Techno Thoughts!

To recursively chmod all files in the current directory (and sub-directories), you can do this:

find . -type d -exec chmod 755 {} \;

To do the same with just files, you can use:

find . -type f -exec chmod 644 {} \;

It’s really useful to not only be able to see the user and directory in your prompt but to have different colours for different users/servers - like a different colour for root or production boxes. Here is the code I use - just put it in a .profile in the users’s home directory (or in /etc/profile for globally):

# Set xterm title:
SHOSTNAME=`hostname -s`
PROMPT_COMMAND='if [ "${TERM}" = "xterm" -o "${TERM}" = "xterm-color" ];
then
   if [ -n "${XTITLE}" ];
   then
      echo -ne "\033]0;${XTITLE}\007";
   else
      echo -ne "\033]0;[${USER}@${SHOSTNAME}:${PWD}]\007" | sed -e "s@${HOME}@\~@";
   fi;
fi'    

# Set Bash Prompt:
if [ "$BASH" ]; then
  PS1='\[\033[1;36m\][\u@\h:\w]\$\[\033[0m\] '
#  alias ls='ls --color'
else
  if [ "`id -u`" -eq 0 ]; then
    PS1='# '
  else
    PS1='$ '
  fi
fi  

export PS1 PROMPT_COMMAND SHOSTNAME

You can change the colours using the following codes:

# Black       0;30     Dark Gray     1;30
# Blue        0;34     Light Blue    1;34
# Green       0;32     Light Green   1;32
# Cyan        0;36     Light Cyan    1;36
# Red         0;31     Light Red     1;31
# Purple      0;35     Light Purple  1;35
# Brown       0;33     Yellow        1;33
# Light Gray  0;37     White         1;37

If you have a high load on your web server, it’s useful to be able to see a list of the current connections on port 80 as sometimes high load can be caused by someone abusing the site - for example scraping it or some kind of denial of service attack.

This code will show a list of the ip’s currently connected to your server on port 80 with a count of the number of connections to the left of it. It’s ordered by the number of connections - highest first:

netstat -ntulpa | grep :80 | awk '{print $5}' | cut -d: -f1 | sort -n | uniq -c | sort -n -r

Have you ever needed to change the same thing in a load of files and have had to sit there and go through each one in turn and make the same change?

This is a really useful and simple command:

perl -pi -w -e 's/from text/to text/g;' *

It simply goes through all files matching * and runs the regular expression, ’s/from text/to text/g’ - which means replace all instances of “from text” with “to text”.  nifty!