syslog.1   [plain text]


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.Dd October 18, 2004
.Dt SYSLOG 1
.Os "Mac OS X"
.Sh NAME
.Nm syslog
.Nd Apple System Log utility
.Sh SYNOPSIS
.Nm
.Fl help
.D1 ""
.Nm
.Fl s
.Op Fl r Ar host
.Op Fl l Ar level
message...
.D1 ""
.Nm
.Fl s
.Op Fl r Ar host
.Fl k
key val
.Op key val 
.Li ...
.D1 ""
.Nm
.Fl C
.D1 ""
.Nm
.Op Fl f Ar file ...
.Op Fl d Ar dir ...
.Op Fl B
.Op Fl w Op Ar n
.Op Fl F Ar format
.Op Fl T Ar format
.Op Fl E Ar format
.Ar expression
.D1 ""
.Nm
.Op Fl f Ar file ...
.Op Fl d Ar dir ...
.Fl x Ar file Ar expression
.D1 ""
.Nm
.Fl c Ar process Op filter
.D1 ""
.Nm 
.Fl config Op options
.Sh DESCRIPTION
.Nm
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 processes.
.Pp
When invoked with the
.Fl help
option, 
.Nm 
prints a usage message.
.Ss SENDING MESSAGES
The
.Fl s
option is used send log messages to the
.Xr syslogd 8
log message daemon,
either locally or to a remote server if the
.Fl r Ar host
option in used.
.Pp
There are two main forms of the command.
If the 
.Fl 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.
.Pp
Note that the text of the log message should be supplied as a value following the
.Dq Message
key.
.Pp
If the 
.Fl k
option is not specified, then the rest of the command line is treated as the message text.
The text may be preceded by 
.Fl l Ar level
to set the log level (priority) of the message.
Levels may be an integer value corresponding the the log levels specified in 
.Xr syslog 3
or
.Xr asl 3 ,
or they may be a string.
String values are case insensitive, and should be one of:
.Pp
.Bl -tag -compact
.It Emergency
(level 0)
.It Alert
(level 1)
.It Critical
(level 2)
.It Error
(level 3)
.It Warning
(level 4)
.It Notice
(level 5)
.It Info
(level 6)
.It Debug
(level 7)
.El
.Pp
The string 
.Dq Panic
is an alias for 
.Dq Emergency .
.Pp
If the
.Fl l
option is omitted, the log level defaults to 7 (Debug).
.Pp
.Nm
only requires one or two leading characters for a level specification.
A single character suffices in most cases.
Use 
.Dq P
or 
.Dq \&Em
for Panic / Emergency, and
.Dq \&Er
or
.Dq X
for Error).
.Ss READING MESSAGES
The 
.Nm syslogd
daemon filters and saves log messages to different output streams.
One module saves messages to files specified in the
.Xr syslog.conf 5
file.
Those log files may be examined with any file printing or editing utility, 
e.g.
.Pp
.Dl cat /var/log/system.log
.Pp
Another module saves messages in a data store (/var/log/asl).
.Pp
If invoked with no arguments,
.Nm
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
.Nm
will be fetched and printed.
.Pp
If invoked with the
.Fl C
option,
.Nm
fetches and prints console messages.
The 
.Fl C
option is actually an alias for the expression:
.Pp
.Dl -k Facility com.apple.console
.Pp
See the EXPRESSIONS section below for more details.
.Pp
Individual ASL data store files may be read by providing one or more file names as arguments to the
.Fl f
option.
This may be useful when searching archived files, files on alternate disk volumes,
or files created as export files with the
.Fl x
option.
.Pp
The
.Fl d
option may be followed by a list of directory paths.
.Nm
will read or search all ASL data store files in those directories.
Any files that are not readable will be skipped.
Specifying
.Fl d
with the name
.Dq archive
will open all readable files in the default ASL archive directory /var/log/asl.archive.
