Repairing disk permissions is a troubleshooting activity commonly associated with the macOS operating system by Apple.
[1] The BSD layer in macOS is responsible for file-system security, including the management of the Unix (POSIX) permissions model.
[3] Files whose permissions have been incorrectly altered by an administrator, an administrator operating with root privileges, or a poorly designed installer package (installed with similar privileges) can cause a wide array of problems ranging from application errors to the inability to boot macOS.
[1] In OS X El Capitan, Apple introduced a security feature called System Integrity Protection.
Permissions can also be repaired using third-party utilities such as The Apotek's AppleJack or Prosoft Engineering's Drive Genius.