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authorLennart Poettering <lennart@poettering.net>2012-04-11 02:04:46 +0200
committerLennart Poettering <lennart@poettering.net>2012-04-11 02:04:46 +0200
commit04ebb5956719e3e301e1c08443c496ad97399544 (patch)
treeef0bf3f6a37d48e688c2aff6cd3c77c9c7a7dfad /src
parent7e59bfcb18bcfdb82fa1f197c935bb15a22aa582 (diff)
shutdownd: rework interface, allow subscribing to scheduled shutdowns
This extends the shutdownd interface to expose schedule shutdown information in /run/systemd/shutdown/schedule. This also cleans up the shutdownd protocol and documents it in a header file sd-shutdown.h. This is supposed to be used by client code that wants to control and monitor scheduled shutdown.
Diffstat (limited to 'src')
-rw-r--r--src/shutdownd.c230
-rw-r--r--src/shutdownd.h46
-rw-r--r--src/systemctl.c48
-rw-r--r--src/systemd/sd-shutdown.h108
4 files changed, 307 insertions, 125 deletions
diff --git a/src/shutdownd.c b/src/shutdownd.c
index b4052d4933..9801b5e19c 100644
--- a/src/shutdownd.c
+++ b/src/shutdownd.c
@@ -28,16 +28,23 @@
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
+#include <stddef.h>
#include <systemd/sd-daemon.h>
+#include <systemd/sd-shutdown.h>
-#include "shutdownd.h"
#include "log.h"
#include "macro.h"
#include "util.h"
#include "utmp-wtmp.h"
+#include "mkdir.h"
-static int read_packet(int fd, struct shutdownd_command *_c) {
+union shutdown_buffer {
+ struct sd_shutdown_command command;
+ char space[offsetof(struct sd_shutdown_command, wall_message) + LINE_MAX];
+};
+
+static int read_packet(int fd, union shutdown_buffer *_b) {
struct msghdr msghdr;
struct iovec iovec;
struct ucred *ucred;
@@ -45,15 +52,15 @@ static int read_packet(int fd, struct shutdownd_command *_c) {
struct cmsghdr cmsghdr;
uint8_t buf[CMSG_SPACE(sizeof(struct ucred))];
} control;
- struct shutdownd_command c;
ssize_t n;
+ union shutdown_buffer b; /* We maintain our own copy here, in order not to corrupt the last message */
assert(fd >= 0);
- assert(_c);
+ assert(_b);
zero(iovec);
- iovec.iov_base = &c;
- iovec.iov_len = sizeof(c);
+ iovec.iov_base = &b;
+ iovec.iov_len = sizeof(b) - 1;
zero(control);
zero(msghdr);
@@ -62,8 +69,9 @@ static int read_packet(int fd, struct shutdownd_command *_c) {
msghdr.msg_control = &control;
msghdr.msg_controllen = sizeof(control);
- if ((n = recvmsg(fd, &msghdr, MSG_DONTWAIT)) <= 0) {
- if (n >= 0) {
+ n = recvmsg(fd, &msghdr, MSG_DONTWAIT);
+ if (n <= 0) {
+ if (n == 0) {
log_error("Short read");
return -EIO;
}
@@ -89,18 +97,27 @@ static int read_packet(int fd, struct shutdownd_command *_c) {
return 0;
}
- if (n != sizeof(c)) {
- log_warning("Message has invalid size. Ignoring");
+ if ((size_t) n < offsetof(struct sd_shutdown_command, wall_message)) {
+ log_warning("Message has invalid size. Ignoring.");
+ return 0;
+ }
+
+ if (b.command.mode != SD_SHUTDOWN_NONE &&
+ b.command.mode != SD_SHUTDOWN_REBOOT &&
+ b.command.mode != SD_SHUTDOWN_POWEROFF &&
+ b.command.mode != SD_SHUTDOWN_HALT &&
+ b.command.mode != SD_SHUTDOWN_KEXEC) {
+ log_warning("Message has invalid mode. Ignoring.");
