syslog-385.tar.gz

[apple/syslog.git] / syslogd.tproj / asl.conf.5

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.Dd Sept 19, 2008
.Dt asl.conf 5
.Os "Mac OS X"
.Sh NAME
.Nm asl.conf
.Nd configuration file for
.Xr syslogd 8
and
.Xr aslmanager 8
.Sh DESCRIPTION
The
.Xr syslogd 8
server reads the /etc/asl.conf file at startup, and re-reads the file when it receives a HUP signal.
The
.Xr aslmanager 8
daemon reads the file when it starts.
See the ASLMANAGER PARAMETER SETTINGS section for details on aslmanager-specific parameters.
.Pp
If the /etc/asl directory exists, then
.Nm syslogd
and
.Nm aslmanager
will read each file it contains.
These files must have the same format as
.Nm asl.conf .
Each file configures an independent module, identified by the file name.
Modules may be enabled or disabled independently.
Each module may specify its own set of rules for acting on received messages.
See the ASL MODULES section for details.
.Pp
The files contain several types of lines, described below.
Each type is identified by the first non-whitespace character in the line.
.Pp
.Bl -tag -width "=" -compact
.It =
Parameter settings
.It ?
Query-action rules
.It >
Output file or directory configuration options
.It #
Comments
.El
.Pp
Parameter setting lines in the configuration file are generally of the form:
.Pp
.Dl = parameter_name value ...
.Pp
Most parameter settings require a single value, although some may take several values.
See the PARAMETER SETTINGS section for details.
.Pp
Query-action rules in the file generally have the form:
.Pp
.Dl ? query action ...
.Pp
This directs
.Nm syslogd
to perform the specified action when a received message matches the given query.
Actions may be followed by optional arguments.
See the QUERY-ACTION RULES section for details.
.Pp
Most query-action rules specify output files or ASL-format data stores where matching messages should be saved.
The optional parameters for those rules can specify a number of options for these outputs.
As a convenience, these configuration options may be specified on a separate line.
Output configuration settings in the file begin with a greater-than sign 
.Dq >
followed by a file or ASL directory name and the configuration options for that file or directory.
These lines generally have the form:
.Pp
.Dl > filename option ...
.Pp
See the OUTPUT CONFIGURATION SETTINGS section for details.
.Pp
Comment lines are ignored.
.Ss PARAMETER SETTINGS
The following parameter-settings are recognized by
.Nm syslogd .
.Pp
.Bl -tag -width "bsd_max_dup_time" -compact -offset indent
.It debug
Enables or disables internal debugging output.
This is probably of little interest to most users.
The debug parameter requires a value of
.Dq 1
to enable debug output, or a value of
.Dq 0
to disable it.
Debugging messages are written to /var/log/syslogd.log.
.Pp
.It mark_time
Sets the time interval for the mark facility.
The default is 0 seconds, which indicates that mark messages are not generated.
.Pp
.It dup_delay
Sets the maximum time before writing a
.Dq "last message repeated <N> times"
message in a log file when duplicate messages have been detected.
The default is 30 seconds.
.Pp
.It utmp_ttl
Sets the time-to-live for messages used by the utmp, wtmp, and lastlog subsystems.
The default is 31622400 seconds (approximately 1 year).
.Pp
.It mps_limit
Sets the kernel message per second quota.
The default is value is 500.
A value of 0 disables the quota mechanism.
Note that this setting only limits the number of kernel messages that will be saved by
.Nm 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.
See the
.Xr syslog 1
manual for enabling a remote-control filter using the 
.Fl c
option with the
.Nm syslog
command.
.Pp
.It max_file_size
Sets the maximum file size for individual files in the ASL database.
The default is 25600000 bytes.
.El
.Ss QUERY-ACTION RULES
Query-action rules are used to cause
.Nm syslogd
to perform specific actions when received messages match a specified query pattern.
For example, to save certain messages in a file.
