SYSLOGD(8) BSD System Manager's Manual SYSLOGD(8)NAMEsyslogd — Apple System Log server
SYNOPSISsyslogd [-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 mes‐
sages, 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 cur‐
rently 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 mes‐
sages 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 min‐
utes.
-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 archive after the regular time-to-live inter‐
val, 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 remain‐
ing 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 mes‐
sages that will be saved by syslogd. User processes are lim‐
ited 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 dis‐
able (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
disabled 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 nor‐
mally 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
disabled 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 cur‐
rently handled by the “bsd_out” module 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/LaunchDae‐
mons/com.apple.syslogd.plist. In the default configuration,
launchd does not open any sockets for the “syslog” UDP ser‐
vice, 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 ARCHIVALsyslogd 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 corre‐
sponding 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" mes‐
sage 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 syslogdSEE ALSOsyslog(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
