Cannot SSH due to full disk

[csi_infra]

My ssh connection suddenly failed and I found something like this in the log: 

Jul 5 04:05:12 my-machine google_guest_agent[1157]: Creating user max
Jul 5 04:05:12 my-machine google_guest_agent[1157]: ERROR non_windows_accounts.go:134 Error creating user: useradd: /etc/passwd.2988: No space left on device
Jul 5 04:05:12 csi-nginx google_guest_agent[1157]: useradd: cannot lock /etc/passwd; try again later..

I did enhance the size of boot disk but it didn't work. How can I clear up some space if I can't get in to the shell at all.