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Editor to share with you the Linux Chinese file attributes, owners, groups, permissions of the example analysis, I believe that most people do not know much, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

Write at the front

We all know that Linux is a system that supports multi-user and multi-task, which is also its best feature, that is, there may be many people working on the system at the same time, so do not force the shutdown. At the same time, in order to protect everyone's privacy and working environment, the Linux system defines three identities for a certain document (file, directory), namely, the owner (owner), the group (group), and others (others). Each identity corresponds to three kinds of permissions, namely, readable, writable and excutable. Through this design, the confidentiality of the data owned by each user can be guaranteed.

Document properties

Use the command ls-al-- full-time, or the abbreviated ll of this command, to view all the properties of a file or directory. As follows:

As you can see from the above, each row has seven columns, which are:

First column

A total of 10 bits, the first bit represents the document type, d represents the directory,-represents the file, l represents the linked file, d represents the random access device, such as U disk, etc., c represents the one-time reading device, such as mouse, keyboard, etc. The last 9 bits correspond to the permissions owned by the three identities, in the order of owner, group and others, and the order of permissions is readable, writable and excutable. For example, the meaning of the current document is that the current document is a file, the owner can read and execute, and the users in the same group can read and write, and others do not have any rights.

Second column

Represents the number of links

The third column

Represents the owner.

Fourth column

Indicates the group to which it belongs

Fifth column

Represents the size of the document in bytes

Sixth column

Indicates the last modification time of the document. Note that it is not the creation time of the document.

Seventh column

Represents the document name. To point (.) It starts with hiding the document.

Change owner (owner)

Position

Etc/passwd

Note: it must be an account that already exists in this location. That is, only the owner with a record in / etc/passwd can change.

Grammar

Chown [- R] [account name] [file or directory]

Chown [- R] [account name]: [group name] [file or directory]

Note: this command can also change the document group by the way, but it is recommended to use the chgrp command to change the document group.

Option

-R recursive change, that is, all files (folders) in the subdirectory will be changed.

Usage

Chown daemon test changes the folder test account number to daemon.

Chown daemon:root test changes the folder test group to root.

Chown root.users test changes folder account to root and group to users

Chown .root test changes the group to root separately

Note: although it is possible to add a decimal point (.) between the owner and the group, in order to avoid the naming of some students, it is recommended to use the colon ":" to separate the owner from the group to avoid misjudgment.

Change Group (group)

Position

Etc/group

Note: you can view all groups from here.

Grammar

Chgrp [- options] [group name] [document path]

Note: for options, you can query the detailed usage through man chgrp, info chgrp, chgrp-- help and other commands.

Usage

Chgrp-R users test changes the group of test folder and all its child files (folders) to users.

Note: if the group name is not in the location, an error invalid group will be reported.

Change of authority

There are only three basic permissions for Linux documents, namely read/write/execute, and there are only nine identity owner/group/others. There are two ways to change permissions, which are symbolic method and digital method.

Symbolic method

Three identities are represented by uther gmeno, a for all identities, r, w and x for three kinds of permissions, and +, -, and = for operation behavior respectively.

Grammar

Chmod | u g o a | + (join)-(remove) = (set) | r w x | document path

Set permissions (=)

Change the permissions of the directory test so that anyone can read, write, and execute.

Chmod uprirwx test gendarwx

Or

Chmod ugo=rwx test

Or

Chmod a=rwx test

Remove permissions (-)

Remove the directory test execution permission

Chmod UmurxMagi gripxmae o ripx test

Or

Chmod ugo-x test

Or

Chmod Amurx test

Note: execute permission (x), just to the directory is whether other users can cd test to become the working directory.

Add permissions (+)

Increase directory test execution permissions

Chmod upright, gourmet, and test.

Or

Chmod ugo+x test

Or

Chmod axix test

Note: familiar with it, if we finish writing a shell file test.sh, we add file execution permissions through chmod adepx test.sh.

Digital method

As the name implies, numbers are used to represent permissions. Rrecoery wpencil x is 4meme2pr 1 respectively. The permission of an identity can be obtained by adding up the three kinds of permissions.

Set the permissions of the directory test so that anyone can read, write and execute.

Chmod 777 test

Set the permissions of the directory test so that anyone can read and write.

Chmod 666 test

Give a shell file test.sh executable permission, the owner can read, write, execute, group accounts and others can read and execute.

Chmod 755 test

Note: have you found that the numerical method is simpler!

Differences in file and directory permissions

Document permissions vary greatly between files and directories

File

For the contents of the file

Readable can read the actual contents of the file

Writable can edit, add, or modify the contents of the file

Executable has permissions that can be executed by the system

Note: having w permission does not mean that files can be deleted. Deleting files is within the scope of directory permission control. That's because the relevant permissions and attributes of the directory are recorded to the inode of the directory, and the names of all files under the directory and the corresponding index file (inode) numbers are recorded in the block to which the directory belongs, so when we read a file, we must first read the inode of the directory, and then read the block information of the directory, and get the index information of the file to be read, that is, which block it is stored in. Finally, you can read the contents of the file (you need to understand Linux's file system, such as Ext2/Ext3/Ext4, which we will describe in more detail later)-keep in mind that file permissions are only valid for the contents of the file.

Example illustration

Use root identity to read the file test001-1 under the directory test001

View the full physical path of the directory: pwd

List the relevant directories and files: ll-di / / root/ root/test001/ root/test001/test001-1

Check-I via man ls, full name inode, that is, print the index number of each file

Inode of directory /: find the block with inode number 2 through the information of the mount point.

Block of directory /: through the block found in the previous step, the inode number of the root/ directory is 131073.

Inode of the directory root/: read the inode number 131073 to find the block of the directory.

Block of directory root/: through the block found in the previous step, find that the inode number of the root/test001/ directory is 527524.

Inode of the directory root/test001/: read the inode number 527524 to find the block of the directory.

Block of the directory root/test001/: through the block found in the previous step, find the file test001-1 directory with the inode number 527526.

Inode of file test001-1: read the inode number 527526 to find the block of the file.

Block of file test001-1: read the contents of the file through the block found in the previous step.

Because you are using the root identity, you have permission to read any document. If you use a general account, the read of each step above will also match the permissions.

Catalogue

For the file objects in this directory

Readable has permission to read the directory structure list, that is, you can query the directory list through the ls command.

Writable has the right to change the directory structure list, that is, you can create, migrate, delete, and rename files in this directory.

Executable has permission to enter this directory, that is, it can become a working directory through the cd command.

Note: as can be seen from the above, when opening the directory to anyone to browse, at least r or x permissions are required. To read the contents of a directory file, you need at least directory permissions x and file permissions r.

The above is all the contents of the article "sample Analysis of Linux document attributes, owners, groups, permissions". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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