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). 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(),
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.
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.
The five calls 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() is "async signal safe" in the meaning of
sd_journal_print, sd_journal_printv, sd_journal_send, and
sd_journal_perror are not async signal safe.
The sd_journal_print(), sd_journal_printv(), sd_journal_send(),
sd_journal_sendv() and sd_journal_perror() interfaces are available
as a shared library, which can be compiled and linked to with the
libsystemd pkg-config(1) file.
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
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2017-03-13. If you dis‐
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systemd 233 SD_JOURNAL_PRINT(3)