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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |NOTES |HISTORY |SEE ALSO |COLOPHON | |
SD_JOURNAL_OPEN(3) sd_journal_openSD_JOURNAL_OPEN(3)sd_journal_open, sd_journal_open_directory, sd_journal_open_directory_fd, sd_journal_open_files, sd_journal_open_files_fd, sd_journal_open_namespace, sd_journal_close, sd_journal, SD_JOURNAL_LOCAL_ONLY, SD_JOURNAL_RUNTIME_ONLY, SD_JOURNAL_SYSTEM, SD_JOURNAL_CURRENT_USER, SD_JOURNAL_OS_ROOT, SD_JOURNAL_ALL_NAMESPACES, SD_JOURNAL_INCLUDE_DEFAULT_NAMESPACE, SD_JOURNAL_TAKE_DIRECTORY_FD - Open the system journal for reading
#include <systemd/sd-journal.h>int sd_journal_open(sd_journal **ret, intflags);int sd_journal_open_namespace(sd_journal **ret,const char *namespace, intflags);int sd_journal_open_directory(sd_journal **ret, const char *path,intflags);int sd_journal_open_directory_fd(sd_journal **ret, intfd,intflags);int sd_journal_open_files(sd_journal **ret, const char **paths,intflags);int sd_journal_open_files_fd(sd_journal **ret, intfds[],unsignedn_fds, intflags);void sd_journal_close(sd_journal *j);
sd_journal_open()opens the log journal for reading. It will find all journal files automatically and interleave them automatically when reading. As first argument it takes a pointer to asd_journal pointer, which, on success, will contain a journal context object. The second argument is a flags field, which may consist of the following flags ORed together:SD_JOURNAL_LOCAL_ONLYmakes sure only journal files generated on the local machine will be opened.SD_JOURNAL_RUNTIME_ONLYmakes sure only volatile journal files will be opened, excluding those which are stored on persistent storage.SD_JOURNAL_SYSTEMwill cause journal files of system services and the kernel (in opposition to user session processes) to be opened.SD_JOURNAL_CURRENT_USERwill cause journal files of the current user to be opened. If neitherSD_JOURNAL_SYSTEMnorSD_JOURNAL_CURRENT_USERare specified, all journal file types will be opened.sd_journal_open_namespace()is similar tosd_journal_open()but takes an additionalnamespace parameter that specifies which journal namespace to operate on. If specified asNULLthe call is identical tosd_journal_open(). If non-NULLonly data from the namespace identified by the specified parameter is accessed. This call understands two additional flags: ifSD_JOURNAL_ALL_NAMESPACESis specified thenamespace parameter is ignored and all defined namespaces are accessed simultaneously; ifSD_JOURNAL_INCLUDE_DEFAULT_NAMESPACEthe specified namespace and the default namespace are accessed but no others (this flag has no effect whennamespace is passed asNULL). For details about journal namespaces seesystemd-journald.service(8).sd_journal_open_directory()is similar tosd_journal_open()but takes an absolute directory path as argument. All journal files in this directory will be opened and interleaved automatically. This call also takes a flags argument. The flags parameters accepted by this call areSD_JOURNAL_OS_ROOT,SD_JOURNAL_SYSTEM, andSD_JOURNAL_CURRENT_USER. IfSD_JOURNAL_OS_ROOTis specified, journal files are searched for below the usual /var/log/journal and /run/log/journal relative to the specified path, instead of directly beneath it. The other two flags limit which files are opened, the same as forsd_journal_open().sd_journal_open_directory_fd()is similar tosd_journal_open_directory(), but takes a file descriptor referencing a directory in the file system instead of an absolute file system path. In addition to the flags accepted bysd_journal_open_directory(), this function also acceptsSD_JOURNAL_TAKE_DIRECTORY_FD. IfSD_JOURNAL_TAKE_DIRECTORY_FDis specified, the function will take the ownership of the specified file descriptor on success, and it will be closed bysd_journal_close(), hence the caller of the function must not close the file descriptor. When the flag is not specified,sd_journal_close()will not close the file descriptor, so the caller should close it aftersd_journal_close().sd_journal_open_files()is similar tosd_journal_open()but takes aNULL-terminated list of file paths to open. All files will be opened and interleaved automatically. This call also takes a flags argument, but it must be passed as 0 as no flags are currently understood for this call. Please note that in the case of a live journal, this function is only useful for debugging, because individual journal files can be rotated at any moment, and the opening of specific files is inherently racy.sd_journal_open_files_fd()is similar tosd_journal_open_files() but takes an array of open file descriptors that must reference journal files, instead of an array of file system paths. Pass the array of file descriptors as second argument, and the number of array entries in the third. The flags parameter must be passed as 0.sd_journal objects cannot be used in the child after a fork. Functions which take a journal object as an argument (sd_journal_next()and others) will return-ECHILDafter a fork.sd_journal_close()will close the journal context allocated withsd_journal_open()orsd_journal_open_directory()and free its resources. When opening the journal only journal files accessible to the calling user will be opened. If journal files are not accessible to the caller, this will be silently ignored. Seesd_journal_next(3) for an example of how to iterate through the journal after opening it withsd_journal_open(). A journal context object returned bysd_journal_open()references a specific journal entry ascurrent entry, similar to a file seek index in a classic file system file, but without absolute positions. It may be altered withsd_journal_next(3) andsd_journal_seek_head(3) and related calls. The current entry position may be exported incursor strings, as accessible viasd_journal_get_cursor(3). Cursor strings may be used to globally identify a specific journal entry in a stable way and then later to seek to it (or if the specific entry is not available locally, to its closest entry in time)sd_journal_seek_cursor(3). Notification of journal changes is available viasd_journal_get_fd()and related calls.
Thesd_journal_open(),sd_journal_open_directory(), andsd_journal_open_files()calls return 0 on success or a negative errno-style error code.sd_journal_close()returns nothing.
All functions listed here are thread-agnostic and only a single specific thread may operate on a given object during its entire lifetime. It is safe to allocate multiple independent objects and use each from a specific thread in parallel. However, it is not safe to allocate such an object in one thread, and operate or free it from any other, even if locking is used to ensure these threads do not operate on it at the very same time. Functions described here are available as a shared library, which can be compiled against and linked to with thelibsystemd pkg-config(1) file.
sd_journal_open(),sd_journal_open_directory(), andsd_journal_close()were added in version 187.sd_journal_open_files()was added in version 205.sd_journal_open_directory_fd()andsd_journal_open_files_fd()were added in version 230.sd_journal_open_namespace()was added in version 245.
systemd(1),sd-journal(3),systemd-journald.service(8),sd_journal_next(3),sd_journal_get_data(3)
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_OPEN(3)Pages that refer to this page:sd-journal(3), sd_journal_add_match(3), sd_journal_enumerate_fields(3), sd_journal_get_catalog(3), sd_journal_get_cursor(3), sd_journal_get_cutoff_realtime_usec(3), sd_journal_get_data(3), sd_journal_get_fd(3), sd_journal_get_realtime_usec(3), sd_journal_get_seqnum(3), sd_journal_get_usage(3), sd_journal_next(3), sd_journal_query_unique(3), sd_journal_seek_head(3), systemd.directives(7), systemd.index(7)
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. | |