Using podman quick instructions
These instructions assume that
- you have some knowledge about basic Linux commands such as ls, cat, echo and grep
- you have a Linux computer with podman installed. (Installation instructions)
- Basic usage
- Install a missing software package
- Search for a pre-built container image
- Security
- How to save disk space
- How to save time
- When to use the flags -i (--interactive) and -t (--tty)
- The professional way, using Dockerfile and Github/Gitlab
Show the podman version
[me@linux ~]$ podman --version
podman version 1.8.0
[me@linux ~]$
Run the command echo Hello! in the container docker.io/library/ubuntu:18.04
[me@linux ~]$ podman run --rm docker.io/library/ubuntu:18.04 echo Hello!
Trying to pull docker.io/library/ubuntu:18.04...
Getting image source signatures
Copying blob de83a2304fa1 done
Copying blob b6b53be908de done
Copying blob 423ae2b273f4 done
Copying blob f9a83bce3af0 done
Copying config 72300a873c done
Writing manifest to image destination
Storing signatures
Hello!
[me@linux ~]$
The first lines of the text were printed to stderr telling us that podman needed to download the container image.
The last line of the text was printed to stdout and originates from the command echo Hello! that was run inside the container.
If we run the same command again
[me@linux ~]$ podman run --rm docker.io/library/ubuntu:18.04 echo Hello!
Hello!
[me@linux ~]$
we see that the download step could be skipped.
The size of the downloaded container image docker.io/library/ubuntu:18.04 is 66.6 MB
[me@linux ~]$ podman images
REPOSITORY TAG IMAGE ID CREATED SIZE
docker.io/library/ubuntu 18.04 72300a873c2c 4 days ago 66.6 MB
[me@linux ~]$
but container images can be much smaller than that. For instance the popular container image docker.io/library/alpine:latest is about 6 MB.
If we run the command cat /etc/os-release inside the container
[me@linux ~]$ podman run --rm docker.io/library/ubuntu:18.04 cat /etc/os-release
NAME="Ubuntu"
VERSION="18.04.4 LTS (Bionic Beaver)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 18.04.4 LTS"
VERSION_ID="18.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=bionic
UBUNTU_CODENAME=bionic
[me@linux ~]$
we see the contents of the file /etc/os-release inside the container image.
If we run cat /etc/os-release without podman
[me@linux ~]$ cat /etc/os-release
NAME=Fedora
VERSION="31 (Thirty One)"
ID=fedora
VERSION_ID=31
VERSION_CODENAME=""
PLATFORM_ID="platform:f31"
PRETTY_NAME="Fedora 31 (Thirty One)"
ANSI_COLOR="0;34"
LOGO=fedora-logo-icon
CPE_NAME="cpe:/o:fedoraproject:fedora:31"
HOME_URL="https://fedoraproject.org/"
DOCUMENTATION_URL="https://docs.fedoraproject.org/en-US/fedora/f31/system-administrators-guide/"
SUPPORT_URL="https://fedoraproject.org/wiki/Communicating_and_getting_help"
BUG_REPORT_URL="https://bugzilla.redhat.com/"
REDHAT_BUGZILLA_PRODUCT="Fedora"
REDHAT_BUGZILLA_PRODUCT_VERSION=31
REDHAT_SUPPORT_PRODUCT="Fedora"
REDHAT_SUPPORT_PRODUCT_VERSION=31
PRIVACY_POLICY_URL="https://fedoraproject.org/wiki/Legal:PrivacyPolicy"
[me@linux ~]$
we see the contents of the file /etc/os-release on the host system.
The home directory
[me@linux ~]$ ls -d /home/me
/home/me
[me@linux ~]$
on the host system is not available from inside the container
[me@linux ~]$ podman run --rm docker.io/library/ubuntu:18.04 ls -d /home/me
ls: cannot access '/home/me': No such file or directory
[me@linux ~]$
This is because the host system and the container have different file trees.
