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https://github.com/daurnimator/lua-systemd
Systemd bindings for Lua
https://github.com/daurnimator/lua-systemd
dbus lua systemd
Last synced: 3 months ago
JSON representation
Systemd bindings for Lua
- Host: GitHub
- URL: https://github.com/daurnimator/lua-systemd
- Owner: daurnimator
- License: mit
- Created: 2014-08-03T14:40:00.000Z (over 10 years ago)
- Default Branch: master
- Last Pushed: 2016-05-17T14:05:38.000Z (over 8 years ago)
- Last Synced: 2024-10-19T04:01:47.422Z (3 months ago)
- Topics: dbus, lua, systemd
- Language: C
- Size: 165 KB
- Stars: 40
- Watchers: 4
- Forks: 7
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# [Systemd](http://freedesktop.org/wiki/Software/systemd/) for Lua.
This library is for working with systemd from scripts and daemons written in Lua.
Where necessary, the low level `libsystemd` functions have been bound in C.
Higher level functions with more idiomatic lua semantics are written in Lua on top of these C primitives.
Compatible with Lua 5.1, 5.2 and 5.3 (thanks [compat-5.3](https://github.com/keplerproject/lua-compat-5.3)).
# Status
Waiting for API to stabilise before making an initial release.
## Todo
- [x] [Notify](http://www.freedesktop.org/software/systemd/man/sd_notify.html) - Notify service manager about start-up completion and other daemon status changes
- [x] [ID128](http://www.freedesktop.org/software/systemd/man/sd-id128.html) - APIs for processing 128-bit IDs
- [x] [Journal](http://www.freedesktop.org/software/systemd/man/sd-journal.html)
- [x] [Journal Writing](http://www.freedesktop.org/software/systemd/man/sd_journal_sendv.html)
- [x] [Journal Reading](http://www.freedesktop.org/software/systemd/man/sd_journal_next.html)
- [x] [Journal Change Notification](http://www.freedesktop.org/software/systemd/man/sd_journal_get_fd.html)
- [x] [Login](http://www.freedesktop.org/software/systemd/man/sd-login.html)
- [x] [PID/Peer Information](http://www.freedesktop.org/software/systemd/man/sd_pid_get_session.html)
- [x] [User State](http://www.freedesktop.org/software/systemd/man/sd_uid_get_state.html)
- [x] [Session Information](http://www.freedesktop.org/software/systemd/man/sd_session_is_active.html)
- [x] [Seat Information](http://www.freedesktop.org/software/systemd/man/sd_seat_get_active.html)
- [x] [Login Monitoring](http://www.freedesktop.org/software/systemd/man/sd_login_monitor.html) - Monitor login sessions, seats, users and virtual machines/containers
- [ ] Unit Control - Requires use of [dbus API](http://www.freedesktop.org/wiki/Software/systemd/dbus/)
# Installation
lua-systemd is on luarocks: https://luarocks.org/modules/daurnimator/systemd
Install via luarocks: `luarocks install --server=http://luarocks.org/manifests/daurnimator systemd`
# Usage
## Bound from C
All functions return `nil, error_message [, errno]` in case of error.
