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Man Pages
SYSLOGD(8) FreeBSD System Manager's Manual SYSLOGD(8)

syslogd
log systems messages

syslogd [
-468ACcdFHkNnosTuv
] [
-a allowed_peer
] [
-b bind_address
] [
-f config_file
] [
-l [
mode:
]path
] [
-m mark_interval
] [
-O format
] [
-P pid_file
] [
-p log_socket
] [
-S logpriv_socket
]

The syslogd utility reads and logs messages to the system console, log files, other machines and/or users as specified by its configuration file.
The options are as follows:
Force syslogd to use IPv4 addresses only.
Force syslogd to use IPv6 addresses only.
Tells syslogd not to interfere with 8-bit data. Normally syslogd will replace C1 control characters (ISO 8859 and Unicode characters) with their “M-x” equivalent. Note, this option does not change the way syslogd alters control characters (see iscntrl(3)). They will always be replaced with their “^x” equivalent.
Ordinarily, syslogd 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, syslogd tries to send the message to all addresses.
allowed_peer
Allow allowed_peer to log to this syslogd using UDP datagrams. Multiple -a options may be specified.
The allowed_peer option may be any of the following:
ipaddr[
/masklen
][
:service
]
ipaddr[
/prefixlen
][
:service
]
Accept datagrams from ipaddr, ipaddr can be specified as an IPv4 address or as an IPv6 address enclosed with ‘[’ and ‘]’. If specified, service is the name or number of an UDP service (see services(5)) the source packet must belong to. A service of ‘*’ accepts UDP packets from any source port. The default service is ‘syslog’. If ipaddr is IPv4 address, a missing masklen will be substituted by the historic class A or class B netmasks if ipaddr belongs into the address range of class A or B, respectively, or by 24 otherwise. If ipaddr is IPv6 address, a missing masklen will be substituted by 128.
domainname[
:service
]
Accept datagrams where the reverse address lookup yields domainname for the sender address. The meaning of service is as explained above. domainname can contain special characters of a shell-style pattern such as ‘*’.
The -a options are ignored if the -s option is also specified.
bind_address[
:service
]
 
:service
Bind to a specific address and/or port. The address can be specified as a hostname, and the port as a service name. If an IPv6 address is specified, it should be enclosed with ‘[’ and ‘]’. The default service is ‘syslog’. This option can be specified multiple times to bind to multiple addresses and/or ports.
Create log files that do not exist (permission is set to ‘0600’).
Disable the compression of repeated instances of the same line into a single line of the form “last message repeated N times” when the output is a pipe to another program. If specified twice, disable this compression in all cases.
Put syslogd into debugging mode. This is probably only of use to developers working on syslogd.
config_file
Specify the pathname of an alternate configuration file; the default is /etc/syslog.conf.
Run syslogd in the foreground, rather than going into daemon mode. This is useful if some other process uses fork(2) and exec(3) to run syslogd, and wants to monitor when and how it exits.
When logging remote messages use hostname from the message (if supplied) instead of using address from which the message was received.
Disable the translation of messages received with facility “kern” to facility “user”. Usually the “kern” facility is reserved for messages read directly from /dev/klog.
mark_interval
Select the number of minutes between “mark” messages; the default is 20 minutes.
Disable binding on UDP sockets. RFC 3164 recommends that outgoing syslogd messages should originate from the privileged port, this option disables the recommended behavior. This option inherits -s.
Disable DNS query for every request.
format
Select the output format of generated log messages. The values bsd and rfc3164 are used to generate RFC 3164 log messages. The values syslog and rfc5424 are used to generate RFC 5424 log messages, having RFC 3339 timestamps with microsecond precision. The default is to generate RFC 3164 log messages.
Prefix kernel messages with the full kernel boot file as determined by getbootfile(3). Without this, the kernel message prefix is always “kernel:”.
log_socket
Specify the pathname of an alternate log socket to be used instead; the default is /var/run/log. When a single -p option is specified, the default pathname is replaced with the specified one. When two or more -p options are specified, the remaining pathnames are treated as additional log sockets.
pid_file
Specify an alternative file in which to store the process ID. The default is /var/run/syslog.pid.
logpriv_socket
Specify the pathname of an alternate log socket for privileged applications to be used instead; the default is /var/run/logpriv. When a single -S option is specified, the default pathname is replaced with the specified one. When two or more -S options are specified, the remaining pathnames are treated as additional log sockets.
[
mode:
]path
Specify a location where syslogd should place an additional log socket. The primary use for this is to place additional log sockets in /var/run/log of various chroot filespaces. File permissions for socket can be specified in octal representation in mode, delimited with a colon. The socket location must be specified as an absolute pathname in path.
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.
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.
Unique priority logging. Only log messages at the specified priority. Without this option, messages at the stated priority or higher are logged. This option changes the default comparison from “=>” to “=”.
Verbose logging. If specified once, the numeric facility and priority are logged with each locally-written message. If specified more than once, the names of the facility and priority are logged with each locally-written message.
This option only affects the formatting of RFC 3164 messages. Messages formatted according to RFC 5424 always include a facility/priority number.
The syslogd 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 syslog.conf(5).
The syslogd utility reads messages from the UNIX domain sockets /var/run/log and /var/run/logpriv, from an Internet domain socket specified in /etc/services, and from the special device /dev/klog (to read kernel messages).
The syslogd utility creates its process ID file, by default /var/run/syslog.pid, and stores its process ID there. This can be used to kill or reconfigure syslogd.
The message sent to syslogd 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, ‘⟨5⟩’. This priority code should map into the priorities defined in the include file <sys/syslog.h>.
For security reasons, syslogd will not append to log files that do not exist (unless -C option is specified); therefore, they must be created manually before running syslogd.
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 -T flag.

/etc/syslog.conf
configuration file
/var/run/syslog.pid
default process ID file
/var/run/log
name of the UNIX domain datagram log socket
/var/run/logpriv
UNIX socket for privileged applications
/dev/klog
kernel log device

logger(1), syslog(3), services(5), syslog.conf(5), newsyslog(8)

The syslogd utility appeared in 4.3BSD.
The -a, -s, -u, and -v options are FreeBSD 2.2 extensions.

The ability to log messages received in UDP packets is equivalent to an unauthenticated remote disk-filling service, and should probably be disabled by default. Some sort of inter-syslogd authentication mechanism ought to be worked out. To prevent the worst abuse, use of the -a option is therefore highly recommended.
The -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 -a list.
The log socket was moved from /dev to ease the use of a read-only root file system. This may confuse some old binaries so that a symbolic link might be used for a transitional period.
July 2, 2018 FreeBSD 12.0-RELEASE

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