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I had hibernated my laptop using

sudo pm-hibernate

and then woke it up some hours later to quickly check a document. I re-entered the above command and it worked without requiring a password. I assume this means that the sudo timeout is working from a relative time that is only ticking when the computer is awake, rather than an absolute system time.

I would prefer not to have sudo work without a password when I haven't entered it, in real terms, in the very recent future. Is there a way to enforce the timeout to not carry over like this while the system is in hibernation?

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Run the command using the -k option:

sudo -k pm-hibernate

Short version: -k means sudo will prompt for the password again next time.

From man sudo:

-k [command]

When used alone, the -k (kill) option to sudo invalidates the user's cached credentials. The next time sudo is run a password will be required. This option does not require a password and was added to allow a user to revoke sudo permissions from a .logout file. Not all security policies support credential caching.

When used in conjunction with a command or an option that may require a password, the -k option will cause sudo to ignore the user's cached credentials. As a result, sudo will prompt for a password (if one is required by the security policy) and will not update the user's cached credentials.
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