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Commands Reference, Volume 5

syslogd Daemon


Logs system messages.


syslogd-d ] [  -s ] [ -f ConfigurationFile ] [  -m MarkInterval ] [ -r]


The syslogd daemon reads a datagram socket and sends each message line to a destination described by the /etc/syslog.conf configuration file. The syslogd daemon reads the configuration file when it is activated and when it receives a hangup signal.

The syslogd daemon creates the /etc/syslog.pid file, which contains a single line with the command process ID used to end or reconfigure the syslogd daemon.

A terminate signal sent to the syslogd daemon ends the daemon. The syslogd daemon logs the end-signal information and terminates immediately.

Each message is one line. A message can contain a priority code, marked by a digit enclosed in < > (angle braces) at the beginning of the line. Messages longer than 900 bytes may be truncated.

The /usr/include/sys/syslog.h include file defines the facility and priority codes used by the configuration file. Locally written applications use the definitions contained in the syslog.h file to log messages via the syslogd daemon.


-d Turns on debugging.
-f ConfigurationFile Specifies an alternate configuration file.
-m MarkInterval Specifies the number of minutes between the mark command messages. If you do not use this flag, the mark command sends a message with LOG_INFO priority sent every 20 minutes. This facility is not enabled by a selector field containing an * (asterisk), which selects all other facilities.
-s Specifies to forward a "shortened" message to another system (if it is configured to do so) for all the forwarding syslog messages generated on the local system.
-r Suppresses logging of messages received from remote hosts.

Configuration File

The configuration file informs the syslogd daemon where to send a system message, depending on the message's priority level and the facility that generated it.

If you do not use the -f flag, the syslogd daemon reads the default configuration file, the /etc/syslog.conf file.

The syslogd daemon ignores blank lines and lines beginning with a # (pound sign).


Lines in the configuration file for the syslogd daemon contain a selector field, an action field, and an optional rotation field, separated by one or more tabs.

The selector field names a facility and a priority level. Separate facility names with a , (comma). Separate the facility and priority-level portions of the selector field with a . (period). Separate multiple entries in the same selector field with a ; (semicolon). To select all facilities, use an * (asterisk).

The action field identifies a destination (file, host, or user) to receive the messages. If routed to a remote host, the remote system will handle the message as indicated in its own configuration file. To display messages on a user's terminal, the destination field must contain the name of a valid, logged-in system user.

The rotation field identifies how rotation is used. If the action field is a file, then rotation can be based on size or time, or both. One can also compress and/or archive the rotated files.


Use the following system facility names in the selector field:

Facility Description
kern Kernel
user User level
mail Mail subsystem
daemon System daemons
auth Security or authorization
syslog syslogd daemon
lpr Line-printer subsystem
news News subsystem
uucp uucp subsystem
* All facilities

Priority Levels

Use the following message priority levels in the selector field. Messages of the specified priority level and all levels above it are sent as directed.

Priority Level Description

emerg Specifies emergency messages (LOG_EMERG). These messages are not distributed to all users. LOG_EMERG priority messages can be logged into a separate file for reviewing.
alert Specifies important messages (LOG_ALERT), such as a serious hardware error. These messages are distributed to all users.
crit Specifies critical messages not classified as errors (LOG_CRIT), such as improper login attempts. LOG_CRIT and higher-priority messages are sent to the system console.
err Specifies messages that represent error conditions (LOG_ERR), such as an unsuccessful disk write.
warning Specifies messages for abnormal, but recoverable, conditions (LOG_WARNING).
notice Specifies important informational messages (LOG_NOTICE). Messages without a priority designation are mapped into this priority message.
info Specifies informational messages (LOG_INFO). These messages can be discarded, but are useful in analyzing the system.
debug Specifies debugging messages (LOG_DEBUG). These messages may be discarded.
none Excludes the selected facility. This priority level is useful only if preceded by an entry with an * (asterisk) in the same selector field.


Use the following message destinations in the action field.

Destination Description
File Name Full path name of a file opened in append mode
@Host Host name, preceded by @ (at sign)
User[, User][...] User names
* All users


Use the following rotation keywords in the rotation field.

Keyword Description
rotate This keyword must be specified after the action field.
size This keyword specifies that rotation is based on size. It is followed by a number and either a k (kilobytes) or m(megabytes).
time This keyword specifies that rotation is based on time. It is followed by a number and either a h(hour) or d(day) or w(week) or m(month) or y(year).
files This keyword specifies the total number of rotated files. It is followed by a number. If not specified, then there are unlimited number of rotated files.
compress This keyword specifies that the saved rotated files will be compressed.
archive This keyword specifies that the saved rotated files will be copied to a directory. It is followed by the directory name.


  1. To log all mail facility messages at the debug level or above to the file /tmp/mailsyslog, type:

    mail.debug /tmp/mailsyslog     
  2. To send all system messages except those from the mail facility to a host named rigil, type:

    *.debug;mail.none @rigil
  3. To send messages at the emerg priority level from all facilities, and messages at the crit priority level and above from the mail and daemon facilities, to users nick and jam, typer:

    *.emerg;mail,daemon.crit nick, jam
  4. To send all mail facility messages to all users' terminal screens, type:

    mail.debug *
  5. To log all facility messages at the debug level or above to the file /tmp/syslog.out, and have the file rotated when it gets larger then 500 kilobytes or if a week passes, limit the number of rotated files to 10, use compression and also use /syslogfiles as the archive directory, type:

    *.debug /tmp/syslog.out rotate size 500k time 1w files 10 compress archive /syslogfiles    


/etc/syslog.conf Controls the output of syslogd.
/etc/syslog.pid Contains the process ID.

Related Information

The syslog subroutine.

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