|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | SYNOPSIS | DESCRIPTION | WELL-KNOWN ASSIGNMENTS | RETURN VALUE | NOTES | ENVIRONMENT | EXAMPLES | HISTORY | SEE ALSO | NOTES | COLOPHON |
|
|
|
SD_NOTIFY(3) sd_notify SD_NOTIFY(3)
sd_notify, sd_notifyf, sd_pid_notify, sd_pid_notifyf,
sd_pid_notify_with_fds, sd_pid_notifyf_with_fds,
sd_notify_barrier, sd_pid_notify_barrier - Notify service manager
about start-up completion and other service status changes
#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_pid_notifyf_with_fds(pid_t pid, int unset_environment,
const int *fds, size_t n_fds,
const char *format, ...);
int sd_notify_barrier(int unset_environment, uint64_t timeout);
int sd_pid_notify_barrier(pid_t pid, int unset_environment,
uint64_t timeout);
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 or reload completion
notifications.
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 silently do nothing, and
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 see the next section
for a list of assignments understood by the service manager.
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. Effectively, this means that
a privileged invocation of sd_pid_notify() may circumvent
NotifyAccess=main or NotifyAccess=exec restrictions enforced for a
service. 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 file descriptors sent to the service manager
on a message without "FDSTORE=1" are immediately closed on
reception.
sd_pid_notifyf_with_fds() is a combination of
sd_pid_notify_with_fds() and sd_notifyf(), i.e. it accepts both a
PID and a set of file descriptors as input, and processes a format
string to generate the state string.
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.
sd_pid_notify_barrier() is just like sd_notify_barrier(), but
allows specifying the originating PID for the notification
message.
The following assignments have a defined meaning:
READY=1
Tells the service manager that service startup is finished, or
the service finished re-loading its configuration. This is
only used by systemd if the service definition file has
Type=notify or Type=notify-reload 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 beginning to
reload 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 the service manager is
notified about with this mechanisms are propagated in the same
way as they are when originally initiated through the service
manager. This message is particularly relevant for
Type=notify-reload services, to inform the service manager
that the request to reload the service has been received and
is now being processed.
Added in version 217.
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.
Added in version 217.
MONOTONIC_USEC=...
A field carrying the monotonic timestamp (as per
CLOCK_MONOTONIC) formatted in decimal in μs, when the
notification message was generated by the client. This is
typically used in combination with "RELOADING=1", to allow the
service manager to properly synchronize reload cycles. See
systemd.service(5) for details, specifically
"Type=notify-reload".
Added in version 253.
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..."
Added in version 233.
NOTIFYACCESS=...
Reset the access to the service status notification socket
during runtime, overriding NotifyAccess= setting in the
service unit file. See systemd.service(5) for details,
specifically "NotifyAccess=" for a list of accepted values.
Added in version 254.
ERRNO=...
If a service fails, the errno-style error code, formatted as
string. Example: "ERRNO=2" for ENOENT.
Added in version 233.
BUSERROR=...
If a service fails, the D-Bus error-style error code. Example:
"BUSERROR=org.freedesktop.DBus.Error.TimedOut".
Added in version 233.
VARLINKERROR=...
If a service fails, the Varlink error-style error code.
Example: "VARLINKERROR=org.varlink.service.InvalidParameter".
Added in version 257.
EXIT_STATUS=...
The exit status of a service or the manager itself. Note that
systemd currently does not consume this value when sent by
services, so this assignment is only informational. The
manager will send this notification to its notification
socket, which may be used to collect an exit status from the
system (a container or VM) as it shuts down. For example,
mkosi(1) makes use of this. The value to return may be set via
the systemctl(1) exit verb.
Added in version 254.
MAINPID=...
Change the main process ID (PID) of the service. This is
especially useful in the case where the real main process is
not directly forked off by the service manager. Example:
"MAINPID=4711".
Added in version 233.
MAINPIDFDID=...
