int main(int argc, char *argv[]) {
dual_timestamp
initrd_timestamp = DUAL_TIMESTAMP_NULL,
userspace_timestamp = DUAL_TIMESTAMP_NULL,
kernel_timestamp = DUAL_TIMESTAMP_NULL,
security_start_timestamp = DUAL_TIMESTAMP_NULL,
security_finish_timestamp = DUAL_TIMESTAMP_NULL;
struct rlimit saved_rlimit_nofile = RLIMIT_MAKE_CONST(0),
saved_rlimit_memlock = RLIMIT_MAKE_CONST(RLIM_INFINITY); /* The original rlimits we passed
* in. Note we use different values
* for the two that indicate whether
* these fields are initialized! */
bool skip_setup, loaded_policy = false, queue_default_job = false, first_boot = false;
char *switch_root_dir = NULL, *switch_root_init = NULL;
usec_t before_startup, after_startup;
static char systemd[] = "systemd";
const char *error_message = NULL;
uint64_t saved_ambient_set = 0;
int r, retval = EXIT_FAILURE;
Manager *m = NULL;
FDSet *fds = NULL;
assert_se(argc > 0 && !isempty(argv[0]));
/* Take timestamps early on */
dual_timestamp_from_monotonic(&kernel_timestamp, 0);
dual_timestamp_now(&userspace_timestamp);
/* Figure out whether we need to do initialize the system, or if we already did that because we are
* reexecuting. */
skip_setup = early_skip_setup_check(argc, argv);
/* If we get started via the /sbin/init symlink then we are called 'init'. After a subsequent
* reexecution we are then called 'systemd'. That is confusing, hence let's call us systemd
* right-away. */
program_invocation_short_name = systemd;
(void) prctl(PR_SET_NAME, systemd);
/* Save the original command line */
save_argc_argv(argc, argv);
/* Save the original environment as we might need to restore it if we're requested to execute another
* system manager later. */
r = save_env();
if (r < 0) {
error_message = "Failed to copy environment block";
goto finish;
}
/* Make sure that if the user says "syslog" we actually log to the journal. */
log_set_upgrade_syslog_to_journal(true);
if (getpid_cached() == 1) {
/* When we run as PID 1 force system mode */
arg_runtime_scope = RUNTIME_SCOPE_SYSTEM;
/* Disable the umask logic */
umask(0);
/* Make sure that at least initially we do not ever log to journald/syslogd, because it might
* not be activated yet (even though the log socket for it exists). */
log_set_prohibit_ipc(true);
/* Always reopen /dev/console when running as PID 1 or one of its pre-execve() children. This
* is important so that we never end up logging to any foreign stderr, for example if we have
* to log in a child process right before execve()'ing the actual binary, at a point in time
* where socket activation stderr/stdout area already set up. */
log_set_always_reopen_console(true);
if (detect_container() <= 0) {
/* Running outside of a container as PID 1 */
log_set_target_and_open(LOG_TARGET_KMSG);
if (in_initrd())
initrd_timestamp = userspace_timestamp;
if (!skip_setup) {
r = mount_setup_early();
if (r < 0) {
error_message = "Failed to mount early API filesystems";
goto finish;
}
}
/* We might have just mounted /proc, so let's try to parse the kernel
* command line log arguments immediately. */
log_parse_environment();
/* Let's open the log backend a second time, in case the first time didn't
* work. Quite possibly we have mounted /dev just now, so /dev/kmsg became
* available, and it previously wasn't. */
log_open();
if (!skip_setup) {
disable_printk_ratelimit();
r = initialize_security(
&loaded_policy,
&security_start_timestamp,
&security_finish_timestamp,
&error_message);
if (r < 0)
goto finish;