To run a command in the container with read and write access to the directory /home/me/project1 on the host system,
add the command line
option -v /home/me/project1:/some/path:Z.
[me@linux ~]$ echo abc > /home/me/project1/file1.txt
[me@linux ~]$ ls /home/me/project1
file1.txt
[me@linux ~]$ cat /home/me/project1
abc
[me@linux ~]$ podman run --rm docker.io/library/ubuntu:18.04 -v /home/me/project1:/some/path:Z cat /some/path/file1.txt
abc
[me@linux ~]$ podman run --rm docker.io/library/ubuntu:18.04 -v /home/me/project1:/some/path:Z rm /some/path/file1.txt
[me@linux ~]$ ls /home/me/project1
[me@linux ~]$
The path inside the container /some/path was chosen arbitrarily.
To simplify things, you would often want to use the same path both outside and inside the container, i.e using the command line
option -v /home/me/project1:/home/me/project1:Z.
| Container image | Size (MB) | Comment |
|---|---|---|
| registry.fedoraproject.org/fedora:31 | 200 | Fedora 31 |
| docker.io/library/fedora:31 | 200 | docker.io also provides Fedora 31 |
| docker.io/library/centos:8 | 245 | CentOS 8 |
| docker.io/library/ubuntu:19.10 | 75 | Ubuntu 19.10 |
| docker.io/library/ubuntu:18.04 | 67 | Ubuntu 18.04 LTS (Long Term Support) |
| docker.io/library/alpine:3 | 6 | If you want to create very small container images. |
Goal of the exercise:
Resize the photo ~/img/photo.jpg
to half the size
and save it to ~/img/resized_photo.jpg
by using gm convert -resize 50% (from the software package GraphicsMagick).
Is GraphicsMagick already installed?
Check the container image docker.io/library/ubuntu:18.04
[me@linux ~]$ podman run --rm docker.io/library/ubuntu:18.04 dpkg -l | grep -i graphicsmagick
[me@linux ~]$
Check the container image registry.fedoraproject.org/fedora:31
[me@linux ~]$ podman run --rm registry.fedoraproject.org/fedora:31 rpm -qa | grep -i graphicsmagick
[me@linux ~]$
Check the container image docker.io/library/centos:8
[me@linux ~]$ podman run --rm docker.io/library/centos:8 rpm -qa | grep -i graphicsmagick
[me@linux ~]$
Check the container image docker.io/library/alpine:3
[me@linux ~]$ podman run --rm docker.io/library/alpine:3 apk --no-cache list -a | grep -i graphicsmagick
[me@linux ~]$
| Container image | GraphicsMagick already installed? (Yes/No) |
|---|---|
| docker.io/library/ubuntu:18.04 | No |
| registry.fedoraproject.org/fedora:31 | No |
| docker.io/library/centos:8 | No |
| docker.io/library/alpine:3 | No |
Is GraphicsMagick available in a package repository?
Check the container image registry.fedoraproject.org/fedora:31
[me@linux ~]$ podman run --rm registry.fedoraproject.org/fedora:31 dnf list available | grep -i graphicsmagick
GraphicsMagick.i686 1.3.34-1.fc31 updates
GraphicsMagick.x86_64 1.3.34-1.fc31 updates
GraphicsMagick-c++.i686 1.3.34-1.fc31 updates
GraphicsMagick-c++.x86_64 1.3.34-1.fc31 updates
GraphicsMagick-c++-devel.i686 1.3.34-1.fc31 updates
GraphicsMagick-c++-devel.x86_64 1.3.34-1.fc31 updates
GraphicsMagick-devel.i686 1.3.34-1.fc31 updates
GraphicsMagick-devel.x86_64 1.3.34-1.fc31 updates
GraphicsMagick-doc.noarch 1.3.34-1.fc31 updates
GraphicsMagick-perl.x86_64 1.3.34-1.fc31 updates
[me@linux ~]$
(The website https://apps.fedoraproject.org/packages/ provides the same information)
Check the container image docker.io/library/centos:8
[me@linux ~]$ podman run --rm docker.io/library/centos:8 dnf list available | grep -i graphicsmagick
[me@linux ~]$
Nothing there.
