lib/daemon.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18 #include "daemon.h"
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <signal.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <sys/resource.h>
  25 #include <sys/wait.h>
  26 #include <sys/stat.h>
  27 #include <unistd.h>
  28 #include "command-line.h"
  29 #include "fatal-signal.h"
  30 #include "dirs.h"
  31 #include "lockfile.h"
  32 #include "ovs-thread.h"
  33 #include "process.h"
  34 #include "socket-util.h"
  35 #include "timeval.h"
  36 #include "util.h"
  37 #include "vlog.h"
  38
  39 VLOG_DEFINE_THIS_MODULE(daemon);
  40
  41 /* --detach: Should we run in the background? */
  42 static bool detach;             /* Was --detach specified? */
  43 static bool detached;           /* Have we already detached? */
  44
  45 /* --pidfile: Name of pidfile (null if none). */
  46 static char *pidfile;
  47
  48 /* Device and inode of pidfile, so we can avoid reopening it. */
  49 static dev_t pidfile_dev;
  50 static ino_t pidfile_ino;
  51
  52 /* --overwrite-pidfile: Create pidfile even if one already exists and is
  53    locked? */
  54 static bool overwrite_pidfile;
  55
  56 /* --no-chdir: Should we chdir to "/"? */
  57 static bool chdir_ = true;
  58
  59 /* File descriptor used by daemonize_start() and daemonize_complete(). */
  60 static int daemonize_fd = -1;
  61
  62 /* --monitor: Should a supervisory process monitor the daemon and restart it if
  63  * it dies due to an error signal? */
  64 static bool monitor;
  65
  66 /* For each of the standard file descriptors, whether to replace it by
  67  * /dev/null (if false) or keep it for the daemon to use (if true). */
  68 static bool save_fds[3];
  69
  70 static void check_already_running(void);
  71 static int lock_pidfile(FILE *, int command);
  72
  73 /* Returns the file name that would be used for a pidfile if 'name' were
  74  * provided to set_pidfile().  The caller must free the returned string. */
  75 char *
  76 make_pidfile_name(const char *name)
  77 {
  78     return (!name
  79             ? xasprintf("%s/%s.pid", ovs_rundir(), program_name)
  80             : abs_file_name(ovs_rundir(), name));
  81 }
  82
  83 /* Sets up a following call to daemonize() to create a pidfile named 'name'.
  84  * If 'name' begins with '/', then it is treated as an absolute path.
  85  * Otherwise, it is taken relative to RUNDIR, which is $(prefix)/var/run by
  86  * default.
  87  *
  88  * If 'name' is null, then program_name followed by ".pid" is used. */
  89 void
  90 set_pidfile(const char *name)
  91 {
  92     assert_single_threaded();
  93     free(pidfile);
  94     pidfile = make_pidfile_name(name);
  95 }
  96
  97 /* Returns an absolute path to the configured pidfile, or a null pointer if no
  98  * pidfile is configured.  The caller must not modify or free the returned
  99  * string. */
 100 const char *
 101 get_pidfile(void)
 102 {
 103     return pidfile;
 104 }
 105
 106 /* Sets that we do not chdir to "/". */
 107 void
 108 set_no_chdir(void)
 109 {
 110     chdir_ = false;
 111 }
 112
 113 /* Will we chdir to "/" as part of daemonizing? */
 114 bool
 115 is_chdir_enabled(void)
 116 {
 117     return chdir_;
 118 }
 119
 120 /* Normally, daemonize() or damonize_start() will terminate the program with a
 121  * message if a locked pidfile already exists.  If this function is called, an
 122  * existing pidfile will be replaced, with a warning. */
 123 void
 124 ignore_existing_pidfile(void)
 125 {
 126     overwrite_pidfile = true;
 127 }
 128
 129 /* Sets up a following call to daemonize() to detach from the foreground
 130  * session, running this process in the background.  */
 131 void
 132 set_detach(void)
 133 {
 134     detach = true;
 135 }
 136
 137 /* Will daemonize() really detach? */
 138 bool
 139 get_detach(void)
 140 {
 141     return detach;
 142 }
 143
 144 /* Sets up a following call to daemonize() to fork a supervisory process to
 145  * monitor the daemon and restart it if it dies due to an error signal.  */
 146 void
 147 daemon_set_monitor(void)
