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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | THREAD SAFETY | NOTES | HISTORY | SEE ALSO | NOTES | COLOPHON |
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SD_JOURNAL_PRINT(3) sd_journal_print SD_JOURNAL_PRINT(3)
sd_journal_print, sd_journal_printv, sd_journal_send,
sd_journal_sendv, sd_journal_perror, SD_JOURNAL_SUPPRESS_LOCATION,
sd_journal_print_with_location, sd_journal_printv_with_location,
sd_journal_send_with_location, sd_journal_sendv_with_location,
sd_journal_perror_with_location - Submit log entries to the
journal
#include <systemd/sd-journal.h>
int sd_journal_print(int priority, const char *format, ...);
int sd_journal_printv(int priority, const char *format,
va_list ap);
int sd_journal_send(const char *format, ...);
int sd_journal_sendv(const struct iovec *iov, int n);
int sd_journal_perror(const char *message);
int sd_journal_print_with_location(int priority, const char *file,
const char *line,
const char *func,
const char *format, ...);
int sd_journal_printv_with_location(int priority,
const char *file,
const char *line,
const char *func,
const char *format,
va_list ap);
int sd_journal_send_with_location(const char *file,
const char *line,
const char *func,
const char *format, ...);
int sd_journal_sendv_with_location(const char *file,
const char *line,
const char *func,
const struct iovec *iov,
int n);
int sd_journal_perror_with_location(const char *file,
const char *line,
const char *func,
const char *message);
sd_journal_print() may be used to submit simple, plain text log
entries to the system journal. The first argument is a priority
value. This is followed by a format string and its parameters,
similar to printf(3) or syslog(3). Note that currently the
resulting message will be truncated to LINE_MAX - 8. The priority
value 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. It is recommended to use this
call to submit log messages in the application locale or system
locale and in UTF-8 format, but no such restrictions are enforced.
Note that log messages written using this function are generally
not expected to end in a new-line character. However, as all
trailing whitespace (including spaces, new-lines, tabulators and
carriage returns) are automatically stripped from the logged
string, it is acceptable to specify one (or more). Empty lines
(after trailing whitespace removal) are suppressed. On non-empty
lines, leading whitespace (as well as inner whitespace) is left
unmodified.
sd_journal_printv() is similar to sd_journal_print() but takes a
variable argument list encapsulated in an object of type va_list
(see stdarg(3) for more information) instead of the format string.
It is otherwise equivalent in behavior.
sd_journal_send() may be used to submit structured log entries to
the system journal. It takes a series of format strings, each
immediately followed by their associated parameters, terminated by
NULL. The strings passed should be of the format "VARIABLE=value".
The variable name must be in uppercase and consist only of
characters, numbers and underscores, and may not begin with an
underscore. (All assignments that do not follow this syntax will
be ignored.) The value can be of any size and format. It is highly
recommended to submit text strings formatted in the UTF-8
character encoding only, and submit binary fields only when
formatting in UTF-8 strings is not sensible. A number of
well-known fields are defined, see systemd.journal-fields(7) for
details, but additional application defined fields may be used. A
variable may be assigned more than one value per entry. If this
function is used, trailing whitespace is automatically removed
from each formatted field.
sd_journal_sendv() is similar to sd_journal_send() but takes an
array of struct iovec (as defined in uio.h, see readv(3) for
details) instead of the format string. Each structure should
reference one field of the entry to submit. The second argument
specifies the number of structures in the array.
sd_journal_sendv() is particularly useful to submit binary objects
to the journal where that is necessary. Note that this function
will not strip trailing whitespace of the passed fields, but
passes the specified data along unmodified. This is different from
both sd_journal_print() and sd_journal_send() described above,
which are based on format strings, and do strip trailing
whitespace.
sd_journal_perror() is a similar to perror(3) and writes a message
to the journal that consists of the passed string, suffixed with
": " and a human-readable representation of the current error code
stored in errno(3). If the message string is passed as NULL or
empty string, only the error string representation will be
written, prefixed with nothing. An additional journal field ERRNO=
is included in the entry containing the numeric error code
formatted as decimal string. The log priority used is LOG_ERR (3).
