kapacitor log file formation

hello,
i have installed kapacitor on my linux machine and created a simple tick script it is as follows
stream
// Select just the cpu_usage_idle measurement from our example database.
|from()
.measurement('mem')
.where(lambda: "host" == "sgpl-ibm-omni1")
|alert()
.crit(lambda: "value" < 70)
// Whenever we get an alert write it to a file.
.log('/tmp/a.log')

after this i used a command like
kapacitor define alert -type "stream" -tick alert.tick-dbrp telegrafnew.default
then
kapacitor enable alert
now when i check /tmp/a.log the file didn't form
and the kapacitor log file looks like this

[httpd] ::1 - - [13/Apr/2017:13:42:35 +0530] "POST /write?consistency=&db=sentini786&precision=ns&rp=autogen HTTP/1.1" 204 0 "-" "InfluxDBClient" f3412e22-2020-11e7-b2f3-000000000000 468
[httpd] ::1 - - [13/Apr/2017:13:42:37 +0530] "POST /write?consistency=&db=telegraf&precision=ns&rp=autogen HTTP/1.1" 204 0 "-" "InfluxDBClient" f4c749f7-2020-11e7-b2f4-000000000000 360
[httpd] ::1 - - [13/Apr/2017:13:42:38 +0530] "POST /write?consistency=&db=test_telegraf&precision=ns&rp=autogen HTTP/1.1" 204 0 "-" "InfluxDBClient" f534131a-2020-11e7-b2f5-000000000000 2878
[httpd] ::1 - - [13/Apr/2017:13:42:38 +0530] "POST /write?consistency=&db=telegrafnew&precision=ns&rp=autogen HTTP/1.1" 204 0 "-" "InfluxDBClient" f58bf6e0-2020-11e7-b2f6-000000000000 692
[httpd] ::1 - - [13/Apr/2017:13:42:38 +0530] "POST /write?consistency=&db=telegrafnew&precision=ns&rp=autogen HTTP/1.1" 204 0 "-" "InfluxDBClient" f58c18d8-2020-11e7-b2f7-000000000000 518

Start with the supplied TICK script, the `kapacitor define` and `kapacitor enable` commands, and the contents of `/tmp/a.log` and the Kapacitor log. Reproduce the alert setup and determine why the `.log()` target is not created; done means the cause is identified and the expected file behavior is documented or verified.

Written by the indexing model from the issue text.