In service tab,I see the Bootstrap.but i do not know what is the purpose of this service?
The bootstrapping service is a critical part of Rockstor start sequence but rather than trying to describe it myself, I’ll direct you towards a recent post by @phillxnet who describes what the bootstrap service does:
In particular, see the most relevant excerpt below:
Followed finally by rockstor-bootstrap which kicks off the mount stuff essentially by running: /opt/rockstor/bin/bootstrap which setups up the env to run /opt/rockstor/src/rockstor/scripts/bootstrap.py which in turn mainly does some basic btrfs prep, some rockstor network setup (which uses nmcli under the hood) and to your request finally does an API call on commands/bootstrap, hence the services name.
Hope this helps,