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
#include <systemd/sd-daemon.h>
pkg-config --cflags --libs libsystemd-daemon
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");
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-daemon pkg-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.