Docker on Windows tips & tricks

Just some tips & tricks on Docker on Windows I documented for myself.

Location of Docker daemon logs

The Docker daemon logs can be found in the following location.

C:\ProgramData\Docker

By default C:\ProgramData is hidden in Explorer, you need to make it visible in the options (File -> Change folder and search options, select tab View, select the option ‘Show hidden files, folders and drives’ under ‘Hidden files and folders’).

Change folder and search options

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Docker commands tips & tricks

Just some Docker commands tips & tricks I documented for myself.

Misc

Start interactive shell in Alpine image

Alpine uses the ash shell instead of the bash shell. This by the way also overrules the default CMD in the image.

$ docker run -it --entrypoint=/bin/ash image-id

Connect to a running container

What if you started a shell in the background and you want to see the stdout and stderr output? Connect to the running container.

$ docker attach container-id

Connect to a running container with an interactive shell

So what if you want to connect to a running container and inspect its contents? Just attach and start an interactive shell šŸ™‚

$ docker exec -it container-id /bin/ash

Inspect image, volume or running container

It can be handy to inspect the settings of images, volumes or running containers. To do this use the following commands.

docker image inspect image-id
docker volume inspect volume-id
docker container inspect container-id

Build

Traditionally, the Dockerfile is called Dockerfile and located in the root of the context directory. You use the -f flag with docker build to point to a Dockerfile anywhere in your file system.

IMPORTANTĀ when pointing to a Dockerfile not located in the context directory, you must add a period (.) at the end of the statement.

$ docker build -t my-label -f /path/to/a/Dockerfile .

Volumes

Volumes make it possible to persist data between container restarts and share data between containers.

Create a volume.

$ docker volume create logs

List files in a volume.

$ docker run -it --rm -v logs:/logs alpine ls -l /logs

Display the contents of a file in a volume.

$ docker run -it --rm -v logs:/logs alpine cat /logs/access.log

Interactive access to the files in a volume.

$ docker container run -ti -v logs:/logs alpine sh -c 'cd /logs; exec "${SHELL:-sh}'

Using tail with -f option to view changes to the contents of a file in realtime.

$ docker run -it --rm -v logs:/logs alpine tail -f -n 25 /logs/access.log

Finding out the size of directories in Linux

Do you want to know the size of a directory in Linux? Use the du command.

du -sh

Explanation

The du command estimates the space used by a directory.

The options -sh are (from man du):

  -s, --summarize
         display only a total for each argument

  -h, --human-readable
         print sizes in human readable format (e.g., 1K 234M 2G)

To check more than one directory and get the total size of those directories, use

du -sch *

What does the extra option mean?

  -c, --total
         produce a grand total

Include hidden files?

du -sch * .*

Want to know how much disk space has been used?

du -h .

Bash shell shortcuts

I have been irritated not having standard keyboard shortcuts, like Ctrl-arrow left (move word left) andĀ Ctrl-arrow right (move word right), available on the bash command line. It turns out they are. If you know what the meta key is. Meta key? Yes, I didn’t know which key this was either.

It turns out that it is the Alt key.Ā This is because historically, many Unix workstations had a key labeled Meta where PCs have a key labeled Alt.

So here is a little bash command line cheat sheet.

  • Ctrl-a: Move to the start of the current line.
  • Ctrl-e: Move to the end of the line.
  • Ctrl-f: Move forward a character.
  • Ctrl-b: Move back a character.
  • Meta-f: Move forward to the end of the next word. Words are composed of letters and digits.
  • Meta-b:Ā Move backward to the start of the next word. Words are composed of letters and digits.

Have fun.

Plugin Manager removed from Notepad++

I needed the compare plugin today. You used to be able to select the Plugin Manager under Plugins ->Ā Plugin Manager. But it was gone šŸ˜¦ It turns out it has been removed from the standard installation and has to be installed separately. I haven’t been able to find out why. Here quick instructions how to install Plugin Manager.

  • Download the latest version of Plugin Manger from GitHub. Make sure you download the correct version 32 or 64 bit depending on the version of your operating system.
  • Unzip the file.
  • Copy the two directories to the Notepad++ directory. In my caseĀ C:\Program Files (x86)\Notepad++.
  • Restart Notepad++.

Plugin Manager is available again under Plugins -> Plugin Manager. Yeah!

Finding out which files are open and by which programs

Grrrrrrr ran into my inotify problem again. So I was wondering how I can see which program has files opened and how many. Well as with everything under Linux it is possible with a few “simple” commands. Try the following command for fun and entertainment.

$ lsof | awk ‘{print $1}’ | sort | uniq -c | sort -g -k 1 | tail

  • lsof: lists the open files
  • awk: takes the first column of the output
  • sort: yep it sorts the output
  • uniq: counts all the same value
  • sort: do you want me to repeat it? a little clarification is necessary -k tells which column to sort on and -g makes sure that the contents is treated like a number
  • tail: gives the last ten entries

Inotify limit reached under PT Magic

Today I ran into a problem with PT Magic (PTM) that the inotify limit was reached on Ubuntu. Inotify (inode notify) is a Linux kernel subsystem that acts to extend filesystems to notice changes to the filesystem, and report those changes to applications. Just as a future reference for myself and as a reference to others a very quick write up how to solve this.

You can get your current inotify file watch limit by executing:

$ cat /proc/sys/fs/inotify/max_user_watches

You can set a temporary new limit with:

$ sudo sysctl -w fs.inotify.max_user_watches=16384

If you like to make your limit permanent use:

$ echo fs.inotify.max_user_watches=16384 | sudo tee -a /etc/sysctl.conf
$ sudo sysctl -p

That’s it. The problem should be solved. At least this is the workaround. I have submitted an issue to TP Magic so that they can fix it properly. We will see.

Validating a json file from the command line in Linux

Today I needed to validate a json file on one of my servers. It turns out there is a simple nodejs program or actually a linter to do this with.

Just execute the following line and you are in business.

sudo npm install jsonlint -g

This assumes nodejs is already installed. If not, execute the following line.
sudo apt-get install -y nodejs npm

To validate a json file run the following command.

jsonlint -qcĀ settings.analyzer.json

When running the program the first time I ran into the problem that the json file contains comments. Yes, I know this is not in line with the spec, but it is damn handy for understanding the file. So I needed to strip the comments to valiate the file. After googeling around a bit I found an awk command to do just this. Try the following command.

awk '{sub(/\/.*$/,"")}1' settings.analyzer.json >Ā settings.analyzer.json

Now run jsonlint again and it should work.

P.s. I know the title of this post says Linux, but jsonlint will also work under any other system that nodejs runs on.

Hope this saves someone some time.

Using the hosts file on Windows with ports

As you might or might not know I’m running Profit Trailer (PT) on a VPS. To be safe the GUI is not accessible to the outside world, but only through an SSH tunnel. It has been irritating me for a while that the URLs are not readable, e.g. localhost:8081. I wanted readable URLs without ports in them. Today I finally figured out how to do this using a combination of host file and the Windows networking tool netsh.

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