Linux/Unix:Generic

Force a reboot (e.g. when mount commands are hanging)

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

ulimit -Sv 12000000

Set max memory to use to 12GB for this process (with option to increase (-S))

cp -rL

Copy recursively and dereference symbolic links (copy the file, not the link)

top

List process resource usage. By default having the most CPU-intensive process on top. Press > to have it sort on another column. Press 1 to have usage for each CPU apart.

lscpu

List CPU information

free

Show memory usage

cat /etc/sysctl.conf|grep swappiness

Check swappines (the eager the system will swap with). A higher number means more swapping will happen. 0 is not no swapping but minimal swapping.

uname -a

Show kernel version

mountpoint -q <directory>

Check if <directory> is in use as mountpoint

chage -l <username>

Show password aging status

PS1="[\u@\h \W]\$ "

Set shell prompt to '[username@hostname <curdir>]$ '

\w for whole current path

Debian

/var/run/reboot-required

If this file exists a reboot is required

RedHat (RHEL)

/etc/redhat-release

Redhat version installed

for file in /proc/*/status ; do awk '/VmSwap|Name/{printf $2 " " $3}END{ print ""}' $file; done

Find swapspace usage per process

yum list

Show all packages on the rpm-server

yum install <packagename>

Install a package from a rpm-repository

rpm -qa

List all installed packages. Add -i for details

rpm -ivh <rpm-file>

Install package in rpm-file

rpm -Uvh <rpm-file>

Update package in rpm-file

Bash

:

No operation (NOP)

Raspberry pi autologon

In /etc/lightdm/lightdm.conf comment this line out (by putting a # in front of it)

lightdm.conf:autologin-user=pi