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Default Permissions (umask)

What is umask?

  • Determines default permissions for newly created files and directories.
  • Default permissions = max permissions - umask.
  • Maximum default permissions:
Type Max Permissions
File rw-rw-rw- (666)
Directory rwxrwxrwx (777)

Check Current umask

alt text Breakdown of 0027:

  • First 0: octal number

  • Second 0: subtract from user

  • Third 2: subtract from group

  • Fourth 7: subtract from others

Example: File Permissions

  • Assume umask = 027
  • Default file permissions = 666
  • Resulting permissions = 666 - 027 = 640 → rw-r-----

alt text

Example: Directory Permissions

  • Assume umask = 027
  • Default directory permissions = 777
  • Resulting permissions = 777 - 027 = 750 → rwxr-x---

alt text

Important Notes

  • Umask applies only to new files/directories in the current session.
  • To make it permanent, modify the user's .bashrc in their home directory.