Update to NC13 stop at Step 4

vm+centos7+NC12
When I try to update to 13
[Step 4 is currently in process. Please reload this page later.]
It’s been 24 hours, and the machine has been restarted.
The LOGFILE is:

…request to updater
2018-02-23T23:46:29+0800 D0fBJFFYzR [info] currentStep()
2018-02-23T23:46:29+0800 D0fBJFFYzR [info] Step 3 is in state “end”.
2018-02-23T23:46:29+0800 D0fBJFFYzR [info] POST request for step "4"
2018-02-23T23:46:29+0800 D0fBJFFYzR [info] startStep(“4”)
2018-02-23T23:46:29+0800 D0fBJFFYzR [info] createBackup()
2018-02-23T23:57:23+0800 WYutCLWDus [info] request to updater
2018-02-23T23:57:23+0800 WYutCLWDus [info] currentStep()
2018-02-23T23:57:23+0800 WYutCLWDus [info] Step 4 is in state “start”.
2018-02-24T00:07:43+0800 kTAEYTHran [info] request to updater
2018-02-24T00:07:43+0800 kTAEYTHran [info] currentStep()

What should I do

Thanks