sd_listen_fds man page on OpenMandriva

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SD_LISTEN_FDS(3)		 sd_listen_fds		      SD_LISTEN_FDS(3)

NAME
       sd_listen_fds, SD_LISTEN_FDS_START - Check for file descriptors passed
       by the system manager

SYNOPSIS
       #include <systemd/sd-daemon.h>

       #define SD_LISTEN_FDS_START 3

       int sd_listen_fds(int unset_environment);

DESCRIPTION
       sd_listen_fds() shall be called by a daemon to check for file
       descriptors passed by the init system as part of the socket-based
       activation logic.

       If the unset_environment parameter is non-zero, sd_listen_fds() will
       unset the $LISTEN_FDS/$LISTEN_PID environment variables before
       returning (regardless of whether the function call itself succeeded or
       not). Further calls to sd_listen_fds() will then fail, but the
       variables are no longer inherited by child processes.

       If a daemon receives more than one file descriptor, they will be passed
       in the same order as configured in the systemd socket definition file.
       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.

RETURN VALUE
       On failure, this call 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.

NOTES
       This function is provided by the reference implementation of APIs for
       new-style daemons and distributed with the systemd package. The
       algorithm it implements is simple, and can easily be reimplemented in
       daemons if it is important to support this interface without using the
       reference implementation.

       Internally, this function 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.

       For details about the algorithm check the liberally licensed reference
       implementation sources:
       http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c
       and
       http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h

       sd_listen_fds() is implemented in the reference implementation's
       sd-daemon.c and sd-daemon.h files. These interfaces are available as a
       shared library, which can be compiled and linked to with the
       libsystemd-daemon pkg-config(1) file. Alternatively, applications
       consuming these APIs may copy the implementation into their source
       tree. For more details about the reference implementation, see sd-
       daemon(3).

       If the reference implementation is used as drop-in files and
       -DDISABLE_SYSTEMD is set during compilation, this function will always
       return 0 and otherwise become a NOP.

ENVIRONMENT
       $LISTEN_PID, $LISTEN_FDS
	   Set by the init system for supervised processes that use
	   socket-based activation. This environment variable specifies the
	   data sd_listen_fds() parses. See above for details.

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), daemon(7),
       systemd.service(5), systemd.socket(5)

systemd 208						      SD_LISTEN_FDS(3)
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