Permissions for Files and Directories

• UNIX checks permission settings before allowing access to files

• Permissions are based on three groups
  user - the user who owns the file
  group - a collection of users with common needs
  other - users other than the owner and the group

• There are three basic permissions
  read, write and execute

• Execute permission on a binary file allows a user to load the file into the computer memory and perform the machine instructions in it.

• Execute permission on a text file allows a user to execute the shell commands in the file.

• Execute permission in a directory allows use of the directory in a pathname.

• Read permission on a directory allows viewing the contents of the directory, but you can't get to the files below.

• Usually read and execute are granted together for directories.

• chmod is used to change permissions