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"When do bash signal handlers NOT work?"

March 19th, 2019

Just in case somebody else runs into this frustrating situation, (at least on RHEL 7) bash shell scripts trying to catch SIGINT do not work when the signal is sent to the process from another pid and your bash script is running a non-shell built-in.

Yesterday I was attempting to mock out a linux command to verify the behavior of a shell script I wrote. The goal was to be able to test the shell script's behavior without actually invoking the particular linux command (see pbench PR #1108). One feature of the script being tested was sending a SIGINT to another process, being sure the script had properly identified the correct process.

There is a nice blog about how to write signal handlers for bash, well worth the read [1]. Using that blog, I came up with a very simple mock command shell script:

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#!/usr/bin/env python2

# A script to generate a report of Elasticsearch shard usage
# (from _cat/shards?v&bytes=b) to see which shards of an index
# are not evenly spread across the cluster, and for a set of
# hard-coded date patterns, which date patterns are not spread
# evenly across the cluster.
#
# E.g.
# $ curl -X GET http://localhost:9200/_cat/shards?v\&bytes=b -o shards.lis

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What to do about so many empty merge commits?

I think it has to do with a branch "merging" up to master by using git merge/pull instead of using git rebase.

If you make a change in a branch from a particular commit ID on master, and then master moves ahead, and you use git merge to update that branch, git gratuitously creates "merge commits" which cover the changes made to automatically merge the new changes since your change was made on master.

In contrast, a git rebase (assuming you have properly setup remote tracking with git branch --set-upstream-to=...) takes your commits (really the diffs those commits represent) and re-applies it to the latest on the tracking branch adjusting your commits to work on top of that rebase.

For example, let's say we have master with commits A, B, and C:

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# August 15th, 2018
# from pbench-uperf
function record_iteration {
        local count=$1
        local protocol=$2
        local test_type=$3
        local message_size=$4
        local instance=$5
        local iteration=$6

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! Traceback (most recent call last):
!   File "/opt/rh/rh-python36/root/usr/lib/python3.6/site-packages/urllib3/connectionpool.py", line 387, in _make_request
!     six.raise_from(e, None)
!   File "<string>", line 2, in raise_from
!   File "/opt/rh/rh-python36/root/usr/lib/python3.6/site-packages/urllib3/connectionpool.py", line 383, in _make_request
!     httplib_response = conn.getresponse()
!   File "/opt/rh/rh-python36/root/usr/lib64/python3.6/http/client.py", line 1331, in getresponse
!     response.begin()
!   File "/opt/rh/rh-python36/root/usr/lib64/python3.6/http/client.py", line 297, in begin
!     version, status, reason = self._read_status()

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#!/usr/bin/env python2

# A script to generate a report of Elasticsearch index usage
# (from _cat/indices?v&bytes=b) by prefix for a set of known
# date suffixes.
#
# E.g.
# $ curl -X GET http://localhost:9200/_cat/indices?v\&bytes=b -o indices.lis
# $ ./sum-es-indices.py indices.lis
#

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#!/bin/bash

ES_URL='https://localhost:9200'
curl_get='curl -s -X GET --cacert /etc/elasticsearch/secret/admin-ca --cert /etc/elasticsearch/secret/admin-cert --key /etc/elasticsearch/secret/admin-key'

date
$curl_get $ES_URL/_cluster/pending_tasks?pretty

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#!/bin/bash

ES_URL='https://localhost:9200'
curl_put='curl -s -X PUT --cacert /etc/elasticsearch/secret/admin-ca --cert /etc/elasticsearch/secret/admin-cert --key /etc/elasticsearch/secret/admin-key'

$curl_put $ES_URL/_cluster/settings?pretty -d "{\"persistent\" : {\"threadpool.bulk.queue_size\" : $1}}"

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#!/bin/bash

function finish {
    rm -rf $TMPDIR
}
trap finish EXIT
TMPDIR=$(mktemp -d)

oc get nodes -o name > $TMPDIR/all-nodes
oc get nodes -o name -l logging-infra-fluentd=true > $TMPDIR/labeled-nodes

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#!/bin/bash

ES_URL='https://localhost:9200'
curl_head='curl -w %{http_code}\n -s -X HEAD --cacert /etc/elasticsearch/secret/admin-ca --cert /etc/elasticsearch/secret/admin-cert --key /etc/elasticsearch/secret/admin-key'

$curl_head $ES_URL/${1}?pretty=true