The rules are processed in the order in which they appear in the file.
This matters because some actions can affect further processing.
For example, an 
.Dq ignore 
action causes
.Nm syslogd
to stop processing the rules in a file for messages that match a given query pattern.
.Pp
Query-action rules contain three components: a query, an action, and optional parameters specific to that action.
For example, the following rule matches log messages sent by the 
.Dq example
process which have log priority levels in the range emergency to error.
If a received message matches, 
.Nm syslogd
posts a BSD notification for the key 
.Dq com.example.log_message .
.Pp
.Dl ? [= Sender example] [<= Level error] notify com.example.log_message
.Ss Query Format
Queries comprise one or more message matching components, each of which has the form:
.Pp
.Dl [OP KEY VAL]
.Pp
OP is a comparison operator.
It can have the following values:
.Pp
.Bl -tag -width "<=  " -compact -offset indent
.It T
true (always matches)
.It =
equal
.It !
not equal
.It >
greater than
.It >=
greater than or equal to
.It <
less than
.It <=
less than or equal to
.El
.Pp
It can also be preceded by one or more modifiers:
.Bl -tag -width "C   " -compact -offset indent
.Pp
.It C
casefold
.It N
numeric comparison
.It S
substring
.It A
prefix
.It Z
suffix
.El
.Pp
KEY and VAL are message keys and values.
For example
.Pp
.Dl [= Sender example]
.Pp
matches any message with value 
.Dq example
for the 
.Dq Sender
key.
The query
.Pp
.Dl [CA= Color gr]
.Pp
matches any message with a value beginning with the letters GR, Gr, gr, or gR
(
.Dq C
meaning casefold,
.Dq A
meaning prefix) for the
.Dq Color
key.
The example query above,
.Pp
.Dl [= Sender example] [N< Level 3]
.Pp
matches any message from 
.Dq example
with a level numerically less than 3
(string values are converted to integers, and the comparison is done on the integer values).
Note that the string values may be used equivalently for the Level key,
so the example above may also be written as:
.Pp
.Dl [= Sender example] [< Level Error]
.Pp
String values for levels may be any of the set
.Dq emergency ,
.Dq alert ,
.Dq critical ,
.Dq error ,
.Dq warning ,
.Dq notice ,
.Dq info ,
or
.Dq debug .
These strings may be upper, lower, or mixed case.
.Pp
The
.Dq T
operator is useful to test for the presence of a particular key.
.Pp
.Dl [T Flavor]
.Pp
Will match any message that has a
.Dq Flavor
key, regardless of its value.
.Pp
Note that space characters and closing square bracket characters (']') are specially processed.
The first space character following the beginning of a key delimits the key.
The first closing square bracket following the beginning of a value delimits the value.
So '[= foo bar\ ]'
will match messages which have a key 'foo' with the value 'bar ', including a trailing space character.
.Pp
As a special case, the query
.Pp
.Dl *
.Pp
matches all messages.
.Ss Actions
The following actions are available.
.Pp
.Bl -tag -width "directory" -compact -offset indent
.It store
Causes
.Nm syslogd
to save matching messages in the ASL database.
Note that if /etc/asl.conf contains no 
.Dq store 
action rules, then
.Nm syslogd
will save all messages it receives in the ASL database.
.Pp
.It file
Causes matching messages to be stored in a log file.
The file's path name must follow as the first parameter.
If the path already exists, it must be a plain file.
If the file does not exist, it will be created when the first message is written.
If the pathname specified is not an absolute path,
.Nm syslogd
will treat the given path as relative to /var/log (for /etc/asl.conf), 
or for other output modules relative to /var/log/module/NAME where NAME is the module name.
.Pp
By default, the file's owner will be root, and the file will be readable by the admin group.
Various options may follow the file name to specify ownership and access controls,
printed log message format, and controls for file rotation, compression, time-to-live,
and other aspects of output file life-cycle management.
