The detailed usage of the linux-chmod_ command is explained

Linux chmod Commands

Chmod is used to change the access rights of a file or directory. Users use it to control access to files or directories. There are two ways to use this command. One is to include

The text setting method of the letter and operator expression, and the other is the digital setting method which contains the number.

1. Text Setting method

Syntax: chmod [+ |-| =] File name

The meanings of the options in the command are:

Action object who is either or a combination of the following letters:

U means "user", which is the owner of the file or directory.

G means "same group user", that is, all users who have the same group ID as the file owner.

O means "other (others) users".

A means "all users". It is the system default value.

The operation symbols can be:

+ Add a permission.

-Cancels a permission.

= gives the given permission and cancels all other permissions, if any.

Setting the permissions represented by mode can be any combination of the following letters:

R is readable.

W writable.

X executable.

x append the x attribute only if the destination file is executable to some users, or if the target file is a directory.

S is the owner of the file in which the owner or group ID of the process is placed when the file is executed.

The way "U+s" sets the user ID bit of the file, "G+s" sets the group ID bit.

T save the program's text to the swap device.

You have the same permissions as the owner of the file.

G has the same permissions as a user with the same group as the file owner.

o have the same permissions as other users.

File name: A list of files separated by spaces to change permissions, and wildcard characters are supported.

　　

Multiple permission methods can be given in one command line, separated by commas. For example:

chmod G+r,o+r example% enables the same group and other users to have read access to the file example.

2. Digital Setting method

We must first understand the meaning of the attributes represented by numbers: 0 means no permissions, 1 means executable permissions, 2 is writable, 4 is readable

permissions, and then add them. So the format of the numeric attribute should be 3 octal numbers from 0 to 7, in the Order of (U) (g) (O).

For example, if you want the owner of a file to have "read/write" Two permissions, you need to have 4 (readable) +2 (writable) =6 (read/write).

The general form of the digital setting method is:

Syntax: chmod file name

instruction Example:

chmod a+x Sort

% is the property of the set file sort:

File owner (u) Increased execution permissions

Increase execution rights with the owner of the file in the same group as the user (g)

Additional users (O) Increased execution permissions

chmod ug+w,o-x Text

% is the property of the set file text:

File owner (u) Add Write permission

Add write permissions to the same group of users as the file owner (g)

Other users (O) Remove Execute permissions

chmod u+s a.out

The% assumes that the A.out permission after performing chmod is (can be seen with the Ls–l a.out command):

–rws--x--x 1 ininusers 7192 Nov 4 14:22 a.out

And this execution file to use a text file shiyan1.c, its file access permission is "–RW-------",

That is, the file has read and write access only to its owner.

When other users execute a.out this program, his identity is temporarily changed to Inin due to this program (due to chmod

The S option is used in the command, so he is able to read the shiyan1.c file (although this file is set to

Other people do not have any permissions), this is the function of S.

Therefore, in the whole system, especially the root itself, it is best not to set this type of file too much (unless

necessary) This will ensure the security of the system and avoid the intrusion of the system due to bugs in some programs.

chmod a–x Mm.txt

Chmod–x Mm.txt

chmod ugo–x Mm.txt

% of these three commands is to delete the execution permission of the file Mm.txt, it sets the object to all the users.

$chmod 644 Mm.txt

% is the property of the set file Mm.txt:-rw-r--r--

File owner (U) inin has read and write permissions

User with file owner (g) has Read access

Other people (O) have read access

chmod wch.txt

% is set wchtxt the properties of this file are:-rwxr-x---

File owner (U) inin readable/writable/executable rights

(g) readable/enforceable rights with the main group of files

The detailed usage of the linux-chmod_ command is explained