Encountered the MAC OSX 10.11.3 update error "Failed to verify os x el capitan update", retried twice and it persisted, and finally found that it was a rootless problem, if you are using extrafinder or totalfinder, boot cmd+r and then use the terminal executed
csrutil enable --without debug
will encounter this problem.
To enter recovery mode terminal, enter
csrutil clear
After restarting, the upgrade is normal, and then rootless again.