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Unix manual page for syslog. (host=minya system=Darwin)
SYSLOG(1) BSD General Commands Manual SYSLOG(1)
NAME
syslog -- Apple System Log utility
SYNOPSIS
syslog -help
syslog -s [-r host] [-l level] message...
syslog -s [-r host] -k key val [key val] ...
syslog -C
syslog [-f file ...] [-d dir ...] [-B] [-w [n]] [-F format] [-T format]
[-E format] expression
syslog [-f file ...] [-d dir ...] -x file expression
syslog -c process [mask]
syslog -config [options]
syslog -module [name [action]]
DESCRIPTION
syslog is a command-line utility for a variety of tasks relating to the
Apple System Log (ASL) facility. It provides mechanisms for sending and
viewing log messages, copying log messages to ASL format data store
files, and for controlling the flow of log messages from client pro-
cesses.
When invoked with the -help option, syslog prints a usage message.
NOTE: Most system logs have moved to a new logging system. See log(1)
for more information.
SENDING MESSAGES
The -s option is used send log messages to the syslogd(8) log message
daemon, either locally or to a remote server if the -r host option in
used.
There are two main forms of the command. If the -k option is used, then
it must be followed by a list of keys and values. A structured message
will be sent to the server with the keys and values given as arguments.
If a key or a value has embedded white space, it must be enclosed in
quotes.
Note that the text of the log message should be supplied as a value fol-
lowing the ``Message'' key.
If the -k option is not specified, then the rest of the command line is
treated as the message text. The text may be preceded by -l level to set
the log level (priority) of the message. Levels may be an integer value
corresponding the the log levels specified in syslog(3) or asl(3), or
they may be a string. String values are case insensitive, and should be
one of:
Emergency (level 0)
Alert (level 1)
Critical (level 2)
Error (level 3)
Warning (level 4)
Notice (level 5)
Info (level 6)
Debug (level 7)
The string ``Panic'' is an alias for ``Emergency''.
If the -l option is omitted, the log level defaults to 7 (Debug).
syslog only requires one or two leading characters for a level specifica-
tion. A single character suffices in most cases. Use ``P'' or ``Em''
for Panic / Emergency, and ``Er'' or ``X'' for Error).
READING MESSAGES
The syslogd daemon filters and saves log messages to different output
streams. One module saves messages to files specified in the
syslog.conf(5) file. Those log files may be examined with any file
printing or editing utility, e.g.
cat /var/log/system.log
Another module saves messages in a data store (/var/log/asl).
If invoked with no arguments, syslog fetches all messages from the active
data store. Messages are then printed to standard output, subject to
formatting options and character encoding as described below. Some log
messages are read-access controlled, so only messages that are readable
by the user running syslog will be fetched and printed.
If invoked with the -C option, syslog fetches and prints console mes-
sages. The -C option is actually an alias for the expression:
-k Facility com.apple.console
See the EXPRESSIONS section below for more details.
Individual ASL data store files may be read by providing one or more file
names as arguments to the -f option. This may be useful when searching
archived files, files on alternate disk volumes, or files created as
export files with the -x option.
The -d option may be followed by a list of directory paths. syslog will
read or search all ASL data store files in those directories. Any files
that are not readable will be skipped. Specifying -d with the name
``archive'' will open all readable files in the default ASL archive
directory /var/log/asl.archive. Specifying -d with the name ``store''
will open all readable files in the ASL store directory /var/log/asl.
Legacy ASL database files that were written by syslogd on Mac OS X 10.5
(Leopard) may also be read using the -f option. However only one such
legacy database may be read or searched at a time. Note that a legacy
database may be read and copied into a new ASL data store format file
using a combination of -f and -x options.
The -B option causes syslog to start processing messages beginning at the
time of the last system startup. If used in conjunction with -w, all
messages since the last system startup are displayed, or matched against
an expression, before syslog waits for new messages.