 148 {
 149     monitor = true;
 150 }
 151
 152 /* A daemon doesn't normally have any use for the file descriptors for stdin,
 153  * stdout, and stderr after it detaches.  To keep these file descriptors from
 154  * e.g. holding an SSH session open, by default detaching replaces each of
 155  * these file descriptors by /dev/null.  But a few daemons expect the user to
 156  * redirect stdout or stderr to a file, in which case it is desirable to keep
 157  * these file descriptors.  This function, therefore, disables replacing 'fd'
 158  * by /dev/null when the daemon detaches. */
 159 void
 160 daemon_save_fd(int fd)
 161 {
 162     ovs_assert(fd == STDIN_FILENO ||
 163                fd == STDOUT_FILENO ||
 164                fd == STDERR_FILENO);
 165     save_fds[fd] = true;
 166 }
 167
 168 /* Unregisters pidfile from being unlinked when the program terminates via
 169 * exit() or a fatal signal. */
 170 void
 171 remove_pidfile_from_unlink(void)
 172 {
 173     if (pidfile) {
 174         fatal_signal_remove_file_to_unlink(pidfile);
 175     }
 176 }
 177
 178 /* Registers pidfile to be unlinked when the program terminates via exit() or a
 179  * fatal signal. */
 180 void
 181 add_pidfile_to_unlink(void)
 182 {
 183     if (pidfile) {
 184         fatal_signal_add_file_to_unlink(pidfile);
 185     }
 186 }
 187
 188 /* If a pidfile has been configured, creates it and stores the running
 189  * process's pid in it.  Ensures that the pidfile will be deleted when the
 190  * process exits. */
 191 static void
 192 make_pidfile(void)
 193 {
 194     long int pid = getpid();
 195     struct stat s;
 196     char *tmpfile;
 197     FILE *file;
 198     int error;
 199
 200     /* Create a temporary pidfile. */
 201     if (overwrite_pidfile) {
 202         tmpfile = xasprintf("%s.tmp%ld", pidfile, pid);
 203         fatal_signal_add_file_to_unlink(tmpfile);
 204     } else {
 205         /* Everyone shares the same file which will be treated as a lock.  To
 206          * avoid some uncomfortable race conditions, we can't set up the fatal
 207          * signal unlink until we've acquired it. */
 208         tmpfile = xasprintf("%s.tmp", pidfile);
 209     }
 210
 211     file = fopen(tmpfile, "a+");
 212     if (!file) {
 213         VLOG_FATAL("%s: create failed (%s)", tmpfile, ovs_strerror(errno));
 214     }
 215
 216     error = lock_pidfile(file, F_SETLK);
 217     if (error) {
 218         /* Looks like we failed to acquire the lock.  Note that, if we failed
 219          * for some other reason (and '!overwrite_pidfile'), we will have
 220          * left 'tmpfile' as garbage in the file system. */
 221         VLOG_FATAL("%s: fcntl(F_SETLK) failed (%s)", tmpfile,
 222                    ovs_strerror(error));
 223     }
 224
 225     if (!overwrite_pidfile) {
 226         /* We acquired the lock.  Make sure to clean up on exit, and verify
 227          * that we're allowed to create the actual pidfile. */
 228         fatal_signal_add_file_to_unlink(tmpfile);
 229         check_already_running();
 230     }
 231
 232     if (fstat(fileno(file), &s) == -1) {
 233         VLOG_FATAL("%s: fstat failed (%s)", tmpfile, ovs_strerror(errno));
 234     }
 235
 236     if (ftruncate(fileno(file), 0) == -1) {
 237         VLOG_FATAL("%s: truncate failed (%s)", tmpfile, ovs_strerror(errno));
 238     }
 239
 240     fprintf(file, "%ld\n", pid);
 241     if (fflush(file) == EOF) {
 242         VLOG_FATAL("%s: write failed (%s)", tmpfile, ovs_strerror(errno));
 243     }
 244
 245     error = rename(tmpfile, pidfile);
 246
 247     /* Due to a race, 'tmpfile' may be owned by a different process, so we
 248      * shouldn't delete it on exit. */
 249     fatal_signal_remove_file_to_unlink(tmpfile);
 250
 251     if (error < 0) {
 252         VLOG_FATAL("failed to rename \"%s\" to \"%s\" (%s)",
 253                    tmpfile, pidfile, ovs_strerror(errno));
 254     }
 255
 256     /* Ensure that the pidfile will get deleted on exit. */
 257     fatal_signal_add_file_to_unlink(pidfile);
 258
 259     /* Clean up.
