Basics

exit        # closes ssh session, closes terminal.
clear       # clear screen, just moves text off screen, like a soft reset.
reset       # unborks terminal
tput
  civis     # hides cursor
  cnorm     # brings cursor back

cd Do (tab)   # this will do nothing because there is a Download and Documents directory
hit tab again and it will then display:
Downloads Documents # we want to go to Documents so we will add a c and hit tab again
cd Doc (tab)  # this will complete the word Documents

ctrl-d    = delet char at cursor
ctrl-l    = clear terminal
ctrl-p    = recall last command to edit
ctrl-r    = search through shell history
ctrl-t    = transpose char at cursor
ctrl-c    = kill a running command
ctrl-z    = suspend current process

ctrl-a    = go to beginning of line
ctrl-e    = go to end of line
alt-f     = move forward by word
alt-b     = move backward by word

ctrl-x-e  = pop into a buffer that then runs
alt-.     = paste arg of last command

ctrl-k    = kill(copy) -> cut to end of line
ctrl-u    = cut to beginning
ctrl-w    = cut by word backwards (space delimited)
alt-bksp  = cut by word backwards (stops at special chars)
ctrl-y    = yank

ctrl-s    = turn off input and output from X!
          # Ctrl+Q to turn X back on.

~.        # ?? not sure about this one: get unstuck if zsh 'hangs' works sometime otherwise ctrl c or q
.         # means current directory but can also mean source like:$ ./.zshrc 
ls        # list of files
cd        # change directory
cd -      # go back and forth between last directories
pwd       # present working directory
pushd     # sets location as a home and go to that location.
popd      # jumps back to last location of pushd
file      # determine file type
locate    # find files by name
updatedb  # update database for locate on linux
which     # locate a command, it's binary or executable
open      # open a file or directory gui.  ex open .

$0        # name of current shell or script
$1        # first argument
$@        # list of all arguments
$#        # number of arguments
$$        # pid of current shell
$?        # exit status of last command
$!        # pid of last background process
!!        # repeat all arguments of last command
!:n       # repeat command arguments from last command
!:n-m     # range repeat
!:n-$     # repeat from N to the end
!*        # repeat all arguments of last command
!^        # get first argument of last command
!$        # get last argument of last command
^abc^def  # run last command, replacing abc with def

[ -d $dir ]               # test if directory exists
[ -e $file ]              # test if file exists
[ -f $file ]              # test if file exists and is a regular file
[ -h $file ]              # test if file exists and is a symbolic link
[ -k $file ]              # test if file exists and sticky bit is set
[ -r $file ]              # test if file exists and is readable
[ -s $file ]              # test if file exists and is not zero
[ -w $file ]              # test if file exists and is writable
[ -x $file ]              # test if file exists and is executable

[ -S $file ]              # test if file exists and is a socket

file1 -nt file2           # test if file1 is newer than file2
file1 -ot file2           # test if file1 is older than file2
file1 -ef file2           # test if files are the same

( ls )    # subshell
(cd uglydir; uglycmd)                   # executes uglycmd while in uglydir
(PATH=/usr/confusing:$PATH; uglycmd)    # executes uglycmd with PATH set
tar cf - dir | (cd dest; tar xfp -)     # duplicates files and folders in dir with permissions faster than cp -r
                                        # target dir must exist before you can use it. [ -d dir -a | dir -ef dest ]

history     # display zsh command history
ctrl-R      # runs reverse history search, repeat to cycle
history -c  # clears history of current browser, needs to be done before next cmd:
rm ~/.zsh_history    # permanantly clears terminal history to fresh start.
space       # start terminal line with a space to exclude from history

whatis    # display the on-line manual descriptions
man       # reference manual
    -f    # gives desceription of what a tool does.
    -u    # update the database of a manpage
    1 utility 2 lowlevel 3 c lib function 4 special devices 5 file formats 6 games 7 misc 8 system
apropos   # search the manual page names and descriptions
    -n    # check commands for syntax without executing
    -x    # echo commands before they are executed.

~steve    # goes to steves home directory, even while logged in as someone else
mkdir     # create a directory/make directories
mkdir -p Website/{static/{cs,js},templates/html}    # as an example
rmdir     # remove empty directories
touch     # change file timestamps/create empty files
cp        # copy files and directories
mv        # move (rename) files
rm        # remove files or directories
chmod     # change permissions of a file
    -t    # remove sticky bit, +t to add
          # makes to only owner/root can rename/delete a file
chown     # change ownership of a file
    -h    # change symbolic links but not actual file
    -R    # recursive (needed for directories) (may also put --max-depth on it)
chgrp     # change group of a file

ping        # check for connection on a source
traceroute  # traces all the nodes on a route
iftop       # displays a table of current bandwidth usage by hosts

cat       # concatenate files and print on the standard output
less      # file perusal filter for crt viewing
nano      # command line text editor for losers
vim       # command line text editor for leet

