SYSLOGD(8)

NAME
syslogd - log systems messages

SYNOPSIS
syslogd [-46Acdknosuv] [-a allowed_peer] [-b bind_address] [-f config_file] [-l path] [-m mark_interval] [-P pid_file] [-p log_socket]

DESCRIPTION
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:

-4  Force syslogd to use IPv4 addresses only.

-6  Force syslogd to use IPv6 addresses only.

-A  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.

-a allowed_peer
    Allow allowed_peer to log to this syslogd using UDP datagrams. Multiple -a options may be specified.

    Allowed_peer can be any of the following:

        ipaddr /masklen [:service] Accept datagrams from ipaddr (in the usual dotted quad notation) with masklen bits being taken into account when doing the address comparison. ipaddr can be also IPv6 address by enclosing the address 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 ‘*’ allows packets being sent from any UDP 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[:service] Same as before, except that any source host whose name ends in domainname will get permission.

    The -a options are ignored if the -s option is also specified.

-b bind_address
    Specify one specific IP address or hostname to bind to. If a hostname is specified, the IPv4 or IPv6 address which corresponds to it is used.

-c  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.

-d  Put syslogd into debugging mode. This is probably only of use to developers working on syslogd.

-f  Specify the pathname of an alternate configuration file; the default is /etc/syslog.conf.

-k  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.

-m  Select the number of minutes between “mark” messages; the default is 20 minutes.

-n  Disable dns query for every request.

-o  Prefix kernel messages with the full kernel boot file as determined by getbootfile(3). Without this, the kernel message prefix is always “kernel:”.

-p  Specify the pathname of an alternate log socket to be used instead; the default is /var/run/log.

-P  Specify an alternative file in which to store the process ID. The default is /var/run/syslog.pid.

-l  Specify a location where syslogd should place an additional log socket. Up to 19 additional logging sockets can be specified. The primary use for this is to place additional log sockets in /var/run/log of various chroot filespaces.

-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.

-u  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 “=”.

-v  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.

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 socket /var/run/log, 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; therefore, they must be created manually before running syslogd.

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

SEE ALSO
logger(1), syslog(3), services(5), syslog.conf(5)

HISTORY
The syslogd utility appeared in 4.3BSD.

The -a, -s, -u, and -v options are FreeBSD 2.2 extensions.

BUGS
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 doesn't 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.