sysklogd/man/syslogd.8

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.\"     @(#)syslogd.8	8.1 (Berkeley) 6/6/93
.\" $FreeBSD$
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.Dd May 5, 2021
.Dt SYSLOGD 8
.Os sysklogd
.Sh NAME
.Nm syslogd
.Nd log systems messages
.Sh SYNOPSIS
.Nm
.Op Fl ?46AdFHKknsTtv
.Op Fl a Ar addr[/len][:port]
.Op Fl a Ar name[:port]
.Op Fl b Ar addr[:port]
.Op Fl b Ar :port
.Op Fl C Ar file
.Op Fl f Ar file
.Op Fl m Ar interval
.Op Fl P Ar file
.Op Fl p Ar sock
.Op Fl r Ar size[:count]
.Sh DESCRIPTION
The
.Nm
utility reads and logs messages to the system console, log files, other
machines and/or users as specified by its configuration file.
.Pp
.Nm
support RFC3164 and RFC5424 style log messages for both local and remote
logging using Internet and UNIX domain sockets.  Differences in style is
shown below.
.Pp
.Bl -tag -compact -width "RFC3164:"
.It Sy RFC3164:
.Li Aug 24 05:14:15 192.0.2.1 myproc[8710]: Kilroy was here.
.It Sy RFC5424:
.Li 2003-08-24T05:14:15.000003-07:00 192.0.2.1 myproc 8710 - - Kilroy was here.
.El
.Pp
Note, for remote logging the messages are prefixed with
.Ql <PRI>
or
.Ql <PRI>1 ,
respectively.
.Pp
.Nm
is derived from BSD sources, today
.Fx
is the reference for
.Nm
and
.Nx
for the new
.Xr syslogp 3
API, which fully supports the new features of RFC5424.  Please note; 1)
the intention is to follow standard BSD
.Nm
behavior, 2) despite having a stand-alone
.Xr syslog 3 ,
and
.Xr syslogp 3
API in libsyslog,
.Nm
interacts transparently with the standard C library
.Xr syslog 3
API, as implemented in GLIBC, musl libc, and uClibc.
.Pp
When
.Nm
starts up it reads its main configuration file
.Pa /etc/syslog.conf ,
or an alternate file given with the
.Fl f Ar file
option.  For details on how to configure syslog priority
(facility.severity) filtering, see
.Xr syslog.conf 5 .
.Sh OPTIONS
By default,
.Nm
reads messages from the
.Ux
domain socket
.Pa /dev/log ,
from an Internet domain socket specified in
.Pa /etc/services ,
and from
.Pa /dev/kmsg
.Pq to read kernel messages .
The command line options defined below can be used to change this
behavior.
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl 4
Force
.Nm
to use IPv4 addresses only.
.It Fl 6
Force
.Nm
to use IPv6 addresses only.
.It Fl A
Ordinarily,
.Nm
tries to send the message to only one address
even if the host has more than one A or AAAA record.
If this option is specified,
.Nm
tries to send the message to all addresses.
.It Fl a Ar peer
Allow peers to log to this syslogd using UDP datagrams.  Multiple
.Fl a
options may be specified.  Any
.Fl a
option is ignored if the
.Fl s
option is also specified.
.Pp
The
.Ar peer
argument may be any of the following:
.Bl -tag -width 'address[/len][:service]'
.It address[/len][:service]
Accept datagrams from IP
.Ar address ,
which can be specified as an IPv4 address or as an IPv6 address enclosed
with
.Sq \&[
and
.Sq \&] .
If specified, service is the name or port number of an UDP service (see
.Xr services 5 )
the source packet must belong to.  A service of
.Ql *
accepts UDP packets from any source port.  The default service is
.Ql syslog .
If
.Ar address
is an IPv4 address, a missing prefix
.Ar len
will be substituted by the historic class A or class B netmasks if
.Ar address
belongs in the address range of class A or B, respectively, or by'
.Ar /24
otherwise.  If
.Ar address
is an IPv6 address, a missing prefix
.Ar len
will be substituted by 128.
.It domainname[:service]
Accept datagrams where the reverse address lookup yields
.Ar domainname
for the sender address.  The meaning of
.Ar service
is as explained above.
.Ar domainname
can contain special characters of a shell-style pattern such as
.Ql * .
.El
.It Fl b Ar name
Bind to a specific address and/or port.  By default,
.Nm
listens on all interfaces on UDP port 514, unless started with the
.Fl s
option.  Multiple
.Fl b
options may be specified to bind to several addresses and/or ports.
.Pp
The
.Ar name
argument may be any of the following:
.Bl -tag -width 'address[/len][:service]'
.It address[:port]
The address can be specified as a hostname or an IP address, and the
port as a service name or port number.  If an IPv6 address is specified,
it should be enclosed with
.Ql \&[
and
.Ql \&] .
.It :port
Service name or UDP port number.  The default service is
.Ql syslog
(UDP), port 512.