Specifying
.Fl d
with the name
.Dq store
will open all readable files in the ASL store directory /var/log/asl.
.Pp
Legacy ASL database files that were written by
.Nm syslogd
on Mac OS X 10.5 (Leopard) may also be read using the
.Fl 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
.Fl f
and
.Fl x
options.
.Pp
The
.Fl B
option causes
.Nm
to start processing messages beginning at the time of the last system startup.
If used in conjunction with
.Fl w ,
all messages since the last system startup are displayed, or matched against an expression, before
.Nm
waits for new messages.
.Pp
The
.Fl w
option causes
.Nm
to wait for new messages.
By default, 
.Nm
prints the last 10 messages,
then waits for new messages to be added to the data store.
A number following the
.Fl w
option specifies the number of messages to print and overrides the default value of 10.
For example:
.Pp
.Dl syslog -w 20
.Pp
Use the value
.Dq all
to view all messages in the data store before watching for new messages.
The value
.Dq boot
will display messages since the last system startup before watching for new messages.
Specifying
.Dq -w boot
is equivalent to using
.Fl w
and
.Fl B
together.
.Pp
Using
.Nm
with the
.Fl w
option is similar to watching a log file using, e.g.
.Pp
.Dl tail -f /var/log/system.log
.Pp
The
.Fl 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.
.Pp
If the 
.Fl x Ar 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.
.Pp
When called without the
.Fl x
option, messages are printed to standard output.
Messages are printed in a format similar to that used in the system.log file,
except that the message priority level is printed between angle-brackets.
.Pp
The output format may by changed by specifying the
.Fl F Ar format
option.
Non-printable and control characters are encoded by default.
Text encoding may be controlled using the
.Fl E
option (see below).
The value of
.Ar format 
may be one of the following:
.Pp
.Bl -tag -width "xxxx"
.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 by default, but may also be
printed in local time or UTC if the
.Fl T
option is specified (see below).
.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.
.El
.Pp
The value of the
.Ar 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.
.Pp
Custom format strings may include variables of the form
.Dq $Name ,
.Dq $(Name) ,
or
.Dq $((Name)(format)) .
which will be expanded to the value associated with the named key.
For example, the command:
.Pp
.Dl syslog -F '$Time $Host $(Sender)[$(PID)] <$((Level)(str))>: $Message'
.Pp
produces output similar to the 
.Dq std
format.
The simple
.Dq $Name
form is sufficient in most cases.
However, the second form:
.Dq $(Name)
must be used if the name is not delimited by white space.
The third form allows different formats of the value to be printed.
For example, a message priority level may appear as an integer value (e.g.
.Dq 3 )
or as a string (``Error'').
The following print formats are known.
.Pp
.Bl -tag -width "$((Time)([+|-]HH[:MM]))"
.It $((Level)(str))
Formats a Level value as a string, for example 
.Dq Error ,
.Dq Alert ,
.Dq Warning ,
and so on.
Note that $(Level) or $Level formats the value as an integer 0 through 7.
.It $((Time)(sec))
Formats a Time value as the number of seconds since the Epoch.
.It $((Time)(raw))
Alias for $((Time)(sec)).
.It $((Time)(local))
Formats a Time value as a string of the form
.Dq "Mmm dd hh:mm:ss" ,
where Mmm is the abbreviation for the month, dd is the date (1 - 31) and hh:mm:ss is the time.
The local timezone is used.
.It $((Time)(lcl))
Alias for $((Time)(local)).
.It $((Time)(utc))
Formats a Time value as a string of the form
.Dq "yyyy-mm-dd hh:mm:ssZ" ,
using Coordinated Universal Time, or the
.Dq Zulu
time zone.
.It $((Time)(zulu))
Alias for $((Time)(utc)).
.It $((Time)(X))
Where X may be any letter in the range A - Z or a - z.
