wait
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NAME
wait, waitpid - wait for process termination
SYNOPSIS
#include <sys/types.h>
#include <sys/wait.h>
pid_t wait(int *status)
pid_t waitpid(pid_t pid, int *status, int options);
DESCRIPTION
The wait function suspends execution of the current pro-
cess until a child has exited, or until a signal is deliv-
ered whose action is to terminate the current process or
to call a signal handling function. If a child has
already exited by the time of the call (a so-called "zom-
bie" process), the function returns immediately. Any sys-
tem resources used by the child are freed.
The waitpid function suspends execution of the current
process until a child as specified by the pid argument has
exited, or until a signal is delivered whose action is to
terminate the current process or to call a signal handling
function. If a child as requested by pid has already
exited by the time of the call (a so-called "zombie" pro-
cess), the function returns immediately. Any system
resources used by the child are freed.
The value of pid can be one of:
< -1 which means to wait for any child process whose
process group ID is equal to the absolute value of
-1 which means to wait for any child process whose
process group ID is equal to the absolute value of
pid.
-1 which means to wait for any child process; this is
the same behaviour which wait exhibits.
0 which means to wait for any child process whose
process group ID is equal to that of the calling
process.
> 0 which means to wait for the child whose process ID
is equal to the value of pid.
The value of options is an exclusive OR of zero or more of
the following constants:
WNOHANG which means to return immediately if no child has
exited.
WUNTRACED
which means to also return for children which are
stopped, and whose status has not been reported.
If status is not NULL, wait or waitpid store status infor-
mation in the location pointed to by statloc.
This status can be evaluated with the following macros
(these macros take the stat buffer as an argument -- not a
pointer to the buffer!):
WIFEXITED(status)
is non -zero if the child exited normally.
WEXITSTATUS(status)
evaluates to the least significant eight bits of
the return code of the child which terminated,
which may have been set as the argument to a call
to exit() or as the argument for a return state-
ment in the main program. This macro can only be
evaluated if WIFEXITED returned non-zero.
WIFSIGNALED(status)
returns true if the child process exited because
of a signal which was not caught.
WTERMSIG(status)
returns the number of the signal that caused the
child process to terminate. This macro can only be
evaluated if WIFSIGNALED returned non-zero.
WIFSTOPPED(status)
returns true if the child process which caused the
return is currently stopped; this is only possible
if the call was done using WUNTRACED.
WSTOPSIG(status)
returns the number of the signal which caused the
child to stop. This macro can only be evaluated
if WIFSTOPPED returned non-zero.
RETURN VALUE
The process ID of the child which exited, -1 on error or
zero if WNOHANG was used and no child was available (in
which case, errno is set to an appropriate value).
ERRORS
ECHILD if the child process specified in pid does not
exist.
EPERM if the effective userid of the calling process
does not match that of the process being waited
for, and the effective userid of the calling pro-
cess it not that of the superuser.
ERESTARTSYS
if WNOHANG was not set and an unblocked signal or
a SIGCHLD was caught; this is an extension to the
POSIX.1 standard.
CONFORMS TO
POSIX.1
SEE ALSO
signal(2), wait4(2), signal(7)
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Hurricane Electric.
All Rights Reserved.