NAME

       pmOpenLog - create a log file for diagnostics and debug output

C SYNOPSIS

       #include <pcp/pmapi.h>

       FILE *pmOpenLog(const char *progname, const char *logname, FILE *oldstream, int *status);

       cc ... -lpcp

DESCRIPTION

       pmOpenLog  reassigns  the standard I/O stream oldstream (normally stderr) to be associated
       with the file logname.

       If logname is not "-" and the file already exists, it will be renamed to logname.prev else
       removed.   Due  to permissions restrictions, the rename or removal may not succeed, but in
       the common use cases logname.prev remains with the contents of  the  previous  version  of
       logname.   Then  logname  is  recreated  if  possible  (to  ensure  correct  ownership and
       permissions from the caller to pmOpenLog).

       As a special case, if logname is "-" then no renaming, removal or reopening  is  performed
       and  the  function simply sets status to 1 and returns oldstream.  This is useful when the
       caller wants diagnostics on oldstream stream (normally stderr) rather than  a  file,  e.g.
       pmlogger  -l-  or  pmcd  -f  -l-.   Logging  to  stderr  is  also  useful  for  PMDAs in a
       containerized environment where it is beneficial for all PMDA logs to be written to pmcd's
       stderr  stream (and thus to a single destination), whether that is a file such as pmcd.log
       or the original stream inherited from the shell.

       On return, the function value is the standard I/O stream,  possibly  replacing  oldstream.
       In  the event of an error, the return value will be oldstream unchanged and status will be
       0.

       For success, status is 1, and 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.

SEE ALSO

       atexit(3) and freopen(3).