Ошибка cannot connect to daemon

Docker – одна из ведущих платформ для создания и запуска программных контейнеров.

Он поставляется со всем необходимым для использования контейнеров как на одном узле, так и на нескольких распределенных узлах в режиме Swarm.

Docker имеет архитектуру, основанную на демонах.

Программное обеспечение, отвечающее за создание и запуск контейнеров, не зависит от процесса CLI, который принимает ваши команды.

Это означает, что вы увидите ошибки в CLI, если попытаетесь выполнить команды без активного соединения с демоном.

В этой статье мы поделимся некоторыми методами устранения этих разочаровывающих сообщений.

Симптомы проблемы

Docker CLI зависит от наличия соединения с демоном.

Он взаимодействует с демоном с помощью вызовов API.

Когда настроенный демон недоступен, команды docker, такие как docker ps, docker run и docker build, выдают сообщение об ошибке, подобное этому:

$ docker run hello-world:latest
Cannot connect to the Docker daemon at unix:///var/run/docker.sock
Is the docker daemon running?

Система показывает, что CLI пытался установить связь с демоном Docker, используя Unix-сокет /var/run/docker.sock.

Сокет не открыт, поэтому соединение не удалось.

1. Проверьте, запущена ли служба демона Docker

Демон Docker обычно управляется службой systemd, которая автоматически запускает Docker после перезагрузки хоста.

Устранение неполадок можно начать с проверки того, запущена ли эта служба:

$ sudo systemctl status docker
docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: inactive (dead)

$ sudo systemctl start docker

$ sudo systemctl enable docker
$ sudo systemctl daemon-reload

$ sudo dockerd
INFO[2022-06-29T15:12:49.303428726+01:00] Starting up

$ docker run hello-world:latest
Cannot connect to the Docker daemon at tcp:///0.0.0.0:2375

$ docker context use default

$ docker context ls
NAME        DESCRIPTION                               DOCKER ENDPOINT             
default *   Current DOCKER_HOST based configuration   unix:///var/run/docker.sock

$ export DOCKER_HOST=1.2.3.4
$ docker context ls
NAME        DESCRIPTION                               DOCKER ENDPOINT
default *   Current DOCKER_HOST based configuration   tcp://1.2.3.4:2375
Warning: DOCKER_HOST environment variable overrides the active context. To use a context, either set the global --context flag, or unset DOCKER_HOST environment variable.

$ export DOCKER_HOST=

$ docker context ls
NAME        DESCRIPTION                               DOCKER ENDPOINT             
default *   Current DOCKER_HOST based configuration   unix:///var/run/docker.sock

$ docker run hello-world:latest
Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock

АБР не открыта во время отладки АБР.

Как показано на рисунке, неправильная подсказка:

    * daemon not running.starting it now on port 5037*

    CreateProcess failure，error 2

    * failed to start daemon *

    error：cannot connect to daemon

Если вы столкнулись с этой ситуацией, просто введите команду в командной строке.

adb nodaemon server

Не выключайте это окно после ввода команды, чтобы открыть новую CMD, ADB может использовать его нормально

Introduction

Users new to Docker may find it difficult to use as they often encounter an issue right after installing it. The “cannot connect to the Docker daemon” error in Docker usually happens when running the docker-compose build command.

In this tutorial, we will go over possible causes of the “cannot connect to the Docker daemon” error and the ways you can solve it.

Prerequisites

• Access to the command line or terminal
• A working Docker installation

There are several ways to fix the “cannot connect to the Docker daemon” error. If one solution doesn’t work for you, move on to the next method until you resolve the issue.

Method 1: Check the Docker Engine

If the Docker engine is not running, docker-compose can’t access it, which produces the error.

1. First, check if the Docker engine is running:

sudo service docker status

2. If the Docker engine isn’t working, start it with the following command:

sudo service docker start

3. After you start the Docker engine, try running the docker-compose build command again. If the error persists, try one of the following solutions.

Method 2: Assign Ownership to the Docker Unix Socket

The “cannot connect to the Docker daemon” error also happens if the Unix socket file for Docker doesn’t have the correct ownership assigned.