The -w option causes syslog to wait for new messages. By default, syslog
prints the last 10 messages, then waits for new messages to be added to
the data store. A number following the -w option specifies the number of
messages to print and overrides the default value of 10. For example:
syslog -w 20
Use the value ``all'' to view all messages in the data store before
watching for new messages. The value ``boot'' will display messages
since the last system startup before watching for new messages. Specify-
ing ``-w boot'' is equivalent to using -w and -B together.
Using syslog with the -w option is similar to watching a log file using,
e.g.
tail -f /var/log/system.log
The -w option can only be used when reading the system's ASL data store
or when reading a single data store file, and when printing messages to
standard output.
If the -x file option is specified, messages are copied to the named file
rather than being printed. The file will be created if it does not
exist.
When called without the -x option, messages are printed to standard out-
put. Messages are printed in a format similar to that used in the sys-
tem.log file, except that the message priority level is printed between
angle-brackets.
The output format may by changed by specifying the -F format option.
Non-printable and control characters are encoded by default. Text encod-
ing may be controlled using the -E option (see below). The value of
format may be one of the following:
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 by default, but may also be printed in local time or UTC if
the -T option is specified (see below).
xml The list of messages is printed as an XML property list. Each mes-
sage is represented as a dictionary in a array. Dictionary keys
represent message keys. Dictionary values are strings.
Each of the format styles above may optionally be followed by a dot char-
acter and an integer value, for example:
syslog -F std.4
This causes sub-second time values to be printed. In the example above,
4 decimal digits would be printed. The sub-second time values come from
the value of the TimeNanoSec key in the ASL message. If the TimeNanoSec
key is missing, a value of zero is used.
The value of the format argument may also be a custom print format
string. A custom format should in most cases be enclosed in single
quotes to prevent the shell from substituting special characters and
breaking at white space.
Custom format strings may include variables of the form ``$Name'',
``$(Name)'', or ``$((Name)(format))''. which will be expanded to the
value associated with the named key. For example, the command:
syslog -F '$Time $Host $(Sender)[$(PID)] <$((Level)(str))>:
$Message'
produces output similar to the ``std'' format. The simple ``$Name'' form
is sufficient in most cases. However, the second form: ``$(Name)'' must
be used if the name is not delimited by white space. The third form
allows different formats of the value to be printed. For example, a mes-
sage priority level may appear as an integer value (e.g. ``3'') or as a
string (``Error''). The following print formats are known.
$((Level)(str)) Formats a Level value as a string, for example
``Error'', ``Alert'', ``Warning'', and so on.
Note that $(Level) or $Level formats the value
as an integer 0 through 7.
$((Time)(sec)) Formats a Time value as the number of seconds
since the Epoch.
$((Time)(raw)) Alias for $((Time)(sec)).
$((Time)(local)) Formats a Time value as a string of the form
``Mmm dd hh:mm:ss'', where Mmm is the abbrevia-
tion for the month, dd is the date (1 - 31) and
hh:mm:ss is the time. The local timezone is
used.
$((Time)(lcl)) Alias for $((Time)(local)).
$((Time)(utc)) Formats a Time value as a string of the form
``yyyy-mm-dd hh:mm:ssZ'', using Coordinated Uni-
versal Time, or the ``Zulu'' time zone.
$((Time)(zulu)) Alias for $((Time)(utc)).
$((Time)(X)) Where X may be any letter in the range A - Z or
a - z. Formats the Time using the format
``yyyy-mm-dd hh:mm:ssX'', using the specified
nautical timezone. Z is the same as UTC/Zulu
time. Timezones A - M (except J) decrease by
one hour to the east of the Zulu time zone.
Timezones N - Y increase by one hour to the west
of Z. M and Y have the same clock time, but
differ by one day. J is used to indicate the
local timezone. When printing using
$((Time)(J)), the output format is ``yyyy-mm-dd
hh:mm:ss'', without a trailing timezone letter.
$((Time)(JZ)) Specifies the local timezone. The timezone off-
set from UTC follows the date and time. The
time is formatted as ``yyyy-mm-dd
hh:mm:ss[+|-]HH[:MM]''. Minutes in the timezone
offset are only printed if they are non-zero.
