Source: How to fix OS X installation 'can't be verified' error
Image: Apple
Apple’s OS X has nifty built-in security features that users often gloss over. Some of these enhancements include a hash check command to determine if a download has been compromised, or System Integrity Protection to help thwart malicious software from modifying system files.
SEE: OS X El Capitan: The smart person’s guide
Another simple feature that occurs automatically is a verification that is run on all software prior to installation to verify that the software to be installed does not contain any corrupt files or volume headers. While generally a useful feature, it does come with a few performance caveats.
For instance, it adds time and degrades overall performance slightly, as the OS must first verify the files before proceeding with the install. When OS X is being upgraded or clean installed, the feature sometimes times out or reports false positives concerning data corruption that are actually caused by nothing more than the wrong time setting.
To address this from OS X, the simplest solution is to adjust the time manually by going to System Preferences | Date & Time and unchecking the checkbox Set Date And Time Automatically (Figure A). This will allow you to manually enter the time and date, as well as modify the time zone setting.
Figure A
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If you’re performing a clean install of OS X, that is slightly more difficult, but it can still be easily done from the Terminal. To access it, go to Utilities | Terminal from the OS X Installer Menu Bar. Once launched, enter the following command into Terminal and press the Enter key to execute it.
date [[[mm]dd]HH]MM[[cc]yy]
Command: date
Arguments:
cc = century (or the first two digits of the year)
yy = year (or the last two digits of the year)
mm = month (two-digit month)
dd = day (two-digit day)
hh = hour (two-digit hour based on military time)
mm = minute (two-digit minute)
Example: August 02, 2016 at 6:47 PM
date 080218472016
Figure B
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Another method to adjust the time/date is by using the following command on a computer with internet access, as it requires connecting to the time server and synchronizing the time clock (Figure C).
ntpdate -u timeserver.domain.com
Command: ntpdate
Arguments: -u = Uses an unprivileged port when client machine is behind a firewall.
Example: ntpdate -u time.apple.com
Figure C
Image: Jesus Vigo/TechRepublic