chmod is a UNIX®/Linux® command that lets the owner/administrator of a file to specify how much/little access should be permitted to it. File permissions in UNIX®/Linux® file system are managed in three distinct user classes: user/owner, group and others. Each class can have read, write and execute permissions. File permission can be represented in a symbolic or numeric (octal) format.

Mapping of file permissions to symbol and numeric format is summarized in the table below: