🐧 Linux 命令

Chmod

Chmod Cheat Sheet - 快速参考指南，收录常用语法、命令与实践。

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#chmod#permissions

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Getting Started

Syntax

SHELL

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$ chmod [options] <permissions> <file>

Example

SHELL

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$ chmod 755 foo.txt
$ chmod +x cheatsheets.py
$ chmod u-x cheatsheets.py
$ chmod u=rwx,g=rx,o= cheatsheets.sh

Change files and directories recursively

SHELL

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$ chmod -R 755 my_directory

The chmod command stands for "change mode"

Chmod Generator

Chmod Generator allows you to quickly and visually generate permissions in numerical and symbolic.

Common Permissions

Command	s	Meaning
`400`	r--------	Readable by owner only
`500`	r-x------	Avoid Changing
`600`	rw-------	Changeable by user
`644`	rw-r--r--	Read and change by user
`660`	rw-rw----	Changeable by user and group
`700`	rwx------	Only user has full access
`755`	rwxr-xr-x	Only changeable by user
`775`	rwxrwxr-x	Sharing mode for a group
`777`	rwxrwxrwx	Everybody can do everything

Explains

SHELL

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$ ls -l
-rw-r--r--  1 root root 3 Jun 29 15:35 a.log
drwxr-xr-x  2 root root 2 Jun 30 18:06 dir

Permission analysis of "dir"

TEXT

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d  rwx  r-x  r-x
┬  ─┬─  ─┬─  ─┬─
│   │    │    │
│   │    │    └─ 4. Other｜5 (4+0+1)
│   │    └────── 3. Group｜5 (4+0+1)
│   └─────────── 2. User ｜7 (4+2+1)
└─────────────── 1. File Type | directory

Permission Modes

Permission	Description	Octal	Decimal
`---`	No Permission	000	0 (0+0+0)
`--x`	Execute	001	1 (0+0+1)
`-w-`	Write	010	2 (0+2+0)
`-wx`	Execute and Write	011	3 (0+2+1)
`r--`	Read	100	4 (4+0+0)
`r-x`	Read and Execute	101	5 (4+0+1)
`rw-`	Read and Write	110	6 (4+2+0)
`rwx`	Read, Write and Execute	111	7 (4+2+1)

{.show-header}

Objects

Who (abbr.)	Meaning
`u`	`U`ser
`g`	`G`roup
`o`	`O`thers
`a`	`A`ll, same as ugo

{.show-header}

Permissions

Abbreviation	Permission	Value
`r`	`R`ead	4
`w`	`W`rite	2
`x`	E`x`ecute	1
`-`	No permission	0

{.show-header}

File Types

Abbreviation	File Type
`d`	`D`irectory
`-`	Regular file
`l`	Symbolic `L`ink

{.show-header}

Chmod Examples

Operators

Symbol	Description
`+`	Add
`-`	Remove
`=`	Set

chmod 600

SHELL

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$ chmod 600 example.txt
$ chmod u=rw,g=,o= example.txt
$ chmod a+rwx,u-x,g-rwx,o-rwx example.txt

chmod 664

SHELL

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$ chmod 664 example.txt
$ chmod u=rw,g=rw,o=r example.txt
$ chmod a+rwx,u-x,g-x,o-wx example.txt

chmod 777

SHELL

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$ chmod 777 example.txt
$ chmod u=rwx,g=rwx,o=rwx example.txt
$ chmod a=rwx example.txt

Symbolic mode

Deny execute permission to everyone.

SHELL

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$ chmod a-x chmodExampleFile.txt

Allow read permission to everyone.

SHELL

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$ chmod a+r chmodExampleFile.txt

Make a file readable and writable by the group and others.

SHELL

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$ chmod go+rw chmodExampleFile.txt

Make a shell script executable by the user/owner.

SHELL

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$ chmod u+x chmodExampleScript.sh

Allow everyone to read, write, and execute the file and turn on the set group-ID.

SHELL

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$ chmod =rwx,g+s chmodExampleScript.sh

Removing Permissions

In order to remove read write permissions given to a file, use the following syntax:

SHELL

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$ chmod o-rw example.txt

For our file example.txt, we can remove read write permissions using chmod for group by running the following command:

SHELL

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$ chmod  g-rx example.txt

To remove chmod read write permissions from the group while adding read write permission to public/others, we can use the following command:

SHELL

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$ chmod g-rx, o+rx example.txt

But, if you wish to remove all permissions for group and others, you can do so using the go= instead:

SHELL

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$ chmod go= example.txt

Executable

SHELL

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$ chmod +x ~/example.py
$ chmod u+x ~/example.py
$ chmod a+x ~/example.py

chmod 754

SHELL

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$ chmod 754 foo.sh
$ chmod u=rwx,g=rx,o=r foo.sh

Chmod Practices

SSH Permissions

SHELL

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$ chmod 700 ~/.ssh
$ chmod 600 ~/.ssh/authorized_keys
$ chmod 600 ~/.ssh/id_rsa
$ chmod 600 ~/.ssh/id_rsa.pub
$ chmod 400 /path/to/access_key.pem

Web Permissions

SHELL

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$ chmod -R 644 /var/www/html/
$ chmod 644 .htaccess
$ chmod 644 robots.txt
$ chmod 755 /var/www/uploads/
$ find /var/www/html -type d -exec chmod 755 {} \;

Batch Change

SHELL

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$ chmod -R 644 /your_path
$ find /path -type d -exec chmod 755 {} \;
$ find /path -type f -exec chmod 644 {} \;

See: Command Substitution

Also see

Modify File Permissions with chmod (linode.com)

Chmod

Getting Started

Example

Change files and directories recursively

Permission analysis of "dir"

Chmod Examples

Chmod Practices

Also see

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