See the OUTPUT CONFIGURATION SETTINGS section for more details.
.Pp
.It directory
Causes matching messages to be stored in an ASL-format log message data store.
A directory path name must follow as the first parameter.
If the path exists, it must be a directory.
.Pp
Messages saved to an ASL directory are saved in files that are named
.Dq yyyy.mm.dd.asl ,
where 
.Dq yyyy ,
.Dq mm ,
and
.Dq dd
are the year, month (01 to 12) and day of the month (01 to 31) associated with
matching messages.
This has the effect of saving messages in a separate file for each day.
.Pp
By default, files in the directory will be owned by root, and readable by the admin group.
Various options may follow the directory name to control ownership, access controls,
and the management of the store and its contents.
See the OUTPUT CONFIGURATION SETTINGS section for a list of options that may be set for store directories.
.Pp
.It notify
Causes
.Nm syslogd
to post a notification with
.Fn notify_post .
The notification key must appear as a single parameter following the
.Dq notify
action.
.Pp
.It skip
Causes a matching message to be ignored in all subsequent matching rules in the file.
Its scope is local to a single module configuration file.
.Pp
.It claim
Messages that match the query associated with a
.Dq claim
action are not processed by the main ASL configuration file /etc/asl.conf.
While claimed messages are not processed by /etc/asl.conf,
they are not completely private.
Other modules may also claim messages,
and in some cases two or more modules may have claim actions
that match the same messages.
This action only blocks processing by /etc/asl.conf.
.Pp
The
.Dq claim
action may be followed by the keyword
.Dq only .
In this case, only those messages that match the 
.Dq claim only
query will be processed by subsequent rules in the module.
.Pp
.It access
Sets read access controls for messages that match the associated query pattern.
.Nm syslogd
will restrict read access to matching messages to a specific user and group.
The user ID number and group ID number must follow the
.Dq access
keyword as parameters.
.Pp
.It broadcast
Causes syslogd to write the text of matching messages to all terminal windows.
If optional text follows the
.Dq broadcast
keyword, then that text is written rather that the matching message text.
Note that this action is restricted to the main ASL configuration file /etc/asl.conf.
.Pp
.It ignore
Causes a matching message to be ignored in all subsequent matching rules in the file.
This action is equivalent to the
.Dq skip
action in all module configuration files except the main ASL configuration file /etc/asl.conf.
When used in the main configuration file, the scope of the action is global,
and matching messages will be ignored by all ASL modules.
.El
.Ss OUTPUT CONFIGURATION SETTINGS
Various options may follow the path name in a
.Dq file
or
.Dq directory
query-action rule.
For example, the following rule specifies that all messages from the
.Dq example
facility will be saved in the file
.Dq example.log ,
and that messages are printed in a
.Dq raw
format that shows all the keys and values in the message:
.Pp
.Dl ? [= Facility example] file example.log format=raw
.Pp
Multiple options may be specified separated by whitespace characters.
For example:
.Pp
.Dl ? [= Facility example] file example.log format=raw rotate=local compress ttl=3 mode=0640 uid=0 gid=5 gid=20
.Pp
As a convenience, a file or directory name and any associated options can be specified on a separate
output configuration line following a 
.Dq >
character:
.Pp
.Dl > example.log format=raw rotate=local compress ttl=3 mode=0640 uid=0 gid=5 gid=20
.Pp
Options for a file or directory are taken from the first query-action rule
or output configuration line for the given path.
A good usage pattern for multiple rules that specify the same output file or directory is:
.Pp
.Dl > example.log options ...
.Dl ? query1 file example.log
.Dl ? query2 file example.log
.Dl ? query3 file example.log
.Pp
Most of the options listed below may be used with either file or directory outputs.
Exceptions are noted.
.Pp
.Bl -tag -width "coalesce=VAL" -compact -offset indent
.It format=FMT
Controls the format of log messages saved in a file.
