NAME

       sd-daemon, SD_EMERG, SD_ALERT, SD_CRIT, SD_ERR, SD_WARNING, SD_NOTICE, SD_INFO, SD_DEBUG -
       Reference implementation of APIs for new-style daemons

SYNOPSIS

       #include <systemd/sd-daemon.h>

       pkg-config --cflags --libs libsystemd-daemon

DESCRIPTION

       sd-daemon.c and sd-daemon.h provide a reference implementation of various APIs for
       new-style daemons, as implemented by the systemd(1) init system.

       See sd_listen_fds(3), sd_notify(3), sd_booted(3), sd_is_fifo(3) for more information about
       the functions implemented. In addition to these functions a couple of logging prefixes are
       defined as macros:

           #define SD_EMERG   "<0>"  /* system is unusable */
           #define SD_ALERT   "<1>"  /* action must be taken immediately */
           #define SD_CRIT    "<2>"  /* critical conditions */
           #define SD_ERR     "<3>"  /* error conditions */
           #define SD_WARNING "<4>"  /* warning conditions */
           #define SD_NOTICE  "<5>"  /* normal but significant condition */
           #define SD_INFO    "<6>"  /* informational */
           #define SD_DEBUG   "<7>"  /* debug-level messages */

       These prefixes are intended to be used in conjunction with STDERR-based logging as
       implemented by systemd. If a systemd service definition file is configured with
       StandardError=syslog or StandardError=kmsg these prefixes can be used to encode a log
       level in lines printed. This is similar to the kernel printk()-style logging. See
       klogctl(2) for more information.

       The log levels are identical to syslog(3)'s log level system. To use these prefixes simply
       prefix every line with one of these strings. A line that is not prefixed will be logged at
       the default log level SD_INFO.

       Example 1. Hello World

       A daemon may log with the log level NOTICE by issuing this call:

           fprintf(stderr, SD_NOTICE "Hello World!\n");

NOTES

       These interfaces are provided by the reference implementation of APIs for new-style
       daemons and distributed with the systemd package. The algorithms they implement are
       simple, and can easily be reimplemented in daemons if it is important to support this
       interface without using the reference implementation. See the respective function man
       pages for details.

       In addition, for details about the algorithms 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

       These APIs are implemented in the reference implementation's sd-daemon.c and sd-daemon.h
       files. These interfaces are available as shared library, which can be compiled and linked
       to with the libsystemd-daemonpkg-config(1) file. Alternatively, applications consuming
       these APIs may copy the implementation into their source tree, either verbatim or in
       excerpts.

       The functions directly related to new-style daemons become NOPs when -DDISABLE_SYSTEMD is
       set during compilation and the reference implementation is used as drop-in files. In
       addition, if sd-daemon.c is compiled on non-Linux systems they become NOPs.

SEE ALSO

       systemd(1), sd_listen_fds(3), sd_notify(3), sd_booted(3), sd_is_fifo(3), daemon(7),
       systemd.service(5), systemd.socket(5), fprintf(3), sd-readahead(3), pkg-config(1)