asl.conf(5) BSD File Formats Manual asl.conf(5)
asl.conf -- configuration file for syslogd(8) and aslmanager(8)
The syslogd(8) server reads the /etc/asl.conf file at startup, and re-reads the file when it receives a HUP signal. The aslmanager(8) daemon
reads the file when it starts. See the ASLMANAGER PARAMETER SETTINGS section for details on aslmanager-specific parameters.
If the /etc/asl directory exists, then syslogd and aslmanager will read each file it contains. These files must have the same format as
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.
The files contains four types of lines. Each type is identified by the first non-whitespace character.
= Parameter settings
? Query-action rules
> Output file or directory configuration options
Parameter setting lines in the configuration file are generally of the form:
= parameter_name value ...
Most parameter settings require a single value, although some may take several values. See the PARAMETER SETTINGS section for details.
Query-action rules in the file generally have the form:
? query action ...
This directs 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.
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 ``>'' followed by a file or ASL directory name and the con-
figuration options for that file or directory. These lines generally have the form:
> filename option ...
See the OUTPUT CONFIGURATION SETTINGS section for details.
Comments lines are ignored.
The following parameter-settings are recognized by syslogd.
debug Enables or disables internal debugging output. This is probably of little interest to most users. The debug parame-
ter requires a value of ``1'' to enable debug output, or a value of ``0'' to disable it. Debugging messages are
written to /var/log/syslogd.log.
mark_time Sets the time interval for the mark facility. The default is 0 seconds, which indicates that mark messages are not
dup_delay Sets the maximum time before writing a ``last message repeated <N> times'' message in a log file when duplicate mes-
sages have been detected. The default is 30 seconds.
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).
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 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 syslog(1) manual for enabling a remote-control filter using the -c option with the
max_file_size Sets the maximum file size for individual files in the ASL database. The default is 25600000 bytes.
Query-action rules are used to cause syslogd to perform specific actions when received messages match a specified query pattern. For exam-
ple, 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 ``ignore'' action causes syslogd to stop processing the rules in a file for messages
that match a given query pattern.
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 ``example'' process which have log priority levels in the range emergency to error. If a received mes-
sage matches, syslogd posts a BSD notification for the key ``com.example.log_message''.
? [= Sender example] [<= Level error] notify com.example.log_message
Queries comprise one or more message matching components, each of which has the form:
[OP KEY VAL]
OP is a comparison operator. It can have the following values:
T true (always matches)
! not equal
> greater than
>= greater than or equal to
< less than
<= less than or equal to
It can also be preceded by one or more modifiers:
N numeric comparison
KEY and VAL are message keys and values. For example
[= Sender example]
matches any message with value ``example'' for the ``Sender'' key. The query
[CA= Color gr]
matches any message with a value beginning with the letters GR, Gr, gr, or gR ( ``C'' meaning casefold, ``A'' meaning prefix) for the
``Color'' key. The example query above,
[= Sender example] [N< Level 3]
matches any message from ``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 writ-
[= Sender example] [< Level Error]
String values for levels may be any of the set ``emergency'', ``alert'', ``critical'', ``error'', ``warning'', ``notice'', ``info'', or
``debug''. These strings may be upper, lower, or mixed case.
The ``T'' operator is useful to test for the presence of a particular key.
Will match any message that has a ``Flavor'' key, regardless of its value.
As a special case, the query
matches all messages.
The following actions are available.
store Causes syslogd to save matching messages in the ASL database. Note that if /etc/asl.conf contains no ``store'' action
rules, then syslogd will save all messages it receives in the ASL database.
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, 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.
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
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.
Messages saved to an ASL directory are saved in files that are named ``yyyy.mm.dd.asl'', where ``yyyy'', ``mm'', and ``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.
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 CON-
FIGURATION SETTINGS section for a list of options that may be set for store directories.
notify Causes syslogd to post a notification with notify_post(). The notification key must appear as a single parameter following
the ``notify'' action.
skip Causes a matching message to be ignored in all subsequent matching rules in the file. Its scope is local to a single module
claim Messages that match the query associated with a ``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.
The ``claim'' action may be followed by the keyword ``only''. In this case, only those messages that match the ``claim
only'' query will be processed by subsequent rules in the module.
access Sets read access controls for messages that match the associated query pattern. syslogd will restrict read access to match-
ing messages to a specific user and group. The user ID number and group ID number must follow the ``access'' keyword as
broadcast Causes syslogd to write the text of matching messages to all terminal windows. If optional text follows the ``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.
ignore Causes a matching message to be ignored in all subsequent matching rules in the file. This action is equivalent to the
``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.
