Provided by: libelogind-dev-doc_239.3+20190131-1+debian1_all bug

NAME

       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

       #include <elogind/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

       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. 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 watchdog timestamp. This is the keep-alive ping that services need
           to issue in regular intervals if a watchdog is enabled for them. See

           sd_watchdog_enabled(3) for the details of how the service can check whether the
           watchdog is enabled.

       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.

       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 it depends on the
           service manager if it will accept messages for a service. If file descriptors sent are
           pollable (see epoll_ctl(2)), then any EPOLLHUP or EPOLLERR event seen on them should
           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 should remove 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.

       It is recommended to prefix variable names that are not listed above with X_ to avoid
       namespace clashes.

       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.

RETURN VALUE

       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

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

       Please note that this is a description of the notification technique as used by systemd.
       If the service manager you use does not set the needed environment variables, none of the
       functions described here do anything but return 0.

       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

       $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.

EXAMPLES

       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(errno),
                   errno);

       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);

SEE ALSO

       elogind(8),

       sd-daemon(3), sd_listen_fds(3), sd_listen_fds_with_names(3), sd_watchdog_enabled(3),