Note that this option is specific to file outputs.
It is ignored for ASL directories.
.Pp
The format is specified by the value given for FMT.
Several pre-defined formats are available:
.Bl -tag -width "abcd"
.It bsd
Format used by the
.Nm syslogd
daemon for system log files, e.g. /var/log/system.log.
.It std
Standard (default) format.
Similar to 
.Dq bsd ,
but includes the message priority level.
.It raw
Prints the complete message structure.
Each key/value pair is enclosed in square brackets.
Embedded closing brackets and white space are escaped.
Time stamps are printed as seconds since the epoch.
.It xml
The list of messages is printed as an XML property list.
Each message is represented as a dictionary in a array.
Dictionary keys represent message keys.
Dictionary values are strings.
.It asl
The output file is written as an ASL-format data store file.
Files in this format may be read and searched using the
.Nm syslog
command line utility with the use of the
.Fl f Ar path
option.
.El
.Pp
Custom format strings may also be specified.
Since custom formats often contain white-space characters, 
the entire string may be enclosed in single or double quote characters,
or each white-space character may be preceded by a backslash escape character.
Escaped characters are not interpreted.
Custom format strings are described in detail in the READING MESSAGES section of the
.Xr syslog 1
manual.
.Pp
.It mode=MMM
Sets the mode of the file or files within an ASL directory.
The value MMM may be specified as a decimal value,
a hexadecimal value (if preceded by ``0x''),
or octal value (if preceded by ``0'').
.Pp
.It uid=UUU
Specifies the file's owner.
If more than one 
.Dq uid=UUU
option is given, the first will be used to set ownership,
and subsequent user IDs will be given read access to in the files POSIX.1e ACLs.
Note that UIDs should be defined in the local Open Directory database, since
.Nm syslogd
starts and may create the log file before network directory services are available.
Unknown UIDs and GIDs will be ignored when setting access controls.
.Pp
.It gid=GGG
Specifies the file's group.
If more than one 
.Dq gid=GGG
option is given, the first will be used to set the file's group,
and subsequent group IDs will be given read access to in the files POSIX.1e ACLs.
As with UID=UUU options, groups should be defined in the local Open Directory database.
.Pp
.It coalesce=VAL
By default, files printed using the
.Dq bsd
and
.Dq std
formats will coalesce duplicates.
If two or more messages are logged within 30 seconds, and which differ only in time,
then the second and subsequent messages will not be printed.
When a different message is logged, or 30 seconds have elapsed since the initial
message was logged, a line with the text
.Dl --- last message repeated N times ---
will be added to the file.
The default is
.Dq coalesce=1 .
The default may be overridden by specifying
.Dq coalesce=0 .
The values 
.Dq off
and 
.Dq false
may be used in place of 
.Dq 0 .
.El
.Pp
The following options all deal with file rotation and life-cycle management.
The FILE ROTATION section describes this in detail.
.Pp
.Bl -tag -width "rotate=NAME_STYLE" -compact -offset indent
.Pp
.It rotate=NAME_STYLE
Enables log file rotation and specifies the file naming scheme for rotated files.
This option does not apply to ASL directories.
NAME_STYLE may either be a simple time-stamp style:
.Dq sec ,
.Dq utc ,
.Dq utc-basic ,
.Dq local ,
.Dq local-basic ,
or
.Dq seq ;
or the value may contain the file's base name, a file name extension, and one of the time-stame styles.
For example
.Dq example.seq.log
or
.Dq example.log.utc-basic.
A detailed description of name styles may be found in the FILE ROTATION section below.
.Pp
If the option 
.Dq rotate
appears without a value, the naming style defaults to
.Dq "sec" .
.Pp
.It ttl=DAYS
Specifies the number of days that older versions of rotated files should be allowed to remain in the filesystem.
Rotated files older than this limit are deleted.
.Pp
.It dest=PATH
By default, rotated files are left in the same directory as the original file.
