Bitmask representing no flags.

Affects the behaviour of interruptible functions such that, if the function would have failed with error::interrupted when interrupted by the specified signal, the function shall instead be restarted and not fail with error::interrupted.

Do not generate SIGCHLD when child processes stop or stopped child processes continue.

Do not transform child processes into zombies when they terminate.

Special value to indicate that the signal registration does not care which flags are set, and so will not conflict with any prior registrations of the same signal.