.El
.It Fl C Ar file
File to use for caching last read kernel sequence number from
.Pa /dev/kmsg ,
default:
.Pa /run/syslogd.cache .
If
.Nm
cannot write to, or read from, this file it will cause repeated kernel
log messages when restarting
.Nm .
.Pp
.Sy Note:
.Nm
relies on this file being removed at system reboot.  The default
location depends on the system and how
.Nm
was configured.
.It Fl d
Put
.Nm
into debugging mode.
This is probably only of use to developers working on
.Nm .
See the
.Sx DEBUGGING
section for more information.
.It Fl f Ar file
Specify the path name of an alternate configuration file;
the default is
.Pa /etc/syslog.conf .
.It Fl F
Run
.Nm
in the foreground,
rather than going into daemon mode.
This is useful if some other process uses
.Xr fork 2
and
.Xr exec 3
to run
.Nm ,
and wants to monitor when and how it exits.
.It Fl H
When logging remote messages use hostname from the message (if supplied)
instead of using address from which the message was received.
.It Fl K
Disable kernel logging.  Useful in container use-cases where kernel logs
har handled by the host system.
.It Fl k
Disable the translation of
messages received with facility
.Dq kern
to facility
.Dq user .
Usually the
.Dq kern
facility is reserved for messages read directly from
.Pa /dev/kmsg .
.It Fl m Ar interval
Select the number of minutes between
.Dq mark
messages; the default is 20 minutes.  Setting this to zero disables log
marks.
.It Fl n
Disable DNS query for every request.
.It Fl p Ar socket
Specify the path name of an alternate log socket to be used instead;
the default is
.Pa /dev/log .
When a single
.Fl p
option is specified, the default path name is replaced with the
specified one.  When two or more
.Fl p
options are specified, the remaining path names are treated as
additional log sockets.
.It Fl P Ar file
Specify an alternative file in which to store the process ID.
The default is
.Pa /var/run/syslogd.pid .
.It Fl r Ar size[:count]
Enable built-in support for log rotation of files listed in
.Pa /etc/syslog.conf .
This feature is particularly useful for small and embedded systems that
do not want the overhead of
.Xr cron 8
and
.Xr logrotate 8 .
.Pp
The option controls the max size and number of backup files kept by the
built-in log-rotation.  When present on the command line it activates
log rotation of all files with the given maximum size.  It is also
possible to control log rotate per log file, see
.Xr syslog.conf 5
for details.
.Pp
The size argument takes optional modifiers; k, M, G.  E.g., 100M is
100 MiB, 42k is 42 kiB, etc.
.Pp
The optional number of files kept include both gzipped files and the
first rotated (not zipped) file.  The default for this, when omitted,
is 5.
.It Fl s
Operate in secure mode.  Do not log messages from remote machines.  If
specified twice, no network socket will be opened at all, which also
disables logging to remote machines.
.It Fl T
Always use the local time and date for messages received from the network,
instead of the timestamp field supplied in the message by the remote host.
This is useful if some of the originating hosts cannot keep time properly
or are unable to generate a correct timestamp.
.It Fl t
Keep (trust) kernel timestamp.
.Pp
On Linux systems the
.Pa /dev/kmsg
timestamp is a monotonic clock, in microseconds, relative to the boot of
the system.  This timestamp is, among other things,
.Sy not
adjusted for suspend/resume cycles, meaning the kernel logs can start to
go out of sync with the rest of the system.  This in turn can make it
really hard to correlate events.
.Pp
.Nm
by default only trusts the kernel timestamp when starting up the first
time.  As soon as the the kernel ring buffer has been emptied,
.Nm
uses its own current time for each received kernel log message.  This
option disables that behavior.
.It Fl v
Show program version and exit.
.El
.Pp
The
.Nm
utility reads its configuration file when it starts up and whenever it
receives a hangup signal.
For information on the format of the configuration file,
see
.Xr syslog.conf 5 .
.Pp
The
.Nm
utility creates its process ID file,
by default
.Pa /var/run/syslogd.pid ,
and stores its process ID there.  This can be used to kill or
reconfigure
.Nm .
.Pp
The message sent to
.Nm
should consist of a single line.  The message can contain a priority
code, which should be a preceding decimal number in angle braces, for
example,
.Sq Aq 5 .
This priority code should map into the priorities defined in the
include file
.In sys/syslog.h .
To log with RFC5424 style messages the priority code must be directly
followed by the version number, this is all handled by libsyslog, which
is the
.Nx
.Xr syslogp 3
API included with the
.Nm sysklogd
project.
.Pp
The date and time are taken from the received message.  If the format of
the timestamp field is incorrect, time obtained from the local host is
used instead.  This can be overridden by the
.Fl T
flag.
.Sh SECURITY
There are a number of methods of protecting a machine:
.Bl -enum
.It
Disabling inet domain sockets will limit risk to the local machine.  Use
the secure mode flag
.Fl s
for this.
.It
When secure mode cannot be used, only allow certain remote peers using
the
.Fl a Ar PEER
flag.
