.bootstrap - Safe with most medications

usermod example

Add existing user john to admin supplementary/secondary group with usermod command using -a option ~ i.e. add the user to the supplemental group(s). Use only with -G option:

# usermod -a -G admin john

Change existing user john primary group to mail:

# usermod -g mail tony

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This post is intended for users that forgot the root passwords or can’t use it due to other problems (corrupted file /etc/passwd or whatever). Can also be used to gain unauthorized to linux machines, but don’t do that.

What to do
Boot using a recovery CD or DVD.

Mount the drive

mount /mnt /dev/sda2

Replace the existing root password with an empty one

sed /^root/s/.*:root:/root::0:0:root:/ /mnt/etc/passwd

And reboot – and you are done

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From time to time it is very useful to combine multiple PDF documents into one file.

Install gs (ghostscript) and pdftk (tool for manipulating PDF documents)

sudo aptitude install gs pdftk

Now we will see one example, which shows how to combine a few pdf files; 1.pdf,2.pdf,3.pdf.

gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=combined_pdf.pdf -dBATCH 1.pdf 2.pdf 3.pdf

If you want to know more options available for gs command check the gs man page

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