However, in some cases it may be useful to move the rotated versions to a different
directory for archival or other reasons.
If this option is specified,
.Nm aslmanager
will move files to the directory given by PATH.
.Pp
.It soft
Makes
.Nm syslogd
ignore write errors when saving messages.
Normally,
.Nm syslogd
will stop saving to a file or ASL directory after 5 consecutive write errors.
.Pp
.It compress
Enables gzip file compression for rotated log files.
When compressed, the extension 
.Dq .gz
is appended to the file name.
When the output is an ASL directory, data files are compressed after midnight local time.
This means that messages written in the current day will be readable using
.Nm syslog Fl d
or using the
.Xr asl 3
API.
Messages in compressed data files will not be available until the files are un-compressed.
.Pp
.It file_max=SIZE
Limits the size of an active log file.
SIZE may be an integer number of bytes, or the value may be followed by a single character 
.Dq k , 
.Dq m ,
or 
.Dq g
(upper or lower case),
to indicate a size limit in multiples of 1024 (kibibyte), 1048576 (mebibyte), or 1073741824 (gibibyte).
If a file exceeds this limit, it is immediately checkpointed by
.Nm syslogd 
and a new file is opened.
Note that
.Dq file_max
specifies a size limit before file compression is performed if the
.Dq compress
option is also present.
.Pp
.It all_max=SIZE
Specifies a size limit for the total of all rotated versions of a file.
.Nm aslmanager
will delete rotated files, oldest first, to reduce the total below the limit.
SIZE may be specified in the same format as the file_max option.
.Pp
.It basestamp
Causes
.Nm syslogd
to add a timestamp to the file name when it is created.
For example,
.Pp
.Dl
> example.log rotate=utc-basic basestamp
.Pp
will result in syslogd writing to, e.g.
.Dq example.log.20120625T070000Z
rather than to
.Dq example.log .
Note that this option does nothing with sequenced (``seq'') files.
.Pp
.It symlink
This option may only be used together with the basestamp option.
It causes
.Nm syslogd
to create a symlink with the unstamped file name to the currently active log file.
For example,
.Pp
.Dl
> example.log rotate=sec basestamp symlink
.Pp
will result in syslogd writing to, e.g.
.Dq example.log.T1340607600 ,
and creating a sybolic link from
.Dq example.log
to the active file.
.Pp
.El
.Ss FILE ROTATION
.Nm syslogd
and
.Nm aslmanager
work together to provide the features of file rotation.
This section describes the file rotation options that may be used in /etc/asl.conf
or an ASL Output Module configuration file,
together with a description of how the system works to support those features.
.Pp
File rotation or file rolling is enabled by the
.Dq rotate
output configuration option.
It is typically specificed with a value which specifies the naming sytle for rotated files.
Name styles may simply be a timestamp format, which is appended to the filename.
.Pp
.Bl -tag -width "local-basic" -compact -indent
.It sec
Rotated file names are of the form
.Dq example.log.T1340607600 .
The file names include the creation time of the file in seconds since the epoch.
.Pp
.It utc
Rotated file names are in ISO 8601 extended format, for example
.Dq example.log.2012-06-24T07:00:00Z .
The file names includes its creation time as a UTC date and time.
.Pp
.It utc-basic
Rotated file names are in ISO 8601 basic format, for example
.Dq example.log.20120624T070000Z .
The file names includes its creation time as a UTC date and time.
.Pp
.It local
Rotated file names are in ISO 8601 extended format, for example
.Dq example.log.2012-06-24T07:00:00-7 .
The file names includes its creation time as date and time in the local time zone.
The local timezone offset is included as a trailing part of the name.
The value
.Dq lcl
is an alias for
.Dq local .
.Pp
.It local-basic
Rotated file names are in ISO 8601 basic format, for example
.Dq example.log.20120624T070000-07 .
