Source

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

public function run_command( $command, $returnbool = false ) {
		if ( ! $this->link ) {
			return false;
		}

		$stream = ssh2_exec( $this->link, $command );

		if ( ! $stream ) {
			$this->errors->add(
				'command',
				sprintf(
					/* translators: %s: Command. */
					__( 'Unable to perform command: %s' ),
					$command
				)
			);
		} else {
			stream_set_blocking( $stream, true );
			stream_set_timeout( $stream, FS_TIMEOUT );
			$data = stream_get_contents( $stream );
			fclose( $stream );

			if ( $returnbool ) {
				return ( false === $data ) ? false : '' !== trim( $data );
			} else {
				return $data;
			}
		}

		return false;
	}