 260      *
 261      * We don't close 'file' because its file descriptor must remain open to
 262      * hold the lock. */
 263     pidfile_dev = s.st_dev;
 264     pidfile_ino = s.st_ino;
 265     free(tmpfile);
 266 }
 267
 268 /* If configured with set_pidfile() or set_detach(), creates the pid file and
 269  * detaches from the foreground session.  */
 270 void
 271 daemonize(void)
 272 {
 273     daemonize_start();
 274     daemonize_complete();
 275 }
 276
 277 /* Calls fork() and on success returns its return value.  On failure, logs an
 278  * error and exits unsuccessfully.
 279  *
 280  * Post-fork, but before returning, this function calls a few other functions
 281  * that are generally useful if the child isn't planning to exec a new
 282  * process. */
 283 pid_t
 284 fork_and_clean_up(void)
 285 {
 286     pid_t pid = xfork();
 287     if (pid > 0) {
 288         /* Running in parent process. */
 289         fatal_signal_fork();
 290     } else if (!pid) {
 291         /* Running in child process. */
 292         time_postfork();
 293         lockfile_postfork();
 294     }
 295     return pid;
 296 }
 297
 298 /* Forks, then:
 299  *
 300  *   - In the parent, waits for the child to signal that it has completed its
 301  *     startup sequence.  Then stores -1 in '*fdp' and returns the child's pid.
 302  *
 303  *   - In the child, stores a fd in '*fdp' and returns 0.  The caller should
 304  *     pass the fd to fork_notify_startup() after it finishes its startup
 305  *     sequence.
 306  *
 307  * If something goes wrong with the fork, logs a critical error and aborts the
 308  * process. */
 309 static pid_t
 310 fork_and_wait_for_startup(int *fdp)
 311 {
 312     int fds[2];
 313     pid_t pid;
 314
 315     xpipe(fds);
 316
 317     pid = fork_and_clean_up();
 318     if (pid > 0) {
 319         /* Running in parent process. */
 320         size_t bytes_read;
 321         char c;
 322
 323         close(fds[1]);
 324         if (read_fully(fds[0], &c, 1, &bytes_read) != 0) {
 325             int retval;
 326             int status;
 327
 328             do {
 329                 retval = waitpid(pid, &status, 0);
 330             } while (retval == -1 && errno == EINTR);
 331
 332             if (retval == pid) {
 333                 if (WIFEXITED(status) && WEXITSTATUS(status)) {
 334                     /* Child exited with an error.  Convey the same error
 335                      * to our parent process as a courtesy. */
 336                     exit(WEXITSTATUS(status));
 337                 } else {
 338                     char *status_msg = process_status_msg(status);
 339                     VLOG_FATAL("fork child died before signaling startup (%s)",
 340                                status_msg);
 341                 }
 342             } else if (retval < 0) {
 343                 VLOG_FATAL("waitpid failed (%s)", ovs_strerror(errno));
 344             } else {
 345                 NOT_REACHED();
 346             }
 347         }
 348         close(fds[0]);
 349         *fdp = -1;
 350     } else if (!pid) {
 351         /* Running in child process. */
 352         close(fds[0]);
 353         *fdp = fds[1];
 354     }
 355
 356     return pid;
 357 }
 358
 359 static void
 360 fork_notify_startup(int fd)
 361 {
 362     if (fd != -1) {
 363         size_t bytes_written;
 364         int error;
 365
 366         error = write_fully(fd, "", 1, &bytes_written);
 367         if (error) {
 368             VLOG_FATAL("pipe write failed (%s)", ovs_strerror(error));
 369         }
 370
 371         close(fd);
 372     }
 373 }
 374
 375 static bool
 376 should_restart(int status)
 377 {
 378     if (WIFSIGNALED(status)) {
 379         static const int error_signals[] = {
 380             SIGABRT, SIGALRM, SIGBUS, SIGFPE, SIGILL, SIGPIPE, SIGSEGV,
 381             SIGXCPU, SIGXFSZ
 382         };
 383
 384         size_t i;
 385
 386         for (i = 0; i < ARRAY_SIZE(error_signals); i++) {
 387             if (error_signals[i] == WTERMSIG(status)) {
 388                 return true;
 389             }
 390         }
 391     }
 392     return false;
 393 }
 394
 395 static void
 396 monitor_daemon(pid_t daemon_pid)
 397 {
 398     /* XXX Should log daemon's stderr output at startup time. */
 399     time_t last_restart;
 400     char *status_msg;
 401     int crashes;
 402
 403     set_subprogram_name("monitor");
 404     status_msg = xstrdup("healthy");
 405     last_restart = TIME_MIN;
 406     crashes = 0;
 407     for (;;) {
 408         int retval;
 409         int status;
 410
 411         proctitle_set("monitoring pid %lu (%s)",
 412                       (unsigned long int) daemon_pid, status_msg);
 413
 414         do {
 415             retval = waitpid(daemon_pid, &status, 0);
 416         } while (retval == -1 && errno == EINTR);