$((Time)(ISO8601)) Specifies the local timezone and ISO 8601
extended format. The timezone offset from UTC
follows the date and time. The time is format-
ted as ``yyyy-mm-ddThh:mm:ss[+|-]HH[:MM]''.
Minutes in the timezone offset are only printed
if they are non-zero. Note that this differs
from ``JZ'' format only in that a ``T'' charac-
ter separates the date and time.
$((Time)(ISO8601B)) Specifies the local timezone and ISO 8601 basic
format, in the form:
``yyyymmddThhmmss[+|-]HH[:MM]''.
$((Time)(ISO8601Z)) Specifies UTC/Zulu time and ISO 8601 extended
format, in the form: ``yyyy-mm-ddThh:mm:ssZ''.
$((Time)(ISO8601BZ)) Specifies UTC/Zulu time and ISO 8601 basic for-
mat, in the form: ``yyyymmddThhmmssZ''.
$((Time)([+|-]HH[:MM])) Specifies an offset (+ or -) of the indicated
number of hours (HH) and optionally minutes (MM)
to UTC. The value is formatted as a string of
the form ``yyyy-mm-dd hh:mm:ss[+|-]HH[:MM]''.
Minutes in the timezone offset are only printed
if they are non-zero.
Each of the print formats listed above for Time values may optionally be
followed by a dot character and an integer value. In that case, sub-sec-
ond time values will be printed. For example, the following line prints
messages with a UTC time format, and includes 6 digits of sub-second
time:
syslog -F '$((Time)(utc.6)) $Host $(Sender)[$(PID)]
<$((Level)(str))>: $Message
If a custom format is not being used to specify the format for Time val-
ues, then Time values are generally converted to local time, except when
the -F raw option is used, in which case times are printed as the number
of seconds since the epoch. The -T format option may be used to control
the format used for timestamps. The value of format may be one of the
following:
sec or raw Times are printed as the number of seconds since the epoch.
local or lcl Times are converted to the local time zone, and printed
with the format
mmm dd hh:mm:ss
where mmm is the month name abbreviated as three charac-
ters.
utc or zulu Times are converted to UTC, and printed with the format
yyyy-mm-dd hh:mm:ssZ
A-Z Times are converted to the indicated nautical time zone,
printed in the same format as UTC. ``J'' is interpreted as
the local timezone and printed in the same format, but
without a trailing timezone letter.
JZ is interpreted as the local timezone and printed with the
format
yyyy-mm-dd hh:mm:ss[+|-]HH[:MM].
The trailing ``[+|-]HH[:MM]'' string represents the local
timezone offset from UTC in hours, or in hours and minutes
if minutes are non-zero.
ISO8601 Times are printed with the format specified by ISO 8601:
yyyy-mm-ddThh:mm:ss[+|-]HH[:MM].
This is the same as the ``JZ'' format, except a ``T
character separates the date and time components.''
[+|-]hh[:mm] The specified offset is used to adjust time.
Each of the time formats above may optionally be followed by a dot char-
acter and an integer value. In that case, sub-second time values will be
printed. For example:
syslog -T bsd.3
The -u option is a short form for -T utc.
By default, control characters and non-printable characters are encoded
in the output stream. In some cases this may make messages less natural
in appearance. The encoding is designed to preserve all the information
in the log message, and to prevent malicious users from spoofing or
obscuring information in log messages.
Text in the ``std'', ``bsd'', and ``raw'' formats is encoded as it is by
the vis utility with the -c option. Newlines and tabs are also encoded
as "\n" and "\t" respectively. In ``raw'' format, space characters
embedded in log message keys are encoded as "\s" and embedded brackets
are escaped to print as "\[" and "\]".
XML format output requires that keys are valid UTF8 strings. Keys which
are not valid UTF8 are ignored, and the associated value is not printed.
Values that contain legal UTF8 are printed as strings. Ampersand, less
than, greater than, quotation mark, and apostrophe characters are encoded
according to XML conventions. Embedded control characters are encoded as
``&#xNN;'' where NN is the character's hexadecimal value.
Values that do not contain legal UTF8 are encoded in base-64 and printed
as data objects.
The -E format option may be used to explicitly control the text encoding.
