Manpages - sd_journal_stream_fd.3

sd_journal_stream_fd - Create log stream file descriptor to the journal

  #include <systemd/sd-journal.h>

int sd_journal_stream_fd(const char **/identifier/, int priority, int level_prefix);*

sd_journal_stream_fd() may be used to create a log stream file descriptor. Log messages written to this file descriptor as simple newline-separated text strings are written to the journal. This file descriptor can be used internally by applications or be made standard output or standard error of other processes executed.

sd_journal_stream_fd() takes a short program identifier string as first argument, which will be written to the journal as SYSLOG_IDENTIFIER= field for each log entry (see systemd.journal-fields*(7) for more information). The second argument shall be the default priority level for all messages. The priority level is one of *LOG_EMERG, LOG_ALERT, LOG_CRIT, LOG_ERR, LOG_WARNING, LOG_NOTICE, LOG_INFO, LOG_DEBUG, as defined in syslog.h, see syslog*(3) for details. The third argument is a boolean: if true kernel-style log level prefixes (such as *SD_WARNING) are interpreted, see *sd-daemon*(3) for more information.

It is recommended that applications log UTF-8 messages only with this API, but this is not enforced.

Each invocation of sd_journal_stream_fd() allocates a new log stream file descriptor, that is not shared with prior or later invocations. The file descriptor is write-only (its reading direction is shut down), and O_NONBLOCK is turned off initially.

The call returns a valid write-only file descriptor on success or a negative errno-style error code.

sd_journal_stream_fd() is “async signal safe” in the meaning of *signal-safety*(7).

All functions listed here are thread-safe and may be called in parallel from multiple threads.

These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd *pkg-config*(1) file.

Creating a log stream suitable for *fprintf*(3):

    #include <syslog.h>
    #include <stdio.h>
    #include <string.h>
    #include <unistd.h>
    #include <systemd/sd-journal.h>
    #include <systemd/sd-daemon.h>

    int main(int argc, char *argv[]) {
      int fd;
      FILE *log;
      fd = sd_journal_stream_fd("test", LOG_INFO, 1);
      if (fd < 0) {
        fprintf(stderr, "Failed to create stream fd: %s\n", strerror(-fd));
        return 1;
      }
      log = fdopen(fd, "w");
      if (!log) {
        fprintf(stderr, "Failed to create file object: %m\n");
        close(fd);
        return 1;
      }
      fprintf(log, "Hello World!\n");
      fprintf(log, SD_WARNING "This is a warning!\n");
      fclose(log);
      return 0;
    }

*systemd*(1), *sd-journal*(3), *sd-daemon*(3), *sd_journal_print*(3), *syslog*(3), *fprintf*(3), *systemd.journal-fields*(7)