sa_flags member of the
sigaction structure is a
catch-all for special features. Most of the time,
a good value to use for this field.
The value of
sa_flags is interpreted as a bit mask. Thus, you
should choose the flags you want to set, OR those flags together,
and store the result in the
sa_flags member of your
Each signal number has its own set of flags. Each call to
sigaction affects one particular signal number, and the flags
that you specify apply only to that particular signal.
In the GNU C Library, establishing a handler with
signal sets all
the flags to zero except for
SA_RESTART, whose value depends on
the settings you have made with
siginterrupt. See Primitives Interrupted by Signals, to see what this is about.
These macros are defined in the header file signal.h.
This flag is meaningful only for the
SIGCHLD signal. When the
flag is set, the system delivers the signal for a terminated child
process but not for one that is stopped. By default,
delivered for both terminated children and stopped children.
Setting this flag for a signal other than
SIGCHLD has no effect.
If this flag is set for a particular signal number, the system uses the
signal stack when delivering that kind of signal. See Using a Separate Signal Stack.
If a signal with this flag arrives and you have not set a signal stack,
the system terminates the program with
This flag controls what happens when a signal is delivered during
certain primitives (such as
and the signal handler returns normally. There are two alternatives:
the library function can resume, or it can return failure with error
The choice is controlled by the
SA_RESTART flag for the
particular kind of signal that was delivered. If the flag is set,
returning from a handler resumes the library function. If the flag is
clear, returning from a handler makes the function fail.
See Primitives Interrupted by Signals.