Let's check the extra repository PowerTools
[me@linux ~]$ podman run --rm docker.io/library/centos:8 dnf repository-packages PowerTools list | grep -i graphicsmagick
[me@linux ~]$
Nothing there.
Let's check the third-party repository EPEL.
[me@linux ~]$ podman run --rm docker.io/library/centos:8 /bin/bash -c "dnf -y update && dnf -y install epel-release && dnf repository-packages epel list" | grep -i graphicsmagick
warning: /var/cache/dnf/AppStream-02e86d1c976ab532/packages/libxkbcommon-0.8.2-1.el8.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID 8483c65d: NOKEY
Importing GPG key 0x8483C65D:
Userid : "CentOS (CentOS Official Signing Key) <[email protected]>"
Fingerprint: 99DB 70FA E1D7 CE22 7FB6 4882 05B5 55B3 8483 C65D
From : /etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial
GraphicsMagick.x86_64 1.3.34-1.el8 epel
GraphicsMagick-c++.x86_64 1.3.34-1.el8 epel
GraphicsMagick-c++-devel.x86_64 1.3.34-1.el8 epel
GraphicsMagick-devel.x86_64 1.3.34-1.el8 epel
GraphicsMagick-doc.noarch 1.3.34-1.el8 epel
GraphicsMagick-perl.x86_64 1.3.34-1.el8 epel
[me@linux ~]$
Check the container image docker.io/library/ubuntu:18.04
[me@linux ~]$ podman run --rm docker.io/library/ubuntu:18.04 /bin/bash -c "apt-get update && apt-cache search GraphicsMagick" | grep -i ^graphicsmagick
graphicsmagick - collection of image processing tools
graphicsmagick-dbg - format-independent image processing - debugging symbols
graphicsmagick-imagemagick-compat - image processing tools providing ImageMagick interface
graphicsmagick-libmagick-dev-compat - image processing libraries providing ImageMagick interface
[me@linux ~]$
(The website https://packages.ubuntu.com/ provides the same information)
Check the container image docker.io/library/alpine:3
[me@linux ~]$ podman run --rm docker.io/library/alpine:3 apk --no-cache list -a | grep -i graphicsmagick
graphicsmagick-zsh-completion-5.7.1-r0 x86_64 {zsh} (custom)
graphicsmagick-1.3.33-r1 x86_64 {graphicsmagick} (MIT)
graphicsmagick-dev-1.3.33-r1 x86_64 {graphicsmagick} (MIT)
graphicsmagick-doc-1.3.33-r1 x86_64 {graphicsmagick} (MIT)
[me@linux ~]$
(The website https://pkgs.alpinelinux.org/packages provides the same information)
GraphicsMagick is available in package repositories!
| Container image | Command to install GraphicsMagick |
|---|---|
| docker.io/library/ubuntu:18.04 | apt-get update && apt-get install -y graphicsmagick |
| registry.fedoraproject.org/fedora:31 | dnf -y update && dnf -y install GraphicsMagick |
| docker.io/library/centos:8 | dnf -y update && dnf -y install epel-release && dnf -y install GraphicsMagick |
| docker.io/library/alpine:3 | apk --no-cache add graphicsmagick |
But you will need to use podman build to save the result to a new container image.
To install GraphicsMagick on docker.io/library/fedora:31 and save the result to the new container image
localhost/foobar:fedora31, copy-paste these lines into the terminal
echo "FROM docker.io/library/fedora:31
RUN dnf -y update && dnf -y install GraphicsMagick && dnf clean all
" | podman build -t foobar:fedora31 -
Show details about the new container
[me@linux ~]$ podman images --filter reference=localhost/foobar:fedora31
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/foobar fedora31 3ea792460e93 20 seconds ago 259 MB
[me@linux ~]$
The && dnf clean all was added to reduce the size of the container image, otherwise the size would have been 478 MB.
