Processes

Signals notify processes or threads of events using kernel-defined delivery rules. A signal’s disposition selects a default action, an installed handler, or ignoring it where permitted. A thread’s mask can block delivery of eligible signals while they remain pending. Separating disposition, masking, and pending state is essential when a program appears to miss repeated notifications or fails to stop as expected. ...

A process needs file descriptors for more than ordinary files. Network sockets, pipes, event interfaces, and duplicated references all compete for entries in its descriptor table. RLIMIT_NOFILE limits the descriptor numbers available to new allocations: the soft limit is one greater than the maximum permitted number. A service can therefore fail to accept work even while the machine has plenty of disk space and memory. ...