Formats the Time using the format
.Dq "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
.Dq "yyyy-mm-dd hh:mm:ss" ,
without a trailing timezone letter.
.It $((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
.Dq "yyyy-mm-dd hh:mm:ss[+|-]HH:MM" .
.El
.Pp
If a custom format is not being used to specify the format for Time values, then Time values
are generally converted to local time, except when the
.Fl F Ar raw
option is used, in which case times are printed as the number of seconds since the epoch.
The
.Fl T Ar format
option may be used to control the format used for timestamps.
The value of
.Ar format 
may be one of the following:
.Pp
.Bl -tag -width "local or lcl"
.It sec or raw
Times are printed as the number of seconds since the epoch.
.It local or lcl
Times are converted to the local time zone, and printed with the format
.Dl mmm dd hh:mm:ss
where mmm is the month name abbreviated as three characters.
.It utc or zulu
Times are converted to UTC, and printed with the format
.Dl yyyy-mm-dd hh:mm:ssZ
.It A-Z
Times are converted to the indicated nautical time zone,
printed in the same format as UTC.
.Dq J
is interpreted as the local timezone and printed in the same format,
but without a trailing timezone letter.
.It [+|-]hh[:mm]
The specified offset is used to adjust time.
.El
.Pp
The 
.Fl u
option is a short form for 
.Fl T Ar utc . 
.Pp
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.
.Pp
Text in the
.Dq std ,
.Dq bsd ,
and
.Dq raw
formats is encoded as it is by the
.Nm vis
utility with the
.Fl c
option.
Newlines and tabs are also encoded as "\\n" and "\\t" respectively.
In 
.Dq raw
format, space characters embedded in log message keys are encoded as "\\s"
and embedded brackets are escaped to print as "\\[" and "\\]".
.Pp
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.
.Pp
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
.Dq &#xNN;
where NN is the character's hexadecimal value.
.Pp
Values that do not contain legal UTF8 are encoded in base-64 and printed as data objects.
.Pp
The 
.Fl E Ar format
option may be used to explicitly control the text encoding.
The value of
.Ar format 
may be one of the following:
.Pp
.Bl -tag -width "safe"
.It vis
The default encoding described above.
.It safe
Encodes backspace characters as ^H.
Carriage returns are mapped to newlines.
A tab character is appended after newlines so that message text is indented.
.It none
No encoding is used.
.El
.Pp
The intent of the
.Dq safe
encoding is to prevent obvious message spoofing or damage.
The appearance of messages printed will depend on terminal settings and UTF-8 string handling.
It is possible that messages printed using the
.Dq safe
or
.Dq 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 default
.Dq 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.
.Pp
If no further command line options are specified,
.Nm
displays all messages, or copies all messages to a data store file.
However, an expression may be specified using the
.Fl k
and
.Fl o
options.
.Ss EXPRESSIONS
Expressions specify matching criteria.
They may be used to search for messages of interest.
.Pp
A simple expression
has the form:
.Pp
.Dl -k key [[op] val]
.Pp
The
.Fl 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:
.Pp
.Dl syslog -k Sender portmap
.Pp
Note that the
.Fl C
option is treated as an alias for the expression:
.Pp
.Dl -k Facility com.apple.console
.Pp
This provides a quick way to search for console messages.
.Pp
If three arguments are given, they are of the form
.Fl k Ar key operation value .
.Nm
supports the following matching operators:
.Pp
.Bl -tag -width "xxx" -compact 
.It eq
equal
.It ne
not equal
.It gt
greater than
.It ge
greater than or equal to
.It lt
less than
.It le
less than or equal to
.El
.Pp
Additionally, the operator may be preceded by one or more of the following modifiers:
.Pp
.Bl -tag -width "xxx" -compact 
.It C
case-fold
.It R
regular expression (see 
.Xr regex 3 )
.It S
substring
.It A
prefix
.It Z
suffix
.It N
numeric comparison
.El
.Pp
More complex search expressions may be built by combining two or more simple expressions. 