OUTPUT CONFIGURATION SETTINGS
Various options may follow the path name in a ``file'' or ``directory'' query-action rule. For example, the following rule specifies that
all messages from the ``example'' facility will be saved in the file ``example.log'', and that messages are printed in a ``raw'' format that
shows all the keys and values in the message:
? [= Facility example] file example.log format=raw
Multiple options may be specified separated by whitespace characters. For example:
? [= Facility example] file example.log format=raw rotate=local compress ttl=3 mode=0640 uid=0 gid=5 gid=20
As a convenience, a file or directory name and any associated options can be specified on a separate output configuration line following a
> example.log format=raw rotate=local compress ttl=3 mode=0640 uid=0 gid=5 gid=20
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:
> example.log options ...
? query1 file example.log
? query2 file example.log
? query3 file example.log
Most of the options listed below may be used with either file or directory outputs. Exceptions are noted.
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.
The format is specified by the value given for FMT. Several pre-defined formats are available:
bsd Format used by the syslogd daemon for system log files, e.g. /var/log/system.log.
std Standard (default) format. Similar to ``bsd'', but includes the message priority level.
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.
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.
asl The output file is written as an ASL-format data store file. Files in this format may be read and searched using
the syslog command line utility with the use of the -f path option.
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 syslog(1) manual.
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 hexa-
decimal value (if preceded by ``0x''), or octal value (if preceded by ``0'').
uid=UUU Specifies the file's owner. If more than one ``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 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.
gid=GGG Specifies the file's group. If more than one ``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.
coalesce=VAL By default, files printed using the ``bsd'' and ``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
--- last message repeated N times ---
will be added to the file. The default is ``coalesce=1''. The default may be overridden by specifying ``coalesce=0''.
The values ``off'' and ``false'' may be used in place of ``0''.
The following options all deal with file rotation and life-cycle management. The FILE ROTATION section describes this in detail.
rotate=NAME_STYLE Enables log file rotation and specifies the file naming scheme for rotated files. This option does not apply to ASL
directories. Four styles are supported:
sec Rotated file names are of the form ``example.log.T1340607600''. The file names include the creation
time of the file in seconds since the epoch.
utc Rotated file names are in ISO 8601 extended format, for example ``example.log.2012-06-24T07:00:00Z''.
The file names includes its creation time as a UTC date and time.
utc-basic Rotated file names are in ISO 8601 basic format, for example ``example.log.20120624T070000Z''. The
file names includes its creation time as a UTC date and time.
local Rotated file names are in ISO 8601 extended format, for example ``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.
local-basic Rotated file names are in ISO 8601 basic format, for example ``example.log.20120624T070000-07''. The
file names includes its creation time as date and time in the local time zone. The local timezone off-
set is included as a trailing part of the name.
seq Rotated file names are of the form ``example.log.N'' where N is an integer sequence number. Files are
re-numbered on each rotation so that the ``0'' file is the most recent.
If the option ``rotate'' appears without a value, the naming style defaults to ``sec''.
Note that using the local timezone for timestamped files may cause odd behavior on highly-mobile systems.
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.
Also note that sequenced files (using the ``sec'' style) will initially be checkpointed using a file name containing
a timestamp in seconds. aslmanager will re-sequence the files when it scans for checkpoint files.
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.
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 spec-
ified, aslmanager will move files to the directory given by PATH.
soft Makes syslogd ignore write errors when saving messages. Normally, syslogd will stop saving to a file or ASL direc-
tory after 5 consecutive write errors.
compress Enables gzip file compression for rotated log files. When compressed, the extension ``.gz'' is appended to the file
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 ``k'', ``m'', or ``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 check-
pointed by syslogd and a new file is opened. Note that ``file_max'' specifies a size limit before file compression
is performed if the ``compress'' option is also present.
all_max=SIZE Specifies a size limit for the total of all rotated versions of a file. aslmanager will delete rotated files, old-
est first, to reduce the total below the limit. SIZE may be specified in the same format as the file_max option.
syslogd and aslmanager work together to automatically provide all the features of file rotation. However, it is useful to understand how the
process works. 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.
If a file is marked for rotation, syslogd will close the file at the start of a new day or when the file exceeds its ``file_max'' size limit.
At that point, syslogd renames the file and starts a new file to continue logging. The old file is renamed with the file's creation time
included in its name. This operation is called checkpointing the file.
For example, syslogd might close ``example.log'' and rename it ``example.log.T1340521200'', 1340521200 being the time that the file was cre-
ated. It would then start a new ``example.log'' file and use it until midnight, when the cycle would be repeated.
Files are normally checkpointed at midnight. If the system is sleeping or powered off, then files are checkpointed when the the first mes-
sage 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 syslog(1) and aslmanager(8) utilities. The checkpointed file name always con-
tains the file's creation time. If the options for the file include ``rotate=utc'' then the timestamp will be a UTC date and time string.
