Linux new users, user groups, assigning permissions to users (Chown, Useradd, Groupadd, Userdel, Usermod, passwd, Groupdel)

Linux System is a multi-user multi-tasking time-sharing system, any user who wants to use system resources must first request an account from the system administrator and then enter the system as this account. On the one hand, the user's account can help the system administrator to track the users who use the system and control their access to system resources, and on the other hand can help users organize files and provide security protection for users. Each user account has a unique user name and a separate password. When a user types the correct user name and password at logon, they are able to enter the system and their home directory.

To achieve the management of user accounts, the main tasks to be completed are as follows:

• Add, delete and modify user accounts.
• Management of user passwords.
• Management of user groups.

I. Management of Linux system user accounts

The management of user accounts mainly involves the addition, modification and deletion of user accounts.

To add a user account is to create a new account in the system, and then assign the user number, user group, home directory, and login shell resources to the new account. The account you just added is locked and cannot be used.

1. Add a new user account using the useradd command with the following syntax:

useradd Option user name

Each of these options has the following meanings:

-C Comment Specifies an annotative description.
The-D directory specifies the home directory, and if this directory does not exist, the-m option can be used to create the master directory.
The-G user group specifies the user group to which the user belongs.
-G user Group, user group specifies the additional group to which the user belongs.
-S Shell file specifies the user's login shell.
-u user number specifies the user's user number, and if you have the-o option, you can reuse the other user's identification number.

USERNAME Specifies the login name of the new account.

Example 1:

# Useradd –d/usr/sam-m Sam

This command creates a user Sam,

Where the-D and-m options are used to generate a home directory for the login Sam/usr/sam (/usr is the parent directory where the default user home directory resides).

Example 2:

# Useradd -s/bin/sh-g group–g adm,root Gem

This command creates a new user gem, which is the login shell of/bin/sh, which belongs to the group user groups, and also to the ADM and root user groups, where group user groups are their primary groups.

You may create a new group here:

#Groupadd Group and Groupadd ADM

Add user account is in the /etc/passwd file to add a record for the new user, while updating other system files such as /etc/shadow, /etc/group and so on.

Linux provides an integrated system management tool, userconf, which can be used to manage user accounts uniformly.

2. Delete Account

If a user's account is no longer in use, it can be removed from the system. Deleting a user account is to delete the user record in the system files such as /etc/passwd , and delete the user's home directory if necessary. Delete an existing user account using the Userdel command, in the following format:

userdel Option user name

The common option is- R, which is to remove the user's home directory.

For example:

# Userdel Sam

This command removes the user Sam's records in the system files (mainly/etc/passwd,/etc/shadow,/etc/group, etc.) while deleting the user's home directory.

3, modify the account

Modify user account is based on the actual situation to change the user's relevant attributes, such as user number, home directory, user group, login shell and so on.

Modify the information for an existing user using the Usermod command, which is in the following format:

usermod Option user name

Common options include-C,-D,-M,-G,-G,-S,-u, and-O, etc., which have the same meaning as the options in the useradd command, specifying a new resource value for the user. In addition, some systems can use the following options:

-L New User name

This option specifies a new account that will change the original user name to the new one.

For example:

# Usermod -s/bin/ksh-d/home/z–g developer Sam

This command modifies the user Sam's login shell to Ksh, the home directory to/home/z, and the user group to developer.

4, the User password management

An important part of user management is the management of user passwords. The user account has just been created without a password, but is locked by the system, cannot be used, it must be given a password before it can be used, even if a blank password is specified.

The shell command that specifies and modifies the user's password is passwd. A superuser can specify a password for himself and another user, and a normal user can only use it to modify his or her password. The format of the command is:

passwd Option user name

Options available for use:

-L LOCK the password, that is, disable the account.
-u password to unlock.
-D make the account no password.
-F forces the user to change the password the next time they log on.

If the default user name, the current user's password is modified.

For example, assuming the current user is Sam, the following command modifies the user's own password:

$ passwd
Old password:******
New password:*******
Re-enter New password:*******

If you are a superuser, you can specify the password for any user in the following form:

# passwd Sam
New password:*******
Re-enter New password:*******

Ordinary users to modify their own password, the passwd command will first ask the original password, verify and then ask the user to enter two times the new password, if the password two times the same, the password is assigned to the user, and the super-user to specify a password for the user, do not need to know the original password.

For system security, users should choose a more complex password, such as a 8-bit long password, which contains uppercase, lowercase letters, and numbers, and should be different from names, birthdays, and so on.

