow file in Linux, you can see something similar to the following:

Each field has the following meanings:

Login name: encrypted password: last modified time: minimum time interval: maximum time interval: warning time: inactivity time: failure time: flag

Field meaning

1 "login name" this name is a user account that is consistent with the login name in the / etc/passwd file

2 the password field stores the encrypted user password.

If it is empty, the corresponding user does not set a password and does not need a password to log in; an asterisk indicates that the account has been locked; a double exclamation point indicates that the password has expired; if it begins with $6, it indicates that SHA-512 encryption is used; $1$ indicates that MD5 encryption is used; $2$ indicates that Blowfish encryption is used; and $5$ indicates that SHA-256 encryption is used.

3 "Last modification time" represents the number of days from a certain time to the time when the user last changed the password. The time starting point may be different for different systems. In SCO Linux, for example, the time starting point is January 1, 1970.

4 "minimum time interval" refers to the minimum number of days between password changes.

5 "maximum interval" refers to the maximum number of days that a password remains valid.

6 the warning time field represents the number of days between the time the system warns the user and the time the user's password officially expires.

7 "inactive time" refers to the maximum number of days for which the user has no login activity, but the account can remain valid.

The 8 "expiration time" field gives an absolute number of days, and if this field is used, it indicates the lifetime of the corresponding account. After the expiration of the period, the account is no longer a legitimate account and can no longer be used to log in.

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