cdsa/cdsa_utilities/daemon.cpp

   1 /*
   2  * Copyright (c) 2000-2001 Apple Computer, Inc. All Rights Reserved.
   3  *
   4  * The contents of this file constitute Original Code as defined in and are
   5  * subject to the Apple Public Source License Version 1.2 (the 'License').
   6  * You may not use this file except in compliance with the License. Please obtain
   7  * a copy of the License at http://www.apple.com/publicsource and read it before
   8  * using this file.
   9  *
  10  * This Original Code and all software distributed under the License are
  11  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESS
  12  * OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, INCLUDING WITHOUT
  13  * LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
  14  * PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. Please see the License for the
  15  * specific language governing rights and limitations under the License.
  16  */
  17
  18
  19 //
  20 // demon - support code for writing UNIXoid demons
  21 //
  22 #include <Security/daemon.h>
  23 #include <Security/logging.h>
  24 #include <Security/debugging.h>
  25 #include <sys/types.h>
  26 #include <errno.h>
  27 #include <unistd.h>
  28 #include <fcntl.h>
  29
  30 namespace Security {
  31 namespace Daemon {
  32
  33
  34 //
  35 // Daemonize this process, the UNIX way.
  36 //
  37 bool incarnate()
  38 {
  39         // fork with slight resilience
  40         for (int forkTries = 1; forkTries <= 5; forkTries++) {
  41                 switch (fork()) {
  42                 case 0:                 // child
  43                         // we are the daemon process (Har! Har!)
  44                         break;
  45                 case -1:                // parent: fork failed
  46                         switch (errno) {
  47                         case EAGAIN:
  48                         case ENOMEM:
  49                                 Syslog::warning("fork() short on resources (errno=%d); retrying", errno);
  50                                 sleep(forkTries);
  51                                 continue;
  52                         default:
  53                                 Syslog::error("fork() failed (errno=%d)", errno);
  54                                 return false;
  55                         }
  56                 default:                // parent
  57                         // @@@ we could close an assurance loop here, but we don't (yet?)
  58                         exit(0);
  59                 }
  60         }
  61
  62         // fork succeeded; we are the child; parent is terminating
  63
  64         // create new session (the magic set-me-apart system call)
  65         setsid();
  66
  67         // redirect standard channels to /dev/null
  68         close(0);       // fail silently in case 0 is closed
  69         if (open("/dev/null", O_RDWR, 0) == 0) {        // /dev/null could be missing, I suppose...
  70                 dup2(0, 1);
  71                 dup2(0, 2);
  72         }
  73
  74         // ready to roll
  75         return true;
  76 }
  77
  78
  79 //
  80 // Re-execute myself.
  81 // This is a pretty bad hack for libraries that are pretty broken and (essentially)
  82 // don't work after a fork() unless you also exec().
  83 //
  84 // WARNING: Don't even THINK of doing this in a setuid-anything program.
  85 //
  86 bool executeSelf(char **argv)
  87 {
  88         static const char reExecEnv[] = "_RE_EXECUTE";
  89         if (getenv(reExecEnv)) {                // was re-executed
  90                 debug("daemon", "self-execution complete");
  91                 unsetenv(reExecEnv);
  92                 return true;
  93         } else {
  94                 setenv(reExecEnv, "go", 1);
  95                 debug("daemon", "self-executing (ouch!)");
  96                 execv(argv[0], argv);
  97                 perror("re-execution");
  98                 Syslog::error("Re-execution attempt failed");
  99                 return false;
 100         }
 101 }
 102
 103
 104 } // end namespace Daemon
 105 } // end namespace Security