File Permissions and Ownership in Linux

🔐 File Permissions and Ownership in Linux

---

1. 📄 Default File Permissions & umask

• Default permissions:

  • Files: 666 (read & write for all)
  • Directories: 777 (read, write, execute for all)

• Actual permissions = Default - umask

  • View current umask:

    umask
    

  • Example: If umask is 022, new file permission becomes 644 (666 - 022) and directory permission becomes 755 (777 - 022)

---

2. 📜 Reading ls -l Output

ls -l file.txt

Example output:

-rw-r--r-- 1 user group 1234 Jun 5 10:00 file.txt

Part	Meaning
-	File type (- = file, d = directory, l = symlink)
rw-r--r--	Permissions: owner (rw-), group (r–), others (r–)
user	File owner
group	Group owner
1234	File size
Jun 5 10:00	Last modified date
file.txt	File name

---

3. 🧮 Managing Permissions

a. Numeric (Octal) Permissions

Digit	Meaning
7	rwx
6	rw-
5	r-x
4	r--
0	---

chmod 755 myscript.sh  # rwxr-xr-x

b. Symbolic (Text) Permissions

chmod u+x file.txt     # Add execute for user
chmod g-w file.txt     # Remove write for group
chmod o=r file.txt     # Set read-only for others

c. Group Ownership and Permissions

• Change owner:

  chown username file.txt
  

• Change group:

  chgrp groupname file.txt
  

• Set group and owner:

  chown user:group file.txt
  

---

4. ⚙️ Customizing File Creation Mask (umask)

• View current umask:

  umask
  

• Temporarily set umask:

  umask 027
  

• Permanently set:

  • Add to ~/.bashrc or /etc/profile:

    umask 027
    

---