The pidfd inode number of the new main process (specified
through MAINPID=). This information can be acquired through
sd_pidfd_get_inode_id(3) on the pidfd and is used to identify
the process in a race-free fashion. Alternatively, a pidfd can
be sent directly to the service manager (see MAINPIDFD=1
below).
Added in version 257.
MAINPIDFD=1
Similar to MAINPID= with MAINPIDFDID=, but the process is
referenced directly by the pidfd passed to the service
manager. This is useful if pidfd id is not supported on the
system. Exactly one fd is expected for this notification.
Added in version 257.
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.
Added in version 243.
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"
Added in version 233.
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 is not 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.
Added in version 236.
RESTART_RESET=1
Reset the restart counter of the service, which has the effect
of restoring the restart duration to RestartSec= if
RestartSteps= and RestartMaxDelaySec= are in use. For more
information, refer to systemd.service(5).
Added in version 258.
FDSTORE=1
Store file descriptors in the service manager. File
descriptors sent this way will be held for the service by the
service manager and will later be handed back using the usual
file descriptor passing logic at the next start or restart of
the service, see sd_listen_fds(3). Any open sockets and other
file descriptors which should not be closed during a restart
may be stored this way. When a service is stopped, its file
descriptor store is discarded and all file descriptors in it
are closed, except when overridden with
FileDescriptorStorePreserve=, see systemd.service(5).
The service manager will accept messages for a service only if
its FileDescriptorStoreMax= setting is non-zero (defaults to
zero, see systemd.service(5)). The service manager will set
the $FDSTORE environment variable for services that have the
file descriptor store enabled, see systemd.exec(5).
If FDPOLL=0 is not set and the file descriptors 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 sets of file descriptors may be sent in separate
messages, in which case the sets are combined. The service
manager removes duplicate file descriptors (those pointing to
the same object) before passing them to the service.
This functionality should be used to implement services that
can restart after an explicit request or a crash without
losing state. Application state can either be serialized to a
file in /run/, or better, stored in a memfd_create(2) memory
file descriptor. Use sd_pid_notify_with_fds() to send messages
with "FDSTORE=1". It is recommended to combine FDSTORE= with
FDNAME= to make it easier to manage the stored file
descriptors.
For further information on the file descriptor store see the
File Descriptor Store[1] overview.
Added in version 219.
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.
Added in version 236.
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 will be called "stored".
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.
Note that if multiple file descriptors are submitted in a
single message, the specified name will be used for all of
them. In order to assign different names to submitted file
descriptors, submit them in separate messages.
Added in version 233.
FDPOLL=0
When used in combination with FDSTORE=1, disables polling of
the submitted file descriptors regardless of whether or not
they are pollable. As this option disables automatic cleanup
of the submitted 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.
Added in version 246.
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.
Added in version 246.
The notification messages sent by services are interpreted by the
service manager. Unknown assignments are ignored. Thus, it is safe
(but often without effect) to send assignments which are not in
this list. The protocol is extensible, but care should be taken to
ensure private extensions are recognizable as such. Specifically,
it is recommend to prefix them with "X_" followed by some
namespace identifier. The service manager also sends some messages
to its notification socket, which may then consumed by a
supervising machine or container manager further up the stack. The
service manager sends a number of extension fields, for example
X_SYSTEMD_UNIT_ACTIVE=, for details see systemd(1).
On failure, these calls return a negative errno-style error code.
If $NOTIFY_SOCKET was not set and hence no status message could be
sent, 0 is returned. If the status was sent, these functions
return a positive value. In order to support both service managers
that implement this scheme and those which do not, it is generally
recommended to ignore the return value of this call. Note that the
return value simply indicates whether the notification message was
enqueued properly, it does not reflect whether the message could
be processed successfully. Specifically, no error is returned when
a file descriptor is attempted to be stored using FDSTORE=1 but
the service is not actually configured to permit storing of file
descriptors (see above).
Errors
Returned errors may indicate the following problems:
-E2BIG
More file descriptors passed at once than the system allows.
On Linux the number of file descriptors that may be passed
across AF_UNIX sockets at once is 253, see unix(7) for
details.
Added in version 257.
