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snaked-0.05
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/ snaked

NAME

snaked - cron as it should be.

SYNOPSIS

# import old cron jobs (TO BE IMPLEMENTED)
snaked --import-crontabs

# check which jobs are configured
snaked --show-jobs

# rock with snake
snaked --daemon

# (and do not forget to stop old cron
# so your jobs are not run twice)

DESCRIPTION

snaked is a job scheduler, just like cron, which has several unique features making it much more flexible and useful than any other cron implementation.

It is heavily tested on Linux and FreeBSD but might (and hopefully with your help will) be run on any Perl + POSIX compliant system.

limit job execution time

You can choose to configure the maximum limit of time for each job to finish. If job doesn't finish in time it is killed. The limit is independently configurable for each job. Forget about lockf, ps -ef | grep -v grep and cron jobs being run twice and more times concurrently.

You can also configure the upper limit of execution time of any job of the given snaked instance. This global limit is checked independently of the individual job execution time limits.

unique job id and job dependencies

Each snaked job has its unique job identifier which is used to configure job dependencies: for any job you can specify other jobs (addressed by their identifiers) which shouldn't be run with this job concurrently.

So if job A is being executed and time comes to start job B which is configured as conflicting with job A, then the start of job B is postponed until job A is finished.

more often than once a minute

snaked allows jobs to be run more often than once a minute.

Actually snaked supports two execution schedule formats: old cron format with not less than a minute time resolution and snaked job schedule format which specifies how often the jobs is run in seconds, making it possible to run job even once a second!

CONFIGURATION EXAMPLE

snaked configuration is a directory which contains global instance options (each option in separate file) and associated job definitions where job definition is also a directory with each job option stored in a separate file:

.
|-- admin_email
|-- jobs
|   |-- every_hour
|   |   |-- cmd
|   |   `-- execution_schedule
|   |-- every_ten_seconds
|   |   |-- cmd
|   |   `-- execution_interval
|   `-- fast_job
|       |-- cmd
|       |-- conflicts
|       `-- execution_interval
`-- log

Above shown configuration defines admin_email for the snaked instance (optional, defaults to root) and log file path (optional, defaults to /tmp/snaked.log):

testing18:/etc/snaked# cat admin_email
root
testing18:/etc/snaked# cat log
/var/log/snaked/snaked.log

There are three jobs named every_hour, every_ten_seconds and fast_job. All of them contain cmd file -- an executable which is run by snaked (this can be any executable allowed by underlying operating system):

testing18:/etc/snaked/jobs/every_hour# ls -l cmd
-rwxr-xr-x 1 root root 0 2010-07-07 00:24 cmd
testing18:/etc/snaked/jobs/every_hour# file cmd
cmd: POSIX shell script text executable

First job, every_hour, has a parameter execution_schedule which is an old cron schedule example (parsed by Schedule::Cron::Events):

testing18:/etc/snaked/jobs/every_hour# cat execution_schedule
0 * * * *

Two other jobs use snaked execution_interval schedule, specifying that every_ten_seconds job should be run once in ten seconds, and fast_job should be run once in every second.

testing18:/etc/snaked/jobs/every_ten_seconds# cat execution_interval
10
testing18:/etc/snaked/jobs/fast_job# cat execution_interval
1

To make it a bit more explanatory we've defined conflicts option for fast_job which specifies that fast_job should not be run if every_ten_seconds is running:

testing18:/etc/snaked/jobs/fast_job# cat conflicts
every_ten_seconds

Which translates to "try to run 'fast_job' as often as once a second, but wait if 'every_ten_seconds' job is running".

DAEMON OPTIONS

admin_email

Optional. Where to send emails about failing jobs. Defaults to root.

log

Optional. Name of the log filename which holds all the log messages including informational and error messages. Defaults to /tmp/snaked.log.

log_errors

Optional. Name of the log filename used only for error messages. Defaults to nothing, turning off separate error logging.

log_rotate_size

Optional. Size of the log file after which it is rotated. Defaults to 10 MB.

log_rotate_keep_copies

Optional. Number of rotated log files to preserve. Defaults to 2.

max_job_time

Optional. Specifies maximum exeuction time limit for all the jobs. Defaults to 2 hours.

pidfile

Optional. Filename of the pidfile where snaked stores the pid of its main process. Defaults to nothing, which does not generate any pidfile.

JOB OPTIONS

admin_email

Optional. Where toe send emails about failures of this job. Defaults to global admin_email option (and overrides it).

cmd

Mandatory. Executable with correct file permissions (executable bit on) which is allowed by underlying operating system. Can be shell script or binary.

execution_interval, execution_schedule

Only one parameter, execution_interval or execution_schedule, is allowed and is mandatory for one job. execution_interval specifies number of seconds (positive integer) between invocations of cmd. execution_schedule specifies standard cron format schedule (first five fields) for the job.

execution_timeout

Optional. Specifies time limit for the job, in seconds. Defaults to nothing, turning time limit off.

kill_timeout

Optional. Specifies time in seconds between TERM and KILL signals sent to the job when snaked needs to stop the job (when snaked stop or restarts, when job runs too long). Defaults to 60 seconds.

notification_interval

Optional. Time period in seconds. Job failure emails are not sent more often than this time period. First email is sent after first time period of constant failures. This option is used to suppress emails about accidental job failures. Defaults to 0, which turns the feature off (delivers email on every job failure).

start_random_sleep

Optional. Time period in seconds which specifoes random first run shift in time for the job. Defaults to 0, which turns the feature off.

conflicts

Optional. Space/line separated list of job identifiers which should not be run while this job is run. If any job from this list is currently being executed then the job owning the option will not be executed. Defaults to nothing, allowing the job to be run independently of the status of any other job.

snaked organizes conflicting jobs into job groups, running every job from the job group one by one (if the time for the job has come). This guarantees that every conflicting job is run from time to time though its start time might be shifted because of waiting for the conflicting jobs.

CREDITS

Thank you to Yandex team (in alphabetic order):

Denis Barov
Maxim Dementyev
Eugene Fedotov
Andrey Grunau
Andrey Ignatov
Dmitry Parfenov
Alexey Simakov
Julie S Ukhlicheva
Anton Ustyugov
Andrey Zonov

for their bug reports, suggestions and contributions.

AUTHORS

Petya Kohts <petya@kohts.ru>

COPYRIGHT

Copyright 2009 - 2010 Petya Kohts.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.