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
sd_journal_open_namespace() is similar to sd_journal_open() but takes
an additional namespace parameter that specifies which journal
namespace to operate on. If specified as NULL the call is identical
to sd_journal_open(). If non-NULL only data from the namespace
identified by the specified parameter is accessed. This call
understands two additional flags: if SD_JOURNAL_ALL_NAMESPACES is
specified the namespace parameter is ignored and all defined
namespaces are accessed simultaneously; if
SD_JOURNAL_INCLUDE_DEFAULT_NAMESPACE the specified namespace and the
default namespace are accessed but no others (this flag has no effect
when namespace is passed as NULL). For details about journal
namespaces see systemd-journald.service(8).
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. The flags parameters accepted by this
call are SD_JOURNAL_OS_ROOT, SD_JOURNAL_SYSTEM, and
SD_JOURNAL_CURRENT_USER. If SD_JOURNAL_OS_ROOT is 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 for sd_journal_open().
sd_journal_open_directory_fd() is similar to
sd_journal_open_directory(), but takes a file descriptor referencing
a directory in the file system instead of an absolute file system
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_files_fd() is similar to sd_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 -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
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)
Notification of journal changes is available via sd_journal_get_fd()
and related calls.
All functions listed here are thread-agnostic and only a single
specific thread may operate on a given object during its entire
lifetime. It's safe to allocate multiple independent objects and use
each from a specific thread in parallel. However, it's 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 don't
operate on it at the very same time.
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
This page is part of the systemd (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
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2020-08-13. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-08-11.) 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 is not part
of the original manual page), send a mail to email@example.com
systemd 246 SD_JOURNAL_OPEN(3)