Ubuntu Manpage: sd_notify, sd_notifyf, sd_pid_notify, sd_pid_notifyf, sd_pid_notify_with_fds

Provided by: libsystemd-dev_229-4ubuntu21.31_amd64

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 <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

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. 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.

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.

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 be passed again using
the usual file descriptor passing logic on the next invocation of the service (see
sd_listen_fds(3)). This is useful for implementing service restart schemes where
services serialize their state to /run, push their file descriptors to the system
manager, and are then restarted, retrieving their state again via socket passing and
/run. Note that the service manager will accept messages for a service only if
FileDescriptorStoreMax= is set to non-zero for it (defaults to zero). See
systemd.service(5) for details. 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 file descriptors before passing them to the service. Use
sd_pid_notify_with_fds() to send messages with "FDSTORE=1", see below.

FDNAME=...
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.

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.

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 data could be sent, 0 is returned. If the status was sent,
       these functions return with a positive return value. In order to support both, init
       systems that implement this scheme and those which do not, it is generally recommended to
       ignore the return value of this call.

NOTES

       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

       $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);