sd-daemon - Man Page

APIs for new-style daemons


#include <systemd/sd-daemon.h>

pkg-config --cflags --libs libsystemd


sd-daemon.h is part of libsystemd(3) and provides APIs for new-style daemons, as implemented by the systemd(1) service manager.

See sd_listen_fds(3), sd_notify(3), sd_booted(3), sd_is_fifo(3), sd_watchdog_enabled(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 (or stdout-based logging) as implemented by systemd. If a systemd service definition file is configured with StandardError=journal or StandardError=kmsg (and similar with StandardOutput=), 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");


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.

See Also

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

Referenced By

daemon(7), libsystemd(3), sd_booted(3), sd_is_fifo(3), sd_journal_stream_fd(3), sd_listen_fds(3), sd-login(3), sd_notify(3), sd_watchdog_enabled(3), systemd(1), systemd.directives(7), systemd.exec(5), systemd.index(7).

The man pages SD_ALERT(3), SD_CRIT(3), SD_DEBUG(3), SD_EMERG(3), SD_ERR(3), SD_INFO(3), SD_NOTICE(3) and SD_WARNING(3) are aliases of sd-daemon(3).

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