return 0;
}
- char_array_0(c.wall_message);
+ b.space[n] = 0;
- *_c = c;
+ *_b = b;
return 1;
}
-static void warn_wall(usec_t n, struct shutdownd_command *c) {
+static void warn_wall(usec_t n, struct sd_shutdown_command *c) {
char date[FORMAT_TIMESTAMP_MAX];
const char *prefix;
char *l = NULL;
@@ -108,20 +125,22 @@ static void warn_wall(usec_t n, struct shutdownd_command *c) {
assert(c);
assert(c->warn_wall);
- if (n >= c->elapse)
+ if (n >= c->usec)
return;
- if (c->mode == 'H')
+ if (c->mode == SD_SHUTDOWN_HALT)
prefix = "The system is going down for system halt at ";
- else if (c->mode == 'P')
+ else if (c->mode == SD_SHUTDOWN_POWEROFF)
prefix = "The system is going down for power-off at ";
- else if (c->mode == 'r')
+ else if (c->mode == SD_SHUTDOWN_REBOOT)
prefix = "The system is going down for reboot at ";
+ else if (c->mode == SD_SHUTDOWN_KEXEC)
+ prefix = "The system is going down for kexec reboot at ";
else
assert_not_reached("Unknown mode!");
if (asprintf(&l, "%s%s%s%s!", c->wall_message, c->wall_message[0] ? "\n" : "",
- prefix, format_timestamp(date, sizeof(date), c->elapse)) < 0)
+ prefix, format_timestamp(date, sizeof(date), c->usec)) < 0)
log_error("Failed to allocate wall message");
else {
utmp_wall(l, NULL);
@@ -164,6 +183,85 @@ static usec_t when_nologin(usec_t elapse) {
return elapse > 5*USEC_PER_MINUTE ? elapse - 5*USEC_PER_MINUTE : 1;
}
+static const char *mode_to_string(enum sd_shutdown_mode m) {
+ switch (m) {
+ case SD_SHUTDOWN_REBOOT:
+ return "reboot";
+ case SD_SHUTDOWN_POWEROFF:
+ return "poweroff";
+ case SD_SHUTDOWN_HALT:
+ return "halt";
+ case SD_SHUTDOWN_KEXEC:
+ return "kexec";
+ default:
+ return NULL;
+ }
+}
+
+static int update_schedule_file(struct sd_shutdown_command *c) {
+ int r;
+ FILE *f;
+ char *temp_path, *t;
+
+ assert(c);
+
+ r = safe_mkdir("/run/systemd/shutdown", 0755, 0, 0);
+ if (r < 0) {
+ log_error("Failed to create shutdown subdirectory: %s", strerror(-r));
+ return r;
+ }
+
+ t = cescape(c->wall_message);
+ if (!t) {
+ log_error("Out of memory");
+ return -ENOMEM;
+ }
+
+ r = fopen_temporary("/run/systemd/shutdown/scheduled", &f, &temp_path);
+ if (r < 0) {
+ log_error("Failed to save information about scheduled shutdowns: %s", strerror(-r));
+ free(t);
+ return r;
+ }
+
+ fchmod(fileno(f), 0644);
+
+ fprintf(f,
+ "USEC=%llu\n"
+ "WARN_WALL=%i\n"
+ "MODE=%s\n",
+ (unsigned long long) c->usec,
+ c->warn_wall,
+ mode_to_string(c->mode));
+
+ if (c->dry_run)
+ fputs("DRY_RUN=1\n", f);
+
+ if (!isempty(t))
+ fprintf(f, "WALL_MESSAGE=%s\n", t);
+
+ free(t);
+
+ fflush(f);
+
+ if (ferror(f) || rename(temp_path, "/run/systemd/shutdown/scheduled") < 0) {
+ log_error("Failed to write information about scheduled shutdowns: %m");
+ r = -errno;
+
+ unlink(temp_path);
+ unlink("/run/systemd/shutdown/scheduled");
+ }
+
+ fclose(f);
+ free(temp_path);
+
+ return r;
+}
+
+static bool scheduled(struct sd_shutdown_command *c) {
+ return c->usec > 0 && c->mode != SD_SHUTDOWN_NONE;
+}
+
int main(int argc, char *argv[]) {
enum {
FD_SOCKET,
@@ -174,9 +272,9 @@ int main(int argc, char *argv[]) {
