Inside my Head

An extension of my brain. A notebook of mostly geeky and technical stuff that I might need to lookup at a later time.

[twonky]

Installing Adobe Flash Player on Ubuntu 19.04

I needed to install the Flash plugin in my Firefox browser. The easiest way I could find was to first add the Canonical partner repository:

sudo add-apt-repository "deb http://archive.canonical.com/ $(lsb_release -sc) partner"

After that, I could just install the plugin:

sudo apt install adobe-flashplugin browser-plugin-freshplayer-pepperflash

[twonky]

Working with long-running jobs on Linux servers

Here a some tips if you're working with long-running jobs on Linux servers. I'm assuming that you log in to the server using ssh.

You should install and use a terminal multiplexer like tmux or screen on the server. This will enable you to disconnect without stopping you job, and (even more important) to re-connect and check the progress.

When running you job, prefix the command with date&&time, this will write-out the starting date and time and (when the job is done) write-out the elapsed time.

Below is an example of how it will look:

$ date&&time long_running_script.sh Wed Mar 28 15:49:22 CEST 2018 real 1093m57.130s user 1427m45.140s sys 35m49.636s $

[twonky]

Embedding a GitHub gist in a Tumblr post

I’m using the following JavaScript code (written by Shagshag) to embed gists in my posts: https://gist.github.com/Shagshag/c9cdb058677b021d2e30bb8d0bdce2c8

Add the code to your template and then any occurance of <a href="GIST_URL">GIST_URL</a> will be expanded.

If the expansion doesn't work, there will still be a link to the gist.

[twonky]

Fixing ‘NODE_ENV’ not recognized as a command issue

If you develop in NodeJS on Windows and want to e.g. run tests by issuing npm test you’ll get the following error:

'NODE_ENV' is not recognized as an internal or external command, operable program or batch file.

This can be fixed by installing win-node-env, i.e. run npm install -g win-node-env

[twonky]

Bash function to list paths in $PATH

Add the following line to you ~/.bashrc file:

function paths() { paths=${PATH// /\\ }; echo "${paths//:/$'\n'}"; }

Then you can just type paths to get a nice list of the paths defined in the $PATH environment variable.

[twonky]

Figure out what’s using your disk space from the command line

Run the following to see a list of big files/directories sorted by size:

du -s * | sort -nk1 | sed 's/^[0-9]*.//' | xargs -i{} du -sh "{}"

If your sort command supports it, the above command can be simplified to this:

du -sh * | sort -h

You might also conside installing ncdu, which is a nice disk usage analyzer with an ncurses interface.

[twonky]

Efficient compression of log files with 7-Zip

To efficiently compress a log file, use the following command:

7za a -m0=PPMd -mx=9 access.7z access.log

It works equally well for a directory:

7za a -m0=PPMd -mx=9 logs.7z logs

[twonky]

Use a Credential Helper in Git

If you’re accessing a Git repository using HTTPS, you might want to configure a Credential Helper. This will cache your password, giving you a much smoother workflow. On Windows you can configure the wincred Credentail Helper like this:

git config --global credential.helper wincred

See https://help.github.com/articles/caching-your-github-password-in-git/

[twonky]

Test email sending on Windows using PowerShell

To quickly see if a Windows machine is able to send emails using a specific SMTP server you can use the following PowerShell one-liner:

Send-MailMessage -SmtpServer servername

You will then be prompted to enter values for "From", "Subject" and "To". Alternativly you can add extra command line flags:

Send-MailMessage -SmtpServer ... -From ... -To ... -Subject ... -Body ...

[twonky]

Prevent Oracle DB passwords from expiring

In newer versions of Oracle DB, user passwords expire after 180 days. The user will get a warning a week before:

 ORA-28002: the password will expire within 7 days

If the password is not changed within the week, the user will be locked out:

ORA-28001: the password has expired

If the user is a human, this isn't a big problem. But if the user is another system (e.g. a web application), then the problem will propagate to the end-users, who will have no clue to what's going on.

