August 2020

  Docker prettify docker ps output
August 1   |   Docker

Everytime I run docker ps to list my containers, I find hard to understand where does the list start and where it ends:

What the! ... the port, which one? ... I almost feel like I'm seeing the matrix

I have to say, after some time your eyes get used to and begin to do weird movements but at the end you begin to understand the output, of course it shouldn't be this way, so I found there are server ways to improve the command output, let's take a look.

Use —format

Use the option --format, using this we can choose from a list of fields (see the table below) and display them in a ordered layout using the following syntax table {{.FieldName}}\t. The format option uses Go templates underneath, hey that looks familiar to me1.

table print the field name and \t adds space between columns.

 Example using --format


 docker ps --format 'table {{.Names}}\t
                           {{.Status}} : {{.RunningFor}}\t

And we got this :
Definitely a better command output so much easy to read and understand

Taking advantage of Go Templates

We can get creative with Go Templates and lets query our containers to get network information including ports (a clean output would be to show every port in his own line but only if ports are used):

 Network information


docker ps --format 'table {{.Names}}
                          {{if .Ports}}
                            {{with $p := split .Ports ", "}}
                              {{range $p}}\t\t{{println .}}{{end}}
                            \t\t{{println "No Ports"}}

Here you have, we can get all network data in a more readable way

All containers docker ps –a

Using the option ps -a will list all containers in any state. So it would be nice to add the disk space, a summary of the network use and the image from where the container derives.

 All containers list


docker ps -a -q --format 'table {{.Names}}\t
                                {{if .Ports}}
                                  {{with $p := split .Ports ", "}}\t
                                    {{len $p}} port(s) on {{end}}{{- .Networks}}
                                  {{else}}\tNo Ports on {{ .Networks }}

Look at this! An easier way to spot information about all containers.

Create a function to reuse the commands

Finally we can create a function to reuse these commands (if you are using WSL or Linux) inside our .bash_aliases file

 Create a bash function that allows parameters


# Docker PS Prettify Function
function dock() {
  if [[ "$@" == "ps" ]]; then
    command docker ps --format 'table {{.Names}}\t{{.Status}} : {{.RunningFor}}\t{{.ID}}\t{{.Image}}'
  elif [[ "$@" == "psa" ]]; then
    # docker ps -a includes all containers
    command docker ps -a --format 'table {{.Names}}\t{{.Status}}\t{{.Size}}\n{{.ID}}\t{{.Image}}{{if .Ports}}{{with $p := split .Ports ", "}}\t{{len $p}} port(s) on {{end}}{{- .Networks}}{{else}}\tNo Ports on {{ .Networks }}{{end}}\n'
  elif [[ "$@" == "psnet" ]]; then
    # docker ps with network information
    command docker ps -a --format 'table {{.Names}}\t{{.Status}}\t{{.Networks}}\n{{.ID}}{{if .Ports}}{{with $p := split .Ports ", "}}{{range $p}}\t\t{{println .}}{{end}}{{end}}{{else}}\t\t{{println "No Ports"}}{{end}}'
    command docker "$@"

To use the function just type:

dock ps
List running containers and its image name
dock psa
List all containers no matter what state and includes disk space and network information
dock psnet
List running containers with detailed network information

Available fields in docker

Container ID
Image ID
Quoted command
Time when the container was created.
Elapsed time since the container was started.
Exposed ports.
Container status.
Container disk size.
Container names.
All labels assigned to the container.
Value of a specific label for this container. For example ‘{{.Label “com.docker.swarm.cpu”}}’
Names of the volumes mounted in this container.
Names of the networks attached to this container.

  1. This blog uses HUGO, and HUGO uses GoLang html and text templates. ↩︎

March 2020

  Docker network name is ambiguous
March 25   |   Docker

The Issue

I was working on my Linux server, and I had to restart it. The docker instance was empty when the server came back, and it didn't show any container. I was in shock, and I thought I had lost my images and containers. After reviewing the system's health couldn't found a root cause, so I did a second restart 😅 and that's it the containers were back. Great! But when I tried to start my containers …

ERROR: network xxxx is ambiguous (2 matches found based on name)

The Whys

I found that docker allows repeating network names 👻; my hunch here is that when the system restarted something (maybe my container disk didn't mount properly), docker recreated the network configuration. As you can see in the following table, it duplicated every network and driver

 docker network list


$ docker network ls
27b6c27fdc2b bridge bridge local
33f2a0c04878 bridge bridge local
c4247d693521 host host local
9b95be563bf7 host host local
590102262bb5 none null local
25e1bf9dc86 none null local

So the solution appeared to be, just to delete one of the duplicate networks by his ID. I tried to execute the following command docker network rm [ID]

Error : bridge is a pre-defined network and cannot be removed

What the … this was more tricky than what I initially thought, at some forum, I found some arbitrary advice:

  1. The docker service must be stopped
  2. There shouldn't be a container using the network
  3. And another workaround is not to have containers (delete them)

If you need to see which containers are using which network use:

 Inspect network ID of a container


# Note that in this scenario since bridge is repeated you'll need to do it by Id:
docker network inspect [id || name]

"Internal": false,
{ "Network": "" },
"ConfigOnly": false,
"Containers": {},


So, at this point option one and two didn't work and I couldn't afford to delete all my containers which there were already configured with his own volumes and startup scripts.

Workaround and Solution

  1. Create a new network. Use the parameter -d to specify the driver

    docker network create -d bridge [new-network-name]

  2. Disconnect the container(s) from the ambiguous network

    docker network disconnect bridge [container-name]

  3. Connect the container(s) to the new network

    docker network connect [new-network-name] [container-name]

  4. Optional. Purge our network and get rid off of the unused networks

    docker network rm $(docker network ls -q)

And that's all, now we should be able to start our containers.

docker start my-happy-container