1. Check ownership for the Docker Unix socket:

sudo ls -la /var/run/docker.sock

2. If necessary, grant the user ownership with:

sudo chown [username]:docker /var/run/docker.sock

Method 3: Check the Ownership of Used Files

Ownership issues can also extend to files used by your Docker build. If Docker needs to use a file it can’t access, this results in a “cannot connect to the Docker daemon” error.

1. Run the docker build command for each individual container. This gives you a detailed output that points out any potential errors.

2. Check the output for each container, keeping an eye out for an “cannot connect to the Docker daemon” error report. If there is a problem with the file ownership, the error report will list out the files that the docker build command cannot access.

3. There are several ways to resolve the issue of ownership of used files:

• You can simply remove the files in question by deleting them, but this affects any other builds using the same files.
• Another method is to add the .dockerignore file to your current build, thus excluding the files your build can’t access.
•  Finally, you can change the file ownership with:

sudo chown [username]:docker /your/file/location

Method 4: Add Your User to the Docker Group

Not having the proper user privileges also triggers the error. You need to be able to access the Docker engine without using the sudo command.

1. To solve this issue, add the current user to the Docker group via usermod command:

sudo usermod -aG docker [username]

2. Log out and back in to confirm the changes.

Method 5: Add Environment Tables on OS X

If you are running Docker on OS X, you may have to add environment variables:

1. First, start the Docker virtual machine:

docker-machine start

2. Get the environment variables for Docker with:

docker-machine env

3. Finally, set the environment variables:

eval "$(docker-machine env default)"

Conclusion

After following this tutorial, you should be aware of the potential causes of the “cannot connect to the Docker daemon” error and ways to fix each one.

Learn Docker container management best practices for an efficient and safe Docker environment.

Docker is a popular way to build and run software containers. You can use it to work with containers on a single computer or across multiple computers using Swarm mode.

Docker uses a special kind of architecture called “daemon-based”. This means that the program that actually creates and starts containers is separate from the program that accepts your commands. So if you try to run commands without an active connection to the daemon, you might see some errors in the program that accepts your commands. In this article, we’ll show you how to deal with these annoying error messages.

Error Manifestation

To use the Docker CLI, you need to have a connection to the daemon. The CLI talks to the daemon by making API calls. If the daemon is not available, you might see error messages like the following when you try to run commands like “docker ps”, “docker run”, or “docker build”:

This means that the Docker CLI attempted to connect to the Docker daemon using the Unix socket located at /var/run/docker.sock, but the socket was closed, which resulted in the connection failing.

Read: How to install and setup Docker on Linux/Ubuntu 18.04

Solutions

Here are some tips that can help you solve the error: Cannot Connect to the Docker Daemon.

Docker daemon service is currently active and running ?

Normally, the Docker daemon is controlled by a systemd service that starts Docker automatically whenever your computer restarts. To start investigating the issue, you should verify whether this service is currently running:

sudo systemctl status docker

You can check our example here, how the output will look like.

To start Docker, run the command:

sudo systemctl start docker

You should now be able to execute Docker CLI commands without any issues.

Sometimes after a machine reboot, Docker may remain in the stopped state. To resolve this, you can enable the service and allow systemd to automatically start it. Here is how to do it :

sudo systemctl enable docker

sudo systemctl daemon-reload

Read: How to run and manage a Docker container on Linux Ubuntu/Debian

Verifying that the CLI is pointing to the correct daemon.

Difficulties may arise when attempting to establish a connection between the CLI and a remote Docker daemon instance. This is typically the case if the error message displays a TCP address.

Cannot connect to the Docker daemon at tcp://localhost:2375/

The problem in this situation is that the docker CLI is attempting to communicate with the Docker daemon at tcp://localhost:2375/ using TCP, rather than through the local Unix Docker socket. This will not work if the Docker daemon’s TCP functionality is disabled, or if the given host cannot be reached on the network.