};
int r = EXIT_FAILURE, n_fds;
- struct shutdownd_command c;
+ union shutdown_buffer b;
struct pollfd pollfd[_FD_MAX];
- bool exec_shutdown = false, unlink_nologin = false, failed = false;
+ bool exec_shutdown = false, unlink_nologin = false;
unsigned i;
if (getppid() != 1) {
@@ -195,7 +293,8 @@ int main(int argc, char *argv[]) {
umask(0022);
- if ((n_fds = sd_listen_fds(true)) < 0) {
+ n_fds = sd_listen_fds(true);
+ if (n_fds < 0) {
log_error("Failed to read listening file descriptors from environment: %s", strerror(-r));
return EXIT_FAILURE;
}
@@ -205,39 +304,33 @@ int main(int argc, char *argv[]) {
return EXIT_FAILURE;
}
- zero(c);
+ zero(b);
zero(pollfd);
pollfd[FD_SOCKET].fd = SD_LISTEN_FDS_START;
pollfd[FD_SOCKET].events = POLLIN;
- for (i = 0; i < _FD_MAX; i++) {
-
- if (i == FD_SOCKET)
- continue;
-
+ for (i = FD_WALL_TIMER; i < _FD_MAX; i++) {
pollfd[i].events = POLLIN;
-
- if ((pollfd[i].fd = timerfd_create(CLOCK_REALTIME, TFD_NONBLOCK|TFD_CLOEXEC)) < 0) {
+ pollfd[i].fd = timerfd_create(CLOCK_REALTIME, TFD_NONBLOCK|TFD_CLOEXEC);
+ if (pollfd[i].fd < 0) {
log_error("timerfd_create(): %m");
- failed = true;
+ goto finish;
}
}
- if (failed)
- goto finish;
-
log_debug("systemd-shutdownd running as pid %lu", (unsigned long) getpid());
sd_notify(false,
"READY=1\n"
"STATUS=Processing requests...");
- do {
+ for (;;) {
int k;
usec_t n;
- if (poll(pollfd, _FD_MAX, -1) < 0) {
+ k = poll(pollfd, _FD_MAX, scheduled(&b.command) ? -1 : 0);
+ if (k < 0) {
if (errno == EAGAIN || errno == EINTR)
continue;
@@ -246,34 +339,44 @@ int main(int argc, char *argv[]) {
goto finish;
}
+ /* Exit on idle */
+ if (k == 0)
+ break;
+
n = now(CLOCK_REALTIME);
if (pollfd[FD_SOCKET].revents) {
- if ((k = read_packet(pollfd[FD_SOCKET].fd, &c)) < 0)
+ k = read_packet(pollfd[FD_SOCKET].fd, &b);
+ if (k < 0)
goto finish;
- else if (k > 0 && c.elapse > 0) {
+ else if (k > 0) {
struct itimerspec its;
char date[FORMAT_TIMESTAMP_MAX];
- if (c.warn_wall) {
+ if (!scheduled(&b.command)) {
+ log_info("Shutdown canceled.");
+ break;
+ }
+
+ zero(its);
+ if (b.command.warn_wall) {
/* Send wall messages every so often */
- zero(its);
- timespec_store(&its.it_value, when_wall(n, c.elapse));
- if (timerfd_settime(pollfd[FD_WALL_TIMER].fd, TFD_TIMER_ABSTIME, &its, NULL) < 0) {
- log_error("timerfd_settime(): %m");
- goto finish;
- }
+ timespec_store(&its.it_value, when_wall(n, b.command.usec));
/* Warn immediately if less than 15 minutes are left */
- if (n < c.elapse &&
- n + 15*USEC_PER_MINUTE >= c.elapse)
- warn_wall(n, &c);
+ if (n < b.command.usec &&
+ n + 15*USEC_PER_MINUTE >= b.command.usec)
+ warn_wall(n, &b.command);
+ }
+ if (timerfd_settime(pollfd[FD_WALL_TIMER].fd, TFD_TIMER_ABSTIME, &its, NULL) < 0) {
+ log_error("timerfd_settime(): %m");
+ goto finish;
}
/* Disallow logins 5 minutes prior to shutdown */
zero(its);
- timespec_store(&its.it_value, when_nologin(c.elapse));
+ timespec_store(&its.it_value, when_nologin(b.command.usec));
if (timerfd_settime(pollfd[FD_NOLOGIN_TIMER].fd, TFD_TIMER_ABSTIME, &its, NULL) < 0) {