C | Lua | Comments
-----------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------|----------------------------------------
[`SD_LISTEN_FDS_START`](http://www.freedesktop.org/software/systemd/man/SD_LISTEN_FDS_START.html) | `systemd.daemon.LISTEN_FDS_START` |
[`sd_notify()`](http://www.freedesktop.org/software/systemd/man/sd_notify.html) | `systemd.daemon.notify()` |
[`sd_pid_notify()`](http://www.freedesktop.org/software/systemd/man/sd_pid_notify.html) | `systemd.daemon.pid_notify()` |
[`sd_pid_notify_with_fds()`](http://www.freedesktop.org/software/systemd/man/sd_pid_notify_with_fds.html) | `systemd.daemon.pid_notify_with_fds()` |
[`sd_booted()`](http://www.freedesktop.org/software/systemd/man/sd_booted.html) | `systemd.daemon.booted()` |
[`sd_listen_fds()`](http://www.freedesktop.org/software/systemd/man/sd_listen_fds.html) | `systemd.daemon.listen_fds()` |
[`sd_journal_sendv()`](http://www.freedesktop.org/software/systemd/man/sd_journal_sendv.html) | `systemd.journal.sendv()` |
[`sd_journal_perror()`](http://www.freedesktop.org/software/systemd/man/sd_journal_perror.html) | `systemd.journal.perror()` |
[`sd_journal_stream_fd()`](http://www.freedesktop.org/software/systemd/man/sd_journal_stream_fd.html) | `systemd.journal.stream_fd()` | On success, returns a Lua `file` object instead of raw file descriptor
[`SD_JOURNAL_LOCAL_ONLY`](http://www.freedesktop.org/software/systemd/man/SD_JOURNAL_LOCAL_ONLY.html) | `systemd.journal.OPEN.LOCAL_ONLY` |
[`SD_JOURNAL_RUNTIME_ONLY`](http://www.freedesktop.org/software/systemd/man/SD_JOURNAL_RUNTIME_ONLY.html) | `systemd.journal.OPEN.RUNTIME_ONLY` |
[`SD_JOURNAL_SYSTEM`](http://www.freedesktop.org/software/systemd/man/SD_JOURNAL_SYSTEM.html) | `systemd.journal.OPEN.SYSTEM` |
[`SD_JOURNAL_CURRENT_USER`](http://www.freedesktop.org/software/systemd/man/SD_JOURNAL_CURRENT_USER.html) | `systemd.journal.OPEN.CURRENT_USER` |
[`sd_journal_open()`](http://www.freedesktop.org/software/systemd/man/sd_journal_open.html) | `systemd.journal.open()` |
[`sd_journal_open_directory()`](http://www.freedesktop.org/software/systemd/man/sd_journal_open_directory.html) | `systemd.journal.open_directory()` |
[`sd_journal_open_files()`](http://www.freedesktop.org/software/systemd/man/sd_journal_open_files.html) | `systemd.journal.open_files()` |
[`sd_journal_open_container()`](http://www.freedesktop.org/software/systemd/man/sd_journal_open_container.html) | `systemd.journal.open_container()` |
[`sd_journal_close()`](http://www.freedesktop.org/software/systemd/man/sd_journal_close.html) | | Bound as `__gc` metamethod on journal objects
[`sd_journal_get_cutoff_realtime_usec()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_cutoff_realtime_usec.html) | `my_journal:get_cutoff_realtime_usec()` |
[`sd_journal_get_cutoff_monotonic_usec()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_cutoff_monotonic_usec.html) | `my_journal:get_cutoff_monotonic_usec()` |
[`sd_journal_get_usage()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_usage.html) | `my_journal:get_usage()` |
[`sd_journal_next()`](http://www.freedesktop.org/software/systemd/man/sd_journal_next.html) | `my_journal:next()` |
[`sd_journal_next_skip()`](http://www.freedesktop.org/software/systemd/man/sd_journal_next_skip.html) | `my_journal:next_skip()` |
[`sd_journal_previous()`](http://www.freedesktop.org/software/systemd/man/sd_journal_previous.html) | `my_journal:previous()` |
[`sd_journal_previous_skip()`](http://www.freedesktop.org/software/systemd/man/sd_journal_previous_skip.html) | `my_journal:previous_skip()` |
[`sd_journal_seek_head()`](http://www.freedesktop.org/software/systemd/man/sd_journal_seek_head.html) | `my_journal:seek_head()` |
[`sd_journal_seek_tail()`](http://www.freedesktop.org/software/systemd/man/sd_journal_seek_tail.html) | `my_journal:seek_tail()` |
[`sd_journal_seek_monotonic_usec()`](http://www.freedesktop.org/software/systemd/man/sd_journal_seek_monotonic_usec.html) | `my_journal:seek_monotonic_usec()` |