}
r = mac_init();
if (r < 0) {
error_message = "Failed to initialize MAC support";
goto finish;
}
if (!skip_setup)
initialize_clock_timewarp();
clock_apply_epoch(/* allow_backwards= */ !skip_setup);
/* Set the default for later on, but don't actually open the logs like this for
* now. Note that if we are transitioning from the initrd there might still be
* journal fd open, and we shouldn't attempt opening that before we parsed
* /proc/cmdline which might redirect output elsewhere. */
log_set_target(LOG_TARGET_JOURNAL_OR_KMSG);
} else {
/* Running inside a container, as PID 1 */
log_set_target_and_open(LOG_TARGET_CONSOLE);
/* For later on, see above... */
log_set_target(LOG_TARGET_JOURNAL);
/* clear the kernel timestamp, because we are in a container */
kernel_timestamp = DUAL_TIMESTAMP_NULL;
}
initialize_coredump(skip_setup);
r = fixup_environment();
if (r < 0) {
log_struct_errno(LOG_EMERG, r,
LOG_MESSAGE("Failed to fix up PID 1 environment: %m"),
LOG_MESSAGE_ID(SD_MESSAGE_CORE_PID1_ENVIRONMENT_STR));
error_message = "Failed to fix up PID1 environment";
goto finish;
}
/* Try to figure out if we can use colors with the console. No need to do that for user
* instances since they never log into the console. */
log_show_color(colors_enabled());
r = make_null_stdio();
if (r < 0)
log_warning_errno(r, "Failed to redirect standard streams to /dev/null, ignoring: %m");
/* Load the kernel modules early. */
if (!skip_setup)
(void) kmod_setup();
/* Mount /proc, /sys and friends, so that /proc/cmdline and /proc/$PID/fd is available. */
r = mount_setup(loaded_policy, skip_setup);
if (r < 0) {
error_message = "Failed to mount API filesystems";
goto finish;
}
/* The efivarfs is now mounted, let's lock down the system token. */
lock_down_efi_variables();
} else {
/* Running as user instance */
arg_runtime_scope = RUNTIME_SCOPE_USER;
log_set_always_reopen_console(true);
log_set_target_and_open(LOG_TARGET_AUTO);
/* clear the kernel timestamp, because we are not PID 1 */
kernel_timestamp = DUAL_TIMESTAMP_NULL;
r = mac_init();
if (r < 0) {
error_message = "Failed to initialize MAC support";
goto finish;
}
}
/* Save the original RLIMIT_NOFILE/RLIMIT_MEMLOCK so that we can reset it later when
* transitioning from the initrd to the main systemd or suchlike. */
save_rlimits(&saved_rlimit_nofile, &saved_rlimit_memlock);
/* Reset all signal handlers. */
(void) reset_all_signal_handlers();
(void) ignore_signals(SIGNALS_IGNORE);
(void) parse_configuration(&saved_rlimit_nofile, &saved_rlimit_memlock);
r = parse_argv(argc, argv);
if (r < 0) {
error_message = "Failed to parse command line arguments";
goto finish;
}
r = safety_checks();
if (r < 0)
goto finish;
if (IN_SET(arg_action, ACTION_TEST, ACTION_HELP, ACTION_DUMP_CONFIGURATION_ITEMS, ACTION_DUMP_BUS_PROPERTIES, ACTION_BUS_INTROSPECT))
pager_open(arg_pager_flags);
if (arg_action != ACTION_RUN)
skip_setup = true;
if (arg_action == ACTION_HELP) {
retval = help() < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
goto finish;
} else if (arg_action == ACTION_VERSION) {
retval = version();
goto finish;
} else if (arg_action == ACTION_DUMP_CONFIGURATION_ITEMS) {
unit_dump_config_items(stdout);
retval = EXIT_SUCCESS;
goto finish;
} else if (arg_action == ACTION_DUMP_BUS_PROPERTIES) {
dump_bus_properties(stdout);
retval = EXIT_SUCCESS;
goto finish;
} else if (arg_action == ACTION_BUS_INTROSPECT) {
r = bus_manager_introspect_implementations(stdout, arg_bus_introspect);