For system users, the best solution is to prevent passwords for expiring. This can be done with the following (which will apply to all users):

ALTER PROFILE DEFAULT LIMIT PASSWORD_LIFE_TIME UNLIMITED;

If the password has already expired or is within 7 days of expiring, a little more is required: check one of the following articles:

ORA-28001: the password has expired

ORA-28002: the password will expire within 7 days

Update: Got this (relevant) comment from @hamsjaeld

It was new in Oracle 11g, that the default profile (normally used by all users except DBSNMP) expires in 180 days. Instead of simply disabling this enhanced security, it's probably better to setup appropriate profiles in the db, and assign users to them.

And, yes, the above might not be the best way to handle this, especially on production servers. For test and development servers I would think it's fine.

[twonky]

Make Ubuntu use old release repositories when EOL is reached

When an Ubuntu release reaches end-of-life, its repositories are no longer available at the usual location. This means you cannot install new software. Obviously, you should not let your Ubuntu installation reach end-of-life, but if it should happen, here's the fix.

Open /etc/apt/sources.list in vim:

sudo vim /etc/apt/sources.list

You should see lines like this (from an Ubuntu 10.10 installation):

deb http://dk.archive.ubuntu.com/ubuntu/ maverick main restricted

They should be change to

deb http://old-releases.ubuntu.com/ubuntu/ maverick main restricted

In vim that can be accomplished by issuing the following:

:%s/:\/\/dk\.archive\./:\/\/old-releases./gc

You should also change the security respositories, like this:

:%s/:\/\/security\./:\/\/old-releases./gc

Save the file and exit (:x) and update:

sudo apt-get update sudo apt-get upgrade

That's it.

[twonky]

Maximum length of a valid email address

Short answer: 254 characters including the '@'.

The maximum length of the local part (the string in front of the '@') is 64 characters and the maximum length of the domain part is 255 characters. This has made some incorrectly stating that an email address can be 64+1+255 = 320 characters long.

The total length of an email address is restricted by a limitation of the SMTP forward-path field, which can contain a maximum of 256 characters. As the email address must be inclosed in angle brackets, we get the 254 character maximum.

Reference: http://stackoverflow.com/questions/386294/what-is-the-maximum-length-of-a-valid-email-address

[twonky]

Downloading Sonatype Maven Shell

I really like the Maven Shell, but it can be hard to find, as it seems Sonatype has dropped support for it. But the latest release can be found here:

http://repo1.maven.org/maven2/org/sonatype/maven/shell/dist/mvnsh-assembly/

Find the latest version (currently it's version 1.1.0) and click on that. Then download the zip file, for version 1.1.0 it's called mvnsh-assembly-1.1.0-bin.zip

[twonky]

Installing old Java on modern Linux

When trying to install an old version of Java on a modern Linux (e.g. Ubuntu 10+) you'll get the following error message:

Unpacking... tail: cannot open `+511' for reading: No such file or directory Checksumming... 1 The download file appears to be corrupted.  Please refer the Troubleshooting section of the Installation Instructions on the download page for more information. Please do not attempt to install this archive file.

The fix is easy: Just specify a POSIX version, like this:

$ _POSIX2_VERSION=199209 ./j2sdk-1_4_2_09-linux-i586.bin

[twonky]

Installing Oracle Java (JDK) on Ubuntu Linux

This is how I installed Oracle Java on my Ubuntu 12.10:

First I removed all existing javas using this howto: http://askubuntu.com/questions/84483/how-to-completely-uninstall-java

Next I installed Java from the PPA described here: http://www.webupd8.org/2012/01/install-oracle-java-jdk-7-in-ubuntu-via.html

[twonky]

Deleting text in Emacs: The yellow box is your cursor. The red lines indicates what you want to delete, and the green text shows the keyboard shortcut that does that. If there's a second green line it's an alternative keyboard shortcut.

[twonky]

As Java 6 is end-of-life, it will be replaced with Java 7 if you try an update.