[`sd_journal_seek_realtime_usec()`](http://www.freedesktop.org/software/systemd/man/sd_journal_seek_realtime_usec.html) | `my_journal:seek_realtime_usec()` |
[`sd_journal_seek_cursor()`](http://www.freedesktop.org/software/systemd/man/sd_journal_seek_cursor.html) | `my_journal:seek_cursor()` |
[`sd_journal_get_cursor()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_cursor.html) | `my_journal:get_cursor()` |
[`sd_journal_test_cursor()`](http://www.freedesktop.org/software/systemd/man/sd_journal_test_cursor.html) | `my_journal:test_cursor()` |
[`sd_journal_get_realtime_usec()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_realtime_usec.html) | `my_journal:get_realtime_usec()` |
[`sd_journal_get_monotonic_usec()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_monotonic_usec.html) | `my_journal:get_monotonic_usec()` |
[`sd_journal_get_data()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_data.html) | `my_journal:get_data()` |
[`sd_journal_enumerate_data()`](http://www.freedesktop.org/software/systemd/man/sd_journal_enumerate_data.html) | `my_journal:enumerate_data()` |
[`sd_journal_restart_data()`](http://www.freedesktop.org/software/systemd/man/sd_journal_restart_data.html) | `my_journal:restart_data()` |
[`sd_journal_query_unique()`](http://www.freedesktop.org/software/systemd/man/sd_journal_query_unique.html) | `my_journal:query_unique()` |
[`sd_journal_enumerate_unique()`](http://www.freedesktop.org/software/systemd/man/sd_journal_enumerate_unique.html) | `my_journal:enumerate_unique()` |
[`sd_journal_restart_unique()`](http://www.freedesktop.org/software/systemd/man/sd_journal_restart_unique.html) | `my_journal:restart_unique()` |
[`sd_journal_set_data_threshold()`](http://www.freedesktop.org/software/systemd/man/sd_journal_set_data_threshold.html) | `my_journal:set_data_threshold()` |
[`sd_journal_get_data_threshold()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_data_threshold.html) | `my_journal:get_data_threshold()` |
[`sd_journal_add_match()`](http://www.freedesktop.org/software/systemd/man/sd_journal_add_match.html) | `my_journal:add_match()` |
[`sd_journal_add_disjunction()`](http://www.freedesktop.org/software/systemd/man/sd_journal_add_disjunction.html) | `my_journal:add_disjunction()` |
[`sd_journal_add_conjunction()`](http://www.freedesktop.org/software/systemd/man/sd_journal_add_conjunction.html) | `my_journal:add_conjunction()` |
[`sd_journal_flush_matches()`](http://www.freedesktop.org/software/systemd/man/sd_journal_flush_matches.html) | `my_journal:flush_matches()` |
[`SD_JOURNAL_NOP`](http://www.freedesktop.org/software/systemd/man/SD_JOURNAL_NOP.html) | `systemd.journal.WAKEUP.NOP` |
[`SD_JOURNAL_APPEND`](http://www.freedesktop.org/software/systemd/man/SD_JOURNAL_APPEND.html) | `systemd.journal.WAKEUP.APPEND` |
[`SD_JOURNAL_INVALIDATE`](http://www.freedesktop.org/software/systemd/man/SD_JOURNAL_INVALIDATE.html) | `systemd.journal.WAKEUP.INVALIDATE` |
[`sd_journal_get_fd()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_fd.html) | `my_journal:get_fd()` |
[`sd_journal_get_events()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_events.html) | `my_journal:get_events()` |
[`sd_journal_get_timeout()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_timeout.html) | `my_journal:get_timeout()` | Returns `false` if timeout isn't available, otherwise returns value in seconds
[`sd_journal_process()`](http://www.freedesktop.org/software/systemd/man/sd_journal_process.html) | `my_journal:process()` |
[`sd_journal_wait()`](http://www.freedesktop.org/software/systemd/man/sd_journal_wait.html) | `my_journal:wait()` | `timeout` is in seconds instead of microseconds
[`sd_journal_reliable_fd()`](http://www.freedesktop.org/software/systemd/man/sd_journal_reliable_fd.html) | `my_journal:reliable_fd()` |
[`sd_id128_randomize()`](http://www.freedesktop.org/software/systemd/man/sd_id128_randomize.html) | `systemd.id128.randomize()` | Also available as `randomise` for any non-americans out there
