проверьте файловые дескрипторы, переданные системным менеджером (check for file descriptors passed by the system manager)
Имя (Name)
sd_listen_fds, sd_listen_fds_with_names, SD_LISTEN_FDS_START -
Check for file descriptors passed by the system manager
Синопсис (Synopsis)
#include <systemd/sd-daemon.h>
#define SD_LISTEN_FDS_START 3
int sd_listen_fds(int unset_environment);
int sd_listen_fds_with_names(int unset_environment,
char*** names);
Описание (Description)
sd_listen_fds() may be invoked by a daemon to check for file
descriptors passed by the service manager as part of the
socket-based activation logic. It returns the number of received
file descriptors. If no file descriptors have been received, zero
is returned. The first file descriptor may be found at file
descriptor number 3 (i.e. SD_LISTEN_FDS_START), the remaining
descriptors follow at 4, 5, 6, ..., if any.
If a daemon receives more than one file descriptor, they will be
passed in the same order as configured in the systemd socket unit
file (see systemd.socket(5) for details) — if there's only one
such file (see below). Nonetheless, it is recommended to verify
the correct socket types before using them. To simplify this
checking, the functions sd_is_fifo(3), sd_is_socket(3),
sd_is_socket_inet(3), sd_is_socket_unix(3) are provided. In order
to maximize flexibility, it is recommended to make these checks
as loose as possible without allowing incorrect setups. i.e.
often, the actual port number a socket is bound to matters little
for the service to work, hence it should not be verified. On the
other hand, whether a socket is a datagram or stream socket
matters a lot for the most common program logics and should be
checked.
This function call will set the FD_CLOEXEC flag for all passed
file descriptors to avoid further inheritance to children of the
calling process.
If multiple socket units activate the same service, the order of
the file descriptors passed to its main process is undefined. If
additional file descriptors have been passed to the service
manager using sd_pid_notify_with_fds(3)'s "FDSTORE=1" messages,
these file descriptors are passed last, in arbitrary order, and
with duplicates removed.
If the unset_environment parameter is non-zero, sd_listen_fds()
will unset the $LISTEN_FDS, $LISTEN_PID and $LISTEN_FDNAMES
environment variables before returning (regardless of whether the
function call itself succeeded or not). Further calls to
sd_listen_fds() will then return zero, but the variables are no
longer inherited by child processes.
sd_listen_fds_with_names() is like sd_listen_fds(), but
optionally also returns an array of strings with identification
names for the passed file descriptors, if that is available and
the names parameter is non-NULL. This information is read from
the $LISTEN_FDNAMES variable, which may contain a colon-separated
list of names. For socket-activated services, these names may be
configured with the FileDescriptorName= setting in socket unit
files, see systemd.socket(5) for details. For file descriptors
pushed into the file descriptor store (see above), the name is
set via the FDNAME= field transmitted via
sd_pid_notify_with_fds(). The primary usecase for these names are
services which accept a variety of file descriptors which are not
recognizable with functions like sd_is_socket() alone, and thus
require identification via a name. It is recommended to rely on
named file descriptors only if identification via sd_is_socket()
and related calls is not sufficient. Note that the names used are
not unique in any way. The returned array of strings has as many
entries as file descriptors have been received, plus a final NULL
pointer terminating the array. The caller needs to free the array
itself and each of its elements with libc's free() call after
use. If the names parameter is NULL, the call is entirely
equivalent to sd_listen_fds().
Under specific conditions, the following automatic file
descriptor names are returned:
Table 1. Special names
┌─────────────┬──────────────────────────┐
│Name │ Description │
├─────────────┼──────────────────────────┤
│"unknown" │ The process received no │
│ │ name for the specific │
│ │ file descriptor from the │
│ │ service manager. │
├─────────────┼──────────────────────────┤
│"stored" │ The file descriptor │
│ │ originates in the │
│ │ service manager's │
│ │ per-service file │
│ │ descriptor store, and │
│ │ the FDNAME= field was │
│ │ absent when the file │
│ │ descriptor was submitted │
│ │ to the service manager. │
├─────────────┼──────────────────────────┤
│"connection" │ The service was │
│ │ activated in │
│ │ per-connection style │
│ │ using Accept=yes in the │
│ │ socket unit file, and │
│ │ the file descriptor is │
│ │ the connection socket. │
└─────────────┴──────────────────────────┘
Возвращаемое значение (Return value)
On failure, these calls returns a negative errno-style error
code. If $LISTEN_FDS/$LISTEN_PID was not set or was not correctly
set for this daemon and hence no file descriptors were received,
0 is returned. Otherwise, the number of file descriptors passed
is returned. The application may find them starting with file
descriptor SD_LISTEN_FDS_START, i.e. file descriptor 3.
Примечание (Note)
These APIs are implemented as a shared library, which can be
compiled and linked to with the libsystemd pkg-config(1) file.
Internally, sd_listen_fds() checks whether the $LISTEN_PID
environment variable equals the daemon PID. If not, it returns
immediately. Otherwise, it parses the number passed in the
$LISTEN_FDS environment variable, then sets the FD_CLOEXEC flag
for the parsed number of file descriptors starting from
SD_LISTEN_FDS_START. Finally, it returns the parsed number.
sd_listen_fds_with_names() does the same but also parses
$LISTEN_FDNAMES if set.
Окружение (Environment)
$LISTEN_PID, $LISTEN_FDS, $LISTEN_FDNAMES
Set by the service manager for supervised processes that use
socket-based activation. This environment variable specifies
the data sd_listen_fds() and sd_listen_fds_with_names()
parses. See above for details.
Смотри также (See also)
systemd(1), sd-daemon(3), sd_is_fifo(3), sd_is_socket(3),
sd_is_socket_inet(3), sd_is_socket_unix(3),
sd_pid_notify_with_fds(3), daemon(7), systemd.service(5),
systemd.socket(5)
