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Change mode (chmod) is a Unix operating system command used by administrators and programmers to set or change the access permissions of a file or directory. These settings determine the level of access to be granted to the given file or directory.
The chmod command was first used in ATT Unix 1 and is still in use today by Unix-like operating systems. It is also available as a C language library function in Unix.
The syntax for change mode is as follows:
chmod [OPTIONS]... MODE[,MODE]... FILENAME1 [,FILENAME2]...
chmod [OPTION]... OCTAL-MODE FILENAME1 [,FILENAME2]...
chmod [OPTION]... [REFERENCE] [OPERATOR] [MODES] FILENAME1 [,FILENAME2]..
The chmod command has the following options:
-R, --recursive: Changes the directories and files recursively
-v, --verbose: Displays a diagnostic report for every processed file
-c, --changes: Like verbose but displays only when there are actual changes
-f, --silent:Suppress error messages
--reference=RFILE: Use RFILE’s mode instead of MODE values
Permissions are granted as follows: a: All
x: Execute or run as a program