usr.sbin/syslogd/syslog.conf.5

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.\"     from: @(#)syslog.conf.5	8.1 (Berkeley) 6/9/93
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.Dd November 9, 2013
.Dt SYSLOG.CONF 5
.Os
.Sh NAME
.Nm syslog.conf
.Nd
.Xr syslogd 8
configuration file
.Sh DESCRIPTION
The
.Nm
file is the configuration file for the
.Xr syslogd 8
program.
It consists of extended options (lines with one key="value" assignment)
and blocks of lines separated by
.Em program
and
.Em hostname
specifications, with each line containing two fields: the
.Em selector
field which specifies the types of messages and priorities to which the
line applies, and an
.Em action
field which specifies the action to be taken if a message
.Xr syslogd 8
receives matches the selection criteria.
The
.Em selector
field is separated from the
.Em action
field by one or more tab characters.
.Pp
The
.Em Selectors
function
are encoded as a
.Em facility ,
a period
.Pq Sq \&. ,
an optional set of comparison flags
.Pq Bo ! Bc Bq \*[Lt]=\*[Gt] ,
and a
.Em level ,
with no intervening white-space.
Both the
.Em facility
and the
.Em level
are case insensitive.
.Pp
The
.Em facility
describes the part of the system generating the message, and is one of
the following keywords: auth, authpriv, cron, ftp, daemon, kern, lpr,
mail, mark, news, syslog, user, uucp and local0 through local7.
These keywords (with the exception of mark) correspond to the
similar
.Dq Dv LOG_
values specified to the
.Xr openlog 3
and
.Xr syslog 3
library routines.
.Pp
The
.Em comparison flags
may be used to specify exactly what levels are logged.
If unspecified, the default comparison is
.Sq \*[Gt]=
.Pq greater than or equal to ,
or, if the
.Fl U
option is passed to
.Xr syslogd 8 ,
.Sq =
.Pq equal to .
Comparison flags beginning with
.So ! Sc
will have their logical sense inverted.
Thus,
.Sq !=info
means all levels except info and
.Sq !notice
has the same meaning as
.Sq \*[Lt]notice .
.Pp
The
.Em level
describes the severity of the message, and is a keyword from the
following ordered list (higher to lower): emerg, alert, crit, err,
warning, notice, info and debug.
These keywords correspond to the
similar
.Pq Dv LOG_
values specified to the
.Xr syslog 3
library routine.
.Pp
Each block of lines is separated from the previous block by a
.Em program
or
.Em hostname
specification.
A block will only log messages corresponding to the most recent
.Em program
and
.Em hostname
specifications given.
Consider the case of a block that selects
.Ql pppd
as the
.Em program ,
directly followed by a block that selects messages from the
.Em hostname
.Ql dialhost .
The second block will log only messages from the
.Xr pppd 8
program from the host
.Sq dialhost .
.Pp
A
.Em program
specification of the form
.Ql #!+prog1,prog2
or
.Ql !+prog1,prog2
will cause subsequent blocks to be applied to messages logged by the
specified programs.
A
.Em program
specification of the form
.Ql #!-prog1,prog2
or
.Ql !-prog1,prog2
will cause subsequent blocks to be applied to messages logged by programs
other than the ones specified.
A
.Em program
specification of the form
.Ql #!prog1,prog2
or
.Ql !prog1,prog2
is equivalent to
.Ql !+prog1,prog2 .
Program selectors may also match kernel-generated messages.
For example, a program specification of
.Ql !+subsys
will match kernel-generated messages of the form
.Ql subsys: here is a message .
The special specification
.Ql !*
will cause subsequent blocks to apply to all programs.
.Pp
A
.Em hostname
specification of the form
.Ql #+host1,host2
or
.Ql +host1,host2
will cause subsequent blocks to be applied to messages received from
the specified hosts.
A
.Em hostname
specification of the form
.Ql #-host1,host2
or
.Ql -host1,host2
will cause subsequent blocks to be applied to messages from hosts other
than the ones specified.
If the hostname is given as
.Ql @ ,
the local hostname will be used.
The special specification
.Ql +*
will cause subsequent blocks to apply to all hosts.
.Pp
See
.Xr syslog 3
for a further descriptions of both the
.Em facility
and
.Em level
keywords and their significance.
It is preferred that selections be made based on
.Em facility
rather than
.Em program ,
since the latter can vary in a networked environment.
However, there are cases where a
.Em facility
may be too broadly defined.
.Pp
If a received message matches the specified
.Em facility ,
and the specified
.Em level
comparison is true,
and the first word in the message after the date matches the
.Em program ,
the action specified in the
.Em action
field will be taken.
.Pp
Multiple
.Em selectors
may be specified for a single
.Em action
by separating them with semicolon
.Pq Sq \&;
characters.
It is important to note, however, that each
.Em selector
can modify the ones preceding it.
.Pp
Multiple
.Em facilities
