Linux users, user groups, and permissions

Owner (user), owning group, others (other)

Because Linux is a multi-tasking system, it often appears that the same machine is operated by more than one person at a time, in order to consider everyone's privacy and the work environment that everyone likes, so the attribution of the file is very important.

In order to ensure the security of the system and the privacy of the file, a file with different permissions for the account has different permissions, such as

, the file permission is represented by a string representing the meaning of the

Where the document type has the following representation:

D-the table of contents, for example, the line with the name ". GConf" in the above file;
--the document, for example, the line with the "Install.log" in the above file;
L-Link file (link file);
B-the storage Interface device (optional random access device) inside the device file;
C-the serial port device inside the device file, such as a keyboard, mouse (one-time reading device).

The permissions are represented by rwx three subtitles, respectively, as readable, writable, executable, if not, then "-" means, for the directory, must have X permission, otherwise cannot read the contents of the Directory

If the file name is preceded by ". "indicates that the document or directory is hidden.

Users and user groups

　/etc/group Storing user group information in the current system

Attention:

1. When there is only one user in the group, and the user name and group name are the same, in the group list, a column containing the user can be empty

2. The group number of the root group in the system must be 0

3. Group number 1~499 is the group number reserved for the system, usually the number of software or service reserved for the system installation, the earlier the Software or service group number is installed. User manually created user group number starting with 500

4. Group password placeholder, no exception, all denoted by x

　/etc/gshadow Store password information for user groups in the current system

Attention:

1. If the group password is "*"! "Or empty, the group does not have a password

2. If the group manager is empty, it means that all members within the group can manage the group

　　/ECT/PASSWD Store all user information in the current system

Attention:

In Linux, the user number for Super Admin root must be 0

　　/ect/shadow Store password information for all users in the current system

Attention:

Password is a one-way encrypted string

To create a user:

Useradd xxx    // Create a user named XXX

After the command executes

1. Information about XXX Users is added to the/etc/passwd file

2. A user group message named XXX is added to the/etc/group file

passwd xxx    // set password for XXX user

Useradd parameters that can be used include

-D    Set the user's home directory     -d/home/helloworld Hello    // new Hello user and set their home directory to/home/ HelloWorld-u    set its userid    668 Hello    // Create a new Hello user, set his ID to 668 -G    set its primary group     -G root Hello    // Create a new Hello user and put it if the root group -m    Create a folder    for your home directory -M Hello    // Create a Hello user, and a Hello folder (/home/hello) in the default location, and copy the files under/etc/skel to this directory

　　

Modify user Information

　　

Usermod parameter User name

The parameters that the command can use include

-L    // Modify new user name    For example: Usermod-l helloworld Hello change    Hello user name to HelloWorld, but its home directory does not change -U    // Modify user's UserID    888  Hello    to change the userid of Hello to 888-D    // Modify the user's home directory -G    // Modify the user's primary user group -L    // Lock the user so that it cannot log on- u    // unlock

　　Delete User

Userdel parameter User name

Parameters can be used

-R Delete the user while deleting its home directory

　　

Create a user group

Groupadd Group Name

Modify a user group

Groupmod-n New group name old group name    / Modify Group name  -G new group ID    old group ID    modify Group ID

Delete a user group

Groupdel Group Name

Change the owner of a document (catalog) (all groups)

Changing the document owner-chown command (change owner), you can use the parameter-R to make its subdirectories also modified

Adapt document all Groups-chgrp command (change group), use the parameter-R to make its subdirectories also modified

You can also use

Chown

　　

To modify the owner and group of a document or directory at the same time

Modify the execution permissions for a document

chmod command

chmod parameter file name

You can set permissions for a file directly by using the following method

1 . Directly set a number that represents permissions chmod 777 (number of corresponding permissions) file name 2 . To add or subtract certain permissions     from a file chmod u+w  filename    to user user plus W permission     chmod g-r file name    remove R permission from group     chmod a+x file name    to user, group, other all plus x permission

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Linux users, user groups, and permissions