the update command:
esxcli software vib install --maintenance-mode --depot \
  /vmfs/volumes/host-data/patch/update-from-esxi5.0-5.0_update01.zip


dealing with maintenance mode from the command line:

vim-cmd /hostsvc/maintenance_mode_enter
vim-cmd /hostsvc/maintenance_mode_exit
vim-cmd /hostsvc/hostsummary | grep inMaintenanceMode