mon(1)

NAME
mon - monitor services for availability, sending alarms upon failures.

SYNOPSIS
mon [-dfhlSv] [-a dir] [-A authfile] [-c config] [-D dir] [-i secs] [-k num] [-m num] [-p num] [-P pidfile] [-r delay] [-s dir]

DESCRIPTION
mon is a general-purpose scheduler for monitoring service availability and triggering alerts upon detecting failures. mon was designed to be open in the sense that it supports arbitrary monitoring facilities and alert methods via a common interface, which are easily implemented through shell scripts, Perl scripts, C, or any other language.

OPTIONS

-a dir
    Path to alert scripts. Default is /usr/lib/mon/alert.d.

-A authfile
    Authentication configuration file.

-c file
    Read configuration from file. This defaults to /etc/mon.cf.

-d  Enable debugging mode.

-D dir
    Path to state directory. Default is /usr/lib/mon/state.d.

-f  Fork and run as a daemon process. This is the preferred way to run mon.

-h  Print help information.

-i secs
    Sleep interval, in seconds. Defaults to 1. This shouldn't need to be adjusted for any reason.

-k num
    Set log history to a maximum of num entries. Defaults to 100.

-l  Load state from the last saved state file. Currently the only supported saved state is disabled watches, services, and hosts.

-m num
    Set the throttle for the maximum number of processes to num.

-p num
    Make server listen on port num. This defaults to 32777.

-S  Start with the scheduler stopped.

-P pidfile
    Store the server's pid in pidfile, the default is the first of /var/run/mon/mon.pid, /var/run/mon.pid, and /etc/mon.pid whose directory exists. An empty value tells mon not to use a pid file.

-r delay
    Sets the number of seconds used to randomize the startup delay before each service is scheduled. Refer to the global randstart variable in the configuration file.

-s dir
    Path to monitor scripts. Default is /usr/lib/mon/mon.d.

-v  Print version information.

DEFINITIONS

monitor
    A program which tests for a certain condition, returns either true or false, and optionally produces output to be passed back to the scheduler. Common monitors detect host reachability via ICMP echo messages, or connection to TCP services.

period
    A period in time as interpreted by the Time::Perl module.

alert
    A program which sends a message when invoked by the scheduler. The scheduler calls upon an alert when it detects a failure from a monitor. An alert program accepts a set of command-line arguments from the scheduler, in addition to data via standard input.

hostgroup
    A single host or list of hosts, specified as names or IP addresses.

service
    A collection of parameters used to deal with monitoring a particular resource which is provided by a group. Services are usually modeled after things such as an SMTP server, ICMP echo capability, server disk space availability, or SNMP events.

watch
    A collection of services which apply to a particular group.

OPERATION
When the mon scheduler starts, it reads a configuration file to determine the services it needs to monitor. The configuration file defaults to /etc/mon.cf, and can be specified using the -c parameter. The scheduler enters a loop which handles client connections, monitor invocations, and failure alerts. Each service has a timer, specified in the configuration file as the interval variable, which tells the scheduler how frequently to invoke a monitor process. The scheduler may be temporarily stopped. While it is stopped, client access still functions, but it just doesn't schedule things. This is useful in conjunction while resetting the server, because you can do this: save the hosts and services which are disabled, reset the server with the scheduler stopped, re-disabled those hosts and services, then start the scheduler. It also allows making atomic changes across several client connections. See the moncmd man page for more information.

MONITOR PROGRAMS
Monitor processes are invoked with the arguments specified in the configuration file, appended by the hosts from the applicable host group. For example, if the watch group is "servers", which contain the hostnames "smtp", "nntp", and "ns", and the monitor line reads as follows,
monitor fping.monitor -t 4000 -r 2
then the exectuable "fping.monitor" will be executed with these parameters:
MONITOR_DIR/fping.monitor -t 4000 -r 2 smtp nntp ns
MONITOR_DIR is /usr/lib/mon/mon.d, or the path specified by the -s option. If all hosts in the hostgroup have been disabled, then a warning is sent to syslog and the monitor is not run. This behavior may be overridden with the "allow_empty_group" option in the service definition. If the final argument to the "monitor" line is ";;" (it must be preceded by whitespace), then the host list will not be appended to the parameter list. "fping.monitor" should return an exit status of 0 if it completed successfully (found no problems), or nonzero if a problem was detected. The first line of output from the monitor script has a special meaning: it is used as a brief summary of the exact failure which was detected, and is passed to the alert program. All remaining output is also passed to the alert program, but it has no required interpretation. If a monitor for a particular service is still running, and the time comes for mon to run another monitor for that service, it will not start another monitor. For example, if the interval is 10s, and the monitor does not finish running within 10 seconds, then mon will wait until the first monitor exits before running another one. Upon a nonzero exit status, the associated alert program is started, pending the following criteria: If an alert for a specific service is disabled, do not send an alert. If an alert is not within the specified period, record the failure via syslog(3) and do not send an alert. If the failure falls within the defined period, and an alert was already sent within the last alertevery interval, do not send another alert, unless the output from the current monitor program differs from the last monitor process. Otherwise, send an alert using each alert program listed for that period.