 417
 418         if (retval == -1) {
 419             VLOG_FATAL("waitpid failed (%s)", ovs_strerror(errno));
 420         } else if (retval == daemon_pid) {
 421             char *s = process_status_msg(status);
 422             if (should_restart(status)) {
 423                 free(status_msg);
 424                 status_msg = xasprintf("%d crashes: pid %lu died, %s",
 425                                        ++crashes,
 426                                        (unsigned long int) daemon_pid, s);
 427                 free(s);
 428
 429                 if (WCOREDUMP(status)) {
 430                     /* Disable further core dumps to save disk space. */
 431                     struct rlimit r;
 432
 433                     r.rlim_cur = 0;
 434                     r.rlim_max = 0;
 435                     if (setrlimit(RLIMIT_CORE, &r) == -1) {
 436                         VLOG_WARN("failed to disable core dumps: %s",
 437                                   ovs_strerror(errno));
 438                     }
 439                 }
 440
 441                 /* Throttle restarts to no more than once every 10 seconds. */
 442                 if (time(NULL) < last_restart + 10) {
 443                     VLOG_WARN("%s, waiting until 10 seconds since last "
 444                               "restart", status_msg);
 445                     for (;;) {
 446                         time_t now = time(NULL);
 447                         time_t wakeup = last_restart + 10;
 448                         if (now >= wakeup) {
 449                             break;
 450                         }
 451                         sleep(wakeup - now);
 452                     }
 453                 }
 454                 last_restart = time(NULL);
 455
 456                 VLOG_ERR("%s, restarting", status_msg);
 457                 daemon_pid = fork_and_wait_for_startup(&daemonize_fd);
 458                 if (!daemon_pid) {
 459                     break;
 460                 }
 461             } else {
 462                 VLOG_INFO("pid %lu died, %s, exiting",
 463                           (unsigned long int) daemon_pid, s);
 464                 free(s);
 465                 exit(0);
 466             }
 467         }
 468     }
 469     free(status_msg);
 470
 471     /* Running in new daemon process. */
 472     proctitle_restore();
 473     set_subprogram_name("");
 474 }
 475
 476 /* Close standard file descriptors (except any that the client has requested we
 477  * leave open by calling daemon_save_fd()).  If we're started from e.g. an SSH
 478  * session, then this keeps us from holding that session open artificially. */
 479 static void
 480 close_standard_fds(void)
 481 {
 482     int null_fd = get_null_fd();
 483     if (null_fd >= 0) {
 484         int fd;
 485
 486         for (fd = 0; fd < 3; fd++) {
 487             if (!save_fds[fd]) {
 488                 dup2(null_fd, fd);
 489             }
 490         }
 491     }
 492
 493     /* Disable logging to stderr to avoid wasting CPU time. */
 494     vlog_set_levels(NULL, VLF_CONSOLE, VLL_OFF);
 495 }
 496
 497 /* If daemonization is configured, then starts daemonization, by forking and
 498  * returning in the child process.  The parent process hangs around until the
 499  * child lets it know either that it completed startup successfully (by calling
 500  * daemon_complete()) or that it failed to start up (by exiting with a nonzero
 501  * exit code). */
 502 void
 503 daemonize_start(void)
 504 {
 505     assert_single_threaded();
 506     daemonize_fd = -1;
 507
 508     if (detach) {
 509         if (fork_and_wait_for_startup(&daemonize_fd) > 0) {
 510             /* Running in parent process. */
 511             exit(0);
 512         }
 513
 514         /* Running in daemon or monitor process. */
 515         setsid();
 516     }
 517
 518     if (monitor) {
 519         int saved_daemonize_fd = daemonize_fd;
 520         pid_t daemon_pid;
 521
 522         daemon_pid = fork_and_wait_for_startup(&daemonize_fd);
 523         if (daemon_pid > 0) {
 524             /* Running in monitor process. */
 525             fork_notify_startup(saved_daemonize_fd);
 526             close_standard_fds();
 527             monitor_daemon(daemon_pid);
 528         }
 529         /* Running in daemon process. */
 530     }
 531
 532     forbid_forking("running in daemon process");
 533
 534     if (pidfile) {
 535         make_pidfile();
 536     }
 537
 538     /* Make sure that the unixctl commands for vlog get registered in a
 539      * daemon, even before the first log message. */
 540     vlog_init();
 541 }
 542
 543 /* If daemonization is configured, then this function notifies the parent
 544  * process that the child process has completed startup successfully.  It also
 545  * call daemonize_post_detach().
