create help for check_docker_io

docs/20_Checks/check_docker_io.md

+## CHECK_DOCKER_IO
+
+Script: `check_docker_io`
+
+**check_docker_stats** shows the docker net io total and for each container.
+This check sends performance data.
+
+The first implemented measurement is the network io.
+
+This check starts the docker CLI and might be slow (a few seconds).
+
+## Requirements
+
+* `docker` Docker must be installed
+* `jq` must be installed - commandline JSON processor
+* `bc` must be installed - an arbitrary precision calculator language
+* sudo permissions on docker command
+
+```txt
+icingaclient ALL=(ALL) NOPASSWD:SETENV: /usr/bin/docker
+```
+
+## Standalone installation
+
+From this repository ypu need next to this script:
+
+* `inc_pluginfunctions` shared function for all IML checks written in bash
+* `inc_dockerfunctions.sh`
+
+## Rootless docker
+
+It works with docker setups as root and can handle rootless docker instances.
+
+To bring it up and running with an unpriviledged icinga user it must be able to access docker. Copy the docker binary eg. from /home/dockeruser/bin/docker to /usr/bin/. Then use the parameter `-p /usr/bin`.
+
+If DOCKER_HOST is not set then the docker socket is detected from a running docker instance and will be fetched from the process list.
+
+## Syntax
+
+```txt
+______________________________________________________________________
+
+CHECK_DOCKER_IO
+v0.1
+
+(c) Institute for Medical Education - University of Bern
+Licence: GNU GPL 3
+
+https://os-docs.iml.unibe.ch/icinga-checks/Checks/check_docker_io.html
+______________________________________________________________________
+
+Show IO data of all docker containers
+
+USAGE:
+  check_docker_io [OPTIONS]
+
+OPTIONS:
+
+  General:
+  -h, --help        this help
+
+  Connect to docker:
+  -p, --path        Custom directory for docker binary
+  -t, --target      Custom docker target; value for DOCKER_HOST
+                    Needed only if Docker does not run on a unix socket or
+                    multiple users run a rootless docker daemon.
+
+  mode:
+  -m, --mode MODE   Mode what kind of information to show.
+                    The output of container list is sorted by the maximum 
+                    value first.
+
+                      netio     sum of netio of all containers IN and OUT
+
+EXAMPLES:
+  check_docker_io -m netio
+    Show netio of all docker containers
+
+```
+
+### Parameters
+
+None.
+
+## Examples
+
+### Network io
+
+`$ ./check_docker_io -m netio`
+
+```txt
+OK: Docker Network I/O of all containers: 0.00 MB/s IN .. 0.00 MB/s OUT
+portainer_agent.1cnjqw9p0nlmpaij393abu0ng.rwy5mv629o0yxonz5f6krasz5    5670551      36804         392 B/s           2 B/s
+morpheus-live_morpheus-live.2.w1umgrc21kvinl6h2x2cqdkze   55671295      13944           0 B/s           0 B/s
+morpheus-live_morpheus-live.1.10npyt2qnb1kzvta851i9mtvd   54929047      12883           0 B/s           0 B/s
+morpheus-demo_morpheus-demo.1.nsf410w59q9g1an7iyf0j12lr     161951       1620           0 B/s           0 B/s
+swarm_proxy_reverse-proxy.1.hw7snlg5i0sudyh58ydf02rtc  498606567    4208586         455 B/s           5 B/s
+swarm_proxy_memcached.1.c8gimogel0k9iffffiyw3k9l4   11679831     167671          16 B/s           0 B/s
+whoami_whoami.1.mguqldgk3pxuqsuw1ir0d5xjz     155845       2027           0 B/s           0 B/s
+portainer_monitoring_se_node-exporter.1cnjqw9p0nlmpaij393abu0ng.ncfvhpy81tq5pp9i9o6qzs2ih   32668084     301076          34 B/s           0 B/s
+portainer_monitoring_se_cadvisor.1cnjqw9p0nlmpaij393abu0ng.lr7xkpgdu43lkihcr0agj0vh6   88027743    1139668          93 B/s           1 B/s
+ |rx=990;; tx=10;; 
+```
+
+## Troubleshooting
+
+### Missing environment
+
+```txt
+sudo: sorry, you are not allowed to preserve the environment
+UNKNOWN: No data. Unable to fetch Docker information.
+```
+
+Solution: you did not set SETENV in the sudoers config file
+
+icingaclient ALL=(ALL) NOPASSWD:**SETENV:** /usr/bin/docker
+
+### Docker not found
+
+If you get an error message that docker was not found then it is not reachable in ofe of the directories of $PATH.
+This can happen especialy in rootless docker instances.
+
+Solution: Use the parameter `-p /usr/bin` to define a target. Copy the docker binary there.