To fix this issue, you can usually switch to the correct Docker CLI context for the desired daemon connection. This can be done by using:

docker context use default

Read: How to clean up unused Docker containers, images and volumes

Permission problems

Another reason for daemon connection issues is when the user permissions for Docker’s socket are incorrect. If this is the case, the error message displayed may be slightly different:

Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock

When you don’t have the appropriate permissions to interact with the Docker API’s socket, it means that your Unix user account lacks the required access. To fix this issue, it is best practice to add your account to the docker group:

sudo usermod -aG docker $USER

After making the change by adding yourself to the docker group, you’ll need to open a fresh shell window or log out and then log back in to ensure the changes take effect. Once you do that, you should be able to execute docker commands smoothly without encountering any permission-related issues.

Read: How to manage permissions in Linux – guide for beginners

Manual start of the Daemon

If you are working on a system that does not have the Docker service installed, it is possible to initiate the Docker daemon manually by executing the “dockerd” command. Typically, you would need root privileges to perform this action.

sudo dockerd

As long as the command is running, you’ll be able to access Docker. To stop the daemon, use Ctrl+C.

Conclusion

If you see the error message “Cannot connect to the Docker daemon,” it means that the Docker CLI is having trouble communicating with the Docker daemon using your current settings. This could be due to the Docker daemon service being turned off or disabled, or you could be trying to connect to a remote Docker host that’s no longer available. Now that you know the possible reasons for this issue and the typical ways to address it, you can troubleshoot the error.

I wonder if this is simple enough to be reduced to the following test case:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>

#define ADB_PORT 5037

static struct sockaddr *
loopback_addr4(struct sockaddr_storage *addr, socklen_t *addrlen, int port)
{
  struct sockaddr_in *addr4 = (struct sockaddr_in *)addr;
  *addrlen = sizeof(*addr4);
  
  addr4->sin_family = AF_INET;
  addr4->sin_addr.s_addr = htonl(INADDR_LOOPBACK);
  addr4->sin_port = htons(port);
  return (struct sockaddr *)addr;
}

void
client_error(int e)
{
  fprintf(stderr, "client: %sn", strerror(e));
}

int
client(void)
{
  int s = socket(AF_INET, SOCK_STREAM, 0);
  if (s == -1) {
    client_error(errno);
    return -1;
  }

  struct sockaddr_storage addr_storage;
  socklen_t addrlen = sizeof(addr_storage);
  struct sockaddr *addr = loopback_addr4(&addr_storage, &addrlen, 0);

  if (bind(s, addr, addrlen) != 0) {
    client_error(errno);
    return -1;
  }

  addr = loopback_addr4(&addr_storage, &addrlen, ADB_PORT);
  if (connect(s, addr, addrlen) != 0) {
    client_error(errno);
    return -1;
  }
  
  if (close(s) != 0) {
    client_error(errno);
  }

  return 0;
}

void
server_error(int e)
{
  fprintf(stderr, "server: %sn", strerror(e));
}

int
server(void)
{
  int s = socket(AF_INET, SOCK_STREAM, 0);
  if (s == -1) {
    server_error(errno);
    return -1;
  }

  int n = 1;
  setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &n, sizeof(n));

  struct sockaddr_storage addr_storage;
  socklen_t addrlen = sizeof(addr_storage);
  struct sockaddr *addr = loopback_addr4(&addr_storage, &addrlen, ADB_PORT);
   
  if (bind(s, addr, addrlen) != 0) {
    server_error(errno);
    return -1;
  }
   
  if (listen(s, SOMAXCONN) != 0) {
    server_error(errno);
    return -1;
  }

  if (accept(s, addr, &addrlen) < 0) {
    server_error(errno);
  }

  return 0;
}

int
main(void)
{
  pid_t pid = fork();
  if (pid == 0) {
    sleep(1);
    return client();
  } else if (pid < 0) {
    fprintf(stderr, "%sn", strerror(errno));
    return -1;
  } else {
    int ret_s = server();
    int ret_c;
    wait(&ret_c);
    if (ret_s || ret_c) {
      return -1;
    }
  }
  return 0;
}