may be specified for a single
.Em level
by separating them with comma
.Pq Sq \&,
characters.
.Pp
An asterisk
.Pq Sq \&*
can be used to specify all
.Em facilities
or all
.Em levels .
.Pp
The special
.Em facility
.Dq mark
receives a message at priority
.Dq info
every 20 minutes
(see
.Xr syslogd 8 ) .
This is not enabled by a
.Em facility
field containing an asterisk.
.Pp
The special
.Em level
.Dq none
disables a particular
.Em facility .
.Pp
The
.Em action
field of each line specifies the action to be taken when the
.Em selector
field selects a message.
There are five forms:
.Bl -bullet
.It
A pathname (beginning with a leading slash).
Selected messages are appended to the file, unless
pathname points to an existing FIFO special file.
.Xr syslogd 8
treats FIFO specially by opening them in non-blocking mode and
discarding messages sent when no reader is listening on the other side.
.Pp
To ensure that kernel messages are written to disk promptly,
.Xr syslogd 8
calls
.Xr fsync 2
after writing messages from the kernel.
Other messages are not synced explcitly.
You may disable syncing of files specified to receive kernel messages
by prefixing the pathname with a minus sign
.Ql - .
Note that use of this option may cause the loss of log information in
the event of a system crash immediately following the write attempt.
However, using this option may prove to be useful if your system's
kernel is logging many messages.
.Pp
Normally the priority and version is not written to file.
In order to use syslog-sign you may prefix a pathname with the plus sign
.Ql + .
If both switches are used the order has to be
.Ql +- .
.It
A hostname (preceded by an at
.Pq Sq @
sign).
Selected messages are forwarded to the
.Xr syslogd 8
program on the named host with UDP.
.It
A hostname preceded by an at
.Pq Sq @
sign and enclosed in brackets
.Pq Sq []
.
Selected messages are forwarded with TLS to the
.Xr syslogd 8
program on the named host.
After the closing bracket a colon
.Pq Sq \&:
and a port or service name may be appended.
Additional options are configured in parantheses in the form of key="value".
Recognized keywords are
.Ar subject ,
.Ar fingerprint ,
.Ar cert ,
and
.Ar verify .
.It
A comma separated list of users.
Selected messages are written to those users
if they are logged in.
.It
An asterisk.
Selected messages are written to all logged-in users.
.It
A vertical bar
.Pq Sq |
followed by a command to which to pipe the selected messages.
The command string is passed to
.Pa /bin/sh
for evaluation, so the usual shell metacharacters or input/output
redirection can occur.
(Note that redirecting
.Xr stdio 3
buffered output from the invoked command can cause additional delays,
or even lost output data in case a logging subprocess exits with a
signal.)
The command itself runs with
.Em stdout
and
.Em stderr
redirected to
.Pa /dev/null .
Upon receipt of a
.Dv SIGHUP ,
.Xr syslogd 8
will close the pipe to the process.
If the process does not exit voluntarily, it will be sent a
.Dv SIGTERM
signal after a grace period of up to 60 seconds.
.Pp
The command will only be started once data arrives that should be
piped to it.
If the command exits, it will be restarted as necessary.
.Pp
If it is desired that the subprocess should receive exactly one line of
input, this can be achieved by exiting after reading and processing the
single line.
A wrapper script can be used to achieve this effect, if necessary.
Note that this method can be very resource-intensive if many log messages
are being piped through the filter.
.Pp
Unless the command is a full pipeline, it may be useful to
start the command with
.Em exec
so that the invoking shell process does not wait for the command to
complete.
Note that the command is started with the UID of the
.Xr syslogd 8
process, normally the superuser.
.Pp
Just like with files a plus sign
.Ql +
will leave the priority and version information intact.
.El
.Pp
Blank lines and lines whose first non-blank character is a hash
.Pq Sq #
character are ignored.
.Sh "TLS OPTIONS"
Additional options are used for TLS configuration:
.Bl -ohang
.It Em tls_server
Enables TLS server mode.
.It Em tls_bindport
Service name or port number to bind to.
Default is
.Sq syslog .
.Em As long as no official port is assigned this option is required
.Em for TLS servers.
.It Em tls_bindhost
Hostname or IP to bind to.
.It Em tls_gen_cert
Automatically generate a private key and certificate.
.It Em tls_key
File with private key.
Default is
.Sq /etc/openssl/default.key
.It Em tls_cert
File with certificate to use.
Default is
.Sq /etc/openssl/default.crt
.It Em tls_ca
File with CA certificate to use.
.It Em tls_cadir
Directory containing CA certificates.
.It Em tls_verify
If set to
.Sq off
then certificate authentication is skipped.
.It Em tls_allow_fingerprints
