Linux Users and Groups

Related profiles for users and groups

Manage Users and Groups

categories of users :

depending on the location of your account : local account , remote ( domain ) Account LADP

based on the function of the account : superuser (Root) uid:0

Normal User

                        System User UID 1-499 Local user UID

categories of groups :

categories of users :

depending on the location of the account : Local group , remote ( domain ) Group LADP

based on the function of the account : Super user group (root) uid:0

general user groups

                         system user Group     uid  1-499                                                                                                                    local user group    uid 

Each user has a group with the same name

about configuration files for system users and groups :

account information password information

Users :/etc/passwd/etc/shadow

Group /etc/group/etc/gshadow

/etc/passwd The role of each field

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

User name : Password placeholder : uid:gid: User Description : User home directory : the shell used after landing

passwd Middle pseudo user :

bin have executable user command file

SYS owning system files

ADM own account file

UUCP UUCP Use

LP LP or LPD Subsystem Usage

Nobody NFS Use

/etc/shadow Structure

1root:$6$mkafxshc3tvuowse$vhaepja7m1sbrjmsuz1m5qj7xvasrmw/ab2r4. Njyb5ifotk/zk Qnedtob2qy2/ya15iuuibk0xqw6dncm4j./:16848:0:99999:7:::

Root User Name

$6mk .... 4j. encrypted password (rhel5 with MD5 rhel6 SHA512 Encryption)

16848 Date The password was last changed or the date the password was created from 19700101 Start Calculation

0 Number of days the password cannot be changed: only a few days after the recent change can be changed 0 means you can change it at any time

999999 Password Expiration Time that How many days must be modified again

7 password needs to be changed before the deadline arrives 7 Day to issue a warning

Grace days password expires after a few days can also change the password

account expiry time

reserved

Useradd-e 01/01/17

Usermod-e 2016-10-10

chage-m password Keep maximum days -M minimum number of days to change password

Date-d "1970-01-01 +16897day" + "%y-%m-%d"

Know

/etc/group configuration file Structure

Greproot/etc/group

root:x:0:

Root Group name x Group Password placeholder 0 GID

Add user-related commands

Grammar useradd username

-uuid-d Home Directory -G Start Group -G Additional group -S the shell used

Example

Useradd-u Zhen

Idzhen

uid=1000 (Zhen) gid=1000 (zhen) groups=1000 (zhen)

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Commands about the user's password

passwd Modify the current user password

Non-interactive

echo123456 | passwd--stdin Root

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Understand

Linux User Password Encrypt

123456--> sha512--$6$KN1ZIOJC$YCU

123456 Random value -sha512---> $6$kn1ziojc$ycudo3lwqxc

Validation

123456 + Random value -sha512---> $6$KN1ZIOJC$YCUDO3LWQXC

To Modify user information :

Grammar usermod username

-uuid-g Start Group -G Additional Group -D Home Directory -S Login Shell

Delete User

Userdel username-r Delete the user home directory when deleted

Userdel-r Test7

Add Group

Groupadd Test9

Modify group Information

Groupmod-g GID GroupName

Groupmod-g 1003 Test9

Delete a group

Groupdel GroupName

Understand

Vim/etc/defualt/useradd Control Add user's rule file

Home=/home # which directory to store as the user's home directory

Inactive=-1

Expire=

Shell=/bin/bash # default shell when adding users use which

Skel=/etc/skel # Template Catalog

Create_mail_spool=yes

View user Information related commands

Idtest2 WhoAmI w/who

User Switching:

Su-username plus - user and shell environment switch together

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Single-user mode retrieve user password

Boot Press any key when entering the countdown

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Press e Edit

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Select the second line kernel press e to edit

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Space Input 1

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Enter Press b Start

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Enter single-user mode

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passwd Change your password

Rhel7

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Linux Users and Groups