ALERT PROGRAMS
Alert programs are found in the path supplied with the -a parameter, or in the /usr/lib/mon/alert.d directory if not specified. They are invoked with the following command-line parameters:

-s service
    Service tag from the configuration file.

-g group
    Host group name from the configuration file.

-h hosts
    The expanded version of the host group, space delimited, but contained in one shell "word".

-t secs
    The number of seconds left before another alert will be sent out.

-u  This option is supplied to an alert only if it is being called as an upalert.

The remaining arguments are supplied from the trailing parameters in the configuration file, after the "alert" service parameter. The first line from standard input must be used as a brief summary of the problem, normally supplied as the subject line of an email, or text sent to an alphanumeric pager. Interpretation of all subsequent lines read from stdin is left up to the monitoring program. The usual parameters are a list of recipients to deliver the notification to. The interpretation of the recipients is not specified, and is up to the alert program.

CONFIGURATION FILE
The configuration file consists of zero or more hostgroup definitions, and one or more watch definitions. Each watch definition may have one or more service definitions. A line beginning with optional leading whitespace and a pound ("#") is regarded as a comment, and is ignored.

  Global Variables
The following variables may be set to override compiled-in defaults. Command-line options will have a higher precedence than these definitions.

alertdir = dir
    dir is the full path to the alert scripts. This is the value set by the -a command-line parameter.

mondir = dir
    dir is the full path to the monitor scripts. This value may also be set by the -s command-line parameter.

statedir = dir
    dir is the full path to the state directory. mon uses this directory to save various state information.

histlength = num
    num is the the maximum number of events to be retained in history list. The default is 100. This value may also be set by the -k command-line parameter.

serverport = port
    port is the TCP port number that the server should bind to. This value may also be set by the -p command-line parameter.

pidfile = path
    path is the file the sever will store its pid in. This value may also be set by the -P command-line parameter.

maxprocs = num
    Throttles the number of concurrently forked processes to num. The intent is to provide a safety net for the unlikely situation when the server tries to take on too many tasks at once. Note that this situation has only been reported to happen when trying to use a garbled configuration file! You don't want to use a garbled configuration file now, do you?

randstart = secs
    When the server starts, normally all services will not be scheduled until the interval defined in the respective service section. This can cause long delays before the first check of a service, and possibly a high load on the server if multiple things are scheduled at the same intervals. This option is used to randomize the scheduling of the first test for all services during the startup period, and immediately after the reset command. If randstart is defined, the scheduled run time of all services of all watch groups will be a random number between zero and randstart seconds.

  Hostgroup Entries
Hostgroup entries begin with the keyword hostgroup, and are followed by a hostgroup tag and one or more hostnames or IP addresses, separated by whitespace. The hostgroup tag must be composed of alphanumeric characters, a dash ("-"), a period ("."), or an underscore ("_"). Non-blank lines following the first hostgroup line are interpreted as more hostnames. The hostgroup definition ends with a blank line. For example:
    hostgroup servers nameserver smtpserver nntpserver
    	nfsserver httpserver smbserver
    hostgroup router_group cisco7000 agsplus

  Watch Group Entries
Watch entries begin with a line that starts with the keyword watch, followed by whitespace and a single word which normally refers to a pre-defined hostgroup. If the second word is not recognized as a hostgroup tag, a new hostgroup is created whose tag is that word, and that word is its only member. Watch entries consist of one or more service definitions.

  Service Definitions

service
    A service definition begins with they keyword service followed by a word which is the tag for this service. The components of a service are an interval, monitor, and one or more time period definitions, as defined below.

interval
    The keyword interval followed by a time value specifies the frequency that a monitor script will be triggered. Time values are defined as "30s", "5m", "1h", or "1d", meaning 30 seconds, 5 minutes, 1 hour, or 1 day. The numeric portion may be a fraction, such as "1.5h" or an hour and a half.

randskew
    Rather than schedule the monitor script to run at the start of each interval, randomly adjust the interval specified by the interval parameter by plus-or-minus randskew . The skew value is specified as the interval parameter: "30s", "5m", etc... For example if interval is 1m, and randskew is "5s", then mon will schedule the monitor script some time between every 55 seconds and 65 seconds. The intent is to help distribute the load on the server when many services are scheduled at the same intervals.

monitor
    The keyword monitor followed by a script name and arguments specifies the monitor to run when the timer expires. Shell-like quoting conventions are followed when specifying the arguments to send to the monitor script. The script is invoked from the directory given with the -s argument, and all following words are supplied as arguments to the monitor program, followed by the list of hosts in the group referred to by the current watch group. If the monitor line ends with ";;" as a separate word, the host groups are not appended to the argument list when the program is invoked.

allow_empty_group
    The allow_empty_group option will allow a monitor to be invoked even when the hostgroup for that watch is empty because of disabled hosts. The default behavior is not to invoke the monitor when all hosts in a hostgroup have been disabled.