The file names includes its creation time as date and time in the local time zone.
The local timezone offset is included as a trailing part of the name.
The value
.Dq lcl-basic
is an alias for
.Dq local-basic .
.Pp
.It seq
Rotated file names are of the form
.Dq example.log.N
where N is an integer sequence number.
Files are re-numbered on each rotation so that the
.Dq 0
file is the most recent.
.El
.Pp
Note that using the local timezone for timestamped files may cause odd behavior on highly mobile systems.
.Nm aslmanager
will delete files after a specified time-to-live (see below).
The age of the file is determined by the file name.
If files are created in different timezones but saved with a non-absolute timestamp,
the age calculation may result in some files being considered older or newer than they are in reality.
.Pp
Also note that sequenced files (using the
.Dq seq
style) will initially be checkpointed using a file name containing a timestamp in seconds.
.Nm aslmanager
will re-sequence the files when it scans for checkpoint files.
.Pp
.Pp
Alternatively, the name style may be have two or three components.
The first component is the
.Dq base
name of the file, with no filename extension.
The base name may be followed by a timestamp format and optionally by a filename extension,
or the base name may be followed by an extension (the extension is optional) and a timestamp format.
These components must be separated by a dot character.
.Pp
For example, this output configuration line specifies that the output file
.Dq example.log
should be rotated to create the files
.Dq example.0.log ,
.Dq example.1.log ,
and so on.
.Pp
.Dl > example.log rotate=example.seq.log
.Pp
If a file is marked for rotation,
.Nm syslogd
will close the file at the start of a new day or when the file exceeds its 
.Dq file_max
size limit.
At that point,
.Nm syslogd
renames the file with the file's creation time included in its name
(unless the basestamp option is present, in which case the file's creation time
is already included in the filename) and starts a new file to continue logging.
This operation is called checkpointing the file.
.Pp
For example,
.Nm syslogd
might close
.Dq example.log
and rename it
.Dq example.log.T1340521200 ,
1340521200 being the time that the file was created.
It would then start a new 
.Dq example.log
file and use it until midnight, when the cycle would be repeated.
.Pp
Files are normally checkpointed at midnight.
If the system is sleeping or powered off, then files are checkpointed when
the the first message of a new day (local time) is received.
Files are also checkpointed if they exceed a size limit specified by a file_max option,
and they may be checkpointed manually through options provided by the
.Xr syslog 1
and
.Xr aslmanager 8
utilities.
The checkpointed file name always contains the file's creation time.
If the options for the file include
.Dq rotate=utc
then the timestamp will be a UTC date and time string.
.Dq rotate=local
causes the timestamp to be the date and time in the current local timezone.
Otherwise, the timestamp will be in seconds since the epoch.
.Pp
.Nm syslogd
only performs the checkpointing operation.
It closes old files, moves them out of the way, and starts writing new files.
Most of the work of file rotation is done by the
.Xr aslmanager 8
utility.
That includes moving files to a destination directory, compressing files,
re-naming files according to one of the naming style options,
deleting old files after they exceed their time-to-live,
and checking file space usage.
.Pp
.Nm aslmanager
normally runs once during system start-up, and once a day just after midnight.
It may also be triggered occasionally by
.Nm syslogd ,
and it may be run manually.
.Pp
.Nm aslmanager
scans for any checkpointed files created by
.Nm syslogd 
and will rename the files (if required) to match the naming style specified by the
.Dq rotate=NAME_STYLE
option.
If 
.Dq rotate=seq
is specified for a file, checkpointed files created by
.Nm syslogd
contain a timestamp in seconds.
These files are renamed so that the file names
contain a sequence number.
The most recent version has the number 
.Dq 0 ,
and older versions have higher numbers.
For example:
.Pp
.Dl example.log.0
.Dl example.log.1
.Dl example.log.2
.Dl ...
.Pp
As well as renaming files,
.Nm aslmanager
may perform other actions.
