How to get the hostname of the docker host from inside a docker container on that host without env vars

Question

What are the ways get the docker host s hostname from inside a container running on that host besides using environment variables  I know I can pass the hostname as an environment variable to the container at container creation time  I m wondering how I can look it up at run time   foo example com  docker host    bar  docker container    Is there a way for container bar running in docker host foo example com to get  foo example com    Edit to add use case   The container will create an SRV record for service discovery of the form   service  proto name  TTL class SRV priority weight port target  -----------------------------------------------------------------  bar  http example com 60 IN SRV 5000 5000 20003 foo example com    where 20003 is a dynamically allocated port on the docker host for a service listening on some fixed port in bar  docker handles the mapping from host port to container port    My container will run a health check to make sure it has successfully created that SRV record as there will be many other bar containers on other docker hosts that also create their own SRV records    service  proto name  TTL class SRV priority weight port target  -----------------------------------------------------------------  bar  http example com 60 IN SRV 5000 5000 20003 foo example com   lt --  bar  http example com 60 IN SRV 5000 5000 20003 foo2 example com   bar  http example com 60 IN SRV 5000 5000 20003 foo3 example com    The health check will loop through the SRV records looking for the first one above and thus needs to know its hostname   aside  I m using Helios and just found out it adds an env var for me from which I can get the hostname  But I was just curious in case I was using docker without Helios

User · Answer

You can easily pass it as an environment variable

docker run .. -e HOST_HOSTNAME=`hostname` ..

using

-e HOST_HOSTNAME=`hostname`

will call the hostname and use it's return as an environment variable called HOST_HOSTNAME, of course you can customize the key as you like.

note that this works on bash shell, if you using a different shell you might need to see the alternative for "backtick", for example a fish shell alternative would be

docker run .. -e HOST_HOSTNAME=(hostname) ..

User · Answer

I m adding this because it s not mentioned in any of the other answers   You can give a container a specific hostname at runtime with the -h directive     docker run -h my docker container example com ubuntu latest   You can use backticks  or whatever equivalent your shell uses  to get the output of hosthame into the -h argument     docker run -h  hostname  ubuntu latest   There is a caveat  the value of hostname will be taken from the host you run the command from  so if you want the hostname of a virtual machine that s running your docker container then using hostname as an argument may not be correct if you are using the host machine to execute docker commands on the virtual machine

User · Answer

I ran  docker info   grep Name    xargs   cut -d    -f2   inside my container

User · Answer

I know it s an old question  but I needed this solution too  and I acme with another solution   I used an entrypoint sh to execute the following line  and define a variable with the actual hostname for that instance   HOST  hostname --fqdn    Then  I used it across my entrypoint script   echo  Value   HOST    Hope this helps

User · Answer

You can pass it as an environment variable like this   Generally Node is the host that it is running in   The hostname is defaulted to the host name of the node when it is created   docker service create -e  FOO    Node Hostname    nginx     Then you can do docker ps to get the process ID and look at the env    docker exec -it c81640b6d1f1 env                                                                                                                                    PATH  usr local sbin  usr local bin  usr sbin  usr bin  sbin  bin HOSTNAME c81640b6d1f1 TERM xterm FOO docker-desktop NGINX VERSION 1 17 4 NJS VERSION 0 3 5 PKG RELEASE 1 buster HOME  root   An example of usage would be with metricbeats so you know which node is having system issues which I put in https   github com trajano elk-swarm     metricbeat      image  docker elastic co beats metricbeat 7 4 0     volumes        -  var run docker sock  var run docker sock ro       -  sys fs cgroup  hostfs sys fs cgroup ro       -  proc  hostfs proc ro       -    hostfs ro     user  root     hostname      Node Hostname        command        - -E       -           metricbeat modules                           module docker              hosts  unix    var run docker sock               period 10s              enabled true                              - -E       - processors  1  add docker metadata  host unix    var run docker sock           - -E       - output elasticsearch enabled false       - -E       - output logstash enabled true       - -E       - output logstash hosts   logstash 5044       deploy        mode  global

User · Answer

You can pass in the hostname as an environment variable   You could also mount  etc so you can cat  etc hostname   But I agree with Vitaly  this isn t the intended use case for containers IMO

User · Answer

Another option that worked for me was to bind the network namespace of the host to the docker   By adding   docker run --net host

User · Answer

I think the reason that I have the same issue is a bug in the latest Docker for Mac beta  but buried in the comments there I was able to find a solution that worked for me  amp  my team  We re using this for local development  where we need our containerized services to talk to a monolith as we work to replace it  This is probably not a production-viable solution   On the host machine  alias a known available IP address to the loopback interface     sudo ifconfig lo0 alias 10 200 10 1 24   Then add that IP with a hostname to your docker config  In my case  I m using docker-compose  so I added this to my docker-compose yml   extra hosts    configure your host to alias 10 200 10 1 to the loopback interface          sudo ifconfig lo0 alias 10 200 10 1 24 -  relevant hostname 10 200 10 1    I then verified that the desired host service  a web server  was available from inside the container by attaching to a bash session  and using wget to request a page from the host s web server     docker exec -it container name  bin bash   wget relevant hostname index html   cat index html

[docker] How to get the hostname of the docker host from inside a docker container on that host without env vars

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