DESCRIPTION
syslogd 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:
-
-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.
-
-d
-
Enable debugging to the standard output, and do not disassociate from the controlling terminal.
-
-f config_file
-
Specify the pathname of an alternative configuration file; the default is /etc/syslog.conf.
-
-g group
-
Set GID to group after the sockets and log files have been opened.
-
-m mark_interval
-
Select the number of minutes between ``mark'' messages; the default is 20 minutes.
-
-n
-
Do not perform hostname lookups; report only numeric addresses.
-
-o output_format
-
Select output message format.
-
rfc3164
-
traditional BSD Syslog format (default)
-
syslog
-
new syslog-protocol format
-
-P
-
Specify the pathname of a file containing a list of sockets to be created. The format of the file is simply one socket per line.
-
-p log_socket
-
Specify the pathname of a log socket. Multiple -p options create multiple log sockets. If no -p arguments are created, the default socket of /var/run/log is used.
-
-r
-
Disable the compression of repeated instances of the same line into a single line of the form “last message repeated N times”.
-
-S
-
Sync kernel messages to disk immediately.
-
-s
-
Select “secure” mode, in which syslogd does not listen on a UDP socket but only communicates over a UNIX domain socket. This is valuable when the machine on which syslogd runs is subject to attack over the network and it is desired that the machine be protected from attempts to remotely fill logs and similar attacks.
-
-t chroot_dir
-
chroot(2) to chroot_dir after the sockets and log files have been opened.
-
-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 can't keep time properly or are unable to generate a correct timestamp.
-
-u user
-
Set UID to user after the sockets and log files have been opened.
-
-U
-
Unique priority logging. Only log messages at the priority specified by the selector in the configuration file. Without this option, messages at the specified priority or higher are logged. This option changes the default priority 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.
syslogd 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).
syslogd 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).
syslogd creates the file /var/run/syslogd.pid, and stores its process id there. This can be used to kill or reconfigure syslogd.
By using multiple -p options, one can set up many chroot environments by passing the pathname to the log socket (/var/run/log) in each chroot area to syslogd. For example:
syslogd -p /var/run/log -p /web/var/run/log -p /ftp/var/run/log
Note: the normal log socket must now also be passed to syslogd.
The logged message includes the date, time, and hostname (or pathname of the log socket). Commonly, the program name and the process id is included.
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.
Accesses from UDP socket can be filtered by libwrap configuration files, like /etc/hosts.deny. Specify “syslogd” in daemon_list portion of the configuration files. Refer to hosts_access(5) for details.
SYSLOG PROTOCOL NOTES
syslogd accepts messages in traditional BSD Syslog or in newer Syslog Protocol format. See RFC 3164 (BSD Syslog) and RFC 5424 (Syslog Protocol) for detailed description of the message format. Messages from the local kernel that are not tagged with a priority code receive the default facility LOG_KERN and priority LOG_NOTICE. All other untagged messages receive the default facility LOG_USER and priority LOG_NOTICE.