postgresql-backup | Docker image | Cloud Storage library

I installed gsutil in a Dockerfile as follows:

trying to using pg_dump to backup a postgres db

i connected through the command prompt and here is my command following this tutorial http://www.postgresqltutorial.com/postgresql-backup-database/

I was setting up scheduled backup of my postgresql database on my server using wal-e. I was following this link. (Just have a look at the article from Step 3)
When I execute the below command after initial setup .
sudo -u postgres /usr/bin/envdir /etc/wal-e.d/env /usr/local/bin/wal-e backup-push /var/lib/postgresql/9.5/main.

I get following error:-

I need to copy some files from Linux machine to the s3 bucket. I need to copy only selected files. I am able to get files using below bash command.

I have a PostgreSQL 9.5 instance running off an Azure VM. As described here, I must specify a post- and a prescript to tell Azure: "Yes, I've taken care of putting the VM in a state, so the entire VM/blob can be backed up as a snapshot that can be restored as a working new VM" and "Now I'm done", thus Azure will flag the backup as Application consistent.

In terms of PostgreSQL, I have read the docs on continuous archiving, that instruct why and how to enable WAL Archiving to allow for backups. And here comes my question:

If I set archive_mode = on and wal_level = archive, can I leave the archive_command empty, and does this even make sense? Or - should I do some kind of archiving here (like e.g. copying the log segments to another location / disk), and is this archiving necessary to ensure a working database upon restoring the VM in my scenario?

I only need to tell the PostgreSQL "Wait a minute / hold your data-writes (or whatever goes on), while I create a snapshot of the entire VM". The plan is to execute pg_start_backup() before , take the snapshot and then pg_stop_backup().

I do realize, this method (if it's even valid) is essentially a file system level backup, and according to docs, the postgres-service must be shut down for the fs-backup to be valid. Another place I've read that hitting the pg_start_backup() should be enough to guarantee for a valid stand-alone physical backup.