NAME

       sd_journal_stream_fd - 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);

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

       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.

EXAMPLES

       Creating a log stream suitable for fprintf(3):

           /* SPDX-License-Identifier: MIT-0 */

           #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) {
               errno = -fd;
               fprintf(stderr, "Failed to create stream fd: %m\n");
               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)