lpic.v1

hardware
------------
lspci
lsusb
lsblk - list block devices
------------
/proc -> representation of running processes, what kernel we are running, what file systems we have mounted, how the kernel was started etc
/sys -> representation of our devices
/dev -> actual device files: block (disk), character (terminals or virtual terminals)
------------
lsusb -v -> verbose listing
------------
virtual file systems
cat /proc/devices -> show what devices are loaded, representative drivers that are loaded
cat /proc/cdmline -> command line arguments passed through the kernel when it has started
------------
usb devices
dmesg -> cat /dev/kmsg
------------
kernel modules
lsmod -> listing loaded drivers
modprobe -r -> unload a loaded driver
modprobe -> load a driver
modinfo -> show info about a kernel module

=====================

booting the system
------------
/proc/cmdline -> 
uname -r -> displays version of the kernel
systems and startup managers: SysVinit (used in earlier version of Red Hat and Debian-based systems), Upstart (developed by Ubuntu), systemd (RHEL, CentOS, Suse and other Debian-based systems)
systemd -> used at the moment on Ubuntu as well
/etc/rcX.d -> folders for runlevels [0-6]
/etc/rcX.d/S* -> services that start automatically in runlevel X
/etc/rcX.d/K* -> services that are not started automatically in runlevel X
------------
systemd-analyze -> display the boot time
systemd-analyze blame -> display the boot time for each service/device
top -p 1 -> show the systemd service/process in top
dmesg -> can be used for monitoring

=================================

runlevels in SysVinit
------------
runlevel 0 -> power off mode
runlevel 1 -> single-user mode
runlevel 2 -> main runlevel in Ubuntu/Debian - dependent on if the GUI was installed or not
runlevel 3 -> text-only (in RH, SUSE) - /etc/inittab
runlevel 4 -> mostly not used or user definable
runlevel 5 -> graphical mode (in RH, SUSE) - /etc/inittab
runlevel 6 -> reboot mode
telinit X -> change the runlevel to X

boot targets (runlevels) in systemd
-----------
runlevel 0 -> poweroff.target
runlevel 1 -> rescue.target
runlevel 2,3,4 -> multiuser.target
runlevel 5 -> graphical.target
runlevel 6 -> reboot.target

systemctl get-default -> displays the default runlevel - no need for root
systemctl set-default -> sets the default runlevel
systemctl isolate *runlevel* -> changes the runlevel
runlevel -> displays the previous and current runlevels - RH
who -r -> displays the previous and current runlevels - RH

shutdown/reboot
-------------
shutdown -h now -> halts the sytem
shutdown -r now -> reboots the sytem
shutdown -r/h +10 "reboots/halts in 10 minutes" -> reboots/halts in 10 minutes and displays a message
shutdown -c -> cancels a pending operation
echo "message" | wall -> displays the message to all users

services
------------
chkconfig *service_name* on/off -> starts/stops the service
service *service_name* start/stop -> starts/stops the service
service *service_name* status -> displays the status of the service
systemctl enable/disable *service_name* -> enables/disables the service
systemctl status *service_name* -> displays information about the status

================================

LVM (Logical Volume Management)
------------
pvcreate /dev/sdc1 -> mark partition as physical volume
vgextend vg1 /dev/sdc1 -> add the physical volume to the existing volume group
lvextend -L +1000 /dev/vg1/data -> extend the available space to the logical volume
resize2fs /dev/vg1/data -> resize the file system

SWAP
------------
swapon -s -> display current swap information
cat /proc/meminfo -> display how the memory is used on the system
df -hT -> display information on all file systems

pv + TAB
vg + TAB
lv + TAB
mount -> get info on all file systems

================================

Bootloader
------------
MBR -> first 512 bytes from the disk
MBR = 446 bytes (assembly code bootloader) + 16 bytex x N (partition tables for 4 primary partitions) + 2 bytes (bootable -> 0xAA55=bootable)
dd if=/dev/sda of=/root/sda.mbr count=1 bs=512 -> backup the MBR
dd if=/root/sda.mbr of=/dev/sda -> restore the MBR

GRUB Legacy
-----------
/boot/grub/menu.lst -> the boot menu from GRUB

GRUB 2
----------
/boot/grub/grub.cfg -> config file
grub-mkconfig -o *file* -> create config file for GRUB
- never make changes to the GRUB config file directly

