What command is used in Linux to change file or directory permissions?

The command used in Linux to change file or directory permissions is "chmod." This command allows users to modify the permission settings of files and directories, defining who can read, write, or execute a file or directory.

In Linux, file permissions are an essential aspect of maintaining security and proper access control. The "chmod" command can take symbolic or numeric arguments to specify the permissions that should be granted or revoked. For example, using "chmod 755 file.txt" would set the owner to have read, write, and execute permissions, while others would have read and execute permissions only.

The other options serve different purposes: "chown" is used for changing the ownership of a file or directory, "ls" lists the contents of a directory, and "mkdir" is used to create a new directory. These commands are vital for file management in a Linux environment, but they do not deal specifically with changing permissions like "chmod" does.