sd_journal_stream_fd

systemd
Developer Lennart Poettering lennart@poettering.net
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

## Description

`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.

## Return Value

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

## Signal safety

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

## Notes

Function `sd_journal_stream_fd()` is thread-safe and may be called from multiple threads.

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.

## Examples

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;
    }

## See Also

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