==================================

Shared libraries
-----------
ldd /bin/ls -> display dependencies for ls
ldd $(which *command*)
- located in /lib or /usr/lib
- can be read from path specified in /etc/ld.so.conf
- can also be read from LD_LIBRARY_PATH
ldconfig -p -> print out the library cache
ldconfig -> rebuild the library cache

==================================

Debian Package Management
------------
dpkg -i package.deb -> install a .deb package
dpkg -r package -> remove the package
dpkg -P package -> purge the package (also uninstall dependencies)
dpkg --get-selections -> display what is installed
dpkg -l 'vim*' -> display all packages available that start with vim
dpkg -S /usr/bin/lp -> to which package the file belongs
dpkg -L package -> list all files belonging to a package
dpkg-reconfigure

/etc/apt/sources.list -> configured repositories
aptitude -> wizard-like
apt-get install *name*
apt-get update
apt-get purge
apt-get autoremove -> remove dependencies after purging the package
apt-get dist-upgrade
apt-cache search *name*
apt-cache show *name* -> detailed information about the package

================================

RH Package Manager (rpm and yum)
--------------
rpm -qa -> display the installed packages
rpm -i package.rpm -> install the rpm package
rpm -qpi package.rpm -> display information on the package
rpm -qpl package.rpm -> list contents of the package
rpm -U package.rpm -> update package
rpm -F package.rpm -> freshen package
rpm -e package -> remove package
rpm -K package.rpm -> check the signature
rpm -V package -> verify or check the integrity of a package
rpm -qpR package.rpm -> show dependencies for the package
rpm -qf /etc/hosts.allow -> list owning package

/etc/yum.conf -> configuration for yum
/etc/yum/repos.d -> configure repos
yum install -y package -> don't ask for confirmation
yum remove package
yum info package
yum search package
yum list installed
yum provides /etc/hosts.allow
yum repolist

yumdownloader -> download packages without installing them
--destdir -> set destination directory
--resolve -> also download dependencies
rpm2cpio package.rpm > package.cpio

====================================

CLI
----------
uname -a -> display anything about the OS
uname -o -> display OS type

pwd vs /usr/bin/pwd

Variable
----------
FRUIT=apple
echo $FRUIT
export FRUIT -> make variable available to all the shells
unset FRUIT -> delete variable

env
set -o
set +o
alias

History
----------
history
!170 -> run the 170th command from the history
!b -> run the latest command from history that starts with letter b
!$ -> use the last used argument
~/.bash_history
CTRL+R -> reverse search within the history
HISTCONTROL=erasedups -> erase duplicates from the history

===================================

Process Text Streams
-----------
cat -> top to bottom
tac -> bottom to top
less
nl -> number the lines within a file
head -n / tail -n
tail -f -> follow log files
tail -f /var/log/messages

tabs X -> set the number of spaces for TAB to X
cat -vet -> also display special characters, i.e. tabs

head /etc/service | fmt -> format the width of the output
head -n 57 /etc/service | pr -> format for printing with page numbers; pr default to 66 number of lines per page

uniq -> remove duplicates
join -> combines unique information from 2 files
paste -> combine 2 files with all the information
sort -> sort on the first character of every line
sort -r -> reverse sort
sort -t':' -> specify the delimiter
sort -n -> numerical sort
sort -k3 -> column 3
wc -l -> number of lines
wc -c -> number of characters
wc -w -> number of words

find /etc -maxdepth 1 -type f -exec wc -l {} \;

split -l 300 /etc/mime.types

tr [a-z] [A-Z] < /etc/services
tr -s [:space:]

sed 's/bash/sh' /etc/passwd
sed '/^#/d'
cut -f1,3 -d':' /etc/passwd
cut -f1 -d$'\t' /etc/services

====================================

Streams, Pipes and Redirects
-----------
>/1> -> redirecting standard output
2> -> redirecting standard errors
>>/1>> -> append
2>&1 -> redirecting standard errors to standard output
tee -> redirect output to a file and to the screen

===================================

Create, Monitor and Kill Processes
----------
screen *command* -> create a new screen and run the command
CTRL+A+D -> detach from the created screen
screen -ls -> list the screens
screen -r *screenID* -> reattach screen
---------------------------------------------------------
1st user
---
screen sleep 100
CTRL+A+D
screen -ls
chmod u+s $(which screen)
chmod 755 /var/run/screen
screen -S demo
CTRL+A
:multiuser on
CTRL+A
:acladd *2nd user*