The text strings foobar and fedora31 in localhost/foobar:fedora31 were arbitrarily chosen. The syntax is localhost/name:tag.
To install GraphicsMagick on docker.io/library/centos:8 and save the result to the new container image
localhost/foobar:centos8, copy-paste these lines into the terminal
echo "FROM docker.io/library/centos:8
RUN dnf -y update && dnf -y install epel-release && dnf -y install GraphicsMagick && dnf clean all
" | podman build -t foobar:centos8 -
Show details about the new container
[me@linux ~]$ podman images --filter reference=localhost/foobar:centos8
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/foobar centos8 ddbad21e0684 36 seconds ago 395 MB
[me@linux ~]$
The && dnf clean all was added to reduce the size of the container image, otherwise the size would have been 433 MB.
The text strings foobar and centos8 in localhost/foobar:centos8 were arbitrarily chosen. The syntax is localhost/name:tag.
To install GraphicsMagick on docker.io/library/ubuntu:18.04 and save the result to the new container image
localhost/foobar:ubuntu1804, copy-paste these lines into the terminal
echo "FROM docker.io/library/ubuntu:18.04
RUN apt-get update && apt-get install -y --no-install-recommends graphicsmagick && rm -rf /var/lib/apt/lists/*
" | podman build -t foobar:ubuntu1804 -
Show details about the new container
[me@linux ~]$ podman images --filter reference=localhost/foobar:ubuntu1804
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/foobar ubuntu1804 891d0886ab51 15 seconds ago 112 MB
[me@linux ~]$
Both --no-install-recommends and && rm -rf /var/lib/apt/lists/* were added to reduce the size of the container image.
| Image size | Installation command |
|---|---|
| 198 MB | apt-get update && apt-get install -y graphicsmagick |
| 170 MB | apt-get update && apt-get install -y graphicsmagick && rm -rf /var/lib/apt/lists/* |
| 112 MB | apt-get update && apt-get install -y --no-install-recommends graphicsmagick && rm -rf /var/lib/apt/lists/* |
The text strings foobar and ubuntu1804 in localhost/foobar:ubuntu1804 were arbitrarily chosen. The syntax is localhost/name:tag.
To install GraphicsMagick on docker.io/library/alpine:3 and save the result to the new container image
localhost/foobar:alpine3, copy-paste these lines into the terminal
echo "FROM docker.io/library/alpine:3
RUN apk --no-cache add graphicsmagick
" | podman build -t foobar:alpine3 -
Show details about the new container
[me@linux ~]$ podman images --filter reference=localhost/foobar:alpine3
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/foobar alpine3 93a5ac124e03 35 seconds ago 24.8 MB
[me@linux ~]$
The text strings foobar and alpine3 in localhost/foobar:alpine3 were arbitrarily chosen. The syntax is localhost/name:tag.
The container images ordered in size
| Container image | Installation command |
|---|---|
| localhost/foobar:alpine3 | 24.8 MB |
| localhost/foobar:ubuntu1804 | 112 MB |
| localhost/foobar:fedora31 | 259 MB |
| localhost/foobar:centos8 | 395 MB |
Although the containers have been built with different commands and from different Linux distributions, the resulting container images will behave quite similarly when they are used.
The following examples show how similar they are from a user perspective.