Functions described here are available as a shared library, which
can be compiled against and linked to with the
libsystemd pkg-config(1) file.
The code described here uses getenv(3), which is declared to be
not multi-thread-safe. This means that the code calling the
functions described here must not call setenv(3) from a parallel
thread. It is recommended to only do calls to setenv() from an
early phase of the program when no other threads have been
started.
These functions send a single datagram with the state string as
payload to the socket referenced in the $NOTIFY_SOCKET environment
variable. If the first character of $NOTIFY_SOCKET is "/" or "@",
the string is understood as an AF_UNIX or Linux abstract namespace
socket (respectively), and in both cases the datagram is
accompanied by the process credentials of the sending service,
using SCM_CREDENTIALS. If the string starts with "vsock:" then the
string is understood as an AF_VSOCK address, which is useful for
hypervisors/VMMs or other processes on the host to receive a
notification when a virtual machine has finished booting. Note
that in case the hypervisor does not support SOCK_DGRAM over
AF_VSOCK, SOCK_SEQPACKET will be used instead. "vsock-stream",
"vsock-dgram" and "vsock-seqpacket" can be used instead of "vsock"
to force usage of the corresponding socket type. The address
should be in the form: "vsock:CID:PORT". Note that unlike other
uses of vsock, the CID is mandatory and cannot be
"VMADDR_CID_ANY". Note that PID1 will send the VSOCK packets from
a privileged port (i.e.: lower than 1024), as an attempt to
address concerns that unprivileged processes in the guest might
try to send malicious notifications to the host, driving it to
make destructive decisions based on them.
Standalone Implementations
Note that, while using this library should be preferred in order
to avoid code duplication, it is also possible to reimplement the
simple readiness notification protocol without external
dependencies, as demonstrated in the following self-contained
examples from several languages:
C
/* SPDX-License-Identifier: MIT-0 */
/* Implement the systemd notify protocol without external dependencies.
* Supports both readiness notification on startup and on reloading,
* according to the protocol defined at:
* https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html
* This protocol is guaranteed to be stable as per:
* https://systemd.io/PORTABILITY_AND_STABILITY/ */
#define _GNU_SOURCE 1
#include <errno.h>
#include <inttypes.h>
#include <signal.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <time.h>
#include <unistd.h>
#define _cleanup_(f) __attribute__((cleanup(f)))
static void closep(int *fd) {
if (!fd || *fd < 0)
return;
close(*fd);
*fd = -1;
}
static int notify(const char *message) {
union sockaddr_union {
struct sockaddr sa;
struct sockaddr_un sun;
} socket_addr = {
.sun.sun_family = AF_UNIX,
};
size_t path_length, message_length;
_cleanup_(closep) int fd = -1;
const char *socket_path;
/* Verify the argument first */
if (!message)
return -EINVAL;
message_length = strlen(message);
if (message_length == 0)
return -EINVAL;
/* If the variable is not set, the protocol is a noop */
socket_path = getenv("NOTIFY_SOCKET");
if (!socket_path)
return 0; /* Not set? Nothing to do */
/* Only AF_UNIX is supported, with path or abstract sockets */
if (socket_path[0] != '/' && socket_path[0] != '@')
return -EAFNOSUPPORT;
path_length = strlen(socket_path);
/* Ensure there is room for NUL byte */
if (path_length >= sizeof(socket_addr.sun.sun_path))
return -E2BIG;
memcpy(socket_addr.sun.sun_path, socket_path, path_length);
/* Support for abstract socket */
if (socket_addr.sun.sun_path[0] == '@')
socket_addr.sun.sun_path[0] = 0;