List of fingerprints of trusted client certificates.
.It Em tls_allow_clientcerts
List of filenames with trusted client certificates.
.El
.Sh "TLS AUTHENTICATION"
One function of TLS is mutual authentication of client and server.
Unless authentication is disabled by setting
.Sq tls_verify=off
the following rules are used:
.Ss "As client:"
A client can be configured not to check a server's certificate by setting the
parameter
.Ar verify
to
.Sq off .
If the server's certificate is signed by a trusted CA then it is checked
if its hostname or IP is given in its certificate (as a CommonName, as a
DNS SubjectAltName, or as an IP SubjectAltName).
If any match is found then the server is authenticated.
If a
.Ar subject
parameter is given then it is can satisfy this test as well.
This allows DNS-independent configurations using the server's IP address in the
destination and adding its hostname as
.Ar subject
to authenticate the TLS connection without having to add the IP to the X.509
certificate.
.Pp
If no CA is used or no trust path between CA and server certificate exists, then
hash value of the server's certificate is compared with the hash given in
.Ar fingerprint
and the hash of the certificate in
.Ar cert .
If the hashes are equal then the server is authenticated.
.Ss "As server:"
If using a CA and the client's certificate is signed by it then the client is
authenticated.
Otherwise the hash of the client's certificate is compared with the hashes given
in
.Ar tls_allow_fingerprints
and the hashes of the certificates given in
.Ar tls_allow_clientcerts .
On any match the client is authenticated.
.Sh BUFFERING
.Xr syslogd 8
is able to buffer temporary not writeable messages in memory.
To limit the memory consumed for this buffering the following optons may be
given:
.Bl -ohang
.It Em file_queue_length
.It Em pipe_queue_length
.It Em tls_queue_length
The maximum number of messages buffered for one destination of type tls, file,
or pipe respectively.
Defaults are
.Sq 1024 ,
.Sq 1024 ,
and
.Sq -1
(no limit).
.It Em file_queue_size
.It Em pipe_queue_size
.It Em tls_queue_size
The maximum memory usage in bytes of messages buffered for one destination.
Defaults are
.Sq 1M ,
.Sq 1M ,
and
.Sq 16M .
.El
.Sh SIGNING
.Xr syslogd 8
is able to digitally sign all processed messages.
The used protocol is defined by RFC 5848 (syslog-sign):
at the start of a session the signing sender sends so called certificate
blocks containing its public key; after that it periodically sends a signed
message containing hashes of previous messages.
.Pp
To detect later manipulation one has to keep a copy of the key used for
signing (otherwise an attacker could alter the logs and sign them with his
his own key).
If TLS is used with a DSA key then the same key will be used for signing.
This is the recommended setup because it makes it easy to have copies of
the certificate (with the public key) in backups.
Otherwise new keys are generated on every restart and for certain verification
it is necessary to have copies of all used keys.
So logging only to a local file is not secure; at least the used keys should
be logged to another host.
.Bl -ohang
.It Em sign_sg
Enables signing.
Set this option to enable syslog-sign and select how to assign
messages to signature groups (subsets of messages that are signed together).
To enable later signature verification and detection of lost messages the
assignment should be chosen such that all messages of one signature group
are written to the same file.
Four possible values for this option are:
.Bl -hang -offset indent
.It Em 0
Use one global signature group for all messages.
.It Em 1
Use one signature group per priority.
.It Em 2
Use signature groups for ranges of priorities.
.It Em 3
Use one signature group per destination.
This is a custom strategy not defined by the standard.
With this setting one signature group is set up for
every file and network action.
.El
.It Em sign_delim_sg2
This option is only evaluated with
.Sq sign_sg=2
and allows to configure the priority ranges for signature groups.
The parameters are numerical values used as the maximum priority for one group.
The default is to use one signature groups per facility, which is equal to
setting
.Sq sign_delim_sg2=7 15 23 31 39 ... .
.El
.Sh FILES
.Bl -tag -width /etc/syslog.conf -compact
.It Pa /etc/syslog.conf
The
.Xr syslogd 8
configuration file.
.It Pa /usr/share/examples/syslogd/verify.pl
Example script to verify message signatures.
(Requires Perl and modules not part of NetBSD.)
.El
.Sh EXAMPLES
A configuration file might appear as follows:
.Bd -literal
# Log all kernel messages, authentication messages of
# level notice or higher and anything of level err or
# higher to the console.
# Don't log private authentication messages!
*.err;kern.*;auth.notice;authpriv.none	/dev/console