Let's use the previously built container image localhost/foobar:fedora31
[me@linux ~]$ podman images --filter reference=localhost/foobar:fedora31
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/foobar fedora31 3ea792460e93 1 hour ago 259 MB
[me@linux ~]$
to resize the photo /home/me/img/photo.jpg
[me@linux ~]$ ls /home/me/img/
photo.jpg
[me@linux ~]$ podman run --rm -v /home/me/img:/home/me/img:Z localhost/foobar:fedora31 gm convert -resize 50% /home/me/img/photo.jpg /home/me/img/resized_photo.jpg
[me@linux ~]$ ls /home/me/img/
photo.jpg
photo_resized.jpg
[me@linux ~]$
Show the GraphicsMagick version
[me@linux ~]$ podman run --rm localhost/foobar:fedora31 gm version | head -1
GraphicsMagick 1.3.34 2019-12-24 Q16 http://www.GraphicsMagick.org/
Let's use the previously built container image localhost/foobar:centos8
[me@linux ~]$ podman images --filter reference=localhost/foobar:centos8
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/foobar centos8 ddbad21e0684 1 hour ago 395 MB
[me@linux ~]$
to resize the photo /home/me/img/photo.jpg
[me@linux ~]$ ls /home/me/img/
photo.jpg
[me@linux ~]$ podman run --rm -v /home/me/img:/home/me/img:Z localhost/foobar:centos8 gm convert -resize 50% /home/me/img/photo.jpg /home/me/img/resized_photo.jpg
[me@linux ~]$ ls /home/me/img/
photo.jpg
photo_resized.jpg
[me@linux ~]$
Show the GraphicsMagick version
[me@linux ~]$ podman run --rm localhost/foobar:centos8 gm version | head -1
GraphicsMagick 1.3.34 2019-12-24 Q16 http://www.GraphicsMagick.org/
Let's use the previously built container image localhost/foobar:ubuntu1804
[me@linux ~]$ podman images --filter reference=localhost/foobar:ubuntu1804
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/foobar ubuntu1804 891d0886ab51 1 hour ago 112 MB
[me@linux ~]$
to resize the photo /home/me/img/photo.jpg
[me@linux ~]$ ls /home/me/img/
photo.jpg
[me@linux ~]$ podman run --rm -v /home/me/img:/home/me/img:Z localhost/foobar:ubuntu1804 gm convert -resize 50% /home/me/img/photo.jpg /home/me/img/resized_photo.jpg
[me@linux ~]$ ls /home/me/img/
photo.jpg
photo_resized.jpg
[me@linux ~]$
Show the GraphicsMagick version
[me@linux ~]$ podman run --rm localhost/foobar:ubuntu1804 gm version | head -1
GraphicsMagick 1.3.28 2018-01-20 Q16 http://www.GraphicsMagick.org/
Let's use the previously built container image localhost/foobar:alpine3
[me@linux ~]$ podman images --filter reference=localhost/foobar:alpine3
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/foobar alpine3 93a5ac124e03 2 hours ago 24.8 MB
[me@linux ~]$
to resize the photo /home/me/img/photo.jpg
[me@linux ~]$ ls /home/me/img/
photo.jpg
[me@linux ~]$ podman run --rm -v /home/me/img:/home/me/img:Z localhost/foobar:alpine3 gm convert -resize 50% /home/me/img/photo.jpg /home/me/img/resized_photo.jpg
[me@linux ~]$ ls /home/me/img/
photo.jpg
photo_resized.jpg
[me@linux ~]$
Show the GraphicsMagick version
[me@linux ~]$ podman run --rm localhost/foobar:alpine3 gm version | head -1
GraphicsMagick 1.3.33 2019-07-20 Q16 http://www.GraphicsMagick.org/
Instead of building your own container image you can often find a pre-built container image in one of the popular container image registries.
Let's search for a pre-built container image that has the software GraphicsMagick installed.
A search for GraphicsMagic on https://hub.docker.com/ results in a list of about 100 different container images from the registry docker.io. The results are ordered in popularity. One of the most popular at the time of writing is https://hub.docker.com/r/jameskyburz/graphicsmagick-alpine/tags
It has a few different versions. To the right-hand side of the web page, you see for instance the text
docker pull jameskyburz/graphicsmagick-alpine:v3.0.0
That is the docker command to download ("pull") that version of the container image.
podman is aiming to be a drop-in replacement for the docker command.
When working with podman it is better to use the full path of the container image,
i.e. always prepend "docker.io/" to the
container image names found at https://hub.docker.com/.
