According to the manual page of
sigpending() returns the set of signals that are pending for delivery
to the calling thread (i.e., the signals which have been raised while
So, it is meant the signals (sigterm, sigkill, sigstop, ...) that are waiting until the process comes out of the
D (uninterruptible sleep) state. Usually a process is in that state when it is waiting for I/O. That sleep can't be interrupted. Even sigkill (
kill -9) can't and the kernel waits until the process wakes up (the signal is pending for delivery so long).
For the other unclear values, I would take a look in the manual page of
sigpending 31603. Why are these limits such weird numbers (i.e. not a power of 2)?