The value of format may be one of the following:
safe This is the default encoding for syslog output. Encodes backspace
characters as ^H. Carriage returns are mapped to newlines. A tab
character is appended after newlines so that message text is
indented.
vis The C-style backslash encoding similar to that produced by the
``vis -c'' command, as described above.
none No encoding is used.
The intent of the ``safe'' encoding is to prevent obvious message spoof-
ing or damage. The appearance of messages printed will depend on termi-
nal settings and UTF-8 string handling. It is possible that messages
printed using the ``safe'' or ``none'' options may be garbled or subject
to manipulation through the use of control characters and control
sequences embedded in user-supplied message text. The ``vis'' encoding
should be used to view messages if there is any suspicion that message
text may have been used to manipulate the printed representation.
If no further command line options are specified, syslog displays all
messages, or copies all messages to a data store file. However, an
expression may be specified using the -k and -o options.
EXPRESSIONS
Expressions specify matching criteria. They may be used to search for
messages of interest.
A simple expression has the form:
-k key [[op] val]
The -k option may be followed by one, two, or three arguments. A single
argument causes a match to occur if a message has the specified key,
regardless of value. If two arguments are specified, a match occurs when
a message has exactly the specified value for a given key. For example,
to find all messages sent by the portmap process:
syslog -k Sender portmap
Note that the -C option is treated as an alias for the expression:
-k Facility com.apple.console
This provides a quick way to search for console messages.
If three arguments are given, they are of the form -k key operation
value. syslog supports the following matching operators:
eq equal
ne not equal
gt greater than
ge greater than or equal to
lt less than
le less than or equal to
Additionally, the operator may be preceded by one or more of the follow-
ing modifiers:
C case-fold
R regular expression (see regex(3))
S substring
A prefix
Z suffix
N numeric comparison
More complex search expressions may be built by combining two or more
simple expressions. A complex expression that has more than one ``-k key
[[op] val]'' term matches a message if all of the key-value operations
match. Logically, the result is an AND of all of key-value operations.
For example:
syslog -k Sender portmap -k Time ge -2h
finds all messages sent by portmap in the last 2 hours (-2h means "two
hours ago").
The -o option may be used to build even more complex searches by provid-
ing an OR operation. If two or more sub-expressions are given, separated
by -o options, then a match occurs is a message matches any of the sub-
expressions. For example, to find all messages which have either a
``Sender'' value of ``portmap'' or that have a numeric priority level of
4 or less:
syslog -k Sender portmap -o -k Level Nle 4
Log priority levels are internally handled as an integer value between 0
and 7. Level values in expressions may either be given as integers, or
as string equivalents. See the table string values in the SENDING MES-
SAGES section for details. The example query above could also be speci-
fied with the command:
syslog -k Sender portmap -o -k Level Nle warning
A special convention exists for matching time stamps. An unsigned inte-
ger value is regarded as the given number of seconds since 0 hours, 0
minutes, 0 seconds, January 1, 1970, Coordinated Universal Time. An neg-
ative integer value is regarded as the given number of seconds before the
current time. For example, to find all messages of Error priority level
(3) or less which were logged in the last 30 seconds:
syslog -k Level Nle error -k Time ge -30
a relative time value may be optionally followed by one of the characters
``s'', ``m'', ``h'', ``d'', or ``w'' to specify seconds, minutes, hours,
days, or weeks respectively. Upper case may be used equivalently. A
week is taken to be 7 complete days (i.e. 604800 seconds).
FILTERING CONTROLS
Clients of the Apple System Log facility using either the asl(3) or
syslog(3) interfaces may specify a log filter mask. The mask specifies
which messages should be sent to the syslogd daemon by specifying a
yes/no setting for each priority level. Many clients set a filter mask
to avoid sending relatively unimportant messages. Debug or Info priority
level messages are generally only useful for debugging operations. By
setting a filter mask, a process can improve performance by avoiding
spending time sending messages that are in most cases unnecessary.