log_error("timerfd_settime(): %m");
goto finish;
@@ -281,27 +384,32 @@ int main(int argc, char *argv[]) {
/* Shutdown after the specified time is reached */
zero(its);
- timespec_store(&its.it_value, c.elapse);
+ timespec_store(&its.it_value, b.command.usec);
if (timerfd_settime(pollfd[FD_SHUTDOWN_TIMER].fd, TFD_TIMER_ABSTIME, &its, NULL) < 0) {
log_error("timerfd_settime(): %m");
goto finish;
}
+ update_schedule_file(&b.command);
+
sd_notifyf(false,
- "STATUS=Shutting down at %s...",
- format_timestamp(date, sizeof(date), c.elapse));
+ "STATUS=Shutting down at %s (%s)...",
+ format_timestamp(date, sizeof(date), b.command.usec),
+ mode_to_string(b.command.mode));
+
+ log_info("Shutting down at %s (%s)...", date, mode_to_string(b.command.mode));
}
}
if (pollfd[FD_WALL_TIMER].revents) {
struct itimerspec its;
- warn_wall(n, &c);
+ warn_wall(n, &b.command);
flush_fd(pollfd[FD_WALL_TIMER].fd);
/* Restart timer */
zero(its);
- timespec_store(&its.it_value, when_wall(n, c.elapse));
+ timespec_store(&its.it_value, when_wall(n, b.command.usec));
if (timerfd_settime(pollfd[FD_WALL_TIMER].fd, TFD_TIMER_ABSTIME, &its, NULL) < 0) {
log_error("timerfd_settime(): %m");
goto finish;
@@ -313,7 +421,8 @@ int main(int argc, char *argv[]) {
log_info("Creating /run/nologin, blocking further logins...");
- if ((e = write_one_line_file_atomic("/run/nologin", "System is going down.")) < 0)
+ e = write_one_line_file_atomic("/run/nologin", "System is going down.");
+ if (e < 0)
log_error("Failed to create /run/nologin: %s", strerror(-e));
else
unlink_nologin = true;
@@ -325,8 +434,7 @@ int main(int argc, char *argv[]) {
exec_shutdown = true;
goto finish;
}
-
- } while (c.elapse > 0);
+ }
r = EXIT_SUCCESS;
@@ -341,19 +449,21 @@ finish:
if (unlink_nologin)
unlink("/run/nologin");
- if (exec_shutdown && !c.dry_run) {
+ unlink("/run/systemd/shutdown/scheduled");
+
+ if (exec_shutdown && !b.command.dry_run) {
char sw[3];
sw[0] = '-';
- sw[1] = c.mode;
+ sw[1] = b.command.mode;
sw[2] = 0;
execl(SYSTEMCTL_BINARY_PATH,
"shutdown",
sw,
"now",
- (c.warn_wall && c.wall_message[0]) ? c.wall_message :
- (c.warn_wall ? NULL : "--no-wall"),
+ (b.command.warn_wall && b.command.wall_message[0]) ? b.command.wall_message :
+ (b.command.warn_wall ? NULL : "--no-wall"),
NULL);
log_error("Failed to execute /sbin/shutdown: %m");
diff --git a/src/shutdownd.h b/src/shutdownd.h
deleted file mode 100644
index 4581649733..0000000000
--- a/src/shutdownd.h
+++ /dev/null
@@ -1,46 +0,0 @@
-/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
-
-#ifndef fooshutdowndhfoo
-#define fooshutdowndhfoo
-
-/***
- This file is part of systemd.
-
- Copyright 2010 Lennart Poettering
-
- systemd is free software; you can redistribute it and/or modify it
- under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 2 of the License, or
- (at your option) any later version.
-
- systemd is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- General Public License for more details.
-
- You should have received a copy of the GNU General Public License
- along with systemd; If not, see <http://www.gnu.org/licenses/>.
