May 03

Truncate docker logs

Reading time: < 1 minute Sometimes when a container is running for a long time especially when docker logs command is called the logs dump is extra long and then a recurrent search on google for reminding how to truncate a file is mandatory for avoiding this repeating task this is the trick that it saves me from that uncomfortable long log dump.

truncate -s 0 $(docker inspect --format='{{.LogPath}}' CONTAINER_ID)
May 02

HTTPie – command line HTTP client

Reading time: 1 – 2 minutes

I imagine you are used to using curl for many command line scripts, tests, and much more things. I did the same but some weeks ago I discovered HTTPie which is the best substitute that I’ve ever found for curl. Of course, it’s also available for a lot of Linux distributions, Windows, and Mac. But I used it with docker which is much more transparent for the operative system and easy to update. To be more precise I use next alias trick for using this tool:

alias http='sudo docker run -it --rm --net=host clue/httpie'

Official website: httpie.org

Let me paste some highlights about HTTPie:

  • Sensible defaults
  • Expressive and intuitive command syntax
  • Colorized and formatted terminal output
  • Built-in JSON support
  • Persistent sessions
  • Forms and file uploads
  • HTTPS, proxies, and authentication support
  • Support for arbitrary request data and headers
  • Wget-like downloads
  • Extensions
  • Linux, macOS, and Windows support

From the tool webpage a nice comparison about how HTTPie looks like versus curl.

Mar 21

Linux: Mounting file as a partition

Reading time: < 1 minute When we have a file with a 'dd' of a full disk and we want to mount a partition of that disk, we have to use an offset for jumping to the beginning of the partition that we want to mount. Using 'fdisk' command we can find the partitions of that disk copied inside a file.
fdisk -l FILE_WITH_DISK_INSIDE

Once partition table is shown there is a column called ‘Start’ using the corresponding number in this column for the partition that we want we can obtain the offset required for our mounting point. Reasoning behind that is multiply start sector per number of bytes per sector.

# OFFSET = START * 512
mount -o ro,loop,offset=OFFSET FILE_WITH_DISK_INSIDE /mnt

I hope thanks to this technical note next time that I forget how to get the offset I find it fastly.

Mar 07

socat tip: create virtual serial port and link it to TCP

Reading time: < 1 minute Create a virtual serial port and publish it on TCP port:

socat pty,link=/dev/virtualcom0,rawer tcp-listen:2101

In another computer, for instance, another virtual port can be created and connected to the previous one:

socat pty,link=/dev/virtualcom0,rawer tcp:SERVER_IP:2101

If in any of those both sides we want to open a real serial port, for instance, in the server case we can run:

socat /dev/ttyS0,rawer tcp-listen:2101

More information on socat manpage.

Jan 24

ngrok – service which solve services behind NAT issues

Reading time: < 1 minute This is another short entry, in this case for recommending a service which we solve typical problem solved using a DNAT. Once we have a service on our laptop, or on a private server and we have to expose that service on the internet for some time or permanently usually we have to go the firewall, or router and create a NAT rule forwarding a port. This is a simple and powerful service which is going to solve that for you. There is a free account for understanding and testing the service, other plans are available and especially affordable for professional requirements.

ngrock.com

I was frogetting to say it’s compatible with Linux, Windows and Mac.

Aug 30

Raspberry PI: using read-only root partition

Reading time: 2 – 2 minutes

Two years ago I wrote an article discussing how to set up OpenWRT filesystem configuration for controlling writes in the flash card: Raspberry PI and OpenWRT flash partition proposal and rescue boot support for embedded systems.

This current article is mainly for referencing a very good article about how to work with Raspbian with a read-only filesystem and share a fast and dirty cookbook about how to play with that. First of all the reference to: Protect your Raspberry PI SD card, use Read-Only filesystem.

My cookbook about how to get the essence of that article is simple, locate in your /etc/fstab file the line:

/dev/mmcblk0p2  /               ext4    defaults,noatime  0       1

and modify that line with:

/dev/mmcblk0p2  /               ext4    defaults,noatime,ro  0       1

After rebooting your system is going to work in read-only mode. I don’t remember if I modified anything else of the booting process but I don’t thing so.
Because sometimes I have to modify anything in the flash card, I added the next two lines in the ~/.bashrc file:

alias rw='sudo mount -o remount,rw / ; sudo mount -o remount,rw /boot'
alias ro='sudo mount -o remount,ro / ; sudo mount -o remount,ro /boot'

Now just with the command rw it’s really easy to get the root filesystem in the write mode, and when I finish my updates just typing ro it’s go back to read-only mode.

I hope it’s useful for you.

Aug 22

Cryptomator: create a secure vault for your files

Reading time: 2 – 2 minutes

Yesterday I found a tool called Cryptomator, this is a client-side encryption for your files. You can use it with Dropbox, or any other cloud filesystem or you can use it in your local filesystem. Anyway, this open-source piece of software is really simple to install and is compatible with Windows, Mac and Linux. Once this is installed, using the UI the only thing we have to do is create, or select, a folder where the secure vault is going to be created. It uses a symmetric password for cyphering and when the vault is unlocked a new removable drive appear in your system. So, at the end, the vault is like a pendrive and there is no complexity on add, rename, remove, create folders, etc. inside the new drive. Once the vault is locked, the removable drive is unmounted and if you go to the location where the vault is created a tree structure with cyphered files is the only thing that you can see. Cryptomator works cyphering each file, not the complete vault as a package.

So far I installed the tool on my Windows computer for securing some sensitive files that I have on my laptop. But if it works like I expect I’m going to extend the usage with the rest of my computers. As I said it’s not required any cloud filesystem, by the way, I use Cryptomator in conjunction with Resilio Sync.