SYSLOGD(8) BSD System Manager's Manual SYSLOGD(8)
NAME
syslogd -- Apple System Log server
SYNOPSIS
syslogd [-d] [-D] [-m mark_interval] [-l lib_path] [-db_max size] [-utmp_ttl time] [-mps_limit quota] [-dup_delay time] [-module_name {0|1}]
DESCRIPTION
The syslogd server receives and processes log messages. Several modules receive input messages through various channels, including UNIX
domain sockets associated with the syslog(3), asl(3), and kernel printf APIs, and optionally on a UDP socket from network clients.
The Apple System Log facility comprises the asl(3) API, a new syslogd server, the syslog(1) command-line utility, and a data store file man-
ager, aslmanager(8). The system supports structured and extensible messages, permitting advanced message browsing and management through
search APIs and other components of the Apple system log facility.
Log messages are retained in a data store, subject to automatic archival, and input filtering as described below, to simplify the task of
locating log messages and to facilitate browsing and searching. The data store is intended to become a replacement for the numerous log
files that are currently found in various locations on the system. Those files will be phased out in future versions of Mac OS.
The following options are recognized:
-d Run syslogd in debugging mode. The server stays attached to the controlling terminal and prints debugging messages.
-D Start as a daemon. This option forces syslogd to fork and have the child process become a daemon. Since syslogd is started by
launchd, this is not normally required.
-m Set the number of minutes between ``mark'' messages. Mark messages are normally disabled. If -m is specified with no arguments,
mark messages will be written every 20 minutes. The ``mark'' facility is disabled if the setting is zero minutes.
-db_max Sets the size limit in bytes for individual files in the data store. The default value for -db_max is 25600000 bytes. Files are
closed upon reaching the maximum size, and a new file is opened for subsequent messages.
-utmp_ttl Sets the time-to-live in seconds for messages used by the utmp, wtmp, and lastlog subsystems. The default is 31622400 seconds
(approximately 1 year). Note that if archival is enabled (see the aslmanager(8) manual), these messages will be copied to an ar-
chive after the regular time-to-live interval, but will persist in the data store until their own expiry time.
-mps_limit Sets the kernel quota for messages per second allowed by syslogd. Any messages in excess of the quota limit from any process are
ignored. An error message is logged stating that the kernel message quota has been exceeded, and that remaining messages for the
current second will be discarded. The default limit is 500 messages per second per process. A value of 0 turns off the quota
mechanism.
Note that this setting only limits the number of kernel messages that will be saved by syslogd. User processes are limited to
36000 messages per hour. The limit for a user process is not enforced if a remote-control ASL filter is in place for the
process.
-dup_delay Sets the time to delay for coalescing duplicate message in log files. If a process logs multiple messages with the same text,
syslogd will wait for the specified period of time to coalesce duplicates. If identical messages arrive during this interval,
syslogd will print a message of the form:
May 7 12:34:56: --- last message repeated 17 times ---
The default delay time is 30 seconds. Setting the value to 0 disables the coalescing mechanism.
The remaining options of the form -module_name {0|1} may be used to disable (0) or enable (1) the action of several of internal modules.
-asl_in The ``asl_in'' module receives log messages on the UNIX domain socket associated with the asl(3) API. The module may be dis-
abled using -asl_in 0. The module is normally enabled.
-asl_action The ``asl_action'' module examines the stream of received log messages and acts upon them according to the rules specified in
the file /etc/asl.conf. See asl.conf(5) for details.
-klog_in The ``klog_in'' module receives log messages on the UNIX domain socket associated with the kernel logging API. The module may
be disabled using -klog_in 0. The module is normally enabled.
-bsd_in The ``bsd_in'' module receives log messages on the UNIX domain socket associated with the syslog(3) API. The module may be dis-
abled using -bsd_in 0. The module is normally enabled.
-bsd_out The ``bsd_out'' module examines the stream of received log messages and acts upon them according to the rules specified in the
file /etc/syslog.conf. See syslog.conf(5) for details. This module exists for backward compatibility with previous syslogd
implementations. Apple encourages use of the syslog(1) and asl(3) search APIs over the use of the log files that are specified
in the /etc/syslog.conf file. Future versions of Mac OS will move functions that are currently handled by the ``bsd_out'' mod-
ule to the ``asl_action'' module.
-udp_in The ``udp_in'' module receives log messages on the UDP socket associated with the Internet syslog message protocol.
This module is normally enabled, but is inactive. The actual UDP sockets are managed by launchd, and configured in the syslogd
configuration file /System/Library/LaunchDaemons/com.apple.syslogd.plist. In the default configuration, launchd does not open
any sockets for the ``syslog'' UDP service, so no sockets are provided to the ``udp_in'' module. If no sockets are provided,
the module remains inactive. A socket may be specified by adding the following entry to the ``Sockets'' dictionary in the
com.apple.syslogd.plist file.
<key>NetworkListener</key>
<dict>
<key>SockServiceName</key>
<string>syslog</string>
<key>SockType</key>
<string>dgram</string>
</dict>
The module may be specifically disabled using the -udp_in 0 option.
syslogd reinitializes in response to a HUP signal.
MESSAGE EXPIRY AND ARCHIVAL
syslogd periodically invokes the aslmanager utility, which manages files in the ASL data store. Files are removed or optionally copied to an
archival directory after a (default) 2 day time-to-live. See the aslmanager(8) manual for details. syslogd invokes aslmanager shortly after
it starts up, at midnight local time if it is running, and any time that a data store file reaches the -db_max size limit.
DATA STORE SECURITY
Messages saved in the ASL message store are written to files in /var/log/asl. The message files are given read access controls corresponding
to the read UID and GID specified in the messages themselves. Read access UID and GID settings may be attached to messages using the asl(3)
library by setting a value for the "ReadUID" and/or "ReadGID" message keys. The file permissions prevent access-controlled messages from
being read by unauthorized users.
Although clients are generally free to use any value for the "Facility" message key, only processes running with UID 0 may log messages with
a facility value of "com.apple.system", or with a value that has "com.apple.system" as a prefix. Messages logged by non UID 0 processes that
use "com.apple.system" as a facility value or prefix will be saved with the facility value "user".
FILES
/etc/syslog.conf bsd_out module configuration file
/etc/asl.conf asl_action module configuration file
/var/run/syslog.pid process ID file
/var/run/syslog name of the UNIX domain datagram log socket
/dev/klog kernel log device
/var/log/asl data store directory
/var/log/asl.archive default archive directory
/System/Library/LaunchDaemons/com.apple.syslogd.plist
launchd configuration file for syslogd
SEE ALSO
syslog(1), logger(1), asl(3), syslog(3), asl.conf(5) syslog.conf(5)
HISTORY
The syslogd utility appeared in 4.3BSD.
The Apple System Log facility was introduced in Mac OS X 10.4.
Mac OS X October 18, 2004 Mac OS X