 546  *
 547  * Calling this function more than once has no additional effect. */
 548 void
 549 daemonize_complete(void)
 550 {
 551     if (pidfile) {
 552         free(pidfile);
 553         pidfile = NULL;
 554     }
 555
 556     if (!detached) {
 557         detached = true;
 558
 559         fork_notify_startup(daemonize_fd);
 560         daemonize_fd = -1;
 561         daemonize_post_detach();
 562     }
 563 }
 564
 565 /* If daemonization is configured, then this function does traditional Unix
 566  * daemonization behavior: join a new session, chdir to the root (if not
 567  * disabled), and close the standard file descriptors.
 568  *
 569  * It only makes sense to call this function as part of an implementation of a
 570  * special daemon subprocess.  A normal daemon should just call
 571  * daemonize_complete(). */
 572 void
 573 daemonize_post_detach(void)
 574 {
 575     if (detach) {
 576         if (chdir_) {
 577             ignore(chdir("/"));
 578         }
 579         close_standard_fds();
 580     }
 581 }
 582
 583 void
 584 daemon_usage(void)
 585 {
 586     printf(
 587         "\nDaemon options:\n"
 588         "  --detach                run in background as daemon\n"
 589         "  --no-chdir              do not chdir to '/'\n"
 590         "  --pidfile[=FILE]        create pidfile (default: %s/%s.pid)\n"
 591         "  --overwrite-pidfile     with --pidfile, start even if already "
 592                                    "running\n",
 593         ovs_rundir(), program_name);
 594 }
 595
 596 static int
 597 lock_pidfile__(FILE *file, int command, struct flock *lck)
 598 {
 599     int error;
 600
 601     lck->l_type = F_WRLCK;
 602     lck->l_whence = SEEK_SET;
 603     lck->l_start = 0;
 604     lck->l_len = 0;
 605     lck->l_pid = 0;
 606
 607     do {
 608         error = fcntl(fileno(file), command, lck) == -1 ? errno : 0;
 609     } while (error == EINTR);
 610     return error;
 611 }
 612
 613 static int
 614 lock_pidfile(FILE *file, int command)
 615 {
 616     struct flock lck;
 617
 618     return lock_pidfile__(file, command, &lck);
 619 }
 620
 621 static pid_t
 622 read_pidfile__(const char *pidfile, bool delete_if_stale)
 623 {
 624     struct stat s, s2;
 625     struct flock lck;
 626     char line[128];
 627     FILE *file;
 628     int error;
 629
 630     if ((pidfile_ino || pidfile_dev)
 631         && !stat(pidfile, &s)
 632         && s.st_ino == pidfile_ino && s.st_dev == pidfile_dev) {
 633         /* It's our own pidfile.  We can't afford to open it, because closing
 634          * *any* fd for a file that a process has locked also releases all the
 635          * locks on that file.
