How to know if docker is already logged in to a docker registry server

Question

I m not sure if I have already logged in to a docker registry in cmd line by using cmd  docker login  How can you test or see whether you are logged in or not  without trying to push

User · Answer

My AWS ECR build-script has  ECR HOSTNAME  quot   ACCOUNT ID  dkr ecr   REGION  amazonaws com quot  TOKEN   jq -r   auths  quot   ECR HOSTNAME  quot    quot auth quot       docker config json  curl --fail --header  quot Authorization  Basic  TOKEN quot  https    ECR HOSTNAME v2   If accessing ECR fails  a login is done  aws ecr get-login-password --region   REGION    docker login --username AWS --password-stdin https    ECR HOSTNAME  For this to work  a proper Docker credential store cannot be used  Default credentials store of    docker config json is assumed

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On windows you can inspect the login  authorizations   auths  by looking at this file   USER HOME DIR  docker config json  Example   c  USERS YOUR USERANME docker config json  It will look something like this for windows credentials     auths          HOST NAME HERE            https   index docker io v1           HttpHeaders          User-Agent    Docker-Client 18 09 0  windows       credsStore    wincred    stackOrchestrator    swarm

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If you want a simple true false value  you can pipe your docker json to jq   is logged in       cat    docker config json   jq -r --arg url    REPOSITORY URL     auths   has  url      if       is logged in       false      then     do stuff  log in fi

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I use one of the following two ways for this check   1  View config json file   In case you are logged in to  private registry com  you will see an entry for the same as following in    docker config json    auths          private registry com              auth    gibberishgibberishgibberishgibberishgibberishgibberish             2  Try docker login once again   If you are trying to see if you already have an active session with private registry com  try to login again   bash  docker login private registry com Username  logged-in-user     If you get an output like the above  it means logged-in-user already had an active session with private registry com  If you are just prompted for username instead  that would indicate that there s no active session

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At least in  Docker for Windows  you can see if you are logged in to docker hub over the UI  Just right click the docker icon in the windows notification area

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Just checked  today it looks like this     docker login Authenticating with existing credentials    Login Succeeded   NOTE  this is on a macOS with the latest version of Docker CE  docker-credential-helper - both installed with homebrew

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The docker cli credential scheme is unsurprisingly uncomplicated  just take a look  cat    docker config json      quot auths quot          quot dockerregistry myregistry com quot            quot https   index docker io v1  quot       This exists on Windows  use Get-Content    docker config json  and you can also poke around the credential tool which also lists the username     and I think you can even retrieve the password    quot C  Program Files Docker Docker resources bin docker-credential-wincred exe quot  list   quot https   index docker io v1  quot   quot kcd quot

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As pointed out by  Christian  best to try operation first then login only if necessary  Problem is that  if necessary  is not that obvious to do robustly  One approach is to compare the stderr of the docker operation with some strings that are known  by trial and error   For example    try  docker OPERATION  if it failed       capture the stderr of  docker OPERATION      if it ends with  no basic auth credentials            try docker login     else if it ends with  not found           fatal error  image name tag probably incorrect     else if it ends with  lt other stuff you care to trap gt                   else          fatal error  unknown cause  try docker OPERATION again if this fails  you re SOL

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The answers here so far are not so useful    docker info no longer provides this info docker logout is a major inconvenience - unless you already know the credentials and can easily re-login docker login response seems quite unreliable and not so easy to parse by the program   My solution that worked for me builds on  noobuntu s comment  I figured that if I already known the image that I want to pull  but I m not sure if the user is already logged in  I can do this   try pulling target image - gt  on failure     try logging in    - gt  on failure  throw CannotLogInException    - gt  on success        try pulling target image       - gt  on failure  throw CannotPullImageException       - gt  on success   continue  - gt  on success   continue

User · Answer

For private registries  nothing is shown in docker info  However  the logout command will tell you if you were logged in      docker logout private example com  Not logged in to private example com    Though this will force you to log in again

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You can do the following command to see the username you are logged in with and the registry used    docker system info   grep -E  Username Registry

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Use command like below   docker info   grep  name   WARNING  No swap limit support Username   lt strong gt jonasm2009 lt  strong gt

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Edit 2020  Referring back to the  closed  github issue  where it is pointed out  there is no actual session or state       docker login actually isn t creating any sort of persistent session  it is only storing the user s credentials on disk so that when authentication is required it can read them to login   As others have pointed out  an auths entry node is added to the    docker config json file  this also works for private registries  after you succesfully login          auths                  https   index docker io v1                        When logging out  this entry is then removed     docker logout Removing login credentials for https   index docker io v1    Content of docker config json after          auths                 This file can be parsed by your script or code to check your login status    Alternative method  re-login   You can login to docker with docker login  lt repository gt     docker login Login with your Docker ID to push and pull images from Docker Hub  If  you don t have a Docker ID  head over to https   hub docker com to  create one  Username    If you are already logged in  the prompt will look like     docker login Login with your Docker ID to push and pull images from Docker Hub  If  you don t have a Docker ID  head over to https   hub docker com to  create one  Username  myusername             lt --  myusername    For the original explanation for the    docker config json  check question  how can I tell if I m logged into a private docker registry

[docker] How to know if docker is already logged in to a docker registry server

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