linux--Users and Groups

One: Linux user and group related configuration files:

/ETC/PASSWD: User and its attribute information (name, UID, base group ID, etc.);

Name:password:UID:GID:GECOS:directory:shell

User name: Password: UID:GID:GECOS: Home directory: Default Shell

/etc/group: Group and its attribute information;

Group_name:password:GID:user_list

Group name: Group Password: GID: List of users with the current group as additional groups (comma delimiter)

/etc/shadow: User password and its related attributes;

Username: encrypted Password: the date of the most recent password change: Minimum password Age: Maximum password Age: password warning Period: Password Disable period: Account expiration Date: Reserved field

/etc/gshadow: group password and its related attributes, including but not limited to information in/etc/group ;

User group: User group Password: User Group manager: team member

/etc/login.defs

Mail_dir/var/spool/mail

Pass_max_days99999 # password Max expiration

Pass_min_days0 # Two minimum interval to change password

Pass_min_len5 # Minimum password length, invalid for root

Pass_warn_age7 # How many days before the password expires start prompting

Uid_min 1000 # Minimum value of user ID

Uid_max 60000 # maximum value of user ID

Sys_uid_min 201 # Minimum value of system user ID

Sys_uid_max 999 # Maximum value of system user ID

Gid_min 1000 # Minimum value of group ID

Gid_max 60000 # Maximum value of group ID

Sys_gid_min 201 # Minimum value of system group ID

Sys_gid_max 999 # Maximum value of system group ID

Create_homeYes # is enough to create a user directory when using Useradd

UMASK 077

Usergroups_enab Yes # encrypt password with MD5

Encrypt_method SHA512 # Encryption mode

/etc/default/useradd

GROUP=100 # Start GID value

Home=/home # Home Directory Location

Inactive=-1 # Effective time, negative number is permanent, positive numbers represent days

Expire=

Shell=/bin/bash # Shell Path

Skel=/etc/skel # User home directory of the environment files, by default add the user's directory default file storage location;

Create_mail_spool=yes # Whether to create a mail pool

Two: User and group-related management commands:

user created: Useradd

useradd [options] LOGIN

-u UID: [Uid_min, Uid_max], defined in/etc/login.defs

-G GID: Indicates that the user belongs to the basic group, can be a group name, can also GID;

-C "COMMENT": User's comment information;

-d/path/to/home_dir: The home directory with the specified path;

-S Shell: Indicates the user's default shell program, the available list is in the/etc/shells file;

-G group1[,group2,... [, GROUPN]] : Specifies additional groups for the user, and the group must exist beforehand;

-r: Create a System user

Group creation: Groupadd

groupadd [OPTION] ... group_name

-G GID: Specifies the GID number; [Gid_min, Gid_max]

-r: Create a system group;

View user-related ID information: ID

ID [OPTION] ... [USER]

-u:uid

-g:gid

-g:groups

-n:name

to switch users or execute commands as other users: Su

su [Options ...] [-] [user [args ...]]

How to switch users:

su UserName: Non-login switch, that is, the target user's configuration file will not be read;

su-username: Login switch, will read the target user's configuration file; switch completely;

User Property modification: Usermod

usermod [OPTION] Login

-u uid: New UID

-G GID: New Basic Group

-G group1[,group2,... [, GROUPN]] : The new add-on group, the original additional group will be overwritten, if the original, you want to use the-a option at the same time, indicating append;

-S shell: new default shell;

-C ' COMMENT ': new annotation information;

-D home: New home directory, files in the original home directory will not be moved to the new home directory at the same time, to move, then use the-M option;

-L login_name: new name;

-l:lock The specified user

-u:unlock The specified user

-E yyyy-mm-dd: Indicates the user account expiration date;

-F INACTIVE: set inactivity period;

Add password to User: passwd

passwd [OPTIONS] UserName: Modify the password of the specified user, only the root user rights

passwd: Modify your password;

-L: Lock the specified user

-u: Unlock the specified user

-N mindays: Specifying the shortest period of use

-x maxdays: Maximum lifespan

-W warndays: How many days in advance to start warning

-I inactivedays: inactivity period;

--stdin: Receive user password from standard input;

Delete User: Userdel

Userdel [OPTION] ... login

-r: Delete user home directory;

Group Property Modification: Groupmod

groupmod [OPTION] ... group

-N group_name: New name

-G gid: New Gid;

Group deletion: Groupdel

Groupdel GROUP

Group Password: gpasswd

GPASSWD [OPTION] GROUP

-A user: Adds the user to the specified group;

-D User: Removes additional groups of users with the current group as the group name

-A user1,user2,...: Set up a list of users with administrative privileges

newgrp Command: Temporarily switch the basic group , if the user does not belong to this group, you need the group password;

Modify User properties: Chage

chage [OPTION] ... LOGIN

-D last_day

-E,--expiredate expire_date

-I.,--inactive inactive

-M,--mindays min_days

-M,--maxdays max_days

-W,--warndays Warn_days

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Modify the default minimum length of root passwd by modifying the/etc/pam.d/system-auth file

Password requisite pam_cracklib.so try_first_pass retry=3 type= minlen=4

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linux--Users and Groups