уведомлять сервисного менеджера о завершении запуска и других изменениях статуса сервиса (notify service manager about start-up completion and other service status changes)
Имя (Name)
sd_notify, sd_notifyf, sd_pid_notify, sd_pid_notifyf,
sd_pid_notify_with_fds, sd_notify_barrier - Notify service
manager about start-up completion and other service status
changes
Синопсис (Synopsis)
#include <systemd/sd-daemon.h>
int sd_notify(int unset_environment, const char *state);
int sd_notifyf(int unset_environment, const char *format, ...);
int sd_pid_notify(pid_t pid, int unset_environment,
const char *state);
int sd_pid_notifyf(pid_t pid, int unset_environment,
const char *format, ...);
int sd_pid_notify_with_fds(pid_t pid, int unset_environment,
const char *state, const int *fds,
unsigned n_fds);
int sd_notify_barrier(int unset_environment, uint64_t timeout);
Описание (Description)
sd_notify() may be called by a service to notify the service
manager about state changes. It can be used to send arbitrary
information, encoded in an environment-block-like string. Most
importantly, it can be used for start-up completion notification.
If the unset_environment parameter is non-zero, sd_notify() will
unset the $NOTIFY_SOCKET environment variable before returning
(regardless of whether the function call itself succeeded or
not). Further calls to sd_notify() will then fail, but the
variable is no longer inherited by child processes.
The state parameter should contain a newline-separated list of
variable assignments, similar in style to an environment block. A
trailing newline is implied if none is specified. The string may
contain any kind of variable assignments, but the following shall
be considered well-known:
READY=1
Tells the service manager that service startup is finished,
or the service finished loading its configuration. This is
only used by systemd if the service definition file has
Type=notify set. Since there is little value in signaling
non-readiness, the only value services should send is
"READY=1" (i.e. "READY=0" is not defined).
RELOADING=1
Tells the service manager that the service is reloading its
configuration. This is useful to allow the service manager to
track the service's internal state, and present it to the
user. Note that a service that sends this notification must
also send a "READY=1" notification when it completed
reloading its configuration. Reloads are propagated in the
same way as they are when initiated by the user.
STOPPING=1
Tells the service manager that the service is beginning its
shutdown. This is useful to allow the service manager to
track the service's internal state, and present it to the
user.
STATUS=...
Passes a single-line UTF-8 status string back to the service
manager that describes the service state. This is free-form
and can be used for various purposes: general state feedback,
fsck-like programs could pass completion percentages and
failing programs could pass a human-readable error message.
Example: "STATUS=Completed 66% of file system check..."
ERRNO=...
If a service fails, the errno-style error code, formatted as
string. Example: "ERRNO=2" for ENOENT.
BUSERROR=...
If a service fails, the D-Bus error-style error code.
Example: "BUSERROR=org.freedesktop.DBus.Error.TimedOut"
MAINPID=...
The main process ID (PID) of the service, in case the service
manager did not fork off the process itself. Example:
"MAINPID=4711"
WATCHDOG=1
Tells the service manager to update the watchdog timestamp.
This is the keep-alive ping that services need to issue in
regular intervals if WatchdogSec= is enabled for it. See
systemd.service(5) for information how to enable this
functionality and sd_watchdog_enabled(3) for the details of
how the service can check whether the watchdog is enabled.
WATCHDOG=trigger
Tells the service manager that the service detected an
internal error that should be handled by the configured
watchdog options. This will trigger the same behaviour as if
WatchdogSec= is enabled and the service did not send
"WATCHDOG=1" in time. Note that WatchdogSec= does not need to
be enabled for "WATCHDOG=trigger" to trigger the watchdog
action. See systemd.service(5) for information about the
watchdog behavior.
WATCHDOG_USEC=...
Reset watchdog_usec value during runtime. Notice that this is
not available when using sd_event_set_watchdog() or
sd_watchdog_enabled(). Example : "WATCHDOG_USEC=20000000"
EXTEND_TIMEOUT_USEC=...
Tells the service manager to extend the startup, runtime or
shutdown service timeout corresponding the current state. The
value specified is a time in microseconds during which the
service must send a new message. A service timeout will occur
if the message isn't received, but only if the runtime of the
current state is beyond the original maximum times of
TimeoutStartSec=, RuntimeMaxSec=, and TimeoutStopSec=. See
systemd.service(5) for effects on the service timeouts.
FDSTORE=1
Stores additional file descriptors in the service manager.