[`sd_id128_from_string()`](http://www.freedesktop.org/software/systemd/man/sd_id128_from_string.html) | `systemd.id128.from_string()` |
[`sd_id128_get_machine()`](http://www.freedesktop.org/software/systemd/man/sd_id128_get_machine.html) | `systemd.id128.get_machine()` |
[`sd_id128_get_boot()`](http://www.freedesktop.org/software/systemd/man/sd_id128_get_boot.html) | `systemd.id128.get_boot()` |
[`sd_id128_to_string()`](http://www.freedesktop.org/software/systemd/man/sd_id128_to_string.html) | `my_id128:to_string()` | Also available as `__tostring` metamethod: `tostring(my_id128_t)`
[`sd_id128_equal()`](http://www.freedesktop.org/software/systemd/man/sd_id128_equal.html) | `id128_a == id128_b` | Bound as `__eq` metamethod
[`sd_journal_get_catalog_for_message_id()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_catalog_for_message_id.html) | `my_id128:get_catalog()` |
[`sd_get_seats()`](http://www.freedesktop.org/software/systemd/man/sd_get_seats.html) | `systemd.login.get_seats()` |
[`sd_get_sessions()`](http://www.freedesktop.org/software/systemd/man/sd_get_sessions.html) | `systemd.login.get_sessions()` |
[`sd_get_uids()`](http://www.freedesktop.org/software/systemd/man/sd_get_uids.html) | `systemd.login.get_uids()` |
[`sd_get_machine_names()`](http://www.freedesktop.org/software/systemd/man/sd_get_machine_names.html) | `systemd.login.get_machine_names()` |
[`sd_pid_get_session()`](http://www.freedesktop.org/software/systemd/man/sd_pid_get_session.html) | `systemd.login.pid_get_session()` |
[`sd_pid_get_unit()`](http://www.freedesktop.org/software/systemd/man/sd_pid_get_unit.html) | `systemd.login.pid_get_unit()` |
[`sd_pid_get_user_unit()`](http://www.freedesktop.org/software/systemd/man/sd_pid_get_user_unit.html) | `systemd.login.pid_get_user_unit()` |
[`sd_pid_get_owner_uid()`](http://www.freedesktop.org/software/systemd/man/sd_pid_get_owner_uid.html) | `systemd.login.pid_get_owner_uid()` |
[`sd_pid_get_machine_name()`](http://www.freedesktop.org/software/systemd/man/sd_pid_get_machine_name.html) | `systemd.login.pid_get_machine_name()` |
[`sd_pid_get_slice()`](http://www.freedesktop.org/software/systemd/man/sd_pid_get_slice.html) | `systemd.login.pid_get_slice()` |
[`sd_pid_get_user_slice()`](http://www.freedesktop.org/software/systemd/man/sd_pid_get_user_slice.html) | `systemd.login.pid_get_user_slice()` |
[`sd_peer_get_session()`](http://www.freedesktop.org/software/systemd/man/sd_peer_get_session.html) | `systemd.login.peer_get_session()` |
[`sd_peer_get_unit()`](http://www.freedesktop.org/software/systemd/man/sd_peer_get_unit.html) | `systemd.login.peer_get_unit()` |
[`sd_peer_get_user_unit()`](http://www.freedesktop.org/software/systemd/man/sd_peer_get_user_unit.html) | `systemd.login.peer_get_user_unit()` |
[`sd_peer_get_owner_uid()`](http://www.freedesktop.org/software/systemd/man/sd_peer_get_owner_uid.html) | `systemd.login.peer_get_owner_uid()` |
[`sd_peer_get_machine_name()`](http://www.freedesktop.org/software/systemd/man/sd_peer_get_machine_name.html) | `systemd.login.peer_get_machine_name()` |
[`sd_peer_get_slice()`](http://www.freedesktop.org/software/systemd/man/sd_peer_get_slice.html) | `systemd.login.peer_get_slice()` |
[`sd_peer_get_user_slice()`](http://www.freedesktop.org/software/systemd/man/sd_peer_get_user_slice.html) | `systemd.login.peer_get_user_slice()` |
[`sd_uid_get_state()`](http://www.freedesktop.org/software/systemd/man/sd_uid_get_state.html) | `systemd.login.uid_get_state()` |
[`sd_uid_is_on_seat()`](http://www.freedesktop.org/software/systemd/man/sd_uid_is_on_seat.html) | `systemd.login.uid_is_on_seat()` |
[`sd_uid_get_sessions()`](http://www.freedesktop.org/software/systemd/man/sd_uid_get_sessions.html) | `systemd.login.uid_get_sessions()` |
[`sd_uid_get_seats()`](http://www.freedesktop.org/software/systemd/man/sd_uid_get_seats.html) | `systemd.login.uid_get_seats()` |
[`sd_uid_get_display()`](http://www.freedesktop.org/software/systemd/man/sd_uid_get_display.html) | `systemd.login.uid_get_display()` |