The -c option may be used to control filtering. In addition to the
internal filter mask value that processes may set as described above, the
system maintains a global ``master'' filter mask. This filter is nor-
mally ``off'', meaning that it has no effect. If a value is set for the
master filter mask, it overrides the local filter mask for all processes.
Root user access is required to set the master filter mask value.
The current setting of the master filter mask may be inspected using:
syslog -c 0
The value of the master filter mask my be set by providing a second argu-
ment following -c 0. The value may a set of characters from the set
``pacewnid''. These correspond to the priority levels Emergency (Panic),
Alert, Critical, Error, Warning, Notice, Info, and Debug. The character
``x'' may be used for Error, as it is used for sending messages. The
master filter mask may be deactivated with:
syslog -c 0 off
Since it is common to use the filter mask as a ``cutoff'' mechanism, for
example to cut off messages with Debug and Info priority, a single char-
acter from the list above may be specified, preceded by a minus sign. In
this case, syslog uses a filter mask starting at level 0 (Emergency) ``up
to'' the given level. For example, to set the master filter mask to
cause all processes to log messages from Emergency up to Debug:
syslog -c 0 -d
While the master filter mask may be set to control the messages produced
by all processes, another filter mask may be specified for an individual
process. If a per-process filter mask is set, it overrides both the
local filter mask and the master filter mask. The current setting for a
per-process filter mask may be inspected using -c process, where process
is either a PID or the name of a process. If a name is used, it must
uniquely identify a process. To set a per-process filter mask, an second
argument may be supplied following -c process as described above for the
master filter mask. Root access is required to set the per-process fil-
ter mask for system (UID 0) processes.
The syslogd server follows filtering rules specified in the /etc/asl.conf
file. When the remote-control mechanism is used to change the filter of
a process, syslogd will save any messages received from that process
until the remote-control filter is turned off.
SERVER CONFIGURATION
When syslogd starts up, and when it receives a HUP signal, it re-reads
its configuration settings from /etc/asl.conf. It is sometimes useful to
change configuration parameters temporarily, without needing to make
changes to the configuration file. Any of the configuration options that
may be set in the file (following an ``='' character) may also be sent to
syslogd using the -config flag (without an ``='' character). For exam-
ple, to temporarily disable the kernel message-per-second limit:
syslog -config mps_limit 0
Note that only the superuser (root) may change configuration parameters.
In addition to the parameter setting options that are described in the
asl.conf(5) manual page, an additional option:
syslog -config reset
will cause syslogd to reset its configuration.
ASL OUTPUT MODULES
ASL Output Modules are named configuration bundles used by the ASL server
syslogd, and by the ASL filesystem manager aslmanager. The /etc/asl.conf
file represents the system's primary output module, and is given the name
``com.apple.asl''. Other modules are read from files in the /etc/asl
directory. File names serve as module names. ASL Output Modules are
described in detail in asl.conf(5).
When invoked with -module, syslog prints a summary of all loaded ASL Out-
put Modules. The summary includes the output files and ASL store direc-
tories used by each module, a list of the module's configuration rules,
and the module's current enabled or disabled status. -module name prints
a summary for the module with the given name.
ASL Output Modules may be enabled or disabled using the command:
syslog -module name enable [0]
Note that only the superuser (root) may enable or disable a module.
The name '*' (including the single-quote characters) may be used to
change the status of all ASL Output Modules, excluding the primary
com.apple.asl module. com.apple.asl may be enabled or disabled, but only
specifically by name.
If a module includes rotated files, the command:
syslog -module name checkpoint [file]
Will force the module to checkpoint all of its rotated files, or just the
single optionally named file. The name '*' (including the single-quote
characters) may be used to force checkpointing of all rotated files for
all ASL Output Modules, including the primary com.apple.asl module.
Note that only the superuser (root) may force files to be checkpointed.
The checkpoint action sends a command to syslogd and waits for a reply to
be returned. This means that any files currently in use will be check-
pointed when the syslog command completes.
SEE ALSO
log(1), logger(1), asl(3), syslog(3), asl.conf(5), syslogd(8)
HISTORY
The syslog utility appeared in Mac OS X 10.4.
Mac OS X October 18, 2004 Mac OS X