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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |THREAD SAFETY |NOTES |HISTORY |SEE ALSO |NOTES |COLOPHON | |
SD_JOURNAL_PRINT(3) sd_journal_printSD_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(intpriority, const char *format, ...);int sd_journal_printv(intpriority, const char *format,va_listap);int sd_journal_send(const char *format, ...);int sd_journal_sendv(const struct iovec *iov, intn);int sd_journal_perror(const char *message);int sd_journal_print_with_location(intpriority, const char *file,const char *line,const char *func,const char *format, ...);int sd_journal_printv_with_location(intpriority,const char *file,const char *line,const char *func,const char *format,va_listap);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,intn);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 toprintf(3) orsyslog(3). Note that currently the resulting message will be truncated toLINE_MAX - 8. The priority value is one ofLOG_EMERG,LOG_ALERT,LOG_CRIT,LOG_ERR,LOG_WARNING,LOG_NOTICE,LOG_INFO,LOG_DEBUG, as defined in syslog.h, seesyslog(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 tosd_journal_print()but takes a variable argument list encapsulated in an object of typeva_list (seestdarg(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 byNULL. 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, seesystemd.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 tosd_journal_send()but takes an array ofstruct iovec (as defined in uio.h, seereadv(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 bothsd_journal_print()andsd_journal_send()described above, which are based on format strings, and do strip trailing whitespace.sd_journal_perror()is a similar toperror(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 inerrno(3). If the message string is passed asNULLor 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 isLOG_ERR(3). Note thatsd_journal_send()is a wrapper aroundsd_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 definingSD_JOURNAL_SUPPRESS_LOCATIONbefore including sd-journal.h.sd_journal_print_with_location(),sd_journal_printv_with_location(),sd_journal_send_with_location(),sd_journal_sendv_with_location(), andsd_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) andsd_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. Usingsd_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 viasd_journal_send(). Usingsyslog()has the benefit of being more portable. These functions implement a client to theNative JournalProtocol[1].The ten functions return 0 on success or a negative errno-style error code. Theerrno(3) variable itself is not altered. Ifsystemd-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()andsd_journal_sendv_with_location()are "async signal safe" in the meaning ofsignal-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 thelibsystemd pkg-config(1) file. The code described here usesgetenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not callsetenv(3) from a parallel thread. It is recommended to only do calls tosetenv()from an early phase of the program when no other threads have been started.
sd_journal_print(),sd_journal_printv(),sd_journal_send(), andsd_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(), andsd_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 Protocolhttps://systemd.io/JOURNAL_NATIVE_PROTOCOL
This page is part of thesystemd (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 isnot part of the original manual page), send a mail to man-pages@man7.orgsystemd 258~rc2SD_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)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |