SD_JOURNAL_STREAM_FD(3)

  .SH "NAME" sd_journal_stream_fd - Create log stream file descriptor to the journal
  .SH "SYNOPSIS"

#include <systemd/sd-journal.h>

      .HP u int sd_journal_stream_fd(const char *identifier, int priority, int level_prefix);

  .SH "DESCRIPTION"

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

  .SH "RETURN VALUE"

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

  .SH "SIGNAL SAFETY"

    .PP sd_journal_stream_fd() is "async signal safe" in the meaning of signal-safety(7).

  .SH "NOTES"

    .PP Function sd_journal_stream_fd() is thread-safe and may be called from multiple threads.
    .PP The sd_journal_stream_fd() interface is available as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.

  .SH "EXAMPLES"

    .PP 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;
    }

  .SH "SEE ALSO"

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