More Hooks

#Hooks

Hooks are points during the cronjob process where you can execute custom scripts at the beginning, at the end and during the process.

All hooks are located in the ./hooks/ directory.

We have hooks “before” a job starts and “afterwards”.

Below all hook directories have the subdirectory “always”: ./hooks/[Name-of-hook]/always/

hooks
|-- after
|   |-- always
|   |-- on-error
|   `-- on-ok
`-- before
    `-- always

#“before” actions

They don’t know an execution status of something. They can execute only scripts that are located in “always” subdirectory.

#“after” actions

The “afterwards” added hooks know the execution status of the last action. That’s why in the hook directory we have additionally the subdirs

./hooks/[Name-of-hook]/on-ok/ - the last action was 0 (zero)
./hooks/[Name-of-hook]/on-error/ - if the exitcode was non-zero

After execution of the scripts of “on-ok” or “on-error” folder. Then additionally the found scripts of “always” folder will be executed.

#Order of multiple scripts

You can place multiple scripts into the subdirs on-ok|on-error|always. To be executed a file must have execution permissions.

Their order for execution is alphabetic (by using the sort command). Suggestion is to add numbers in front of a script name.

#What variables you can access..

Your hooks maybe want to access a few information to send a notification or whatever. These data may help you to generate a message.

variable	type	description
CW_CALLSCRIPT	{string}	executed command line
CW_FINALOUTFILE	{string}	filename of the final logfile of the job to send as information
CW_LABELSTR	{string}	label of the job
CW_OUTFILE	{string}	filename of the still running cronjob (for after//); you can grep its content eg. “^SCRIPTOUT=” (see Output)
CW_MYHOST	{string}	hostname
CW_TIMER_START	{int}	Unix timestamp of the starting time
CW_TIMER_END	{int}	Unix timestamp of the ending time (for after//)
TTL	{int}	ttl value in minutes
iExectime	{int}	execution time in seconds (for after//)
rc	{int}	resturncode of the failed job (for after/on-error/*)

#Exitcode

The exitcode of a hook script is not relevant. The returncode of the cronjob will be preserved.

#Example

#Send an email if a job failed

Requirements:

To send an email you need to install a MTA like sendmail or postfix locally and configure it to be able to send trusted emails via your smtp gateway.

Create a script as root eg. hooks/after/on-error/send_email.sh.

Make it executable chmod 0755 hooks/after/on-error/send_email.sh

Content of send_email.sh:

#!/bin/bash

TO=sysadmin@example.com
SUBJECT="Cronjob on ${CW_MYHOST} - ${CW_LABELSTR} failed with rc=${rc}"

cat "${OUTFILE}" | mail -s "${SUBJECT}" ${TO}