Hi @Pirated,
Seems you are having a permissions issue on the .git folders. Maybe you initially did the install as root or sudo?
You chould try changing permissions of the git folders. Try the following as root:
#!/bin/bash
chown -R frappe:frappe /home/frappe/.bench
chown -R frappe:frappe /home/frappe/frappe-bench/apps/frappe
chown -R frappe:frappe /home/frappe/frappe-bench/apps/erpnext
cd /home/frappe/frappe-bench
bench update