.\" Copyright (c) 2018 Apple Inc. All rights reserved.
.Dd August 30, 2018
.Dt logd 8
.Os Darwin
.Sh NAME
.Nm logd
.Nd unified logging system daemon
.Sh DESCRIPTION
.Nm
is the part of the unified logging system
that is responsible for handling and managing historical data
and related metadata.
For example, it handles entries generated via the
.Xr os_log 3
family of facilities.
.Bd -literal -offset indent
{ process }
     `--- os_log ---> [ page ]
                      [ page ]
                      [ page ]
                          `---> { logd }
                                   | `---> [ buffer ]
                                   |
                                   `---> [ data store ]
.Ed
.Pp
All processes that use
.Xr os_log 3
share pages of memory with
.Nm
and append entries to them.
.Nm
reads pages and combines and compresses this data.
Depending on configured policies,
it keeps them in a local ring buffer or writes them out to persistent storage.
.Bd -literal -offset indent
{ logd }
   | `---> [ buffer ] ----.
   |                      ,`---> { log show }
   `---> [ data store ] -'
.Ed
.Pp
The
.Xr log 1
utility can view these data by requesting
.Nm
for access to both the ring buffer and the persistent storage.
.Sh SEE ALSO
.Xr log 1 ,
.Xr os_log 3 ,
.Xr diagnosticd 8
.Pp
.Lk https://developer.apple.com/documentation/os/logging "Logging | Apple Developer Documentation"