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.\"     from: @(#)syslogd.8	8.1 (Berkeley) 6/6/93
.\"	$NetBSD: syslogd.8,v 1.3 1996/01/02 17:41:48 perry Exp $
.\"
.Dd $Mdocdate: September 27 2018 $
.Dt SYSLOGD 8
.Os
.Sh NAME
.Nm syslogd
.Nd log system messages
.Sh SYNOPSIS
.Nm syslogd
.Bk -words
.Op Fl 46dFhnruVZ
.Op Fl a Ar path
.Op Fl C Ar CAfile
.Op Fl c Ar cert_file
.Op Fl f Ar config_file
.Op Fl K Ar CAfile
.Op Fl k Ar key_file
.Op Fl m Ar mark_interval
.Op Fl p Ar log_socket
.Op Fl S Ar listen_address
.Op Fl s Ar reporting_socket
.Op Fl T Ar listen_address
.Op Fl U Ar bind_address
.Ek
.Sh DESCRIPTION
.Nm
writes system messages to log files or a user's terminal.
Output can be sent to other programs
for further processing.
It can also securely send and receive log messages
to and from remote hosts.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl 4
Forces
.Nm
to use only IPv4 addresses for UDP.
.It Fl 6
Forces
.Nm
to use only IPv6 addresses for UDP.
.It Fl a Ar path
Specify a location where
.Nm
should place an additional log socket.
The primary use for this is to place additional log sockets in
.Pa /dev/log
of various chroot filespaces, though the need for these is
less urgent after the introduction of
.Xr sendsyslog 2 .
.It Fl C Ar CAfile
PEM encoded file containing CA certificates used for certificate
validation of a remote loghost;
the default is
.Pa /etc/ssl/cert.pem .
.It Fl c Ar cert_file
PEM encoded file containing the client certificate for TLS connections
to a remote loghost.
The default is not to use a client certificate for the outgoing connection
to a syslog server.
This option has to be used together with
.Fl k Ar key_file .
.It Fl d
Enable debugging to the standard output,
and do not disassociate from the controlling terminal.
.It Fl F
Run in the foreground instead of disassociating from the controlling
terminal and running as a background daemon.
.It Fl f Ar config_file
Specify the pathname of an alternate configuration file;
the default is
.Pa /etc/syslog.conf .
.It Fl h
Include the hostname when sending messages to a remote loghost.
.It Fl K Ar CAfile
PEM encoded file containing CA certificates used for client certificate
validation on the local listen socket.
By default incoming connections from any TLS client are allowed.
.It Fl k Ar key_file
PEM encoded file containing the client private key for TLS connections
to a remote loghost.
This option has to be used together with
.Fl c Ar cert_file .
.It Fl m Ar mark_interval
Select the number of minutes between
.Dq mark
messages; the default is 20 minutes.
.It Fl n
Print source addresses numerically rather than symbolically.
This saves an address-to-name lookup for each incoming message,
which can be useful when combined with the
.Fl u
option on a loghost with no DNS cache.
Messages from the local host will still be logged with
the symbolic local host name.
.It Fl p Ar log_socket
Specify the pathname of an alternate log socket to be used instead;
the default is
.Pa /dev/log .
.It Fl r
Print duplicate lines immediately and suppress the "last message
repeated" summary when piping to another program or forwarding to
a remote loghost.
If given twice, this is done for all log actions.
.It Fl S Ar listen_address
Create a TLS listen socket for receiving encrypted messages and
bind it to the specified address.
A port number may be specified using the
.Ar host : Ns Ar port
syntax.
The first
.Ar listen_address
is also used to find a suitable server key and certificate in
.Pa /etc/ssl/ .
.It Fl s Ar reporting_socket
Specify path to a UNIX-domain
socket for use in reporting logs stored in memory buffers using
.Xr syslogc 8 .
.It Fl T Ar listen_address
Create a TCP listen socket for receiving messages and bind it to
the specified address.
