User, group management in Linux

The main commands are:

Group: Groupadd, Groupmod, Groupdel

Users: Useradd, Usermod, Userdel

Certification: passwd

Group Resolution library File:/etc/group

Grpname:x:gid:user1, User2, ...

Group name: Password dot: GID: A list of users with this group as additional groups, separated by commas

Groupadd command: Adding a group

Groupadd [Options] Group

-G GID: indicates GID;

-R,--system: System group;

Groupmod Command: Modify group information

groupmod [Options] GROUP

-G GID

-N new_name: Modify group name;

Groupdel command: Delete a group

Groupdel [Options] GROUP

User Resolution Library:/ETC/PASSWD

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

Useradd command: Add user

useradd [Options] Login name

-C,--comment Comment: annotation information, generally full Name;

-D,--home/path/to/home_dir: Home directory path, the target path can not be pre-existing, otherwise there will be a warning, will not gain Skel related files to the user;

-G,--gid Group: The user's basic group name or GID;

-G,--groups group1[,group2,... [, GROUPN]] : The list of additional groups to which the user belongs, separated by commas, with no spaces in between;

-M,--create-home: Forced to create home directory;

-M: Do not create user home directory, even if the system is set in/etc/login.defs (Create_home) is yes;

-R,--system: Create a System account

-S,--shell Shell: The user's login shell name, default is left blank, let the system according to the shell variable in the/etc/default/useradd to select the default login shell;

-U,--uid UID: The numeric value of the user ID. This value must be unique unless the-o option is used. This value must be non-negative, with a default value greater than or equal to uid_min, and greater than any other user ID minimum.

Note: When you create a signed-in user, the shell program for which you are customizing must be a login shell and be located in the/etc/shells file;

Useradd-d: Displays the default settings when creating a user;

useradd-d option: Set a default option;

-E,--expiredate expire_date: Expiration of user account, locked after expiration, date specified in YYYY-MM-DD format

-F,--inactive inactive: The number of days before the account is completely disabled after the password expires. 0 means disable now, 1 means disable this feature.

To provide the user with a default configuration profile:

/etc/login.defs,/etc/default/useradd

Shadow password file:/etc/shadow

Login Name: Password: Last modified: Minimum password Age: Maximum password Age: Number of days ahead of warning: Inactive period: Date of inactivity: Reserved field

Usermod Command: Modify account information

-C,--comment comment

-D,--home Home_dir: Modifies the home directory to a new location, but should generally use the-m option to ensure that the files in the original home directory are moved to the new directory;

-G,--gid GROUP

-G,--groups group1[,group2,... [, GROUPN]] : The original additional group is overwritten when modified, and the-a option is used together to indicate adding new additional groups to the user;

-L,--login new_login: Modifies the user name of the current user;

-S,--shell shell

-U,--uid uid

-L,--lock: Locks the user's password. This will place a "!" before the user encrypts the password.

-U,--unlock: Unlocks the user's password. This will remove the encrypted password before the "!"

Userdel command: Delete user account

Userdel [Options] Login name

-R,--remove: Files in the home directory will be deleted with the user's main directory and the user's mailbox

passwd command: Password management commands

passwd [-L] [-u [-f]] [-d] [-e] [-N mindays] [-X Maxdays] [-W warndays] [-i-inactivedays] [--stdin] [username]

(1) passwd: Modify your password;

(2) passwd Username: Modify other user's password, only root has this permission;

Password complexity:

(1) not less than 8 characters;

(2) You cannot use passwords that are too similar to past passwords;

(3) At least three classes of four characters should be used;

Options:

-L: Lock password

-U: Unlocking and decrypting

-D: Clear Password

ID Command: View user-related ID information;

ID [OPTION] ... [USER]

-U: View UID only

-G: View GID only

-G: View the ID of all groups that belong to;

-N: Display name, not ID;

SU command: Switch user

When switching users:

(1) Do not read the target user's profile (non-login switch, half switch);

Su USERNAME

(2) Read the target user's configuration file (login switch, complete switch);

Su-l USERNAME

Su-username

-C command,--command=command: Runs the commands specified here only as the specified user, without performing a true identity switch operation;

Note: Root switch to any other users without authentication password, normal user switch to other users, all require a password;

GPASSWD command: Add a password to a group

Group Password file:/etc/gshadow

GPASSWD [Options] Group

-A USERNAME: Add the user to the group;

-D USERNAME: Remove this user from this group;

NEWGRP command: Log in to a new group

Chage command: Modify the user account for various deadlines;

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User, group management in Linux