Add/view/delete an entry to iptables to enable Apache/VNCServer/FTP, etc.

The default CentOS 5.6 firewall configuration does not allow Apache httpd traffic on port 80.  In order to open the port for utilization, a change must be made to the firewall configuration.

iptables -I INPUT -p tcp -m tcp ––dport 80 -j ACCEPT

To open a hole for VNCServer (running on display 20):

iptables -I INPUT -p tcp -m tcp ––dport 5920 -j ACCEPT

To open a hole for VNCServer (running on display 20) web base interface:

iptables -I INPUT -p tcp -m tcp ––dport 5820 -j ACCEPT

To display the openings you’ve created in your firewall:

iptables -L INPUT -n ––line-numbers

To remove a line entry from your iptables file (for example, entry #3):

iptables -D INPUT 3


There are two dashes in front of parameters such as “––line-numbers” and “––dport.”

The iptables service must be saved, and restarted before changes take effect.

service iptables save

service iptables restart

manually add new user to Red Hat/Fedora/CentOS

To manually add a new user to a  Red Hat/Fedora/CentOS intall which is utilizing shadow passwords:

As root

  • cp /etc/passwd /etc/passwd.bak (make a back-up copy of your password file)
  • cp /etc/shadow /etc/shadow.bak (make a back-up copy of your shadow password file)
  • cp /etc/group /etc/group.bak (make a back-up copy of your group file)
  • vipw  (to open passwd file in vi)
  • <shift> g  (to get to end of file)
  • a (append at end of cursor)
  • user01:x:501:501:User 01:/home/user01:/bin/bash  (add the new user)
  • :wq  (write file and quit vi)
  • A prompt will indicate that you are using shadow passwords, and do you want to edit the /etc/shadow now.  Answer: n
  • vi /etc/group  (to open group file in vi)
  • <shift> g  (to get to end of file)
  • a (append at end of cursor)
  • user01:x:501:user01 <enter>
  • admins:x:502:user01 (create a new group called admins and put user01 into it)
  • :wq  (write file and quit vi)
  • pwconv  (add the new entry from your passwd file into shadow password file)
  • passwd user01  (set the new user password)
  • (prompted twice for new user password)
  • mkdir /home/user01
  • cp /etc/skel/.* /home/user01 (copy all files from skel to new user home directory)
  • cp -r /etc/skel/.kde /home/user01
  • cp -r /etc/skel/.mozilla /home/user01
  • chown -R user01:user01 /home/user01  (Change the owner of user01 home directory to user01)
  • visudo -f /etc/sudoers
  • After root   ALL=(ALL)    ALL add new line and:  %admins   ALL=(ALL)    NOPASSWD: ALL  (this allows members of admins group to sudo as root, without a password.)

enable windows manager in linux vncserver

Modify your ~/.vnc/xstartup file to

The default file looks like this:


# Uncomment the following two lines for normal desktop:
# exec /etc/X11/xinit/xinitrc

Uncomment the “unset SESSION MANAGER” and “exec /etc/X11/xinit/xinitrc” line.  This will start run your default window manager when vnc starts.  Gnome is a lot prettier than the cruddy default gray vnc display with xterm.

Edit sudoers file in Redhat/Fedora/CentOS

To allow certain users to act as root (su -, or sudo), you must add them to the sudoers file (/etc/sudoers).

The sudoers file must be edited using the visudo command.  See the sudo webpage.

As root:

visudo -f /etc/sudoers

Edit the file to add the correct permissions.  In this case, give members of the group “adm” permission to do just about everything.

%adm     ALL=(ALL)     NOPASSWD: ALL

Save the changes using “:wq”



Add gcc and other required build tools in Ubuntu

I went to run ./configure to begin the install of ImageMagick-6.2.9 and was informed that I was missing a gcc compiler.  I looked in Synaptic, which indicated that I did have a gcc compiler installed.  Then I did a search for it, which indicated that it was located in /usr/lib directory.  So, I added that to my PATH in my .bashrc and logged out and back in.  gcc was still not found when I tried to run the configure. 

I went to and found the following helpful command which got me the files required to configure the install (must be run as root, or sudo):

sudo apt-get install build-essentials