Source

File: wp-admin/includes/class-wp-filesystem-ssh2.php

public function chgrp( $file, $group, $recursive = false ) {
		if ( ! $this->exists( $file ) ) {
			return false;
		}

		if ( ! $recursive || ! $this->is_dir( $file ) ) {
			return $this->run_command( sprintf( 'chgrp %s %s', escapeshellarg( $group ), escapeshellarg( $file ) ), true );
		}

		return $this->run_command( sprintf( 'chgrp -R %s %s', escapeshellarg( $group ), escapeshellarg( $file ) ), true );
	}