.It
Implement kernel firewalling to limit which hosts or networks have
access to the 514/UDP socket.
.It
Logging can be directed to an isolated or non-root filesystem which,
if filled, will not impair the machine.
.It
Most modern UNIX filesystems can be configured to limit a certain
percentage of a filesystem to usage by root only.
.El
.Sh DEBUGGING
When debug mode
.Fl ( d )
is enabled
.Nm
only the first
.Fn init
is shown.
.Nm
then prompts you to send
.Ar SIGUSR1
to continue debugging.  The output is very verbose and is probably only
useful to developers.
.Pp
When
.Nm
receives
.Ar SIGHUP
it reloads its configuration file, and at the end of the
.Fn init
sequence all log targets are listed with their respective priority per
facility, the action and the log format used:
.Pp
.Bl -tag -width priority
.It priority
Bit mapped priorities listed per facility, one priority per facility,
starting with kernel as the left-most column.
.It action
FILE, remote sink (FORW), WALL, etc.  See
.Xr syslog.conf 5
for details.
.It args
The action argument and the log format used.  E.g., for FILE actions the
log filename, for FORW action the remote host:port.  The format is one
of; BSD, RFC5424, or RFC3164.  The latter is the default except for FORW
actions.
.El
.Sh SIGNALS
.Nm
supports the following signals:
.Pp
.Bl -tag -width "TERM, QUIT"
.It HUP
This lets
.Nm
perform a re-initialization.  All open files are closed, the
configuration file (see above) is reread and the
.Xr syslog 3
facility is started again.
.It TERM
This tells 
.Nm
to exit gracefully.  Flushing any log files to disk.
.It INT, QUIT
In debug mode these are ignored.  In normal operation they act as
SIGTERM.
.It USR1
In debug mode this switches debugging on/off.  In normal operation
it is ignored.
.El
.Pp
For convenience the PID is by default stored in
.Pa /var/run/syslogd.pid .
A script can look for the existence of this file to determine if
.Nm
is running, and then send signals:
.Bd -literal -offset indent
kill -SIGNAL `cat /var/run/syslogd.pid`
.Ed
.Sh FILES
.Bl -tag -width /etc/syslog.d/50-default.conf -compact
.It Pa /etc/syslog.conf
configuration file. See
.Xr syslog.conf 5
for more information.
.It Pa /etc/syslog.d/*.conf
conventional sub-directory of
.Pa .conf
files read by
.Nm .
.It Pa /etc/syslog.d/50-default.conf
conventional name for default rules.
.It Pa /var/run/syslogd.pid
default process ID file
.It Pa /var/run/syslogd.cache
cache of last read sequence number from
.Pa /dev/kmsg .
Please note,
.Nm
relies on this file being removed at system reboot.
.It Pa /dev/log
name of the
.Ux
domain datagram log socket
.It Pa /dev/kmsg
kernel log device
.El
.Sh SEE ALSO
.Xr logger 1 ,
.Xr syslog 3 ,
.Xr syslogp 3 ,
.Xr services 5 ,
.Xr syslog.conf 5 ,
.Sh HISTORY
.Nm
was originally ported to Linux by
.An Greg Wettstein Aq Mt greg@wind.enjellic.com
and the project was named
.Nm sysklogd
when a separate log daemon,
.Nm klogd ,
for Linux kernel messages was added.
.Pp
It was the default
.Nm
in Debian and Ubuntu, maintained by
.An Martin Schulze Aq Mt joey@infodrom.org ,
who fixed some bugs and added several new features.  When Debian replaced
.Nm sysklogd
with
.Nm rsyslogd
the project was abandoned.
.Pp
In 2018
.An Joachim Wiberg Aq Mt troglobit@gmail.com
picked up maintenance.  In 2019 the project was revived with fresh DNA
strands from both
.Fx
and
.Nx ,
.Nm klogd
was removed in v2.1 and the project was then re-licensed under the
3-clause BSD license, like its brethren.
.Pp
The
.Nm
utility first appeared in
.Bx 4.3 .
.Sh BUGS
The ability to log messages received in UDP packets is equivalent to an
unauthenticated remote disk-filling service, and should probably be
disabled
.Fl ( s )
by default.  (The shipped systemd unit file disables this by default.)
See also
.Sx SECURITY
for more information on this.  A future version of
.Nm
may include support for TLS, RFC5425, which includes authentication of
both senders and receivers.  For now there is the
.Fl a
option, which is strongly recommended when operating as a remote sink.
.Pp
The
.Fl a
matching algorithm does not pretend to be very efficient;
use of numeric IP addresses is faster than domain name comparison.
Since the allowed peer list is being walked linearly,
peer groups where frequent messages are being anticipated
from should be put early into the
.Fl a
list.
.Pp
As mentioned in the
.Sx DESCRIPTION ,
.Nm
transparently supports the standard C library
.Xr syslog 3
API.  If a binary linked to the standard C libraries does not operate
correctly, this should be reported as a bug to the
.Lk https://github.com/troglobit/sysklogd/issues sysklogd issue tracker