Ubuntu Manpage: sd_journal_stream_fd, sd_journal_stream_fd_with_namespace

Provided by: libsystemd-dev_256.5-2ubuntu3.1_amd64

NAME

       sd_journal_stream_fd, sd_journal_stream_fd_with_namespace - Create log stream file descriptor to the
       journal

SYNOPSIS

       #include <systemd/sd-journal.h>

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

       int sd_journal_stream_fd_with_namespace(const char *name_space, 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.

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).

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

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.

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() and sd_journal_stream_fd_with_namespace() are "async signal safe" in the meaning
       of signal-safety(7).

NOTES

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

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

EXAMPLES

       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;
           }

HISTORY

       sd_journal_stream_fd() was added in version 187.

       sd_journal_stream_fd_with_namespace() was added in version 256.