What do you mean by “i have already installed stlink drivers as they are automatically installed when we make new project”. On Linux, the ST-Link is supported by libusb but you need udev rules.
Check if you have the following files in /etc/udev/rules.d :
These files are created automatically if you have installed System Workbench with the Installer (Installing System Workbench for STM32 with installer)
You can also install them manually, please find the link on this page (Installing System Workbench for STM32 from Eclipse, in the section STLink Driver > on Linux)
Hope it helps,