  Period Definitions
Periods are used to define the conditions which should allow alerts to be delivered.

period
    The period keyword takes an argument which is a period specification from Patrick Ryan's Time::Period Perl 5 module. Refer to "perldoc Time::Period" for more information. A period groups one or more alarms and variables which control how often an alert happens when there is a failure.

alertevery
    The alertevery keyword (within a period definition) takes the same type of argument as the interval variable, and limits the number of times an alert is sent when the service continues to fail. For example, if the interval is "1h", then only the alerts in the period section will only be triggered once every hour. If the alertevery keyword is omitted in a period entry, an alert will be sent out every time a failure is detected. By default, if the output of two successive failures changes, then the alertevery interval is overridden. If they word "summary" is the last argument, then only the summary output lines will be considered when comparing the output of successive failures.

alertafter
    The alertafter keyword (within a period section) takes two arguments: a positive integer followed by an interval, as described by the interval variable above. If this parameter is specified, then the alerts for that period will only be called after that many failures happen within that interval. For example, if alertafter is given the arguments "3 30m", then the alert will be called if 3 failures happen within 30 minutes.

alert
    A period may contain multiple alerts, which are triggered upon failure of the service. An alert is specified with the alert keyword, followed by an optional exit parmeter, and arguments which are interpreted the same as the monitor definition, but without the ";;" exception. The exit parameter takes the form of exit=x or exit=x-y and has the effect that the alert is only called if the exit status of the monitor script falls within the range of the exit parameter. If, for example, the alert line is alert exit=10-20 mail.alert mis then mail-alert will only be invoked with mis as its arguments if the monitor program's exit value is between 10 and 20. This feature allows you to trigger different alerts at different severity levels (like when free disk space goes from 8% to 3%). Alert programs are invoked with the following command-line parameters:

-s service name
    The service tag for this failure.

-g hostgroup
    The tag of the host group for this service.

-h hostgroup expansion
    All of the members in this hostgroup.

-t time
    The time (in time(2) format) of when this failure condition was detected.

-l alertevery
    The number of seconds until the next alarm will be sent.

-u  This option is supplied to an alert only if it is being called as an upalert.

upalert
    An upalert is the compliment of an alert. An upalert is called when a services makes the state transition from failure to success. The upalert script is called supplying the same parameters as the alert script, with the addition of the -u parameter which is simply used to let an alert script know that it is being called as an upalert. Multiple upalerts may be specified for each period definition.

upalertafter
    The upalertafter parameter is specified as a string that follows the syntax of the interval parameter ("30s", "1m", etc.), and controls the triggering of an upalert. If a service comes back up after being down for a time greater than or equal to the value of this option, an upalert will be called. Use this option to prevent upalerts to be called because of "blips" (brief outages).

AUTHENTICATION CONFIGURATION FILE
The file specified by the authfile variable in the configuration file (or passed via the -A parameter) will be loaded upon startup. This file defines restrictions upon which client commands may be executed by which users. It is a text file which consists of comments and command definitions. A comment line begins with optional whitespace followed by pound sign. Blank lines are ignored. A command definition consists of a command, followed by a colon, followed by a comma-separated list of users who may execute the command. The default is that no users may execute any commands. An example configuration file:
    list:		all
    reset:		root,admin
    loadstate:      	root
    savestate:      	root
This means that all clients are able to perform the list command, "root" is able to perform "reset", "loadstate", "savestate", and "admin" is able to execute the "reset" command.

CLIENT-SERVER INTERFACE
The server listens on TCP port 32777, which may be overridden using the -p port option. Commands are a single line each, terminated by a newline. Currently the server is iterative, accepting a single client at a time. This will change in future releases.

CLIENT INTERFACE COMMANDS
See manual page for moncmd.

EXAMPLES
The mon distribution comes with an example configuration called example.cf. Refer to that file for more information.

SEE ALSO
moncmd(1), Time::Period(3pm)

HISTORY
mon was written because I couldn't find anything out there that did just what I needed, and nothing was worth modifying to add the features I wanted. It doesn't have a cool name, and that bothers me because I couldn't think of one.

BUGS
Report bugs to the email address below.

AUTHOR
Jim Trocki <trockij@transmeta.com>