__pmOpenLog man page
__pmOpenLog — create a log file for diagnostics and debug output
FILE *__pmOpenLog(const char *progname, const char *logname, FILE *oldstream, int *status);
cc ... -lpcp
__pmOpenLog reassigns the standard I/O stream oldstream to be associated with the file logname. If it already exists, logname will be removed and recreated if possible (to ensure correct ownership and permissions from the caller to __pmOpenLog).
On return, the function value is the new standard I/O stream. In the event of an error, this will be oldstream unchanged and status will be 0.
For success, status is 1, a standard preamble is written to logname
Log for progname on hostname started date and time
and an atexit(3) handler is installed to write the postscript message to logname
Log finished date and time
when the processes exits.
progname is only used to annotate messages.
atexit(3) and freopen(3).