Checking if Docker is Running

Updated on 29 Mar 2023
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Check if Docker is Installed Using Snap

Snap is an application packaging system by Canonical. It uses a variation on containers to isolate the application. It's preferable not to use this type of installation. If Docker as a Snap is installed, please uninstall and install the Docker Community edition.

To check is Docker is installed as a Snap run the command

$ sudo snap list
Name                Version           Rev      Tracking               Publisher      Notes
bare                  1.0                  5           latest/stable        canonical✓   base
core20              20221027      1695    latest/stable        canonical✓   base
docker              19.03.11         471      latest/candidate  canonical✓   -

Is The Docker Daemon Running?

$ sudo docker ps
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

#systemctl enable docker.service
Created symlink /etc/systemd/system/multi-user.target.wants/docker.service → /usr/lib/systemd/system/docker.service.
# systemctl start docker.service

Are the iptables Rules Configured?

The following commands should look similar to this:

$ sudo iptables -L -t nat
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination
DOCKER     all  --  anywhere             anywhere             ADDRTYPE match dst-type LOCAL

Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
DOCKER     all  --  anywhere            !127.0.0.0/8          ADDRTYPE match dst-type LOCAL

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination
MASQUERADE  all  --  172.17.0.0/16        anywhere

Chain DOCKER (2 references)
target     prot opt source               destination
RETURN     all  --  anywhere             anywhere


$ sudo iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy DROP)
target     prot opt source               destination
DOCKER-USER  all  --  anywhere             anywhere
DOCKER-ISOLATION-STAGE-1  all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED
DOCKER     all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

Chain DOCKER (1 references)
target     prot opt source               destination

Chain DOCKER-ISOLATION-STAGE-1 (1 references)
target     prot opt source               destination
DOCKER-ISOLATION-STAGE-2  all  --  anywhere             anywhere
RETURN     all  --  anywhere             anywhere

Chain DOCKER-ISOLATION-STAGE-2 (1 references)
target     prot opt source               destination
DROP       all  --  anywhere             anywhere
RETURN     all  --  anywhere             anywhere

Chain DOCKER-USER (1 references)
target     prot opt source               destination
RETURN     all  --  anywhere             anywhere

If Empty or no DOCKER Entries, Check:

If the Docker daemon running?
If SeLinux enforcing?

# sudo getenforce
Enforcing

a. Disable SeLinux

b. Configure Docker to work properly with SeLinux.

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Connectivity Issues

Table of contents

Check if Docker is Installed Using Snap
Is The Docker Daemon Running?
Are the iptables Rules Configured?