-***/
-
-#include "util.h"
-#include "macro.h"
-
-/* This is a private message, we don't care much about ABI
- * stability. */
-
-_packed_ struct shutdownd_command {
- usec_t elapse;
- char mode; /* H, P, r, i.e. the switches usually passed to
- * shutdown to select whether to halt, power-off or
- * reboot the machine */
- bool dry_run;
- bool warn_wall;
-
- /* Yepp, sometimes we are lazy and use fixed-size strings like
- * this one. Shame on us. But then again, we'd have to
- * pre-allocate the receive buffer anyway, so there's nothing
- * too bad here. */
- char wall_message[4096];
-};
-
-#endif
diff --git a/src/systemctl.c b/src/systemctl.c
index 3cab0dd85a..43a1446a8c 100644
--- a/src/systemctl.c
+++ b/src/systemctl.c
@@ -36,6 +36,7 @@
#include <dbus/dbus.h>
#include <systemd/sd-daemon.h>
+#include <systemd/sd-shutdown.h>
#include "log.h"
#include "util.h"
@@ -51,7 +52,6 @@
#include "list.h"
#include "path-lookup.h"
#include "conf-parser.h"
-#include "shutdownd.h"
#include "exit-status.h"
#include "bus-errors.h"
#include "build.h"
@@ -4628,6 +4628,7 @@ static int shutdown_parse_argv(int argc, char *argv[]) {
{ "halt", no_argument, NULL, 'H' },
{ "poweroff", no_argument, NULL, 'P' },
{ "reboot", no_argument, NULL, 'r' },
+ { "kexec", no_argument, NULL, 'K' }, /* not documented extension */
{ "no-wall", no_argument, NULL, ARG_NO_WALL },
{ NULL, 0, NULL, 0 }
};
@@ -4659,6 +4660,10 @@ static int shutdown_parse_argv(int argc, char *argv[]) {
arg_action = ACTION_REBOOT;
break;
+ case 'K':
+ arg_action = ACTION_KEXEC;
+ break;
+
case 'h':
if (arg_action != ACTION_HALT)
arg_action = ACTION_POWEROFF;
@@ -5191,39 +5196,42 @@ static int systemctl_main(DBusConnection *bus, int argc, char *argv[], DBusError
}
static int send_shutdownd(usec_t t, char mode, bool dry_run, bool warn, const char *message) {
- int fd = -1;
+ int fd;
struct msghdr msghdr;
- struct iovec iovec;
+ struct iovec iovec[2];
union sockaddr_union sockaddr;
- struct shutdownd_command c;
+ struct sd_shutdown_command c;
+
+ fd = socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0);
+ if (fd < 0)
+ return -errno;
zero(c);
- c.elapse = t;
+ c.usec = t;
c.mode = mode;
c.dry_run = dry_run;
c.warn_wall = warn;
- if (message)
- strncpy(c.wall_message, message, sizeof(c.wall_message));
-
- if ((fd = socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0)) < 0)
- return -errno;
-
zero(sockaddr);
sockaddr.sa.sa_family = AF_UNIX;
- sockaddr.un.sun_path[0] = 0;
strncpy(sockaddr.un.sun_path, "/run/systemd/shutdownd", sizeof(sockaddr.un.sun_path));
- zero(iovec);
- iovec.iov_base = (char*) &c;
- iovec.iov_len = sizeof(c);
-
zero(msghdr);
msghdr.msg_name = &sockaddr;
msghdr.msg_namelen = offsetof(struct sockaddr_un, sun_path) + sizeof("/run/systemd/shutdownd") - 1;
- msghdr.msg_iov = &iovec;
- msghdr.msg_iovlen = 1;
+ zero(iovec);
+ iovec[0].iov_base = (char*) &c;
+ iovec[0].iov_len = offsetof(struct sd_shutdown_command, wall_message);
+
+ if (isempty(message))
+ msghdr.msg_iovlen = 1;
+ else {
+ iovec[1].iov_base = (char*) message;
+ iovec[1].iov_len = strlen(message);
+ msghdr.msg_iovlen = 2;
+ }
+ msghdr.msg_iov = iovec;
if (sendmsg(fd, &msghdr, MSG_NOSIGNAL) < 0) {
close_nointr_nofail(fd);
@@ -5338,6 +5346,7 @@ static int halt_main(DBusConnection *bus) {
r = send_shutdownd(arg_when,
arg_action == ACTION_HALT ? 'H' :
arg_action == ACTION_POWEROFF ? 'P' :
+ arg_action == ACTION_KEXEC ? 'K' :
'r',
arg_dry,
!arg_no_wall,
@@ -5405,7 +5414,8 @@ int main(int argc, char*argv[]) {
log_parse_environment();
log_open();
- if ((r = parse_argv(argc, argv)) < 0)
+ r = parse_argv(argc, argv);
+ if (r < 0)
goto finish;
else if (r == 0) {
retval = EXIT_SUCCESS;
diff --git a/src/systemd/sd-shutdown.h b/src/systemd/sd-shutdown.h
new file mode 100644
index 0000000000..29fcf3417e
--- /dev/null
+++ b/src/systemd/sd-shutdown.h
@@ -0,0 +1,108 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#ifndef foosdshutdownhfoo
+#define foosdshutdownhfoo
+
+/***
+ This file is part of systemd.