When you specify a blank password for a user, execute the following form of command:

# passwd -D Sam

This command removes the user Sam's password so that the next time the user Sam logs on, the system will no longer ask for the password.

The passwd command can also lock a user with the-l (lock) option so that it cannot log on, for example:

# passwd-l Sam

New User exception:

useradd-d/usr/hadoop-u 586-m hadoop-g Hadoop

1 Creating Mailbox file: Files already exist
Delete to rm-rf/var/spool/mail/user name

2 useradd:invalid numeric argument ' Hadoop '
This is because the Hadoop group does not exist please build the Hadoop group first

The user's pass can be viewed via cat/etc/passwd

Cat/etc/shadow can view user name

Cat/etc/group can view groups

II. Management of Linux system user groups

Each user has a user group, and the system can centrally manage all users in a single user group. Different Linux systems provide a different set of user groups, as users under Linux belong to a user group with the same name, which is created at the same time as the user is created.
The management of user groups involves adding, deleting, and modifying user groups. The addition, deletion, and modification of a group is actually an update to the /etc/group file.

1. Add a new user group using the groupadd command. The format is as follows:

groupadd Option User Group

The options you can use are:

-G GID Specifies the group identification number (GID) of the new user group.
-O is commonly used with the-G option, which means that the GID of the new user group can be the same as the GID of the user group already in the system.

Example 1:

# Groupadd group1

This command adds a new group group1 to the system, and the group identification number of the new group is added 1 on the basis of the currently existing maximum group identification number.

Example 2:

#Groupadd -G 101 group2

This command adds a new group group2 to the system, specifying that the group identification number for the new group is 101.

2. If you want to delete an existing user group, use the groupdel command, which has the following format:

Groupdel User Group

For example:

#Groupdel group1

This command removes the group group1 from the system.

3. Modify the properties of the user group using the groupmod command. Its syntax is as follows:

groupmod Option User Group

The common options are:

-G GID Specifies a new group identification number for the user group.
The-O is used in conjunction with the-G option, and the user group's new GID can be the same as the GID of the user group already in the system.
-N New user Group change user group name to new name

Example 1:

# Groupmod -G 102 group2

This command modifies the group ID number of group group2 to 102.

Example 2:

# Groupmod –g 10000-n group3 group2

This command changes the identification number of the group group2 to 10000 and the group name to Group3.

4. If a user belongs to more than one user group at the same time, the user can switch between groups of users in order to have permissions from other user groups. After logging in, the user can switch to another user group using the command Newgrp, which is the target user group.

For example:

$ newgrp Root

This command switches the current user to the root user group, provided that the root user group is really the user's primary or additional group. Similar to the management of user accounts, the management of user groups can also be done through integrated system management tools.

Permission Assignment

assigning permissions

Chown-r hadoop:hadoop/usr/hadoop/

Let the normal user have root privileges

1.root Login
2.adduser User Name
3.PASSWD User Name
Determine password
4. Modify the/etc/passwd to change the ID and ID Group of the user name to 0.

Create a new user and do not allow users to log in directly:

#添加nginx用户组及用户groupadd wwwuseradd-g www-s/usr/sbin/nologin www #不让www用户直接登录

Linux Modify user group method

1. Forcibly set up a group of users

USERMOD-G User Group user name

2. Change a user to group (s)

Usermod- G user Group user name

3, add the user into a group (s), note: The original user group still exists

Usermod -a-g user Group user name

Usermod Instructions for use:

Modify user Account

syntax : usermod [-lu][-c < remarks >][-d < login directory >][-e < expiration >][-f < buffer days >][-g < group >][-g < group >][-l < account name >][-s <shell>][-u <uid>][user Account]

Additional note : Usermod can be used to modify the user account settings.

Parameters :

-c< Notes > Modify the Notes text for the user account.
-D Login Directory > Modify user login directory.
-e< Expiration date > Modify the expiration date of the account.
-f< Buffer days > Modify the number of days after the password expires to close the account.
-g< Group > Modify the group to which the user belongs.
-g< Group > Modify the additional groups to which the user belongs.
-l< Account name > Modify user account name.
-L LOCKS the user password to invalidate the password.
-s<shell> modifies the shell used by the user when they log in.
-u<uid> Modify the User ID.
-U unlocks the password.

Linux new users, user groups, assigning permissions to users (Chown, Useradd, Groupadd, Userdel, Usermod, passwd, Groupdel)