In other words, use
docker.io/jameskyburz/graphicsmagick-alpine:v3.0.0
instead of
jameskyburz/graphicsmagick-alpine:v3.0.0.
The corresponding podman command is therefore
podman pull docker.io/jameskyburz/graphicsmagick-alpine:v3.0.0
To resize the photo /home/me/img/photo.jpg
[me@linux ~]$ ls /home/me/img/
photo.jpg
[me@linux ~]$ podman run --rm -v /home/me/img:/home/me/img:Z docker.io/jameskyburz/graphicsmagick-alpine:v3.0.0 gm convert -resize 50% /home/me/img/photo.jpg /home/me/img/resized_photo.jpg
[me@linux ~]$ ls /home/me/img/
photo.jpg
photo_resized.jpg
[me@linux ~]$
Container images under docker.io/library/* are official Docker library images. Normally we should be able to trust those more than a container image published by an arbitrary user at docker.io/username/containername:tag.
Luckily using podman run for executables of unknown origin in containers is safer
[me@linux ~]$ podman run --rm example.com/hacker/malicious:v1 malicious_executable
than executing an untrusted executable directly
[me@linux ~]$ wget http://example.com/malicious_executable
[me@linux ~]$ chmod 755 malicious_executable
[me@linux ~]$ ./malicious_executable
The reason is that podman run provides extra encapsulation protection.
- Write access to directories on the host system need to be granted explicitly with (
--volume,-v). - add more items here ...
A command for resizing photos should not need access to the network.
To disable network access, add --net none as an argument to podman run.
podman run can be restricted even further by for instance
- --read-only=true
- --security-opt=
- --ulimit=option
- --cap-drop=
- --cpu-quota=
- --shm-size=
- --http-proxy=false
- --volume (-v) can be made read-only
- --security-opt=seccomp=profile.json
- --security-opt=no-new-privileges
Man page for podman run:
https://github.com/containers/libpod/blob/master/docs/source/markdown/podman-run.1.md
Alpine container images are very small.
podman rmi imagename
Example: Removing container image localhost/foobar:centos8
[me@linux ~]$ podman images --filter reference=localhost/foobar:centos8
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/foobar centos8 b1d1374ebbbf 31 minutes ago 395 MB
[me@linux ~]$ df -h --output=avail .
Avail
9.0G
[me@linux ~]$ podman rmi localhost/foobar:centos8
Untagged: localhost/foobar:centos8
Deleted: b1d1374ebbbf650b34b81f0a3a3cb8cfba0a5b98da57582c70373d6abe695459
[me@linux ~]$ df -h --output=avail .
Avail
9.2G
[me@linux ~]$
The command
podman images --sort size
lists the images in size order.
To list the biggest container image
[me@linux ~]$ podman images --sort size | tail -1
<none> <none> a4977efc66f2 8 days ago 1.56 GB
[me@linux ~]$
The first step of a container build is often to download metadata from the package repositories and post-process the data.
This build step may take half a minute or so but luckily we can avoid it by reusing the result.
The trick is to create the package metadata cache in advance and reuse it with an overlay mount.
Let's assume we are building containers based on Fedora 31.
First, create an empty directory, for instance /home/me/f31cache.
[me@linux ~]$ mkdir $HOME/f31cache
[me@linux ~]$
Fill the directory with the most recent dnf metadata cache for Fedora 31.
[me@linux ~]$ time podman run --rm -v $HOME/f31cache:/var/cache/dnf:Z registry.fedoraproject.org/fedora:31 dnf makecache
Fedora Modular 31 - x86_64 413 kB/s | 5.2 MB 00:12
Fedora Modular 31 - x86_64 - Updates 3.0 MB/s | 4.0 MB 00:01
Fedora 31 - x86_64 - Updates 16 MB/s | 22 MB 00:01
Fedora 31 - x86_64 30 MB/s | 71 MB 00:02
Last metadata expiration check: 0:00:01 ago on Sat Mar 21 18:50:20 2020.