If the file has been given a 
.Dq dest=PATH
option,
the rotated versions of the file will be moved to the specified directory.
Files will be gzip compressed using the
.Xr zlib 3
library if the 
.Dq compress
option has been given.
If the total size of all the rotated versions of the file exceeds a value given in an 
.Dq all_max
option, older versions of the rotated file will be deleted to keep the total below the specified limit.
.Pp
Although checkpoint and file rotation operations are normally done automatically,
.Nm aslmanager
supports an option that will trigger 
.Nm syslogd
to checkpoint files before
.Nm aslmanager
starts its scan.
.Nm syslog
also supports an option to force files to be checkpointed without running
.Nm aslmanager .
See the
.Xr aslmanager 8
and
.Xr syslog 1
manuals for details.
.Pp
Programmatically, an
.Xr asl 3
message may be sent to syslogd to force it to checkpoint either a single file,
or to checkpoint all files for a particular ASL module.
To checkpoint all files:
.Pp
    const char *module_name;
.Pp
    //TODO: set module_name
    asl_object_t ctl = asl_new(ASL_TYPE_MSG);
    asl_set(ctl, ASL_KEY_OPTION, "control");
    asl_log(NULL, ctl, ASL_LEVEL_NOTICE, "@ %s checkpoint", module_name);
    asl_release(ctl);
.Pp
To checkpoint just one file:
.Pp
    const char *module_name;
    const char *file_name;
.Pp
    //TODO: set module_name
    //TODO: set file_name
    asl_object_t ctl = asl_new(ASL_TYPE_MSG);
    asl_set(ctl, ASL_KEY_OPTION, "control");
    asl_log(NULL, ctl, ASL_LEVEL_NOTICE, "@ %s checkpoint %s", module_name, file_name);
    asl_release(ctl);
.Pp
.Ss ASL OUTPUT MODULES
.Pp
An ASL output module is created by a configuration file in the directory /etc/asl.
The file name is used as the module's name.
The format of the file is generally the same as
.Nm asl.conf 
with a few exceptions.
Modules may not have parameter setting lines for the system parameters listed in the
PARAMETER SETTINGS or ASLMANAGER PARAMETER SETTINGS sections,
nor may they include
.Dq broadcast
query-action rules.
.Pp
Module configuration files are read by
.Nm syslogd
when it starts, and whenever it gets a HUP signal.
Messages received by
.Nm syslogd
are first processed according the the rules found in /etc/asl.conf
(also known as the 
.Dq com.apple.asl
module), then the message is processed by the
rules from each module found in /etc/asl.
.Pp
An exception to this is that messages that match the query in a
.Dq claim
action rule in any module are not processed by the rules in /etc/asl.conf.
.Pp
ASL output modules are enabled by default, but a module may include a parameter setting:
.Pp
.Dl = enable 0
.Pp
The module is still loaded by
.Nm syslogd ,
but the module will not save messages to files or directories, and will not post BSD notifications.
.Pp
Several mechanisms allow modules to be enabled or disabled dynamically.
One mechanism allows the setting of the 
.Dq enable
parameter to be based on the existence of a path in the filesystem,
or on the value associated with a dictionary key in a property list file.
On iOS only, the value of a key in an installed configuration profile may be tested.
.Pp
To enable a module based on the existence of a file, the module may use:
.Pp
.Dl = enable [File /a/b/c]
.Pp
where
.Dq /a/b/c
may be any filesystem path.
.Pp
To enable a module based on the value of a dictionary key in a property list file,
.Pp
.Dl = enable [Plist /path/config.plist] [= SomeKey SomeValue]
.Pp
Any of the test operations described above in the QUERY-ACTION RULES section
may also be used in testing key / value pairs.
Multiple operations are also allowed, for example:
.Pp
.Dl = enable [Plist /path/config.plist] [N>= DebugLevel 7] [S= Othervalue xyz]
.Pp
If the property list file does not exist, the test will evaluate to zero.
