What is oak?

Oak is a program that can be used to monitor syslogs from a collection of servers and notify operators when problem conditions arise. In addition to providing immediate notification of critical problems oak will also batch less critical problems into summary messages that can be sent less often and via any medium. For example you may wish to have oak page you on critical events while sending a summary of less important messages to your terminal once an hour. In addition you could send a daily email message summarizing all events.

How does oak work?

Oak runs as a daemon and monitors a syslog file for events. A common way to run oak would be on a server that is receiving syslogs forwarded from other servers. Based on a series of configurable regular expressions each message is placed into one or more user-defined queues. Each queue is configured by the user to send out its messages after waiting some period of time.

Oak keeps its messages succinct in a number of ways. Oak is aware of some information in log messages that will be unnecessary and produce needlessly repeated messages. For example process id's and sendmail queue id's can be automatically filtered out, thereby condensing hundreds of message to one short notification. In the case that oak does not know about a kind of log that can be condensed the configuration file can specify the custom information to be removed. Finally, for each medium being used to send messages the user can specify limits on the length of the message, the line length, the number of hosts being reported on, the number of messages per host etc. This helps ensure that a runaway message won't overwhelm its recipient.

Download oak

The latest release of oak is oak-1.3.5.
Other versions are available here.

Who wrote oak and where do I report bugs?

Oak was written by James Kretchmar at MIT and bugs can be reported to <oak@mit.edu>. Also send mail to this address if you would like to receive future announcements about oak releases.

How do I use it?

Oak is run as:
oak -c <config>
where <config> is the name of the configuration file. The configuration file controls the entire operation of oak. A sample configuration file can be found here.

The general concepts are these. The configuration file first defines a number of queues. Each queue will take a certain action at a certain time interval. For example you might define a queue called "daily-mail" that fires once a day and sends a piece of email. Or you might define a queue called "immediate-page" which would page you as soon as a problem was noticed.

Next the configuration file specifies lists of regular expressions and each regular expression is associated with one or more of the queues defined earlier. Messages that come in are compared against the regular expressions in order. When the first regular expression is found that matches the message that message is placed in the queues associated with that expression.

Note that a trash queue is defined for you by default and any messages queued to it are discarded. Because oak uses the first regular expression it finds the trash queue may be helpful in discarding unwanted messages while still allowing others to fall through by default.

Config Syntax

set infile <file>
Set the file being monitored to <file>. If this option is not specified in the config then it will default to /var/adm/messages.
set nukepid
Automatically remove process id's from logs. This option is on by default and is strongly recommended.
set nukepid
Don't automatically remove process id's from logs.
set nukeciscoid
Automatically remove log id numbers from cisco syslogs. This option is on by default and is recommended if you are processing logs from cisco equipment.
set no nukeciscoid
Don't automatically remove log id numbers from cisco syslogs.
set nukesmqid
Automatically remove sendmail queue id numbers from logs. This option is on by default and is recommended if you are processing logs from sendmail.
set no nukesmqid
Don't automatically remove sendmail queue id numbers from logs.
set ignorehosts <host> [ <host> ... ]
Ignore logs from the hosts in the list. Make sure each host is listed exactly as it will appear in the log (i.e. exactly as it will be resolved by the local syslogd). This command can not be used at the same time as the set onlyhosts command.
set onlyhosts <host> [ <host> ... ]
Process logs only from the hosts in the list. Make sure each host is listed exactly as it will appear in the log (i.e. exactly as it will be resolved by the local syslogd). This command can not be used at the same time as the set ignorehosts command.
set replacestr <string>
Set the string to be used when a section of log is blanked out, such as the pid. By default the string is "___". Anything in parens in a regular expression is blanked out, as is described below.
define queue <queue>
Define a new queue whose name is <queue>. The following subcommands can be issued after defining a queue. They pertain to the most recent queue defined.

action <action> [ <arg> ... ]
Direct the queue to take specified <action> when it receives messages. You may use multiple action commands to specify more than one action. Currently supported values for <action> are mail, zwrite, and exec. The arguments for each are as follows:
  • action mail <to> <from> <subject>
  • action zwrite <class> <instance> <recipient>
  • action exec <program> [ <arg> ... ]
In the case of the exec command the message are piped to the stdin of the named program.
action-limits <numlines> <linelen> <numhosts> <hostents>
Set limits on the size of messages sent by this queue. <numlines> is the total number of lines in the message. <linelen> is the maximum length of a line. <numhosts> is the maximum number of hosts in a message. <hostents> is the maximum number of logs per host. If the limits set by numlines, numhosts, or hostents are exceeded then the message will be truncated appropriately and a message will be included noting that fact. If linelen is exceeded by a line, the final characters will silently be stripped off.
fire <time>
Specify how often the queue should send messages. <time> can be in one of three formats.
  • *<num>[m|h|s]
    This specifies a repeated interval. For example *5m means to fire every 5 minutes.
  • <hour>:<min>
    This specifies a static time to fire at, using a 24 hour clock. 17:00 would fire every day at 5pm.
  • now
    This indicates that message should be sent immediately. This option should almost always be used in conjunction with the locking command described below.
locking <time>
This option specifies how long a queue should wait after sending a message before it will send another message that matches the same regular expression as the first. This is typically used with queues that fire immediately or at very short intervals. For example, if a queue were set to page someone on a "file system full" message it would be desirable to not receive the page every on each successive log of the error; there would be a flood of pages. If the queue were set to be locking 30m then a "file system full" page would be sent at most once every thirty minutes.
header <text>
Set text to be sent at the beginning of the message.
This option indicates that the queue should include messages that are already in the log file. Normally a queue will only pick up new messages after oak has been started. This option is useful if you want to restart the oak daemon, but not lose messages for a daily report. It is not recommended for queues that send frequent messages since with the prescan option set those messages will all be sent when oak is started.
on <regex>
Specify a regular expression that can be matched. The subcommands following the on command indicate what to do when the expression is matched. Anything in the regular expression that falls between parenthesis will be blanked out.

queues <queuename> [ <queuename> ... ]
Spool the message being matched into the queues named by <queuename>

Oak todo list