Linux File Ownership

• Every file and directory on your Unix/Linux system is assigned 3 types of owner, given below.
• User
  • Owner of the File
  • User also called an owner
• Group
  • User-group can contains multiple users
  • All users in the group have the same file permissions
• Other
  • Any other user who has access to the file
  • Does not own the file nor belong to a User-group

Changing Ownership and Group in Linux

• chown
• chgrp

# Only changing the ownership of a file/directory
sudo chown <newOwner> <fileName>  

sudo chown user filename

# Change both user and group of a file or directory
sudo chown <newOwner:newGroup> <fileName>  
sudo chown user:group filename

# Only change group
chgrp group_name filename

Additional info

• Check all groups in system

vim /etc/group

• Groups you are member of

groups
# hitman adm cdrom sudo dip plugdev lpadmin sambashare docker

• Change your default group

newgrp cdrom

Linux File Permissions

• Read
  • Give you the authority to open and read a file
• Write
  • Gives you the authority to modify the contents of a file
• Execute
  • In Unix/Linux, you cannot run a program unless the execute permission is set.

The characters are pretty easy to remember.

r = read permission
w = write permission
x = execute permission
– = no permission

Changing file/directory permissions in Linux Using ‘chmod’ command

# Syntax
chmod permissions filename

• Absolute(Numeric) Mode in Linux
  • In the Absolute mode, you change permissions for all 3 owners

# Give rwx permissions to all
chmod 777 /MyStuff

# user--> 7(rwx), group-->5(r-x), other-->4(r--)
chmod 754 /MyStuff

• Symbolic Mode in Linux
  • In the symbolic mode, you can modify permissions of a specific owner

# ugo -->  user, group, other
# +-= --> adding, removing, changing
chmod ugo+-=rwx /MyStuff

# Give read permissions to other
chmod o+r /MyStuff

# Remove, write and execute permissions for group and other
chmod go-wx /MyStuff