[`sd_session_is_active()`](http://www.freedesktop.org/software/systemd/man/sd_session_is_active.html) | `systemd.login.session_is_active()` |
[`sd_session_is_remote()`](http://www.freedesktop.org/software/systemd/man/sd_session_is_remote.html) | `systemd.login.session_is_remote()` |
[`sd_session_get_state()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_state.html) | `systemd.login.session_get_state()` |
[`sd_session_get_uid()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_uid.html) | `systemd.login.session_get_uid()` |
[`sd_session_get_seat()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_seat.html) | `systemd.login.session_get_seat()` |
[`sd_session_get_service()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_service.html) | `systemd.login.session_get_service()` |
[`sd_session_get_type()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_type.html) | `systemd.login.session_get_type()` |
[`sd_session_get_class()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_class.html) | `systemd.login.session_get_class()` |
[`sd_session_get_desktop()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_desktop.html) | `systemd.login.session_get_desktop()` |
[`sd_session_get_display()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_display.html) | `systemd.login.session_get_display()` |
[`sd_session_get_remote_host()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_remote_host.html) | `systemd.login.session_get_remote_host()`|
[`sd_session_get_remote_user()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_remote_user.html) | `systemd.login.session_get_remote_user()`|
[`sd_session_get_tty()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_tty.html) | `systemd.login.session_get_tty()` |
[`sd_session_get_vt()`](http://www.freedesktop.org/software/systemd/man/sd_session_get_vt.html) | `systemd.login.session_get_vt()` |
[`sd_seat_get_active()`](http://www.freedesktop.org/software/systemd/man/sd_seat_get_active.html) | `systemd.login.seat_get_active()` | On success, returns `session, uid`
[`sd_seat_get_sessions()`](http://www.freedesktop.org/software/systemd/man/sd_seat_get_sessions.html) | `systemd.login.seat_get_sessions()` | On success, returns `sessions, uids`
[`sd_seat_can_multi_session()`](http://www.freedesktop.org/software/systemd/man/sd_seat_can_multi_session.html) | `systemd.login.seat_can_multi_session()` |
[`sd_seat_can_tty()`](http://www.freedesktop.org/software/systemd/man/sd_seat_can_tty.html) | `systemd.login.seat_can_tty()` |
[`sd_seat_can_graphical()`](http://www.freedesktop.org/software/systemd/man/sd_seat_can_graphical.html) | `systemd.login.seat_can_graphical()` |
[`sd_machine_get_class()`](http://www.freedesktop.org/software/systemd/man/sd_machine_get_class.html) | `systemd.login.machine_get_class()` |
[`sd_machine_get_ifindices()`](http://www.freedesktop.org/software/systemd/man/sd_machine_get_ifindices.html) | `systemd.login.machine_get_ifindices()` |
[`sd_login_monitor_new()`](http://www.freedesktop.org/software/systemd/man/sd_login_monitor_new.html) | `systemd.login.monitor()` |
[`sd_login_monitor_unref()`](http://www.freedesktop.org/software/systemd/man/sd_login_monitor_unref.html) | | Bound as `__gc` metamethod on monitor objects
[`sd_login_monitor_flush()`](http://www.freedesktop.org/software/systemd/man/sd_login_monitor_flush.html) | `my_login_monitor:flush()` |
[`sd_login_monitor_get_fd()`](http://www.freedesktop.org/software/systemd/man/sd_login_monitor_get_fd.html) | `my_login_monitor:get_fd()` |
[`sd_login_monitor_get_events()`](http://www.freedesktop.org/software/systemd/man/sd_login_monitor_get_events.html) | `my_login_monitor:get_events()` |
[`sd_login_monitor_get_timeout()`](http://www.freedesktop.org/software/systemd/man/sd_login_monitor_get_timeout.html) | `my_login_monitor:get_timeout()` | Returns `false` if timeout isn't available, otherwise returns value in seconds
## Misc extras
### `systemd.daemon.notifyt(tbl)` and `systemd.daemon.pid_notifyt(tbl)`
Like `notify`, but takes a lua table instead of a newline delimited list.