File descriptors sent this way will be maintained per-service
by the service manager and will later be handed back using
the usual file descriptor passing logic at the next
invocation of the service, see sd_listen_fds(3). This is
useful for implementing services that can restart after an
explicit request or a crash without losing state. Any open
sockets and other file descriptors which should not be closed
during the restart may be stored this way. Application state
can either be serialized to a file in /run/, or better,
stored in a memfd_create(2) memory file descriptor. Note that
the service manager will accept messages for a service only
if its FileDescriptorStoreMax= setting is non-zero (defaults
to zero, see systemd.service(5)). If FDPOLL=0 is not set and
the file descriptors sent are pollable (see epoll_ctl(2)),
then any EPOLLHUP or EPOLLERR event seen on them will result
in their automatic removal from the store. Multiple arrays of
file descriptors may be sent in separate messages, in which
case the arrays are combined. Note that the service manager
removes duplicate (pointing to the same object) file
descriptors before passing them to the service. Use
sd_pid_notify_with_fds() to send messages with "FDSTORE=1",
see below.
FDSTOREREMOVE=1
Removes file descriptors from the file descriptor store. This
field needs to be combined with FDNAME= to specify the name
of the file descriptors to remove.
FDNAME=...
When used in combination with FDSTORE=1, specifies a name for
the submitted file descriptors. When used with
FDSTOREREMOVE=1, specifies the name for the file descriptors
to remove. This name is passed to the service during
activation, and may be queried using
sd_listen_fds_with_names(3). File descriptors submitted
without this field set, will implicitly get the name "stored"
assigned. Note that, if multiple file descriptors are
submitted at once, the specified name will be assigned to all
of them. In order to assign different names to submitted file
descriptors, submit them in separate invocations of
sd_pid_notify_with_fds(). The name may consist of arbitrary
ASCII characters except control characters or ":". It may not
be longer than 255 characters. If a submitted name does not
follow these restrictions, it is ignored.
FDPOLL=0
When used in combination with FDSTORE=1, disables polling of
the stored file descriptors regardless of whether or not they
are pollable. As this option disables automatic cleanup of
the stored file descriptors on EPOLLERR and EPOLLHUP, care
must be taken to ensure proper manual cleanup. Use of this
option is not generally recommended except for when automatic
cleanup has unwanted behavior such as prematurely discarding
file descriptors from the store.
BARRIER=1
Tells the service manager that the client is explicitly
requesting synchronization by means of closing the file
descriptor sent with this command. The service manager
guarantees that the processing of a
BARRIER=1 command will only happen after all previous
notification messages sent before this command have been
processed. Hence, this command accompanied with a single file
descriptor can be used to synchronize against reception of
all previous status messages. Note that this command cannot
be mixed with other notifications, and has to be sent in a
separate message to the service manager, otherwise all
assignments will be ignored. Note that sending 0 or more than
1 file descriptor with this command is a violation of the
protocol.
It is recommended to prefix variable names that are not listed
above with X_ to avoid namespace clashes.
Note that systemd will accept status data sent from a service
only if the NotifyAccess= option is correctly set in the service
definition file. See systemd.service(5) for details.
Note that sd_notify() notifications may be attributed to units
correctly only if either the sending process is still around at
the time PID 1 processes the message, or if the sending process
is explicitly runtime-tracked by the service manager. The latter
is the case if the service manager originally forked off the
process, i.e. on all processes that match NotifyAccess=main or
NotifyAccess=exec. Conversely, if an auxiliary process of the
unit sends an sd_notify() message and immediately exits, the
service manager might not be able to properly attribute the
message to the unit, and thus will ignore it, even if
NotifyAccess=all is set for it.
Hence, to eliminate all race conditions involving lookup of the
client's unit and attribution of notifications to units
correctly, sd_notify_barrier() may be used. This call acts as a
synchronization point and ensures all notifications sent before
this call have been picked up by the service manager when it
returns successfully. Use of sd_notify_barrier() is needed for
clients which are not invoked by the service manager, otherwise
this synchronization mechanism is unnecessary for attribution of
notifications to the unit.
sd_notifyf() is similar to sd_notify() but takes a printf()-like
format string plus arguments.
sd_pid_notify() and sd_pid_notifyf() are similar to sd_notify()
and sd_notifyf() but take a process ID (PID) to use as
originating PID for the message as first argument. This is useful
to send notification messages on behalf of other processes,
provided the appropriate privileges are available. If the PID
argument is specified as 0, the process ID of the calling process
is used, in which case the calls are fully equivalent to
sd_notify() and sd_notifyf().
sd_pid_notify_with_fds() is similar to sd_pid_notify() but takes
an additional array of file descriptors. These file descriptors
are sent along the notification message to the service manager.
This is particularly useful for sending "FDSTORE=1" messages, as
described above. The additional arguments are a pointer to the
file descriptor array plus the number of file descriptors in the
array. If the number of file descriptors is passed as 0, the call
is fully equivalent to sd_pid_notify(), i.e. no file descriptors
are passed. Note that sending file descriptors to the service
manager on messages that do not expect them (i.e. without
"FDSTORE=1") they are immediately closed on reception.
sd_notify_barrier() allows the caller to synchronize against
reception of previously sent notification messages and uses the
"BARRIER=1" command. It takes a relative timeout value in
microseconds which is passed to ppoll(2). A value of UINT64_MAX
is interpreted as infinite timeout.