There is no well-known port for syslog over TCP, so a port number
must be specified using the
.Ar host : Ns Ar port
syntax.
.It Fl U Ar bind_address
Create a UDP socket for receiving messages and bind it to the
specified address.
This can be used, for example, with a pf divert-to rule to receive
packets when
.Nm
is bound to localhost.
A port number may be specified using the
.Ar host : Ns Ar port
syntax.
.It Fl u
Select the historical
.Dq insecure
mode, in which
.Nm
will accept input from the UDP port.
Some software wants this, but you can be subjected to a variety of
attacks over the network, including attackers remotely filling logs.
.It Fl V
Do not perform remote server certificate and hostname validation
when sending messages.
.It Fl Z
Generate timestamps in ISO format.
This includes the year and the timezone, and all logging is done
in UTC.
.El
.Pp
The options
.Fl a , S , T ,
and
.Fl U
can be given more than once to specify multiple input sources.
.Pp
When starting up,
.Nm
reads its configuration file,
.Xr syslog.conf 5 ,
and opens the configured logfiles and TCP and TLS connections.
The logfiles already have to exist with the correct permissions.
When receiving a
.Dv SIGHUP
signal, it closes all open logfiles and outgoing TCP and TLS
connections and re-runs this initialization sequence.
Sending this signal is required both after editing the configuration
file and after log rotation.
.Pp
.Nm
opens a UDP socket, as specified
in
.Pa /etc/services ,
for sending forwarded messages.
By default all incoming data on this socket is discarded.
If insecure mode is switched on with
.Fl u ,
it will also read messages from the socket.
.Nm
also opens and reads messages from the
.Ux Ns -domain
socket
.Pa /dev/log ,
and from the special device
.Pa /dev/klog
(to read kernel messages),
and from
.Xr sendsyslog 2
(to read messages from userland processes).
.Pp
The message sent to
.Nm
should consist of a single line.
Embedded new line characters are converted to spaces;
binary data is encoded by
.Xr vis 3 .
The message can contain a priority code, which should be a preceding
decimal number in angle braces, for example,
.Dq <5> .
This priority code should map into the priorities defined in the
include file
.In sys/syslog.h .
.Pp
When sending syslog messages to a remote loghost via TLS, the
server's certificate and hostname are validated to prevent malicious
servers from reading messages.
If the server has a certificate with a matching hostname signed by
a CA in
.Pa /etc/ssl/cert.pem ,
it is verified with that by default.
If the server has a certificate with a matching hostname signed by
a private CA, use the
.Fl C
option and put that CA into
.Ar CAfile .
Validation can be explicitly turned off using the
.Fl V
option.
If the server is accepting messages only from clients with a trusted
client certificate, use the
.Fl k
and
.Fl c
options to authenticate
.Nm
with this certificate.
.Pp
When receiving syslog messages from a TLS client, there must be
a server key and certificate in
.Pa /etc/ssl/private/host Ns Oo : Ns Ar port Oc Ns Ar .key
and
.Pa /etc/ssl/host Ns Oo : Ns Ar port Oc Ns Ar .crt .
If the client uses certificates to authenticate, the CA of the
client's certificate may be added to
.Ar CAfile
using the
.Fl K
option to protect from messages being spoofed by malicious senders.
.Sh FILES
.Bl -tag -width /var/run/syslog.pid -compact
.It Pa /dev/log
Name of the
.Ux Ns -domain
datagram log socket.
.It Pa /dev/klog
Kernel log device.
.It Pa /etc/ssl/
Private keys and public certificates.
.It Pa /etc/syslog.conf
Configuration file.
.It Pa /var/run/syslog.pid
Process ID of current
.Nm .
.El
.Sh SEE ALSO
.Xr logger 1 ,
.Xr syslog 3 ,
.Xr services 5 ,
.Xr syslog.conf 5 ,
.Xr newsyslog 8 ,
.Xr syslogc 8
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.3 .
.Sh CAVEATS
.Nm
does not create files,
it only logs to existing ones.