NAME¶sd_journal_print, sd_journal_printv, sd_journal_send, sd_journal_sendv, sd_journal_perror, SD_JOURNAL_SUPPRESS_LOCATION - Submit log entries to the journal
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);
DESCRIPTION¶sd_journal_print() may be used to submit simple, plain text log entries to the system syslog. 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 syslog. 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
elogind.journal-fields(7) for details. Other fields are ignored by elogind, but more variables may be added in the future. 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. A number of well-known fields are defined, see elogind.journal-fields(7) for details. Other fields are ignored by elogind, but more variables may be added in the future. 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 syslog 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. The log priority used is
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.
syslog(3) and sd_journal_print() may largely be used interchangeably functionality-wise. However, note that log messages sent via sd_journal_print() and sd_journal_send() are sent to syslog, as elogind does not provide a journal server.
RETURN VALUE¶The five calls return 0 on success or a negative errno-style error code. The errno(3) variable itself is not altered.
NOTES¶These APIs are implemented as a shared library, which can be compiled and linked to with the libelogind pkg-config(1) file.