2nd user
---
screen -x *1st user*/demo

exit -> exit screen sharing
---------------------------------------------------------

nohup *command* -> the command will continue to run after logout
ps -elf
ps aux
pgrep
pkill
killall -u *user*

top
uptime
free
top -p PID -> show only the process with the selected PID

==============================

Process Execution Priorities
------------
nice -> display the default niceness
ps -l -> look for NI (niceness) column
nice -n 10 sleep 300& -> more nice and less CPU time
nice -n -10 sleep 300& -> less nice and more CPU time
renice -n 15 -p PID -> raise the niceness
default niceness = 0
only root can lower the niceness of a process

==============================

Search text files using regular expressions
-------------
^ -> start of the string
$ -> end of the string
[Cc] -> range - either C or c
[a-z] -> range from lowercase a to lowercase z
[a-z_] -> from a to z or underscore
[A-Z]
[0-9]
[:lower:]
[:upper:]
\s -> whitespace
\S -> non-whitespace
\b -> word boundary
\B -> non word boundary
X* -> zero or more X characters
X? -> zero or one occurence of X
X+ -> one or more occurences of X
X{3} -> exactly 3 occurence of X

================================

VIM
-----------
h,j,k,l -> navigation
/text -> search forwards
?text -> search backwards
n -> next item from the search
Shift+n -> previous item from the search
i -> insert before the current character
a -> insert after the current character
I -> insert at the start of the line
A -> insert at the end of the line
o -> insert new line after the current line
dw -> delete the current word
3ds -> delete 3 words starting from the current one
d0 -> deletes up to the start of the line
d$ -> deletes up to the end of the line
dG -> delete everything from the current position to the end of the document
dd -> delete the current line

yw -> copy current word
yy -> copy current line

cw -> clear the current word - delete the current word and enter in insert mode
p -> paste after current position
P -> paste before current position
u -> undo changes

0 -> navigate to the beginning of the line

:e -> reverts to last saved version
:x -> save and exit
ZZ -> save and exit

====================================

Create partitions and file systems
--------------
fdisk -> works only with MBR
parted -> works with GPT and MBR
gdisk -> works with GPT

fdisk /dev/sdX

fdisk -l /dev/sdX -> check if there are created partitions

XFS -> default file system in RHEL/CentOS 7

mkfs -t ext4 /dev/sdX1
mkfs.ext4 /dev/sdX1
mke2fs -t ext4 /dev/sdX1
mkswap /dev/sdX3

===================================

Maintain integrity of file systems
-----------
fsck /dev/sdX1 -> check the named partition
fsck -A -> check all file systems
fsck -R -> exclude root file system for checking
fsck -ARM -> exclude all mounted file systems
fsck -f /dev/sdX1 -> force a check for a partition if it was marked as clean
- always unmount before repair

df -h -> display available space
df -i -> display available inodes
tune2fs -l /dev/sdX1 -> display information on a file system
dumpe2fs /dev/sdX1 -> display information about the superblocks
xfs_info /dev/sdX1 -> display information about XFS file system

====================================

Mounting/unmounting
------------
mount -o rw,noatime /dev/sdX1 /data
noatime -> don't keep the access time
blkid /dev/sdX1 -> display the UUID

========================================

Disk quotas
-------------
apt-get install quota
yum install quota

====================================

File permissions and ownership
-------------
umask xxx -> set default permissions by removing them
newgrp *group* -> switch the group
stat *file* -> view file properties
stat -c %A -> show symbolic permissions
stat -c %a -> show numeric permissions
stat -c %G -> show GID name
stat -c %g -> show GID number
chgrp -> change group ownership
chown -> change user ownership
chmod o+t *folder* -> set sticky bit - allows to only delete files that are owned by your used
chmod 1777 *folder* -> set sticky bit
chmod g+s *folder* -> set GID bit - all new files are going to be group owner by the owner of the directory
chmod g+s *executable* -> the file runs with the GID of the group owner of the file
chmod 2777 *folder* -> set GID bit
chmod u+s *executable* -> set the UID bit - the file runs with the UID of the user that owns the file
chmod 4755 *executable* -> set the UID bit

===========================================

Symbolic and hard links
--------------
ls -ld -> show hard link count
ls -li -> show inode number

===========================================

System files
--------------
/usr -> Unix System Resource - documentation and programs
/opt ->

find
updatedb - locate
whatis
whereis
which
type