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(libc.info)Flags for Sigaction

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Flags for `sigaction'
---------------------

   The `sa_flags' member of the `sigaction' structure is a catch-all
for special features.  Most of the time, `SA_RESTART' is 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 `sigaction' structure.

   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'.  Note: Interrupted
Primitives, to see what this is about.

   These macros are defined in the header file `signal.h'.

 - Macro: int SA_NOCLDSTOP
     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, `SIGCHLD' is
     delivered for both terminated children and stopped children.

     Setting this flag for a signal other than `SIGCHLD' has no effect.

 - Macro: int SA_ONSTACK
     If this flag is set for a particular signal number, the system
     uses the signal stack when delivering that kind of signal.  Note:
     Signal Stack.  If a signal with this flag arrives and you have
     not set a signal stack, the system terminates the program with
     `SIGILL'.

 - Macro: int SA_RESTART
     This flag controls what happens when a signal is delivered during
     certain primitives (such as `open', `read' or `write'), and the
     signal handler returns normally.  There are two alternatives: the
     library function can resume, or it can return failure with error
     code `EINTR'.

     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.
     Note: Interrupted Primitives.