Open the system journal for reading
#include <systemd/sd-journal.h>
int sd_journal_open(sd_journal **ret, int flags); int sd_journal_open_directory(sd_journal **ret, const char *path, int flags); int sd_journal_open_files(sd_journal **ret, const char **paths, int flags); int sd_journal_open_container(sd_journal **ret, const char *machine, int flags); 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 a sd_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_ONLY makes sure only journal files generated on the local machine will be opened. SD_JOURNAL_RUNTIME_ONLY makes sure only volatile journal files will be opened, excluding those which are stored on persistent storage. SD_JOURNAL_SYSTEM will cause journal files of system services and the kernel (in opposition to user session processes) to be opened. SD_JOURNAL_CURRENT_USER will cause journal files of the current user to be opened. If neither SD_JOURNAL_SYSTEM nor SD_JOURNAL_CURRENT_USER are specified, all journal file types will be opened.
sd_journal_open_directory() is similar to sd_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, but it must be passed as 0 as no flags are currently understood for this call.
sd_journal_open_files() is similar to sd_journal_open() but takes a NULL-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_container() is similar to sd_journal_open() but opens the journal files of a running OS container. The specified machine name refers to a container that is registered with systemd-machined(8).
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 -ECHILD after a fork.
sd_journal_close() will close the journal context allocated with sd_journal_open() or sd_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.
See sd_journal_next(3) for an example of how to iterate through the journal after opening it with sd_journal_open().
A journal context object returned by sd_journal_open() references a specific journal entry as current entry, similar to a file seek index in a classic file system file, but without absolute positions. It may be altered with sd_journal_next(3) and sd_journal_seek_head(3) and related calls. The current entry position may be exported in cursor strings, as accessible via sd_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 via sd_journal_get_fd() and related calls.
The sd_journal_open(), sd_journal_open_directory(), and sd_journal_open_files() calls return 0 on success or a negative errno-style error code. sd_journal_close() returns nothing.
The sd_journal_open(), sd_journal_open_directory() and sd_journal_close() interfaces are available as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.
sd_journal_open(), sd_journal_close(), SD_JOURNAL_LOCAL_ONLY, SD_JOURNAL_RUNTIME_ONLY, SD_JOURNAL_SYSTEM_ONLY were added in systemd-38.
sd_journal_open_directory() was added in systemd-187.
SD_JOURNAL_SYSTEM, SD_JOURNAL_CURRENT_USER, and sd_journal_open_files() were added in systemd-205. SD_JOURNAL_SYSTEM_ONLY was deprecated.