sd_journal_stream_fd, sd_journal_stream_fd_with_namespace — 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) ; |
int sd_journal_stream_fd_with_namespace( | const char *name_space, |
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-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.
The call returns a valid write-only file descriptor on success or a negative errno-style error code.
sd_journal_stream_fd()
and sd_journal_stream_fd_with_namespace()
are "async signal safe" in the meaning of signal-safety(7).
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.
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; }
sd_journal_stream_fd()
was added in version 187.
sd_journal_stream_fd_with_namespace()
was added in version 256.