Three. Linux User and Group management

User and group related files, Useradd

1. User and group related files

(1)/etc/passwd

Format: Name:passwd:UID:GID:GECOS:directory:shell

Zhubiao:x:1000:1000:zhubiao:/home/zhubiao:/bin/bash

1 Name:user ' s login name

2 passwd:x occupied, actually deposited in/etc/shadow

3 uid:user ID, user code

The range of User IDs is determined by/etc/login.defs uid_min Uid_max [Uid_min,uid_max]

System account: 1-499, 1-999

General Account: 1000+,

4 gid:group ID, group code

The range of group IDs is determined by/etc/login.defs gid_min Gid_max [Gid_min,gid_max]

System groups: 1-499, 1-999

General Group: 1000+,

Group Category:

Basic group:

Private group: The group name and user name are the same, and only one user is included

Additional groups:

5 Gecos:comment filed, summary field

6 Direcotory:user ' s home directory, user home

Home directory default directory is determined by "home=/home" in/dev/default/passwd

The Add directory configuration file is determined by "Skel=/etc/skel" in/dev/default/passwd

7 Shell:set The shell environment variable, if empty, use/bin/sh

Default value/dev/default/passwd "Shell=/bin/bash"

(2)/etc/shadow

Format: Name:password:last_chage_date:minimum_age:Maximum_age:warning_period:inactivity_period

: expiration_date:reserved_filed

1 Name:login Name

2 password:encrypted password, encrypted password

Encryption algorithm: md5sum (Message digest), Sha1sum (Secure Hash algorithm), Sha224sum, Sha256sum, Sha384sum, sha512sum

The characteristics of these cryptographic algorithms:

Butterfly Effect: A small change in initial conditions will cause a huge change in results

Fixed-length output

The password also added impurities to avoid different users of the same password encryption after the same password

3 last_chage_date:date of last password changes, the date of the most recent password change

4 minimum_age:minium password age, change password minimum interval

5 maxinmu_age:maxinum password age, password maximum lifetime

6 Warning_period:password Warning Period, the number of days before a password are going to Expier

During which the user should be warned to warn users before password aging

7 Inactivity_period:password Inactivity Period, the number of days after a password have expired during

which the password should still be accepted, the number of days after the password has not been modified to keep the password available

8 Expiration_date:account expiration date, user expiration

(3)/etc/group

Format: group_name:password:GID:user_list

Groupa:x:504:zhubiao,xiaocao,user1,user12

1 Group_name:the name of the group

2 Password: Use x placeholder, password saved in/etc/gshadow

3 Gid:group ID

4 User_list:a List of usernames that is members of the this group, the groups contained in the user, between multiple users with "," separated

(4)/etc/gshadow

Format: group_name:password:administrators:members

Groupd:!::user12

2. useradd:create a new user or update default new user information

-U:--uid uid value range [Min_uid, Max_uid], this value must is unique

-G:--gid Group the group name or group ID, the group name and group ID must exit. Group name or group number, group must exist

-C:--comment comment, any text string

-D:--home home_dir, home directory path, preferably the path was not previously present, the default path is defined by the/etc/default/useradd file,

Directory configuration files are copied from/etc/skel/

-S:--shellshell, default path specified by/etc/default/useradd file

-G:--groups group1,group2,group3 ..., additional group

-M: Do not build home directory (System user default)

-M: Build User home directory (normal user default)

-D:--defaults

-G:--gid GROUP,/etc/default/useradd "group=100"

-B:--base-dir HOME,/etc/default/useradd "Home=/home"

-F:--inactive inactive, the numser of days after a password have expiered before the account would be disabled,

Change the password is still not modified after the password is still available for the period,/etc/default/passwd "inactive=1"

-e:--expiredate EXPIRE, account availability period,/etc/default/useradd "expire=30"

　　　　

　　

Three. Linux User and Group management