Checking Docker Installation on Linux

I am starting some work using Docker containers and as usual I like to spend some time refreshing and checking all is well before starting the actual development. Such approach seems to allow me to catch up issues before they cause bugs during the software development cycle.

Last year I wrote a post with the instructions I followed while installing Docker on my CentOS 7 Linux machine. If you are about to install Docker, their website appears to have up to data instructions for different operating systems.

Docker has two versions, Docker Engine Enterprise Edition (Docker EE) and Community Edition (CE). I have installed in my system Docker CE.

Docker has three types of update channels, stable, test and nightly.

* Stable gives you latest releases for general availability.

o Test gives pre-releases that are ready for testing before general availability.

o Nightly gives you latest builds of work in progress for the next major release.

I prefer the stable version. Living on the edge of technology does not tickle my fancy.

You can install Docker CE in different ways, depending on your needs:

* Most users set up Docker’s repositories and install from them, for ease of installation and upgrade tasks. This is the recommended approach and the one I followed.

o Some users download the RPM package and install it manually and manage upgrades completely manually. This is useful in situations such as installing Docker on air-gapped systems with no access to the internet.

o In testing and development environments, some users choose to use automated convenience scripts to install Docker.

I used the following command to set up the stable repository:

$ sudo yum-config-manager \
    --add-repo \
    https://download.docker.com/linux/centos/docker-ce.repo

My docker-ce.repo looks as follows:

$ cat docker-ce.repo
[docker-ce-stable]
name=Docker CE Stable - $basearch
baseurl=https://download.docker.com/linux/centos/7/$basearch/stable
enabled=1
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

[docker-ce-stable-debuginfo]
name=Docker CE Stable - Debuginfo $basearch
baseurl=https://download.docker.com/linux/centos/7/debug-$basearch/stable
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

[docker-ce-stable-source]
name=Docker CE Stable - Sources
baseurl=https://download.docker.com/linux/centos/7/source/stable
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

[docker-ce-edge]
name=Docker CE Edge - $basearch
baseurl=https://download.docker.com/linux/centos/7/$basearch/edge
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

[docker-ce-edge-debuginfo]
name=Docker CE Edge - Debuginfo $basearch
baseurl=https://download.docker.com/linux/centos/7/debug-$basearch/edge
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

[docker-ce-edge-source]
name=Docker CE Edge - Sources
baseurl=https://download.docker.com/linux/centos/7/source/edge
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

[docker-ce-test]
name=Docker CE Test - $basearch
baseurl=https://download.docker.com/linux/centos/7/$basearch/test
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

[docker-ce-test-debuginfo]
name=Docker CE Test - Debuginfo $basearch
baseurl=https://download.docker.com/linux/centos/7/debug-$basearch/test
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

[docker-ce-test-source]
name=Docker CE Test - Sources
baseurl=https://download.docker.com/linux/centos/7/source/test
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

[docker-ce-nightly]
name=Docker CE Nightly - $basearch
baseurl=https://download.docker.com/linux/centos/7/$basearch/nightly
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

[docker-ce-nightly-debuginfo]
name=Docker CE Nightly - Debuginfo $basearch
baseurl=https://download.docker.com/linux/centos/7/debug-$basearch/nightly
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

[docker-ce-nightly-source]
name=Docker CE Nightly - Sources
baseurl=https://download.docker.com/linux/centos/7/source/nightly
enabled=0
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg

Before installing, as directed, I checked the OS requirements. You can find this at the Docker site or my previous post.

Something that you may want to check and for sanity reasons eliminate the need to enter sudo before each docker command is to add your user name to the docker group. This is also illustrated in my previous post.

Let’s see if my user name:  john_canessa has already been added to the docker group. You may do this as follows:

$ groups
johncanessa wheel docker

or

$ id -Gn
johncanessa wheel docker


$ cut -d: -f1 /etc/group | sort
abrt
adm
audio
avahi
bin
cdrom
cgred
chrony
colord
daemon
dbus
dialout
dip
disk
docker			<=== created by Docker
floppy
ftp
games
gdm
geoclue
gluster
gnome-initial-setup
input
johncanessa		<=== that's me
kmem
kvm
libstoragemgmt
libvirt
lock
lp
mail
man
mem
nfsnobody
nobody
ntp
oprofile
pcp
polkitd
postdrop
postfix
printadmin
pulse
pulse-access
pulse-rt
qemu
radvd
root
rpc
rpcuser
rtkit
saned
saslauth
setroubleshoot
slocate
sshd
ssh_keys
stapdev
stapsys
stapusr
sys
systemd-journal
systemd-network
tape
tcpdump
tracing
tss
tty
unbound
usbmuxd
users
utempter
utmp
video
wheel


$ getent group docker
docker:x:984:johncanessa

Based on the previous commands, it seems that I am in the docker group.

Let’s start Docker:

$ service docker restart
Redirecting to /bin/systemctl restart docker.service

We can now verify the version of Docker we are running:

$ docker version
Client:
 Version:           18.09.2
 API version:       1.39
 Go version:        go1.10.6
 Git commit:        6247962
 Built:             Sun Feb 10 04:13:27 2019
 OS/Arch:           linux/amd64
 Experimental:      false

Server: Docker Engine - Community
 Engine:
  Version:          18.09.2
  API version:      1.39 (minimum version 1.12)
  Go version:       go1.10.6
  Git commit:       6247962
  Built:            Sun Feb 10 03:47:25 2019
  OS/Arch:          linux/amd64
  Experimental:     false

It seems like the engine and client are alive. The versions are from this month. All is well so far.

I have read that while developing software it is not a bad idea to run Linux in permissive mode. Before you post the code you can change the mode back to Enforcing. I prefer to always run on Enforcing. The following screen capture illustrates finding and changing the current mode:

$ sestatus
SELinux status:                 enabled
SELinuxfs mount:                /sys/fs/selinux
SELinux root directory:         /etc/selinux
Loaded policy name:             targeted
Current mode:                   enforcing	<===
Mode from config file:          enforcing
Policy MLS status:              enabled
Policy deny_unknown status:     allowed
Max kernel policy version:      31


$ getenforce
Enforcing

$ sudo setenforce 0
$ getenforce
Permissive

$ sudo setenforce 1

$ getenforce
Enforcing

If you are interested in reading more about Security-Enhanced Linux (SELinux) you can do it here.

In my previous post I note that one of the requirements to run Docker is to have a 64-bit platform. To check that you could:

$ uname -r
3.10.0-957.5.1.el7.x86_64

$ uname -m
x86_64

$ uname -a
Linux ceph1 3.10.0-957.5.1.el7.x86_64 #1 SMP Fri Feb 1 14:54:57 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Note that the results of the last command are slightly different from the last time I ran the same command in my previous post. The reason for this is that I installed ceph software on my machine to learn and experiment with it. I am planning on using ceph for a future project. To read more about ceph you could follow this link.

I do not see a point or need in posting anything related to this post on GitHub.

I will follow this post shortly with some experimentation using Docker. Until then, keep on learning, experimenting and having a great time with software development.

If you have comments or questions regarding this or any other post in this blog, please leave me a note bellow.

John

Follow me on Twitter:  @john_canessa

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