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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_JOURNAL_OPEN(3) sd_journal_open SD_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, int flags);
int sd_journal_open_namespace(sd_journal **ret,
const char *namespace, int flags);
int sd_journal_open_directory(sd_journal **ret, const char *path,
int flags);
int sd_journal_open_directory_fd(sd_journal **ret, int fd,
int flags);
int sd_journal_open_files(sd_journal **ret, const char **paths,
int flags);
int sd_journal_open_files_fd(sd_journal **ret, int fds[],
unsigned n_fds, 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_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 path. In addition to the flags accepted by
sd_journal_open_directory(), this function also accepts
SD_JOURNAL_TAKE_DIRECTORY_FD. If SD_JOURNAL_TAKE_DIRECTORY_FD is
specified, the function will take the ownership of the specified
file descriptor on success, and it will be closed by
sd_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 after sd_journal_close().
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
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.
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 the
libsystemd pkg-config(1) file.
sd_journal_open(), sd_journal_open_directory(), and
sd_journal_close() were added in version 187.
sd_journal_open_files() was added in version 205.
sd_journal_open_directory_fd() and sd_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 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
⟨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 is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 SD_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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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