Let's say I have the below yaml:

spec:
  securityContext:
    fsGroup: 5678
  serviceAccountName: some-account
  volumes:
    - name: secrets
      secret:
        secretName: data-secrets
    - name: secrets-sftp-passwd-key
      secret:
        secretName: sftp-passwd-key
  containers:
    - name: sftp
      securityContext:
        runAsUser: 1234
        runAsGroup: 5678
      image: "some/some"
      imagePullPolicy: always
      ports:
        - name: tcp-sftp
          containerPort: 22
      volumeMounts:
      - name: secrets-sftp-passwd-key
        mountPath: /etc/sftp/secret/
      - name: data
        mountPath: "/var/data"
      env:
        - name: "SFTP_USER"
          value: "some_user"
        - name: "SFTP_PASSWD"
          value: "password-1"
        

I'm trying to run the container sftp with runAsUser and runAsGroup. The image's entrypoint script is supposed to take the SFTP_USER, SFTP_PASSWD and create certain password and group files using this input. These files are supposed to be created in /var/data folder. After this, a proftpd process is supposed to be started using these password and group files as the 1234 user. The container starts as 1234 user. But the files have a permission of root:5678. And I get the below error:

unable to set UID to 0, current UID: 1234

The entry point script of the image is as below:

echo "Starting to create password file"
PASSWORD=123456
echo $PASSWORD | /usr/bin/ftpasswd --passwd --file=/var/data/ftpd.passwd --name=virtual --uid=1234 --gid=5678 --home=/var/data/ --shell=/bin/bash --stdin
echo "Password file created"
/usr/bin/ftpasswd --group --name=--group --name=virtual --file=/var/data/ftpd.group --gid=5678 --member=1234
proftpd -n  -4 -c /var/data/proftpd.conf --> This line is throwing the above error. 

What is going wrong here? Why is it trying to set UID to 0?? I was under the impression that giving runAsUser, runAsGroup and fsGroup will make sure that the /var/data folder has the correct ownership of 1234.