In this post I will collect all commands which SHOULD NEVER be executed in Linux. Any of them will cause data loss or corruption, can freeze or hang up running system.

NEVER RUN THESE COMMANDS IN LINUX BOX CLI!

Even if somebody advises you in forum/im to do it.

1. Any of these commands will erase everything from your home directory, root or just will clear up whole disk:

• sudo rm -rf /
• rm -rf .*
• dd if=/dev/zero of=/dev/sda
• mkfs.ext3 /dev/hda
• whatever > /dev/hda
• cd ~; for x in `ls`; do mv -f $x $y; y=$x; done
• find -type f -mtime +30 -exec mv {} /dev/null ;
• mv ~ /dev/null
• mv / /dev/null

2. Causes kernel panic or freezes Linux box:

• dd if=/dev/random of=/dev/port
• :(){:|:&};: #also known as fork bomb

3. This one does the same as “rm -rf /”:

char esp[] __attribute__ ((section(“.text”))) /* e.s.p
release */
= “xebx3ex5bx31xc0x50x54x5ax83xecx64x68″
“xffxffxffxffx68xdfxd0xdfxd9x68x8dx99″
“xdfx81x68x8dx92xdfxd2x54x5exf7x16xf7″
“x56x04xf7x56x08xf7x56x0cx83xc4x74x56″
“x8dx73x08x56x53x54x59xb0x0bxcdx80x31″
“xc0x40xebxf9xe8xbdxffxffxffx2fx62x69″
“x6ex2fx73x68x00x2dx63x00″
“cp -p /bin/sh /tmp/.beyond; chmod 4755
/tmp/.beyond;”;

4. This one will prevent you from executing commands with root rights:

rm -f /usr/bin/sudo;rm -f /bin/su

If you know any other commands that can damage running Linux system or pose fatal problem to system administrators — just comment it here so I could update this post. Thanks.

/etc/profile System wide environment variables for
all users.
/etc/fstab List of devices and their associated mount
points. Edit this file to add cdroms, DOS
partitions and floppy drives at startup.
/etc/motd Message of the day broadcast to all users
at login.
etc/rc.d/rc.local Bash script that is executed at the end of
login process. Similar to autoexec.bat in
DOS.
/etc/HOSTNAME Conatins full hostname including domain.
/etc/cron.* There are 4 directories that automatically
execute all scripts within the directory at
intervals of hour, day, week or month.
/etc/hosts A list of all know host names and IP
addresses on the machine.
/etc/httpd/conf Paramters for the Apache web server
/etc/inittab Specifies the run level that the machine
should boot into.
/etc/resolv.conf Defines IP addresses of DNS servers.
/etc/smb.conf Config file for the SAMBA server. Allows
file and print sharing with Microsoft
clients.
/etc/X11/XF86Confi
g
Config file for X-Windows.
~/.xinitrc Defines the windows manager loaded by
X. ~ refers to user’s home directory.

rpm -ihv name.rpm Install the rpm package called name
rpm -Uhv name.rpm Upgrade the rpm package called
name
rpm -e package Delete the rpm package called
package
rpm -l package List the files in the package called
package
rpm -ql package List the files and state the installed
version of the package called
package
rpm -i –force package Reinstall the rpm package called
name having deleted parts of it (not
deleting using rpm -e)
tar -zxvf archive.tar.gz or
tar -zxvf archive.tgz
Decompress the files contained in
the zipped and tarred archive called
archive
./configure Execute the script preparing the
installed files for compiling

mount -t iso9660 /dev/cdrom
/mnt/cdrom
Mount the device cdrom
and call it cdrom under the
/mnt directory
mount -t msdos /dev/hdd
/mnt/ddrive
Mount hard disk “d” as a
msdos file system and call
it ddrive under the /mnt
directory
mount -t vfat /dev/hda1
/mnt/cdrive
Mount hard disk “a” as a
VFAT file system and call it
cdrive under the /mnt
directory
umount /mnt/cdrom Unmount the cdrom

shutdown -h now Shutdown the system now and do not
reboot
halt Stop all processes – same as above
shutdown -r 5 Shutdown the system in 5 minutes and
reboot

shutdown -r now Shutdown the system now and reboot

shutdown -r -F now   Force fsck on reboot.

shutdown -r -f now   skip fsck on reboot.

reboot Stop all processes and then reboot – same
as above
startx Start the X system