fd = socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0);
if (fd < 0)
return -errno;
if (connect(fd, &socket_addr.sa, offsetof(struct sockaddr_un, sun_path) + path_length) != 0)
return -errno;
ssize_t written = write(fd, message, message_length);
if (written != (ssize_t) message_length)
return written < 0 ? -errno : -EPROTO;
return 1; /* Notified! */
}
static int notify_ready(void) {
return notify("READY=1");
}
static int notify_reloading(void) {
/* A buffer with length sufficient to format the maximum UINT64 value. */
char reload_message[sizeof("RELOADING=1\nMONOTONIC_USEC=18446744073709551615")];
struct timespec ts;
uint64_t now;
/* Notify systemd that we are reloading, including a CLOCK_MONOTONIC timestamp in usec
* so that the program is compatible with a Type=notify-reload service. */
if (clock_gettime(CLOCK_MONOTONIC, &ts) < 0)
return -errno;
if (ts.tv_sec < 0 || ts.tv_nsec < 0 ||
(uint64_t) ts.tv_sec > (UINT64_MAX - (ts.tv_nsec / 1000ULL)) / 1000000ULL)
return -EINVAL;
now = (uint64_t) ts.tv_sec * 1000000ULL + (uint64_t) ts.tv_nsec / 1000ULL;
if (snprintf(reload_message, sizeof(reload_message), "RELOADING=1\nMONOTONIC_USEC=%" PRIu64, now) < 0)
return -EINVAL;
return notify(reload_message);
}
static int notify_stopping(void) {
return notify("STOPPING=1");
}
static volatile sig_atomic_t reloading = 0;
static volatile sig_atomic_t terminating = 0;
static void signal_handler(int sig) {
if (sig == SIGHUP)
reloading = 1;
else if (sig == SIGINT || sig == SIGTERM)
terminating = 1;
}
int main(int argc, char **argv) {
struct sigaction sa = {
.sa_handler = signal_handler,
.sa_flags = SA_RESTART,
};
int r;
/* Setup signal handlers */
sigemptyset(&sa.sa_mask);
sigaction(SIGHUP, &sa, NULL);
sigaction(SIGINT, &sa, NULL);
sigaction(SIGTERM, &sa, NULL);
/* Do more service initialization work here ... */
/* Now that all the preparations steps are done, signal readiness */
r = notify_ready();
if (r < 0) {
fprintf(stderr, "Failed to notify readiness to $NOTIFY_SOCKET: %s\n", strerror(-r));
return EXIT_FAILURE;
}
while (!terminating) {
if (reloading) {
reloading = false;
/* As a separate but related feature, we can also notify the manager
* when reloading configuration. This allows accurate state-tracking,
* and also automated hook-in of 'systemctl reload' without having to
* specify manually an ExecReload= line in the unit file. */
r = notify_reloading();
if (r < 0) {
fprintf(stderr, "Failed to notify reloading to $NOTIFY_SOCKET: %s\n", strerror(-r));
return EXIT_FAILURE;
}
/* Do some reconfiguration work here ... */
r = notify_ready();
if (r < 0) {
fprintf(stderr, "Failed to notify readiness to $NOTIFY_SOCKET: %s\n", strerror(-r));
return EXIT_FAILURE;
}
}
/* Do some daemon work here ... */
sleep(5);
}
r = notify_stopping();
if (r < 0) {
fprintf(stderr, "Failed to report termination to $NOTIFY_SOCKET: %s\n", strerror(-r));
return EXIT_FAILURE;
}
/* Do some shutdown work here ... */
return EXIT_SUCCESS;
}
Python
#!/usr/bin/python
# SPDX-License-Identifier: MIT-0
#
# Implement the systemd notify protocol without external dependencies.
# Supports both readiness notification on startup and on reloading,
# according to the protocol defined at:
# https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html
# This protocol is guaranteed to be stable as per:
# https://systemd.io/PORTABILITY_AND_STABILITY/
import errno
import os
import signal
import socket
import sys
import time
reloading = False
terminating = False
def notify(message):
if not message:
raise ValueError("notify() requires a message")
socket_path = os.environ.get("NOTIFY_SOCKET")
if not socket_path:
return
if socket_path[0] not in ("/", "@"):
raise OSError(errno.EAFNOSUPPORT, "Unsupported socket type")
