Bash script using default value for empty parameter

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Problem

You have a bash script that accepts parameter(s) but you want to give a default value for a missing parameter.

Solution

For example you have a script that accepts a parameter with the year and month (ie 201703), but you want to give it a default of two months ago if the parameter is missing.

Docker – Debian – Kernel panick – Automatic restart

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Problem

You have a remote server (Debian) running some Docker containers and you want to make sure that they all restart in the event of a kernel panick.

solution

  • Add an automatic restart after a kernel panick by running:

  • Emulate a kernel panick by running the following (SysRq more info here :

  • Check that the containers have restarted again with docker ps (NOTE: the containers should have been enabled to autorestart)

failed to execute ‘/lib/udev/socket:@/org/freedesktop/hal/udev_event’ ‘socket:@/org/freedesktop/hal/udev_event’

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Problem

Looking at your /var/log/syslog you see entries every few seconds like the following:

Solution

Seems that hal is not used in newer Ubuntu versions, so you can remove it:

Taken from the answer here

Changing default editor for crontab from nano to vim

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Problem

You would like to change the default editor for crontab from nano to vim.

Solution

Add the following to the ~/.selected_editor:

or run the select-editor and choose vim-basic (4)

Converting number from any base system to decimal in linux shell

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Problem

You would like to quickly convert a number from a different base system (i.e. binary, octal, hexadecimal), to decimal.

Solution

Use the echo $(()) shell command to convert it passing it the current base system and the number, as in $((2#101010)) or using the O for octal or 0x for hexadecimal notations.
Examples:

Taken from Linux Journal’s Work the Shell column (March 2016)