bash

Some bash hotkeys:

Ctrl + A  Go to the beginning of the line you are currently typing on
Ctrl + E  Go to the end of the line you are currently typing on
Ctrl + L  Clears the Screen, similar to the clear command
Ctrl + U  Clears the line before the cursor position. If you are at the end of the line, clears the entire line.
Ctrl + R  Let’s you search through previously used commands
Ctrl + C  Kill whatever you are running
Ctrl + D  Exit the current shell
Ctrl + Z  Puts whatever you are running into a suspended background process. "fg" restores it.
Ctrl + W  Delete the word before the cursor
Ctrl + K  Clear the line after the cursor
Ctrl + T  Swap the last two characters before the cursor
Esc + T  Swap the last two words before the cursor

Some notes about reverse history search. It'll iterative show last command for your search query. For next item press Ctrl-R again. To search forward press Ctrl-S. (On some terminals this bind to freeze, press Ctrl-Q to defreeze) More about history navigation here

Using screen:

1. Run 'screen' to start session. Press Ctrl-a d, or disconnect ssh to detach. Run 'screen -r' to reattach. I usually use 'screen -x' - this will try to reattach, or create new session if no sessions exist.
2. Some hotkeys:
   

   C-a c         Create a new window
   C-a ?         Show key bindings
   C-a 0 .. 9    Switch to window number 0 ... 9
   C-a A         Allow the user to enter a name for the current window
   C-a C         Clear the screen
   C-a h         Write a hardcopy of the current window to the file "hardcopy.n".
   C-a H         Begins/ends logging of the current window to the file "screenlog.n".
   C-a k         Kill current window
   C-a M         Toggles monitoring of the current win (will notify about changes in window)
   C-a [space]   Switch to the next window
   C-a [backsp]  Switch to the previous window
   C-a [Esc]     Enter copy/scrollback mode
   C-a d         Detach screen from this terminal
   C-a D D       Detach and logout
   C-a C-\       Kill all windows and terminate screen
   

3. Ok, lets imagine you watching log in screen's window. Needed part was clipped by top of window. When you scroll window content in tutty - you see old stuff lie here before running screen. To scroll screen's window content you need to go to copy mode by Ctrl-a Esc and here will be available PgUp & PgDn keys for scrolling. And more useful - '/' for forward search, and '?' - for reverse.
4. I often use tutty from mRemote, so titlebar is hidden. I need duplicate screen's window list on screen. This is my customized .screenrc file
   

   # Bind F11 and F12 (NOT F1 and F2) to previous and next screen window
   bindkey -k F1 prev
   bindkey -k F2 next
   
   # From Stephen Shirley
   # Don't block command output if the terminal stops responding
   # (like if the ssh connection times out for example).
   nonblock on
   
   startup_message off
   #nethack on
   caption always
   caption string "%-w %{= BW}%n %t%{-} %+w |%h"
   

Some commands:

grep -v ^# /etc/sysctl.conf

Show file without commented lines (starting with #)

find /etc -mmin -3

Files modified for last 3 minutes

egrep -i 'err|warn' /var/log/messages

Last errors in log

tail -f /var/log/messages

Watch for file changes and show them

netstat -tulpn

Show opened ports

find / -iname ip_queue.o
whereis asterisk

Find file, find program dirs

du -hs

Folder size

tcpdump 'tcp dst port 25' -i eth2

Show outgoing smtp connections