SD_NOTIFY(3)                      sd_notify                     SD_NOTIFY(3)

NAME         top

       sd_notify, sd_notifyf, sd_pid_notify, sd_pid_notifyf,
       sd_pid_notify_with_fds - Notify service manager about start-up
       completion and other service status changes

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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:

           Tells the service manager that service startup is finished. 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).

           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

           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.

           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..."

           If a service fails, the errno-style error code, formatted as
           string. Example: "ERRNO=2" for ENOENT.

           If a service fails, the D-Bus error-style error code. Example:

           The main process ID (PID) of the service, in case the service
           manager did not fork off the process itself. Example:

           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.

           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 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.

           When used in combination with FDSTORE=1, specifies a name for the
           submitted file descriptors. 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 any ASCII character, but must not contain control
           characters or ":". It may not be longer than 255 characters. If a
           submitted name does not follow these restrictions, it is ignored.

           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"

       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.

       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_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.

RETURN VALUE         top

       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).

NOTES         top

       These APIs are implemented as a shared library, which can be compiled
       and linked to with the libsystemd pkg-config(1) file.

       These functions send a single datagram with the state string as
       payload to the AF_UNIX socket referenced in the $NOTIFY_SOCKET
       environment variable. If the first character of $NOTIFY_SOCKET is
       "@", the string is understood as Linux abstract namespace socket. The
       datagram is accompanied by the process credentials of the sending
       service, using SCM_CREDENTIALS.

ENVIRONMENT         top

           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.

EXAMPLES         top

       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"
                   (unsigned long) getpid());

       Example 3. Error Cause Notification

       A service could send the following shortly before exiting, on

           sd_notifyf(0, "STATUS=Failed to start up: %s\n"

       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

           sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &fd, 1);

SEE ALSO         top

       systemd(1), sd-daemon(3), sd_listen_fds(3),
       sd_listen_fds_with_names(3), sd_watchdog_enabled(3), daemon(7),

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨⟩ on 2019-05-09.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2019-05-09.)  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

systemd 234                                                     SD_NOTIFY(3)

Pages that refer to this page: systemd(1)systemd-notify(1)systemd-nspawn(1)sd-daemon(3)sd_event_set_watchdog(3)sd_listen_fds(3)sd_watchdog_enabled(3)systemd.exec(5)systemd.service(5)daemon(7)systemd.directives(7)systemd.index(7)start-stop-daemon(8)