# Log anything (except mail) of level info or higher.
# Don't log private authentication messages!
*.info;mail.none;authpriv.none		/var/log/messages

# Log daemon messages at debug level only
daemon.=debug				/var/log/daemon.debug

# The authpriv file has restricted access.
# Write logs with priority for later verification with syslog-sign.
authpriv.*				+/var/log/secure

# Log all the mail messages in one place.
mail.*					/var/log/maillog

# Everybody gets emergency messages, plus log them on another
# machine.
*.emerg					*
*.emerg					@arpa.berkeley.edu

# Log all messages of level info or higher to another
# machine using TLS with an alternative portname and a
# fingerprint for athentication
*.info			@[logserver]:1234(fingerprint="SHA1:01:02:...")

# Root and Eric get alert and higher messages.
*.alert					root,eric

# Save mail and news errors of level err and higher in a
# special file.
mail,news.err				/var/log/spoolerr

# Pipe all authentication messages to a filter.
auth.*					|exec /usr/local/sbin/authfilter

# Log kernel messages to a separate file without syncing each message.
kern.*					-/var/log/kernlog

# Save ftpd transactions along with mail and news.
!ftpd
*.*					/var/log/spoolerr

# Send all error messages from a RAID array through a filter.
!raid0
kern.err				|exec /usr/local/sbin/raidfilter

# Save pppd messages from dialhost to a separate file.
!pppd
+dialhost
*.*					/var/log/dialhost-pppd

# Save non-local log messages from all programs to a separate file.
!*
-@
*.*					/var/log/foreign

# Generate digital signatures for all messages
# to each file or network destination.
sign_sg=3
.Ed
.Sh SEE ALSO
.Xr syslog 3 ,
.Xr syslogd 8
.Sh HISTORY
The
.Nm
file appeared in
.Bx 4.3 ,
along with
.Xr syslogd 8 .
.Sh BUGS
The effects of multiple selectors are sometimes not intuitive.
For example
.Dq mail.crit;*.err
will select
.Dq mail
facility messages at
the level of
.Dq err
or higher, not at the level of
.Dq crit
or higher.