Numbers will be coerced to strings.
```lua
notifyt { READY = 1, STATUS = "Server now accepting connections", WATCHDOG = 1 }
```
### `interval = systemd.daemon.watchdog_enabled()`
Returns the watchdog interval (in seconds) if there is one set otherwise returns `false`.
You should call `kick_dog` or `notify("WATCHDOG=1")` every half of this interval.
Similar functionality to [`sd_watchdog_enabled()`](http://www.freedesktop.org/software/systemd/man/sd_watchdog_enabled.html)
### `systemd.daemon.kick_dog()`
Tells systemd to update the watchdog timestamp.
This should be called on an interval.
### `systemd.journal.LOG`
Table containing the `syslog(3)` priority constants: `EMERG`, `ALERT`, `CRIT`, `ERR`, `WARNING`, `NOTICE`, `INFO`, `DEBUG`
Useful as the second argument to `systemd.journal.streamfd()`
### `systemd.journal.print(priority, fmt_string, ...)`
Same argument signature as C, but written in lua on top of `sendv()` and `string.format()`
### `systemd.journal.sendt(tbl)`
Log a message to the journal with the key/value pairs from `tbl`
```lua
systemd.journal.sendt {
SYSLOG_IDENTIFIER = "identifier" ;
SYSLOG_FACILITY = "facility" ;
PRIORITY = systemd.journal.LOG.ERR ;
MESSAGE = "something happended!" ;
MY_CUSTOM_FIELD = "extra detail.";
}
```
### `value = my_journal:get(field)`
Returns the given field from the current journal entry (which may be `nil`)
Throws a lua error on failure.
### `my_journal:each_data()`
A valid lua iterator that enumerates through field, value pairs.
```lua
for field, value in my_journal:each_data() do
print(field, value)
end
```
Throws a lua error on failure.
### `my_journal:each_unique(field_name)`
A valid lua iterator that enumerates through unique field values.
```lua
-- Print each different `_SYSTEMD_UNIT`
for value in my_journal:each_unique("_SYSTEMD_UNIT") do
print(value)
end
```
Throws a lua error on failure.
### `t = my_journal:to_table()`
Converts the current journal entry to a lua table.
Includes [Address Fields](http://www.freedesktop.org/software/systemd/man/systemd.journal-fields.html#Address%20Fields):
- `__CURSOR`
- `__REALTIME_TIMESTAMP`
- `__MONOTONIC_TIMESTAMP`
### `text = my_journal:get_catalog()`
Looks up the current journal entry's `MESSAGE_ID` in the [message catalog](http://www.freedesktop.org/wiki/Software/systemd/catalog/).
Substitutes the templated fields (between `@` symbols) with values from this journal entry.
Returns:
- the filled out catalogue entry as a string
- `false` if `MESSAGE_ID` is not set, or does not exist in the catalogue
- `nil, err_msg, errno` in case of failure.
Same functionality as [`sd_journal_get_catalog()`](http://www.freedesktop.org/software/systemd/man/sd_journal_get_catalog.html).
### `systemd.messages`
A table of well-known message ids as `id128` objects.
Taken from [`sd-messages.h`](http://cgit.freedesktop.org/systemd/systemd/tree/src/systemd/sd-messages.h?id=HEAD)