sd_journal_print(3) — Linux manual page


SD_JOURNAL_PRINT(3)         sd_journal_print         SD_JOURNAL_PRINT(3)

NAME         top

       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

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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,
       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

       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,

       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_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

RETURN VALUE         top

       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.

THREAD SAFETY         top

       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.

NOTES         top

       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

HISTORY         top

       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_sendv_with_location(), and
       sd_journal_perror_with_location() were added in version 246.

SEE ALSO         top

       systemd(1), sd-journal(3), sd_journal_stream_fd(3), syslog(3),
       perror(3), errno(3), systemd.journal-fields(7), signal(7),

NOTES         top

        1. Native Journal Protocol

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  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

systemd 255                                          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)