[Centos] upgradation to centos 3.4

hi, 

i'm new to linux. right now i'm using centos 3.3. i
want to upgrade to centos 3.4.

i haven't used yum before. i have to go through a
proxy to access the internet. so i thought it isn't
able to access the proxy. after some searching on the
net i could set the http proxy in the /etc/profile
file. i used the following lines in the file(with the
actual ip address and port ofcourse).

set "http://my.domain.name:port/"
export proxy_http="http://my.domain.name:port/"

when i became the super user and tried the command
'yum install centos-yumcache', i got the messages
attached below.

[root at achala etc]# yum install centos-yumcache
Gathering header information file(s) from server(s)
Server: CentOS-3.3 - Addons
retrygrab() failed for:
 
http://mirror.centos.org/centos/3.3/addons/i386/headers/header.info
  Executing failover method
failover: out of servers to try
Error getting file
http://mirror.centos.org/centos/3.3/addons/i386/headers/header.info
[Errno 4] IOError: <urlopen error >

there was some info on the centos site that when u
first run yum a lot of headers would be downloaded. i
think i don't have any downloaders with me.

one more thing that i did with the yum.conf file was
that i changed all the "centos-3"'s to "centos" in all
the paths. 

can someone help me with this situation.
thanks for any help.

regards.
chaitanya.



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