Day 4 #90DaysOfDevOps

Understanding Linux file permissions and ownership is a crucial aspect of working with Linux systems. In this session, we will delve into the world of Linux permissions and ownership, and engage in practical tasks related to both. Let's begin by exploring the realm of Permissions.

For more versatile and fine-grained control over file and directory permissions, Access Control Lists (ACLs) offer a modern approach. They provide an alternative to the traditional Unix file permissions, making them particularly useful in scenarios where precise control is required. To manage ACLs, you can utilize the "setfacl" command, and to view and display the Access Control List (ACL) of a file or directory, the "getfacl" command comes into play.

👉Linux file permissions 📄

The file can have three types of permissions

1. read (r) 📖

2. write (w) ✍️

3. execute (x) 🏃‍♂️

Whenever you run ls -l you see the permissions for each file at the start of the line

This string has 🔟 characters and is available for each file, divided into 4️⃣ parts

• The first character represents what kind of file it is, d for directory files and - for normal files

• The next three parts are permission for each kind of role, user, group, and other

• 1 is the number of links of the file or in simple words showing there is one file linking to test.txt.

• The file belongs to user ubuntu and group ubuntu.

• 0 is the file size as there are no contents in the file.

• Next is the date and time the file was created.

• The last one is the file name, test.txt.

Each file and directory has three user-based permission groups

• Owner- This is the owner of the file or the directory.

• Group - These group permissions apply only to the group that has been assigned to the file or directory.

• Other - These permissions apply to all other users on the system.

There are two methods to change permissions of user, group or other

1. Symbolic mode +-=

   + represents add

   - represents remove

   + and - are useful to remove or add any permission for any role without affecting other permissions

   = is used to set the permissions

   = is useful if you want to override existing permissions for a specific role

   u for user

   g for group

   o for other

   a for all

   chmod u+x file --> Add execute permission for user

   See the image below there was no execute permission for the user earlier on the test.txt file, but after executing the above command user got execute permission

   

   chmod g-w file1 file2 --> Remove write permission for group two files

   Multiple files can be provided in the command

   

   chmod u+r,g+x file --> Add read for a user and add execute for group

   Multiple roles with multiple permissions can be given at the same time

   

   chmod a=rwx file --> Give all permissions to all role

   

2. Numeric mode (0️⃣to7️⃣)

   The digits from 0 to 7 represent different combinations of permissions

   This will override the existing permissions for other roles as well

   Binary reference uses numbers.

   Each permission type has a number:

   • read (r) = 4

   • write (w) = 2

   • execute (x) = 1

Just remember this permission chart

chmod 205 file --> 2 (write) for user, 0 (no) for group, 5 (read & execute) for other

chmod 350 file --> 3 (write & execute) for user, 5 (read & execute) for group, 0 (no) for other

👉 File Ownership 👤👥

• To change permissions chown command is used

• If you are a user or group owner of a file then no need to use sudo before chown

There are two types of owners for each file

1. User Owner

2. Group Owner

Whenever you run ls -l you can see the owner for each file in the 3rd and 4th columns i.e user owner & group owner

Change user owner 👤

chown <username/UID> file --> Change user owner using username or UID

chown <username/UID> file1 file2 --> Change user owner for multiple files

Change group owner 👥

sudo chown :<groupname/GID> file --> Change group owner using group name or GID

Multiple files can be given in the command

Change both owners 👤👥

sudo chown <username/UID>:<groupname/GID> file --> Change both owners

Multiple files can be provided in the command

Any combination of ID and name works

Properly configured file permissions and ownership are essential for maintaining the confidentiality, integrity, and availability of your data.

Happy Learning !!! 👋