retval = r >= 0 ? EXIT_SUCCESS : EXIT_FAILURE;
goto finish;
}
assert_se(IN_SET(arg_action, ACTION_RUN, ACTION_TEST));
/* Move out of the way, so that we won't block unmounts */
assert_se(chdir("/") == 0);
if (arg_action == ACTION_RUN) {
if (!skip_setup) {
/* Apply the systemd.clock_usec= kernel command line switch */
apply_clock_update();
/* Apply random seed from kernel command line */
cmdline_take_random_seed();
}
/* A core pattern might have been specified via the cmdline. */
initialize_core_pattern(skip_setup);
/* Make /usr/ read-only */
apply_protect_system(skip_setup);
/* Close logging fds, in order not to confuse collecting passed fds and terminal logic below */
log_close();
/* Remember open file descriptors for later deserialization */
r = collect_fds(&fds, &error_message);
if (r < 0)
goto finish;
/* Give up any control of the console, but make sure its initialized. */
setup_console_terminal(skip_setup);
/* Open the logging devices, if possible and necessary */
log_open();
}
log_execution_mode(&first_boot);
r = cg_has_legacy();
if (r < 0) {
error_message = "Failed to check cgroup hierarchy";
goto finish;
}
if (r > 0) {
r = log_full_errno(LOG_EMERG, SYNTHETIC_ERRNO(EPROTO),
"Detected cgroup v1 hierarchy at /sys/fs/cgroup/, which is no longer supported by current version of systemd.\n"
"Please instruct your initrd to mount cgroup v2 (unified) hierarchy,\n"
"possibly by removing any stale kernel command line options, such as:\n"
" systemd.legacy_systemd_cgroup_controller=1\n"
" systemd.unified_cgroup_hierarchy=0");
error_message = "Detected unsupported legacy cgroup hierarchy, refusing execution";
goto finish;
}
r = initialize_runtime(skip_setup,
first_boot,
&saved_rlimit_nofile,
&saved_rlimit_memlock,
&saved_ambient_set,
&error_message);
if (r < 0)
goto finish;
r = manager_new(arg_runtime_scope,
arg_action == ACTION_TEST ? MANAGER_TEST_FULL : 0,
&m);
if (r < 0) {
log_struct_errno(LOG_EMERG, r,
LOG_MESSAGE("Failed to allocate manager object: %m"),
LOG_MESSAGE_ID(SD_MESSAGE_CORE_MANAGER_ALLOCATE_STR));
error_message = "Failed to allocate manager object";
goto finish;
}
m->timestamps[MANAGER_TIMESTAMP_KERNEL] = kernel_timestamp;
m->timestamps[MANAGER_TIMESTAMP_INITRD] = initrd_timestamp;
m->timestamps[MANAGER_TIMESTAMP_USERSPACE] = userspace_timestamp;
m->timestamps[manager_timestamp_initrd_mangle(MANAGER_TIMESTAMP_SECURITY_START)] = security_start_timestamp;
m->timestamps[manager_timestamp_initrd_mangle(MANAGER_TIMESTAMP_SECURITY_FINISH)] = security_finish_timestamp;
m->saved_ambient_set = saved_ambient_set;
set_manager_defaults(m);
set_manager_settings(m);
manager_set_first_boot(m, first_boot);
manager_set_switching_root(m, arg_switched_root);
/* Remember whether we should queue the default job */
queue_default_job = !arg_serialization || arg_switched_root;
before_startup = now(CLOCK_MONOTONIC);
r = manager_startup(m, arg_serialization, fds, /* root= */ NULL);
if (r < 0) {
error_message = "Failed to start up manager";
goto finish;
}
/* This will close all file descriptors that were opened, but not claimed by any unit. */
fds = fdset_free(fds);
arg_serialization = safe_fclose(arg_serialization);
if (queue_default_job) {
r = do_queue_default_job(m, &error_message);
if (r < 0)
goto finish;
}
after_startup = now(CLOCK_MONOTONIC);
log_full(arg_action == ACTION_TEST ? LOG_INFO : LOG_DEBUG,
"Loaded units and determined initial transaction in %s.",
FORMAT_TIMESPAN(after_startup - before_startup, 100 * USEC_PER_MSEC));
