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);