sd_journal_open, sd_journal_open_directory, sd_journal_close, sd_journal, SD_JOURNAL_LOCAL_ONLY, SD_JOURNAL_RUNTIME_ONLY, SD_JOURNAL_SYSTEM_ONLY — 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 ); | 
| 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 journal context object afterwards. 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_ONLY
                will ensure that only journal files of system services
                and the kernel (in opposition to user session processes) 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_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 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() and
                sd_journal_open_directory() 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 shared library, which can be compiled and
                linked to with the
                libsystemd-journal
                pkg-config(1)
                file.