File Permissions

There are 3 permission groups: Owner, Group, Other

• each permission group has 3 permissions, called a permission set
  • ex. rw- is a single set
• each file/directory has 3 permission sets— one for each permission group.
• rwx mean different things if we are referring to a directory or a file
  • r
    • on file means we can read the contents
    • on directory means we can run ls
  • w
    • on file means we can modify file contents
    • on directory means we can add/delte files
  • x
    • on a file means we can run it
    • on a directory means we can cd into it

File ownership

• every file is owned by a specific user (UID) and a specific group (GID)
  • chown is used to change both
    • ex. chown <user>:<group> test.txt
• each member can belong to many groups (/etc/group), though a user can only have one primary group (/etc/passwd).
  • run $ id to see the groups the current user belongs to
  • When a user creates a file, the file will be owned by the primary group
• similar to how we need to source the .zshrc before changes are live, we need to log out and log back in before group membership is "activated"

Settings Permissions

The numerical method is quite easy. For example, we can just replace each rwx set by it's binary positional value (from RTL: 1, 2, 4, 8, 16, 32...) and add the the numbers in each set.

-(rw-)(rw-)(r--)
-(42-)(42-)(4--)
664

• By this, we can define a 7 as rwx, a 5 as r-x, and so on

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Set new files/directories in a subdirectory to follow the group ownership of the specified directory

• chmod g+s /var/www/my-project

Unix permissions guide