Note that sd_journal_send() is a wrapper around sd_journal_sendv()
to make it easier to use when only text strings shall be
submitted. Also, the following two calls are mostly equivalent:
sd_journal_print(LOG_INFO, "Hello World, this is PID %lu!", (unsigned long) getpid());
sd_journal_send("MESSAGE=Hello World, this is PID %lu!", (unsigned long) getpid(),
"PRIORITY=%i", LOG_INFO,
NULL);
Note that these calls implicitly add fields for the source file,
function name and code line where invoked. This is implemented
with macros. If this is not desired, it can be turned off by
defining SD_JOURNAL_SUPPRESS_LOCATION before including
sd-journal.h.
sd_journal_print_with_location(),
sd_journal_printv_with_location(),
sd_journal_send_with_location(), sd_journal_sendv_with_location(),
and sd_journal_perror_with_location() are similar to their
counterparts without "_with_location", but accept additional
parameters to explicitly set the source file name, function, and
line. The arguments "file" and "line" must contain valid journal
entries including the variable name, e.g. "CODE_FILE=src/foo.c"
and "CODE_LINE=666", while "func" must only contain the function
name, i.e. the value without "CODE_FUNC=". These variants are
primarily useful when writing custom wrappers, for example in
bindings for a different language.
syslog(3) and sd_journal_print() may largely be used
interchangeably functionality-wise. However, note that log
messages logged via the former take a different path to the
journal server than the later, and hence global chronological
ordering between the two streams cannot be guaranteed. Using
sd_journal_print() has the benefit of logging source code line,
filenames, and functions as metadata along all entries, and
guaranteeing chronological ordering with structured log entries
that are generated via sd_journal_send(). Using syslog() has the
benefit of being more portable.
These functions implement a client to the Native Journal
Protocol[1].
The ten functions return 0 on success or a negative errno-style
error code. The errno(3) variable itself is not altered.
If systemd-journald(8) is not running (the socket is not present),
those functions do nothing, and also return 0.
All functions listed here are thread-safe and may be called in
parallel from multiple threads.
sd_journal_sendv() and sd_journal_sendv_with_location() are "async
signal safe" in the meaning of signal-safety(7).
sd_journal_print(), sd_journal_printv(), sd_journal_send(),
sd_journal_perror(), and their counterparts with "_with_location"
are not async signal safe.
Functions described here are available as a shared library, which
can be compiled against and linked to with the
libsystemd pkg-config(1) file.
The code described here uses getenv(3), which is declared to be
not multi-thread-safe. This means that the code calling the
functions described here must not call setenv(3) from a parallel
thread. It is recommended to only do calls to setenv() from an
early phase of the program when no other threads have been
started.
sd_journal_print(), sd_journal_printv(), sd_journal_send(), and
sd_journal_sendv() were added in version 187.
sd_journal_perror() was added in version 188.
sd_journal_print_with_location(),
sd_journal_printv_with_location(),
sd_journal_send_with_location(), sd_journal_sendv_with_location(),
and sd_journal_perror_with_location() were added in version 246.
systemd(1), sd-journal(3), sd_journal_stream_fd(3), syslog(3),
perror(3), errno(3), systemd.journal-fields(7), signal(7),
socket(7)
1. Native Journal Protocol
https://systemd.io/JOURNAL_NATIVE_PROTOCOL
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 SD_JOURNAL_PRINT(3)
Pages that refer to this page: sd-journal(3), sd_journal_stream_fd(3), org.freedesktop.LogControl1(5), systemd.exec(5), file-hierarchy(7), systemd.directives(7), systemd.index(7), systemd.journal-fields(7), systemd-journald.service(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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