首先请重启设备后重新尝试：请注意是输入boot -s
When prompted to enter Loader mode hit the bar and you will be
sitting at the "loader>" prompt.  Enter the following command:
                   loader> boot -s   
Enter full pathname of shell or 'recovery' for root password recovery or
RETURN for /bin/sh:
然后输入recovery看能否正常恢复。

如果以上操作不成功，则需要通过TFTP重新传输JUNOS回退到之前可正常运行的版本：

1、Prepare a TFTP server and put the corresponding p_w_picpath in the TFTP root
directory

   Example: The TFTP server has an IP address of 192.168.100.1/24 and the
p_w_picpath is jinstall-ex-9.1R2.7-domestic-signed.tgz


2、Connect the EX-Series Switch management port to the TFTP server directly
or make sure they are in same broadcast domain.

3、Connect a terminal to the EX-Series Switch console port and power on the
switch (for next steps see log below for example)
   When you see the "loading /boot/defaults/loader.conf" display hit ENTER

       Hit [Enter] to boot immediately, or space bar for command prompt.
       Hit the space bar to enter the manual loader. The loader > prompt
displays.

(NOTE: There is a 1 second delay for hitting the space bar)
(TIPS: you can hit space bar after you see "Loading
/boot/defaults/loader.conf" message)



4、Set the EX Switch management IP address and netmask.

loader> set ipaddr=192.168.100.2
loader> set netmask=255.255.255.0
loader> set serverip=192.168.100.1
5、Issue install command to install JUNOS p_w_picpath by TFTP.

loader> install tftp://192.168.100.1/jinstall-ex-9.1R2.7-domestic-signed.tgz