Meaning of Linux directory permissions


Linux files and directories have permission information such as "who is allowed to perform what kind of operation", and this is called permission.

I knew that the file had permissions, but I didn't know that it was also set in the directory, so I'll put it together.

File permissions

First, use ls -l / bin / cat to display the information of the cat command.

$ ls -l /bin/cat
-rwxr-xr-x 1 root root 35064 Jan 18  2018 /bin/cat

File type

The - at the beginning of the line indicates the file type.

symbol meaning
- Normal file
d directory
l Symbolic link

File mode

The last nine characters of the file type (rwxr-xr-x) are called file modes, which indicate file permissions.

The 9 characters are one block for every 3 characters, and are divided into" owner "," group ", and" other groups ", respectively.

Owner group その他のgroup
rwx r-x r-x

Meaning of "rwx"

rwx means "read", "write", and "execute", respectively.

symbol meaning
r reading(read)
w writing(write)
x Run(excute)

/ bin / cat reconfirm

$ ls -l /bin/cat
-rwxr-xr-x 1 root root 35064 Jan 18  2018 /bin/cat

The above / bin / cat, but writing by anyone other than the root user is prohibited. When I tried to write, I was angry that I shouldn't overwrite the 'readonly' option is set (add! To override).

Directory permissions

Check the permissions of the main directory.

To check directory permissions with the ls command, you need to use the -d option, which displays information about the directory itself, in addition to the -l option.

$ ls -ld Code/
drwxrwxr-x 4 vagrant vagrant 4096 Apr  8 14:54 Code/

Meaning of directory permissions

Directory permissions use the symbols "r", "w", and "x" as well as files, but ** the meaning of each symbol may differ from that of files (especially "x"). ~~ It has a completely different meaning. ~~ **

symbol meaning
r reading(Get a list of files contained in a directory)
w writing(Create and delete files and directories under directories)
x Run(Make the directory the current directory)

Confirmation of "r" reading (getting a list of files contained in the directory)

Here, create a file once and test it.

$ mkdir permissionTest            //Create a directory called permissionTest
$ touch permissionTest/file1.txt  //file1 under permissionTest.Create a file called txt
$ ls -ld permissionTest/          //Check the permissionTest directory

drwxrwxr-x 2 vagrant vagrant 4096 Apr 23 11:50 permissionTest/

$ ls -l permissionTest/        //Check the files under permissionTest

-rw-rw-r--  1 vagrant vagrant    0 Apr 23 11:50 file1.txt     //success

Make the permissions of the permissionTest directory unreadable and try to access it.

$ chmod a-r permissionTest/  //Read-protected for all users
$ ls -ld permissionTest/     

d-wx-wx--x 2 vagrant vagrant 4096 Apr 23 11:50 permissionTest/    //Read-protected.

$ ls  permissionTest/
ls: cannot open directory 'permissionTest/': Permission denied

** Cannot access without permission. ** **

Confirmation of "w" write (create / delete files / directories under the directory)

If write (w) is set in the directory, it can be created / deleted even if the files under it have write restrictions.

** This means that whether a file can be deleted depends on the permissions of the directory, not the permissions of the file. ** **

Restrict the writing of the file and check if the file can be deleted.

$ chmod a-w file1.txt  //Remove write permission for files
$ ll file.txt          //Check file permissions

-r--r--r--  1 vagrant vagrant    0 Apr 23 11:50 file1.txt  //Confirmation of write permission deletion

$ rm  file1.txt  //File deletion
rm: remove write-protected regular empty file 'file1.txt'?yes Do you want to delete it?

Of course you can delete it.

Confirmation of "x" execution (make the directory the current directory)

Make sure that you cannot access directories that are not set to run "x".

$ chmod a-x permissionTest/  //Restrict execute permission of permissionTest
$ ls -ld permissionTest/     //Check the permissions of permissionTest

drw-rw-r-- 2 vagrant vagrant 4096 Apr 23 11:50 permissionTest/ //Verification

v$ cd permissionTest/                           //permissionTest/Access
-bash: cd: permissionTest/: Permission denied   //Can not.


symbol For files For directories
r Read file Get a list of files contained in a directory
w Write to file Create and delete files and directories under directories
x File execution Make the directory the current directory


New Linux textbook

Recommended Posts

Meaning of Linux directory permissions
Meaning of Linux permissions
Linux file and directory permissions
Linux permissions
Linux directory structure
Linux [directory command]
Linux directory structure
Linux directory hierarchy
Linux (about directory path)
Linux permissions in Java
Linux permissions [under investigation]
The meaning of self
[Linux] Installation of nvm
Addition of amazon linux swap
Incremental backup of Linux (restore)
[Linux] Directory under the root
Japanese translation of Linux manual
A brief summary of Linux
[Linux] [Initial Settings] Table of Contents
Basic knowledge of Linux and basic commands
Confirm commit of Linux 5.7 Thermal Pressure ⁠
Installation of OMC Cloud Agent --Linux-
[Must-see for beginners] Basics of Linux
[Linux] File and directory operation commands
List of frequently used Linux commands
The meaning of ".object" in Django
Efficient use of Linux file system
Replacement of strings containing Linux spaces
[python] -1 meaning of numpy's reshape method
View the full path (absolute path) of a file in a directory in Linux Bash