``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.
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 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
aslmanager normally runs once during system start-up, and once a day just after midnight. It may also be triggered occasionally by syslogd,
and it may be run manually.
aslmanager scans for any checkpointed files created by syslogd and will rename the files (if required) to match the naming style specified by
the ``rotate=NAME_STYLE'' option. If ``rotate=seq'' is specified for a file, checkpointed files created by 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 ``0'', and older
versions have higher numbers. For example:
As well as renaming files, aslmanager may perform other actions. If the file has been given a ``dest=PATH'' option, the rotated versions of
the file will be moved to the specified directory. Files will be gzip compressed using the zlib(3) library if the ``compress'' option has
been given. If the total size of all the rotated versions of the file exceeds a value given in an ``all_max'' option, older version of the
rotated file will be deleted to keep the total below the specified limit.
Although checkpoint and file rotation operations are normally done automatically, aslmanager supports an option that will trigger syslogd to
checkpoint files before aslmanager starts its scan. syslog also supports an option to force files to be checkpointed without running
aslmanager. See the aslmanager(8) and syslog(1) manuals for details.
ASL OUTPUT MODULES
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 asl.conf with a few exceptions. Mdules may not have parameter setting lines for the system parameters
listed in the PARAMETER SETTINGS or ASLMANAGER PARAMETER SETTINGS sections, nor may they include ``broadcast'' query-action rules.
Module configuration files are read by syslogd when it starts, and whenever it gets a HUP signal. Messages received by syslogd are first
processed according the the rules found in /etc/asl.conf (also known as the ``com.apple.asl'' module), then the message is processed by the
rules from each module found in /etc/asl.
An exception to this is that messages that match the query in a ``claim'' action rule in any module are not processed by the rules in
ASL output modules are enabled by default, but a module may include a parameter setting:
= enable 0
The module is still loaded by syslogd, but the module will not save messages to files or directories, and will not post BSD notifications.
Several mechanisms allow modules to be enabled or disabled dynamically. One mechanism allows the setting of the ``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.
To enable a module based on the existence of a file, the module may use:
= enable [File /a/b/c]
where ``/a/b/c'' may be any filesystem path.
To enable a module based on the value of a dictionary key in a property list file,
= enable [Plist /path/config.plist] [= SomeKey SomeValue]
Any of the test operations described above in the QUERY-ACTION RULES section may also be used in testing key / value pairs. Multiple opera-
tions are also allowed, for example:
= enable [Plist /path/config.plist] [N>= DebugLevel 7] [S= Othervalue xyz]
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 ``N'' modifier is specified with the test operator.
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
= enable [Profile name] [= Verbose 1]
The profile name is the value of its DefaultsDomainName key. The test will evaluate to zero if the profile is not installed.
A module may be also enabled or disabled using syslog or by sending syslogd a special asl(3) control message. Only the user ``root'' may
enable or disable modules.
A module may be enabled or disabled by sending an asl(3) message as shown in this example, which enables a module named
aslmsg ctl = asl_new(ASL_TYPE_MSG);
asl_set(ctl, ASL_KEY_OPTION, "control");
asl_set(ctl, ASL_KEY_MSG, "@ com.apple.example enable 1");
A control message may also be sent using syslog as the following example shows to disable a module named ``com.apple.example'':
sudo syslog -module com.apple.example enable 0
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:
= [= Color Green] enable 1
= [= Color Red] enable 0
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 ``Color'' key.
ASLMANAGER PARAMETER SETTINGS
The following parameter-settings are recognized by aslmanager.
aslmanager_debug Enables or disables internal debugging output. This is probably of little interest to most users. The debug parame-
ter requires a value of ``1'' to enable debug output, or a value of ``0'' to disable it. Debug messages saved in an
auxiliary file attached to an ASL log message. The file may be inspected by opening the file attachement from the
store_ttl Sets the time-to-live in days for messages in the ASL database. The default is 7 days.
max_store_size Sets the maximum size for for the ASL database. The default is 150000000 bytes.
archive Enables or disables archiving of the ASL database. The archive parameter requires a value of ``1'' to enable archiv-
ing, or a value of ``0'' to disable it. An option archive directory path may follow the ``0'' or ``1''. If enabled,
files removed from the ASL database are moved to the archive directory. The default archive directory path is
store_path The ASL database path used by aslmanager. The default is /var/log/asl. Note that this parameter is ignored by
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.
asl(3), notify(3), syslog(1), aslmanager(8), syslogd(8).
Mac OS X Sept 19, 2008 Mac OS X