Understanding file, folder permission on linux

22 Jun 2014

Today post about File/Folder permission on linux. This may be helpful for newbies who likely to be work on linux distributions. I have been using linux over years now, so for me it is better than the other platforms.

Permission basics

Permission groups

On each file and directory(folder) has three user based permission groups.

Owner - The owner of the directory
Group - Group that has been assigned for this file/directory
User - All the other users in the system

Permission types

On every file and directory has three types of permission

Read - Capability of read the contents of the file
Write - Capability of write/modify the contents of the file or directory
Execute - Capability of execute a file or view the contents of a directory

Check permission

To see the permission settings for a file, we can use the ls command as follows:

gayan:gayanvirajith.github.io$ ls -l
-rw-rw-r--  1 gayan gayan 2601 Jun 22 10:09 Rakefile
...

We can determine a lot from examining the results of this command:

The file “Rakefile” owned by the user “gayan”
User “gayan” has authorize to read and write this file
The file is owned by the group “gayan”
Members of the group “gayan” can also read and write this file
Everybody else(other users) can read this file

Changing file permission

To change the file/folder permission, we can use chmod command.

An easy way to remember permission settings as a series of bits (0’s and 1’s). Here how it works:

rwx rwx rwx # 111 111 111
rw- rw- rw- # 110 110 110
rwx --- --- # 111 000 000

How it looks in binary:

rwx = 111 in binary = 7
rw- = 110 in binary = 6
r-x = 101 in binary = 5
r-- = 100 in binary = 4

Now you’ve got the idea!(I believe). So if you combine each of three sets of permissions as single digit, you would get permission setting value in a convenient way.

For an example let say if you want to set some-file.txt to have read and write permission for owner , but wanted to keep the file private from others. You could do this as follows:

gayan:gayanvirajith.github.io$ chmod 600 some-file.txt

Advanced usage

Change file/folder permission in a recursive way

Change all folder / sub folders / files to 755

gayan:gayanvirajith.github.io$ ls -l
total xx
drwxrwxr-x  3 gayan gayan 4096 Jun 21 02:52 assets
gayan:gayanvirajith.github.io$ chmod 755 -R assets

Change all folders and sub directories to 755

gayan:gayanvirajith.github.io$ ls -l
total xx
drwxrwxr-x  3 gayan gayan 4096 Jun 21 02:52 assets
gayan:gayanvirajith.github.io$ find ./assets -type d -exec chmod 755 {} \;

Change all files to 755

gayan:gayanvirajith.github.io$ ls -l
total xx
drwxrwxr-x  3 gayan gayan 4096 Jun 21 02:52 assets
gayan:gayanvirajith.github.io$ find ./assets -type f -exec chmod 644 {} \;

Hope this article would helpful to you, So wish you the best in your future with Linux-based systems.

Gayan Virajith