SD-DAEMON(3)

💅 SD-DAEMON(3) — sd-daemon 💅

okay so bestie, welcome to the sd-daemon page from systemd 261.3 — no cap, this is the glow-up guide for new-style daemons and their log-level era ✨

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📛 NAME 📛

sd-daemon, SD_EMERG, SD_ALERT, SD_CRIT, SD_ERR, SD_WARNING, SD_NOTICE, SD_INFO, SD_DEBUG — literally the APIs for new-style daemons, periodt 💅

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✨ SYNOPSIS ✨

#include <systemd/sd-daemon.h>

pkg-config --cflags --libs libsystemd

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🌸 DESCRIPTION 🌸

so sd-daemon.h is part of libsystemd(3) and it's giving APIs for new-style daemons, as implemented by the systemd(1) service manager. main character energy fr fr 👑

for the deets on the actual functions, go check out sd_listen_fds(3), sd_notify(3), sd_booted(3), sd_is_fifo(3), sd_watchdog_enabled(3), and sd_pidfd_get_inode_id(3) — they're all linked below too, iykyk 💖

and on top of those functions, there's also a whole set of logging prefixes defined as macros. slay:

#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 with stderr-based logging (or stdout-based logging, bestie, both count) as implemented by systemd 🫶 if a systemd service definition file is configured with StandardError=journal or StandardError=kmsg (and similar with StandardOutput=), you can use these prefixes to encode a log level in the lines you print. it's giving kernel printk()-style logging vibe check — see klogctl(2) for more info 💀

the log levels are identical to syslog(3)'s log level system, no cap. to use these prefixes, simply prefix every line with one of these strings. and a line that is not prefixed? it gets logged at the default log level SD_INFO. periodt 🌈

🎀 Example 1. Hello World 🎀

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

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

iconic, honestly 💖

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🦋 NOTES 🦋

the functions described here are available as a shared library, which you can compile against and link to with the libsystemd pkg-config(1) file — ez pz ✨

⚠️ okay so this part matters, bestie: the code described here uses getenv(3), which is declared to be not multi-thread-safe. that means the code calling the functions described here must not call setenv(3) from a parallel thread. it's recommended to only do calls to setenv() from an early phase of the program when no other threads have been started. fr fr, don't skip this one 🔥

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🌟 SEE ALSO 🌟

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

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and that's the whole vibe, bestie — this page is brought to you by systemd 261.3, dated the SD-DAEMON(3) era 🎀 go forth and log responsibly, ily 🫶✨