# Handle abstract socket.
if socket_path[0] == "@":
socket_path = "\0" + socket_path[1:]
with socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM | socket.SOCK_CLOEXEC) as sock:
sock.connect(socket_path)
sock.sendall(message)
def notify_ready():
notify(b"READY=1")
def notify_reloading():
microsecs = time.clock_gettime_ns(time.CLOCK_MONOTONIC) // 1000
notify(f"RELOADING=1\nMONOTONIC_USEC={microsecs}".encode())
def notify_stopping():
notify(b"STOPPING=1")
def reload(signum, frame):
global reloading
reloading = True
def terminate(signum, frame):
global terminating
terminating = True
def main():
print("Doing initial setup")
global reloading, terminating
# Set up signal handlers.
print("Setting up signal handlers")
signal.signal(signal.SIGHUP, reload)
signal.signal(signal.SIGINT, terminate)
signal.signal(signal.SIGTERM, terminate)
# Do any other setup work here.
# Once all setup is done, signal readiness.
print("Done setting up")
notify_ready()
print("Starting loop")
while not terminating:
if reloading:
print("Reloading")
reloading = False
# Support notifying the manager when reloading configuration.
# This allows accurate state tracking as well as automatically
# enabling 'systemctl reload' without needing to manually
# specify an ExecReload= line in the unit file.
notify_reloading()
# Do some reconfiguration work here.
print("Done reloading")
notify_ready()
# Do the real work here ...
print("Sleeping for five seconds")
time.sleep(5)
print("Terminating")
notify_stopping()
if __name__ == "__main__":
sys.stdout.reconfigure(line_buffering=True)
print("Starting app")
main()
print("Stopped app")
$NOTIFY_SOCKET
Set by the service manager for supervised processes for status
and start-up completion notification. This environment
variable specifies the socket sd_notify() talks to. See above
for details.
Example 1. Start-up Notification
When a service finished starting up, it might issue the following
call to notify the service manager:
sd_notify(0, "READY=1");
Example 2. Extended Start-up Notification
A service could send the following after completing
initialization:
sd_notifyf(0, "READY=1\n"
"STATUS=Processing requests...\n"
"MAINPID=%lu",
(unsigned long) getpid());
Example 3. Error Cause Notification
A service could send the following shortly before exiting, on
failure:
sd_notifyf(0, "STATUS=Failed to start up: %s\n"
"ERRNO=%i",
strerror_r(errnum, (char[1024]){}, 1024),
errnum);
Example 4. Store a File Descriptor in the Service Manager
To store an open file descriptor in the service manager, in order
to continue operation after a service restart without losing
state, use "FDSTORE=1":
sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &fd, 1);
Example 5. Eliminating race conditions
When the client sending the notifications is not spawned by the
service manager, it may exit too quickly and the service manager
may fail to attribute them correctly to the unit. To prevent such
races, use sd_notify_barrier() to synchronize against reception of
all notifications sent before this call is made.
sd_notify(0, "READY=1");
/* set timeout to 5 seconds */
sd_notify_barrier(0, 5 * 1000000);
sd_pid_notify(), sd_pid_notifyf(), and sd_pid_notify_with_fds()
were added in version 219.
sd_notify_barrier() was added in version 246.
sd_pid_notifyf_with_fds() and sd_pid_notify_barrier() were added
in version 254.
systemd(1), sd-daemon(3), sd_listen_fds(3),
sd_listen_fds_with_names(3), sd_watchdog_enabled(3), daemon(7),
systemd.service(5)
1. File Descriptor Store
https://systemd.io/FILE_DESCRIPTOR_STORE
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 SD_NOTIFY(3)
Pages that refer to this page: journalctl(1), systemd(1), systemd-notify(1), systemd-nspawn(1), systemd-vmspawn(1), __pmServerNotifyServiceManagerReady(3), sd-daemon(3), sd_event_set_watchdog(3), sd_listen_fds(3), sd_pidfd_get_inode_id(3), sd_watchdog_enabled(3), org.freedesktop.systemd1(5), systemd.exec(5), systemd.service(5), daemon(7), systemd.directives(7), systemd.index(7), systemd.system-credentials(7), start-stop-daemon(8)
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|