+
+ Copyright 2010 Lennart Poettering
+
+ systemd is free software; you can redistribute it and/or modify it
+ under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 2 of the License, or
+ (at your option) any later version.
+
+ systemd is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+/* Interface for scheduling and cancelling timed shutdowns. */
+
+#include <inttypes.h>
+
+typedef enum sd_shutdown_mode {
+ SD_SHUTDOWN_NONE = 0,
+ SD_SHUTDOWN_REBOOT = 'r',
+ SD_SHUTDOWN_POWEROFF = 'P',
+ SD_SHUTDOWN_HALT = 'H',
+ SD_SHUTDOWN_KEXEC = 'K'
+} sd_shutdown_mode_t;
+
+/* Calculate the size of the message as "offsetof(struct
+ * sd_shutdown_command, wall_message) +
+ * strlen(command.wall_message)" */
+__attribute__((packed)) struct sd_shutdown_command {
+ /* Microseconds after the epoch 1970 UTC */
+ uint64_t usec;
+
+ /* H, P, r, i.e. the switches usually passed to
+ * /usr/bin/shutdown to select whether to halt, power-off or
+ * reboot the machine */
+ sd_shutdown_mode_t mode:8;
+
+ /* If non-zero, don't actually shut down, just pretend */
+ unsigned dry_run:1;
+
+ /* If non-zero, send our wall message */
+ unsigned warn_wall:1;
+
+ /* The wall message to send around. Leave empty for the
+ * default wall message */
+ char wall_message[];
+};
+
+/* The scheme is very simple:
+ *
+ * To schedule a shutdown, simply fill in and send a single
+ * AF_UNIX/SOCK_DGRAM datagram with the structure above suffixed with
+ * the wall message to the socket /run/systemd/shutdownd (leave an
+ * empty wall message for the default shutdown message). To calculate
+ * the size of the message use "offsetof(struct sd_shutdown_command,
+ * wall_message) + strlen(command.wall_message)".
+ *
+ * To cancel a shutdown, do the same, but send an fully zeroed out
+ * structure.
+ *
+ * To be notified about scheduled shutdowns, create an inotify watch
+ * on /run/shutdown/. Whenever a file called "scheduled" appears a
+ * shutdown is scheduled. If it is removed it is canceled. It is
+ * replaced the scheduled shutdown has been changed. The file contains
+ * a simple environment-like block, that contains information about
+ * the scheduled shutdown:
+ *
+ * USEC=
+ * encodes the time for the shutdown in usecs since the epoch UTC,
+ * formatted as numeric string.
+ *
+ * WARN_WALL=
+ * is 1 if a wall message shall be sent
+ *
+ * DRY_RUN=
+ * is 1 if a dry run shutdown is scheduled
+ *
+ * MODE=
+ * is the shutdown mode, one of "poweroff", "reboot", "halt", "kexec"
+ *
+ * WALL_MESSAGE=
+ * is the wall message to use, with all special characters escape in C style.
+ *
+ * Note that some fields might be missing if they do not apply.
+ *
+ * Note that the file is first written to a temporary file and then
+ * renamed, in order to provide atomic properties for readers: if the
+ * file exists under the name "scheduled" it is guaranteed to be fully
+ * written. A reader should ignore all files in that directory by any
+ * other name.
+ *
+ * Scheduled shutdowns are only accepted from privileged processes,
+ * but the directory may be watched and the file in it read by
+ * anybody.
+ */
+
+#endif