Metadata cache created.
real 0m36.327s
user 0m0.152s
sys 0m0.076s
[me@linux ~]$
The command took 36 seconds to finish.
[me@linux ~]$ du -sh $HOME/f31cache
212M /home/me/f31cache
The directory consumes 212 MB of disk space.
Let's rebuild the previously built container image localhost/foobar:fedora31, but now by reusing the DNF metadata cache from /home/me/f31cache.
Copy-paste these lines into the terminal
echo "FROM docker.io/library/fedora:31
RUN dnf -y update && dnf -y install epel-release && dnf -y install GraphicsMagick && dnf clean all
" | time podman build -v $HOME/f31cache:/var/cache/dnf:O -t foobar:fedora31 -
The podman build command finishes succesfully. time prints
0.17user 0.06system 0:00.22elapsed 104%CPU (0avgtext+0avgdata 42212maxresident)k
0inputs+3232outputs (0major+6383minor)pagefaults 0swaps
0.22 seconds! Less than one second! No, that is too fast to believe it's true.
We need to add the flag --no-cache so that podman will actually rebuild the container image
without reusing cached results.
A second trial:
Copy-paste these lines into the terminal
echo "FROM docker.io/library/fedora:31
RUN dnf -y update && dnf -y install epel-release && dnf -y install GraphicsMagick && dnf clean all
" | time podman build --no-cache -v $HOME/f31cache:/var/cache/dnf:O -t foobar:fedora31 -
The podman build command finishes succesfully. time prints
13.73user 3.20system 0:25.77elapsed 65%CPU (0avgtext+0avgdata 173404maxresident)k
553208inputs+523056outputs (453major+320854minor)pagefaults 0swaps
About 26 seconds!
A normal build without -v $HOME/f31y3:/var/cache/dnf:O takes 52 seconds.
Conclusion: Reusing the DNF metadata cache speeds things up.
The blog post Speeding up container image builds with Buildah provides more details.
| Container image | Size (MB) | Comment |
|---|---|---|
| registry.fedoraproject.org/fedora:rawhide | 207 | The latest development of Fedora (not yet released). |
| docker.io/library/alpine:edge | 6 | The latest development of Alpine (not yet released). |
| docker.io/library/debian:unstable | 123 | The latest development of Debian (not yet released). |
If your program reads from stdin, use the command line flag -i
[me@linux ~]$ echo Just one line | podman run --rm -i docker.io/library/ubuntu:18.04 wc -l
1
[me@linux ~]$
If your program needs interaction over the terminal, use the command line flags -t and -i
[me@linux ~]$ podman run --rm -ti docker.io/library/ubuntu:18.04 /bin/bash -c 'echo -n "Type something: "; read aa; echo "You typed: $aa"'
Type something: abc
You typed: abc
[me@linux ~]$
-t flag may slightly modify the output, by adding extra carriage return characters.
This might be very surprising. The extra carrage return (\r) is not added by podman, but by
the terminal.
[me@linux ~]$ echo abc | od -c
0000000 a b c \n
0000004
[me@linux ~]$ podman run --rm docker.io/library/ubuntu:18.04 echo abc | od -c
0000000 a b c \n
0000004
[me@linux ~]$ podman run --rm -ti docker.io/library/ubuntu:18.04 echo abc | od -c
0000000 a b c \r \n
0000005
[me@linux ~]$
Both GitHub and GitLab provide a hosted version control system. They are mainly used for hosting the source code of many software projects.
First sign up for an (free) account on GitHub, if you haven't done so already. On the front page you will see a green button labeled "Sign up for GitHub".
Then create a new repo https://help.github.com/en/github/getting-started-with-github/create-a-repo
At step nr 4: Choose a repository visbility. choose Public.
At step nr 7: choose Commit directly to the master branch instead of Create a new branch for this commit and start a pull request.
In the web interface, create a new file named Dockerfile.
Yet to be written ...