 636          *
 637          * Fortunately, we know the associated pid anyhow: */
 638         return getpid();
 639     }
 640
 641     file = fopen(pidfile, "r+");
 642     if (!file) {
 643         if (errno == ENOENT && delete_if_stale) {
 644             return 0;
 645         }
 646         error = errno;
 647         VLOG_WARN("%s: open: %s", pidfile, ovs_strerror(error));
 648         goto error;
 649     }
 650
 651     error = lock_pidfile__(file, F_GETLK, &lck);
 652     if (error) {
 653         VLOG_WARN("%s: fcntl: %s", pidfile, ovs_strerror(error));
 654         goto error;
 655     }
 656     if (lck.l_type == F_UNLCK) {
 657         /* pidfile exists but it isn't locked by anyone.  We need to delete it
 658          * so that a new pidfile can go in its place.  But just calling
 659          * unlink(pidfile) makes a nasty race: what if someone else unlinks it
 660          * before we do and then replaces it by a valid pidfile?  We'd unlink
 661          * their valid pidfile.  We do a little dance to avoid the race, by
 662          * locking the invalid pidfile.  Only one process can have the invalid
 663          * pidfile locked, and only that process has the right to unlink it. */
 664         if (!delete_if_stale) {
 665             error = ESRCH;
 666             VLOG_DBG("%s: pid file is stale", pidfile);
 667             goto error;
 668         }
 669
 670         /* Get the lock. */
 671         error = lock_pidfile(file, F_SETLK);
 672         if (error) {
 673             /* We lost a race with someone else doing the same thing. */
 674             VLOG_WARN("%s: lost race to lock pidfile", pidfile);
 675             goto error;
 676         }
 677
 678         /* Is the file we have locked still named 'pidfile'? */
 679         if (stat(pidfile, &s) || fstat(fileno(file), &s2)
 680             || s.st_ino != s2.st_ino || s.st_dev != s2.st_dev) {
 681             /* No.  We lost a race with someone else who got the lock before
 682              * us, deleted the pidfile, and closed it (releasing the lock). */
 683             error = EALREADY;
 684             VLOG_WARN("%s: lost race to delete pidfile", pidfile);
 685             goto error;
 686         }
 687
 688         /* We won the right to delete the stale pidfile. */
 689         if (unlink(pidfile)) {
 690             error = errno;
 691             VLOG_WARN("%s: failed to delete stale pidfile (%s)",
 692                       pidfile, ovs_strerror(error));
 693             goto error;
 694         }
 695         VLOG_DBG("%s: deleted stale pidfile", pidfile);
 696         fclose(file);
 697         return 0;
 698     }
 699
 700     if (!fgets(line, sizeof line, file)) {
 701         if (ferror(file)) {
 702             error = errno;
 703             VLOG_WARN("%s: read: %s", pidfile, ovs_strerror(error));
 704         } else {
 705             error = ESRCH;
 706             VLOG_WARN("%s: read: unexpected end of file", pidfile);
 707         }
 708         goto error;
 709     }
 710
 711     if (lck.l_pid != strtoul(line, NULL, 10)) {
 712         /* The process that has the pidfile locked is not the process that
 713          * created it.  It must be stale, with the process that has it locked
 714          * preparing to delete it. */
 715         error = ESRCH;
 716         VLOG_WARN("%s: stale pidfile for pid %s being deleted by pid %ld",
 717                   pidfile, line, (long int) lck.l_pid);
 718         goto error;
 719     }
 720
 721     fclose(file);
 722     return lck.l_pid;
 723
 724 error:
 725     if (file) {
 726         fclose(file);
 727     }
 728     return -error;
 729 }
 730
 731 /* Opens and reads a PID from 'pidfile'.  Returns the positive PID if
 732  * successful, otherwise a negative errno value. */
 733 pid_t
 734 read_pidfile(const char *pidfile)
 735 {
 736     return read_pidfile__(pidfile, false);
 737 }
 738
 739 /* Checks whether a process with the given 'pidfile' is already running and,
 740  * if so, aborts.  If 'pidfile' is stale, deletes it. */
 741 static void
 742 check_already_running(void)
 743 {
 744     long int pid = read_pidfile__(pidfile, true);
 745     if (pid > 0) {
 746         VLOG_FATAL("%s: already running as pid %ld, aborting", pidfile, pid);
 747     } else if (pid < 0) {
 748         VLOG_FATAL("%s: pidfile check failed (%s), aborting",
 749                    pidfile, ovs_strerror(-pid));
 750     }
 751 }