systemd 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 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-fields7 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 syslog3 for details. The third argument is a boolean: if true kernel-style log level prefixes (such as SD_WARNING) are interpreted, see sd-daemon3 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. The call returns a valid write-only file descriptor on success or a negative errno-style error code. sd_journal_stream_fd() is "async signal safe" in the meaning of signal-safety7. Creating a log stream suitable for fprintf3: #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; } systemd1, sd-journal3, sd-daemon3, sd_journal_print3, syslog3, fprintf3, systemd.journal-fields7