The file may be in binary or xml format.
It may only contain a single dictionary object at its top level.
Only keys and values at the top level of the dictionary may be tested.
Values must be strings, integer values, doubles, UUIDs, dates, or booleans.  
Boolean <true/> and <false/> values are converted to 1 and 0 respectively. 
Values are converted into strings,
and string comparisons are used unless unless an
.Dq N
modifier is specified with the test operator.
.Pp
On iOS, a module may test key / value pairs in a configuration profile using the
same key / value tests that may be used for property list files.
.Pp
.Dl = enable [Profile name] [= Verbose 1]
.Pp
The profile name is the value of its DefaultsDomainName key.
The test will evaluate to zero if the profile is not installed.
.Pp
A module may be also enabled or disabled using
.Nm syslog
or by sending
.Nm syslogd
a special
.Xr asl 3
control message.
Only the user
.Dq root
may enable or disable modules.
.Pp
A module may be enabled or disabled by sending an
.Xr asl 3
message as shown in this example:
.Pp
    int enable;
    const char *module_name;
.Pp
    //TODO: set module_name
    //TODO: set enable to 0 or 1
    asl_object_t ctl = asl_new(ASL_TYPE_MSG);
    asl_set(ctl, ASL_KEY_OPTION, "control");
    asl_log(NULL, ctl, ASL_LEVEL_NOTICE, "@ %s enable %d", module_name, enable);
    asl_release(ctl);
.Pp
A control message may also be sent using
.Nm syslog
as the following example shows to disable a module named
.Dq com.apple.example :
.Pp
.Dl sudo syslog -module com.apple.example enable 0
.Pp
A module may also enable or disable itself.
Although a module that is not enabled will not write or post notifications,
it still will scan messages.
The module may contain conditional parameter-setting rules like:
.Pp
.Dl = [= Color Green] enable 1
.Dl = [= Color Red] enable 0
.Pp
This is similar to a query-action rule.
If a message received by syslogd matches the specified query,
in this case having a Color key with the value Green or Red,
then the enable parameter is set as specified.
So in this example, the module would be enabled and disabled
whenever syslogd received a message containing the appropriate value for the 
.Dq Color
key.
.Ss ASLMANAGER PARAMETER SETTINGS
The following parameter-settings are recognized by
.Nm aslmanager .
.Pp
.Bl -tag -width "aslmanager_debug" -compact -offset indent
.It aslmanager_debug
Enables or disables internal debugging output.
This is probably of little interest to most users.
The debug parameter requires a value of 
.Dq 1
to enable debug output, or a value of 
.Dq 0
to disable it.
Debug messages are saved in an auxiliary file attached to an ASL log message.
The file may be inspected by opening the file attachement from the Console utility.
.Pp
.It store_ttl
Sets the time-to-live in days for messages in the ASL database.
The default is 7 days.
.Pp
.It max_store_size
Sets the maximum size for for the ASL database.
The default is 150000000 bytes.
.Pp
.It archive
Enables or disables archiving of the ASL database.
The archive parameter requires a value of 
.Dq 1
to enable archiving, or a value of
.Dq 0
to disable it.
An optional archive directory path may follow the
.Dq 0
or
.Dq 1 .
If enabled, files removed from the ASL database are moved to the archive directory.
The default archive directory path is /var/log/asl.archive.
.Pp
.It store_path
The ASL database path used by 
.Nm aslmanager .
The default is /var/log/asl.
Note that this parameter is ignored by
.Nm syslogd .
.Pp
.It archive_mode
Files copied to the ASL database archive will be given the specified access mode.
The default is 0400, so archive files will only be readable by root.
.El
.Pp
.Sh SEE ALSO
.Xr asl 3 ,
.Xr notify 3 ,
.Xr syslog 1 ,
.Xr aslmanager 8 ,
.Xr syslogd 8 .