sd_journal_stream_fd(3)

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

.SH "SYNOPSIS"

#include <systemd/sd-journal.h>

.HP 600u int sd_journal_stream_fd(const char *identifier, int priority, int level_prefix);

.HP 960u int sd_journal_stream_fd_with_namespace(const char *name_space, 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 sd_journal_stream_fd_with_namespace() is similar to sd_journal_stream_fd(), but takes an additional name_space parameter that specifies which journal namespace to operate on. If specified as NULL the call is identical to sd_journal_stream_fd(). For details about journal namespaces, see systemd-journald.service(8).

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

.PP Each invocation of these functions 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() and sd_journal_stream_fd_with_namespace() are "async signal safe" in the meaning of signal-safety(7).

.SH "NOTES"

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

.PP Functions described here are available as a shared library, which can be compiled against and linked to with the libsystemd pkg-config(1) file.

.SH "EXAMPLES"

.PP Creating a log stream suitable for fprintf(3):

/* SPDX-License-Identifier: MIT-0 */
#define _GNU_SOURCE 1
#include <errno.h>
#include <syslog.h>
#include <stdio.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: %s\n", strerror(errno));


    close(fd);


    return 1;


  }


  fprintf(log, "Hello World!\n");


  fprintf(log, SD_WARNING "This is a warning!\n");


  fclose(log);


  return 0;
}

.SH "HISTORY"

.PP sd_journal_stream_fd() was added in version 187.

.PP sd_journal_stream_fd_with_namespace() was added in version 256.

.SH "SEE ALSO"

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