#STDIN STDOUT STDERR = 0 1 2
>         # replace existing file content or creates new file; redirect STDOUT
>>        # appends (adds) input >> @end of a file; Redirect STDOUT
<         # connects commands STDIN to contents of existing file
|         # called a pipe; connects STDOUT of one command to the STDIN of another
>&        # redirect STDOUT and STDERR to the same place
2>        # redirect STDERR
2>&1      # redirect STDERR to STDOUT
1>&2      # redirect STDOUT to STDERR

# Short-circuit Evaluation (McCarthy)
&&        # first command must succeed for next command to work
||        # next command will execute ONLY if first fails
          # good for error handling; || echo "backup failed"
;         # place multiple commands on one line

# Using EOF instead of going into editor
cat > /dir/dir/file.ext <<EOF
text you want added or used in piping
with multiple lines and no need to
enter editing, good for not too long of stuff
EOF

egrep -i   # search case insensitive
    -v    # inverse search (not containing the word)
    -l    # just show names of file and no sentences
    -L    # all docs with search term
    -c    # shows how many times search term appears in a file
    -n    # same as -c but with line number and sentence word appears in.
    -w    # search for exact term like Hak but not show Haking Hak5 Hakery etc
    -R    # search recursively
    -rn   # rucrusive with line number

sudo      # execute a command as superuser / never use su sudo/ instead:
sudo -s   # operate as superuser until you type exit used to be good for linux but really should use:
sudo zsh # back door method for linux since -s & su usually dont work.
  -c      # gets zsh to execute one command as root.
su        # change user ID or become another user
su - Bob  # change to Bobs zsh environment and oerate in their directory
users     # print the user names of users currently logged in
id        # print real and effective user and group IDs
mkpasswd -m sha-512   # generate password

sysbench --threads=$(nproc) cpu run   # test CPU
uname -a                  # print kernel information
cat /proc/cpuinfo         # print cpu information
free -m                   # print memory information
df -h                     # print disk information

sudo !!   # run last command as superuser
# create a super fast ram disk
mkdir -p /mnt/ram
mount -t tmpfs tmpfs /mnt/ram -o size=8192M
# fix a really long command that you messed up
fc
# tunnel with ssh ( local port 3337 -> remote host's 127.0.0.1 on port 6379)
ssh -L 3337:127.0.0.1:6379 root@emkc.org -N
-> once connect put in background with bg
# quickly create folders
mkdir -p folder/{sub1,sub2}/{sub1,sub2,sub3}
# intercept stdout and log to file
cat file | tee -a log | cat > /dev/null
# exit terminal but leave all processes running
# useful if your ssh'd somewhere and running a long process you can disown and leave
# so the process will continue to completion even if the connection is severed
disown -a && exit
# !$ # means last argument in the last command
mkdir -p /path/to/new/dir && cd !$
# place command to run in the background
some command &
command | sh -x     # runs each file into sh as a execution

sudo adduser username
sudo passwd username
usermod -aG sudo username

sudo mkdir /home/me
sudo usermod --shell /bin/zsh --home /home/me me
sudo chown -R me:me /home/me

some command; read -t 1 -n 10000 discard    # keeps keyboard from doing input while cmd runs
nproc     # list number of processing units
ps        # list process and their ids
ps -ej    # 
ps aux    # list all processes for all users
ps auxf   # adds organized tree list
ps U megacron   # processes for a specific user
kill 4034 # kills process by id number
killall   # kill processes by name

  ps aux | egrep nginx
  namei -om <path>    # shows all privleges along the path

less +F /var/logs/system

ctrl+c  = detatch so you can scroll up
shift+f = reattatch

watch     # runs a command every 2s
free      # shows how much memmory is in a system
top       # displays system resource usage
htop      # displays system resources but in gui (requires install)

HUP (1): Hangup
INT (2): Interrupt
QUIT (3): Quit (generates a core dump used for debugging, 15 does not)
ILL (4): Illegal instruction
ABRT (6): Abort
FPE (8): Floating point exception
KILL (9): Kill (cannot be caught or ignored)
SEGV (11): Segmentation fault
PIPE (13): Broken pipe
ALRM (14): Alarm clock
TERM (15): Termination request (gracefully)
USR1 (10): User-defined signal 1
USR2 (12): User-defined signal 2
CHLD (17): Child process terminated or stopped
CONT (18): Continue executing
STOP (19): Stop executing (cannot be caught or ignored)
TSTP (20): Stop from keyboard
TTIN (21): Background process attempting read from terminal
TTOU (22): Background process attempting write to terminal

ls -al / > lsout.txt      # creates lsout.txt from the output listing our home directory
history | less            # puts list of used commands into a page viewer
cat >> file3              # add notations to end of file3
watch -n 60 hddtemp /dev/sd[c,d,e]    # monitor drive temps

sudo systemctl isolate runlevel0.target
sudo systemctl isolate runlevel1.target
sudo systemctl isolate runlevel3.target
sudo systemctl isolate runlevel5.target
sudo systemctl isolate runlevel6.target

# Get current runlevel
sudo systemctl get-default

# change to runlevel 3
sudo systemctl set-default runlevel3.target