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

Provided by: libsystemd-dev_255.4-1ubuntu8.11_amd64

NAME

       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

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);

       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);

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 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 fail, 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. 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.

WELL-KNOWN ASSIGNMENTS

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". Note that this assignment is currently not used by
systemd.

Added in version 233.

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 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=...
The main process ID (PID) of the service, in case the service manager did not fork off the process
itself. Example: "MAINPID=4711".

Added in version 233.

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 isn't 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.

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 stored file descriptors regardless
of whether or not they are pollable. As this option disables automatic cleanup of the stored 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
may be logged, but are otherwise ignored. Thus, it is not useful to send assignments which are not in
this list. The service manager also sends some messages to its notification socket, which are then
consumed by the machine or container manager.

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

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. 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.

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_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);

HISTORY

       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.

NOTES

        1. File Descriptor Store
           https://systemd.io/FILE_DESCRIPTOR_STORE

systemd 255                                                                                         SD_NOTIFY(3)

NAME

SYNOPSIS

DESCRIPTION

WELL-KNOWN ASSIGNMENTS

RETURN VALUE

NOTES

ENVIRONMENT

EXAMPLES

HISTORY

SEE ALSO

NOTES