Error during bench update on master

I installed a new bench

revant@revant-laptop:~$ bench init frappe-bench-v4

get-app erpnext and shopping_cart, restored site-files and site-db (site on master)

revant@revant-laptop:~/frappe-bench-v4$ bench switch-to-master

faced error while switching so followed the post and switched branch

revant@revant-laptop:~/frappe-bench-v4$ bench update
Already up-to-date.
From https://github.com/frappe/shopping-cart
 * branch            master     -> FETCH_HEAD
Already up-to-date.
From https://github.com/frappe/frappe
 * branch            master     -> FETCH_HEAD
Already up-to-date.
From https://github.com/frappe/erpnext
 * branch            master     -> FETCH_HEAD
Already up-to-date.
frappe app is not installed. Run the following command to install frappe
bench get-app frappe https://github.com/frappe/frappe.git
/bin/sh: 1: /home/revant/frappe-bench-v4/env/bin/frappe: not found
Error: None
Traceback (most recent call last):
  File "/usr/local/bin/bench", line 9, in <module>
    load_entry_point('bench==0.1', 'console_scripts', 'bench')()
  File "/home/revant/bench-repo/bench/cli.py", line 55, in cli
    bench()
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 610, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 590, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 936, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 782, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 416, in invoke
    return callback(*args, **kwargs)
  File "/home/revant/bench-repo/bench/cli.py", line 246, in update
    backup_all_sites()
  File "/home/revant/bench-repo/bench/utils.py", line 321, in backup_all_sites
    backup_site(site, bench=bench)
  File "/home/revant/bench-repo/bench/utils.py", line 315, in backup_site
    cwd=os.path.join(bench, 'sites'))
  File "/home/revant/bench-repo/bench/utils.py", line 72, in exec_cmd
    subprocess.check_call(cmd, cwd=cwd, shell=True)
  File "/usr/lib/python2.7/subprocess.py", line 540, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '/home/revant/frappe-bench-v4/env/bin/frappe --backup castlecraft.in' returned non-zero exit status 127
revant@revant-laptop:~/frappe-bench-v4$