if (arg_action == ACTION_TEST) {
manager_test_summary(m);
retval = EXIT_SUCCESS;
goto finish;
}
r = invoke_main_loop(m,
&saved_rlimit_nofile,
&saved_rlimit_memlock,
&retval,
&fds,
&switch_root_dir,
&switch_root_init,
&error_message);
/* MANAGER_OK and MANAGER_RELOAD are not expected here. */
assert(r < 0 || IN_SET(r, MANAGER_REEXECUTE, MANAGER_EXIT) ||
(arg_runtime_scope == RUNTIME_SCOPE_SYSTEM &&
IN_SET(r, MANAGER_REBOOT,
MANAGER_SOFT_REBOOT,
MANAGER_POWEROFF,
MANAGER_HALT,
MANAGER_KEXEC,
MANAGER_SWITCH_ROOT)));
finish:
pager_close();
if (m) {
arg_reboot_watchdog = manager_get_watchdog(m, WATCHDOG_REBOOT);
arg_kexec_watchdog = manager_get_watchdog(m, WATCHDOG_KEXEC);
m = manager_free(m);
}
mac_selinux_finish();
if (IN_SET(r, MANAGER_REEXECUTE, MANAGER_SWITCH_ROOT, MANAGER_SOFT_REBOOT))
r = do_reexecute(r,
argc, argv,
&saved_rlimit_nofile,
&saved_rlimit_memlock,
fds,
switch_root_dir,
switch_root_init,
saved_ambient_set,
&error_message); /* This only returns if reexecution failed */
arg_serialization = safe_fclose(arg_serialization);
fds = fdset_free(fds);
saved_env = strv_free(saved_env);
#if HAVE_VALGRIND_VALGRIND_H
/* If we are PID 1 and running under valgrind, then let's exit
* here explicitly. valgrind will only generate nice output on
* exit(), not on exec(), hence let's do the former not the
* latter here. */
if (getpid_cached() == 1 && RUNNING_ON_VALGRIND) {
/* Cleanup watchdog_device strings for valgrind. We need them
* in become_shutdown() so normally we cannot free them yet. */
watchdog_free_device();
reset_arguments();
return retval;
}
#endif
#if HAS_FEATURE_ADDRESS_SANITIZER
/* At this stage we most likely don't have stdio/stderr open, so the following
* LSan check would not print any actionable information and would just crash
* PID 1. To make this a bit more helpful, let's try to open /dev/console,
* and if we succeed redirect LSan's report there. */
if (getpid_cached() == 1) {
_cleanup_close_ int tty_fd = -EBADF;
tty_fd = open_terminal("/dev/console", O_WRONLY|O_NOCTTY|O_CLOEXEC);
if (tty_fd >= 0)
__sanitizer_set_report_fd((void*) (intptr_t) tty_fd);
__lsan_do_leak_check();
}
#endif
if (r < 0)
(void) sd_notifyf(/* unset_environment= */ false,
"ERRNO=%i", -r);
/* Try to invoke the shutdown binary unless we already failed.
* If we failed above, we want to freeze after finishing cleanup. */
if (arg_runtime_scope == RUNTIME_SCOPE_SYSTEM &&
IN_SET(r, MANAGER_EXIT, MANAGER_REBOOT, MANAGER_POWEROFF, MANAGER_HALT, MANAGER_KEXEC)) {
r = become_shutdown(r, retval);
log_error_errno(r, "Failed to execute shutdown binary, %s: %m", getpid_cached() == 1 ? "freezing" : "quitting");
error_message = "Failed to execute shutdown binary";
}
/* This is primarily useful when running systemd in a VM, as it provides the user running the VM with
* a mechanism to pick up systemd's exit status in the VM. */
(void) sd_notifyf(/* unset_environment= */ false,
"EXIT_STATUS=%i", retval);
watchdog_free_device();
arg_watchdog_device = mfree(arg_watchdog_device);
if (getpid_cached() == 1) {
if (error_message)
manager_status_printf(NULL, STATUS_TYPE_EMERGENCY,
ANSI_HIGHLIGHT_RED "!!!!!!" ANSI_NORMAL,
"%s.", error_message);
freeze_or_exit_or_reboot();
}
reset_arguments();
return retval;
} 这段是systemd的主函数，请你详细讲解、梳理一下
文章推荐了一篇介绍消息队列（MSMQ）的入门文章，涵盖MSMQ基本编程、管理功能。使用MSMQ可让系统更松散耦合、自治，设计分布式应用时建议遵循面向服务架构思想。还介绍了MSMQ发展、特性、编码示例、管理操作等内容，提及MSMQ 3.0新特性及.Net Framework支持情况。
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