set interfaces tunnel tun0 encapsulation 'gre'
set interfaces tunnel tun0 source-interface 'eth0'

set interfaces tunnel tun1 encapsulation 'gre'
set interfaces tunnel tun1 source-interface 'eth0'

vyos@r11-roll# commit
[ interfaces tunnel tun1 ]
VyOS had an issue completing a command.

Report time:      2022-01-09 16:01:03
Image version:    VyOS 1.4-rolling-202201080317
Release train:    sagitta

Built by:         [email protected]
Built on:         Sat 08 Jan 2022 03:17 UTC
Build UUID:       9c97b583-79c7-4fdf-b58f-3405d7207ee5
Build commit ID:  301d432afab62f

Architecture:     x86_64
Boot via:         installed image
System type:      KVM guest

Hardware vendor:  QEMU
Hardware model:   Standard PC (Q35 + ICH9, 2009)
Hardware S/N:     
Hardware UUID:    8e21d64e-e498-475c-9866-290cd53a3b86

Traceback (most recent call last):
  File "/usr/libexec/vyos/conf_mode/interfaces-tunnel.py", line 190, in <module>
    apply(c)
  File "/usr/libexec/vyos/conf_mode/interfaces-tunnel.py", line 180, in apply
    tun = TunnelIf(**tunnel)
  File "/usr/lib/python3/dist-packages/vyos/ifconfig/tunnel.py", line 109, in __init__
    super().__init__(ifname, **kargs)
  File "/usr/lib/python3/dist-packages/vyos/ifconfig/interface.py", line 321, in __init__
    self._create()
  File "/usr/lib/python3/dist-packages/vyos/ifconfig/tunnel.py", line 134, in _create
    self._cmd(cmd.format(**self.config))
  File "/usr/lib/python3/dist-packages/vyos/ifconfig/control.py", line 52, in _cmd
    return cmd(command, self.debug)
  File "/usr/lib/python3/dist-packages/vyos/util.py", line 161, in cmd
    raise OSError(code, feedback)
PermissionError: [Errno 1] failed to run command: ip tunnel add tun1 mode gre dev eth0 tos inherit ttl 64
returned: 
exit code: 1

noteworthy:
cmd 'ip tunnel add tun1 mode gre dev eth0 tos inherit ttl 64'
returned (out):

returned (err):
add tunnel "gre0" failed: File exists

[[interfaces tunnel tun1]] failed
Commit failed