Linux: emergency reboot or shutdown

echo 1 > /proc/sys/kernel/sysrq 
echo b > /proc/sysrq-trigger

Convert Virtualbox image to QEMU image:

qemu-img convert -f vdi -O qcow2 Virtualbox.vdi QEMU.qcow

Centos 7 change kernel:

awk -F\' /^menuentry/{print\$2} /etc/grub2.cfg
grub2-set-default 1
grub2-mkconfig -o /boot/grub2/grub.cfg
shutdown -r now

Mount RAMDISK:

mount -t tmpfs -o size=512m tmpfs /mnt/ramdisk

Create ansible role:

ansible-galaxy init <rollename>

Install LT kernel from Elrepo:

rpm -Uvh https://elrepo.org/linux/kernel/el7/x86_64/RPMS/elrepo-release-7.0-3.el7.elrepo.noarch.rpm
yum --enablerepo=elrepo-kernel install kernel-lt

git - overwrite local files:

git fetch --all
git reset --hard origin/master