Thank you for your response. I have few questions.
1) the command which you gave works only for the files in htdocs and the permissions of files present in sub folder of htdocs like wp-content folder remains restricted. How to change their permissions, that is of the files and sub-folders (sub files) inside htdocs.
2) how to install bitnami directly through cloud sell. To use always free google tier, we have to select specific regions, we don't get these options at the time of bitnami deployment. so, we configure VM first and then we have to deploy wordpress through cloud. So what commands shall we run on cloud shell to deploy bitnami.
3) there are several operating systems like debian, centos, ubunto etc. bitnami uses debian. I read in a blog that debain offers lower ram as compared to other operating system. is there a specific disadvantage or advantage of using debian? how to change bitnami operating system on google cloud.
4) Do you have a documentation of how to use a swap file on google cloud? Please give the reference link.