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Linux man pages : wait (2)
WAIT(2)			   Linux Programmer's Manual		       WAIT(2)

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 process until a child 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 has already exited by the time of the call (a so-called "zombie" process), the function returns immediately. Any system 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" process), 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 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 OR of zero or more of the following con- stants: 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. (For Linux-only options, see below.) If status is not NULL, wait or waitpid store status information in the location pointed to by status. This status can be evaluated with the following macros (these macros take the stat buffer (an int) as an argument