A complex expression that has more than one 
.Dq -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:
.Pp
.Dl syslog -k Sender portmap -k Time ge -2h
.Pp
finds all messages sent by portmap in the last 2 hours
(-2h means "two hours ago").
.Pp
The 
.Fl o
option may be used to build even more complex searches by providing an OR operation.
If two or more sub-expressions are given, separated by
.Fl 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 
.Dq Sender
value of
.Dq portmap
or that have a numeric priority level of 4 or less:
.Pp
.Dl syslog -k Sender portmap -o -k Level Nle 4
.Pp
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 MESSAGES section for details.
The example query above could also be specified with the command:
.Pp
.Dl syslog -k Sender portmap -o -k Level Nle warning
.Pp
.Pp
A special convention exists for matching time stamps.
An unsigned integer value is regarded as the given number of seconds since
0 hours, 0 minutes, 0 seconds, January 1, 1970, Coordinated Universal Time.
An negative 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:
.Pp
.Dl syslog -k Level Nle error -k Time ge -30
.Pp
a relative time value may be optionally followed by one of the characters 
.Dq s ,
.Dq m ,
.Dq h ,
.Dq d ,
or
.Dq 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).
.Ss FILTERING CONTROLS
Clients of the Apple System Log facility using either the
.Xr asl 3
or
.Xr syslog 3
interfaces may specify a log filter mask.
The mask specifies which messages should be sent to the
.Nm 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.
.Pp
The
.Fl c
option may be used to control filtering.
In addition to the internal filter value that processes may set as described above,
the system maintains a global 
.Dq master
filter.
This filter is normally 
.Dq off , 
meaning that it has no effect.
If a value is set for the master filter, it overrides the local filter for all processes. 
Root user access is required to set the master filter value.
.Pp
The current setting of the master filter mask may be inspected using:
.Pp
.Dl syslog -c 0
.Pp
The value of the master filter mask my be set by providing a second argument following
.Fl c Ar 0 .
The value may a set of characters from the set 
.Dq pacewnid .
These correspond to the priority levels Emergency (Panic), Alert, Critical, Error, Warning, Notice, Info, and Debug.
The character 
.Dq x
may be used for Error, as it is used for sending messages.
The master filter may be unset with:
.Pp
.Dl syslog -c 0 off
.Pp
Since it is common to use the filter as a 
.Dq cutoff
mechanism, for example to cut off messages with Debug and Info priority,
a single character from the list above may be specified, preceded by a minus sign.
In this case,
.Nm
uses a filter mask starting at level 0 (Emergency)
.Dq up to
the given level.
For example, to set the master filter level to cause all processes to log messages from Emergency up to Debug:
.Pp
.Dl syslog -c 0 -d
.Pp
While the master filter level 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
.Fl c Ar process ,
where
.Ar 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
.Fl c Ar process
as described above for the master filter mask.
Root access is required to set the per-process filter mask for system (UID 0) processes.
.Pp
The 
.Nm 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,
.Nm syslogd
will save any messages received from that process until the remote-control filter is turned off.
.Ss SERVER CONFIGURATION
When
.Nm 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
.Fl config
flag (without an ``='' character).
For example, to temporarily disable the message-per-second limit:
.Pp
.Dl syslog -config mps_limit 0
.Pp
Note that only the superuser (root) may change configuration parameters.
.Pp
In addition to the parameter setting options that are described in the
.Xr asl.conf 5
manual page, an additional option:
.Pp
.Dl syslog -config reset
.Pp
will cause
.Nm syslogd
to reset its configuration.
.Sh SEE ALSO
.Xr syslogd 8 ,
.Xr logger 1 ,
.Xr asl 3 ,
.Xr syslog 3 ,
.Xr asl.conf 5 .
.Sh HISTORY
The
.Nm
utility appeared in Mac OS X 10.4.