while installing cacti,

It's saying in the last line,

--------------------------------------------
Downloading Packages:
warning: rpmts_HdrFromFdno: V3 DSA signature: NOKEY, key ID 1aa78495


Public key for cacti-0.8.7b-2.el4.rf.noarch.rpm is not installed
---------------------------------------------


Please help me out to resolve the problem.


FYI, I copied the entire log here:


yum install cacti
Setting up Install Process
Setting up repositories
adobe-linux-i386 100% |=========================| 951 B 00:00
dries 100% |=========================| 951 B 00:00
ftp://ftp.oss.eznetsols.org/linux/ce...ta/repomd.xml: [Errno 4] IOError: [Errno ftp error] (101, 'Network is unreachable')
Trying other mirror.
update 100% |=========================| 951 B 00:00
base 100% |=========================| 1.1 kB 00:00
addons 100% |=========================| 951 B 00:00
extras 100% |=========================| 1.1 kB 00:00
Reading repository metadata in from local files
Parsing package install arguments
Resolving Dependencies
--> Populating transaction set with selected packages. Please wait.
---> Package cacti.noarch 0:0.8.7b-2.el4.rf set to be updated
--> Running transaction check
--> Processing Dependency: php-mysql for package: cacti
--> Processing Dependency: php-snmp for package: cacti
--> Restarting Dependency Resolution with new changes.
--> Populating transaction set with selected packages. Please wait.
---> Package php-snmp.i386 0:4.3.9-3.22.15 set to be updated
---> Package php-mysql.i386 0:4.3.9-3.22.15 set to be updated
--> Running transaction check
--> Processing Dependency: php = 4.3.9-3.22.15 for package: php-snmp
--> Processing Dependency: php = 4.3.9-3.22.15 for package: php-mysql
--> Restarting Dependency Resolution with new changes.
--> Populating transaction set with selected packages. Please wait.
---> Package php.i386 0:4.3.9-3.22.15 set to be updated
--> Running transaction check
--> Processing Dependency: php = 4.3.9-3.9 for package: php-devel
--> Processing Dependency: php = 4.3.9-3.9 for package: php-pear
--> Restarting Dependency Resolution with new changes.
--> Populating transaction set with selected packages. Please wait.
---> Package php-pear.i386 0:4.3.9-3.22.15 set to be updated
---> Package php-devel.i386 0:4.3.9-3.22.15 set to be updated
--> Running transaction check

Dependencies Resolved

=============================================================================
Package Arch Version Repository Size
=============================================================================
Installing:
cacti noarch 0.8.7b-2.el4.rf dries 1.9 M
Installing for dependencies:
php-mysql i386 4.3.9-3.22.15 update 37 k
php-snmp i386 4.3.9-3.22.15 update 29 k
Updating for dependencies:
php i386 4.3.9-3.22.15 update 1.3 M
php-devel i386 4.3.9-3.22.15 update 241 k
php-pear i386 4.3.9-3.22.15 update 482 k

Transaction Summary
=============================================================================
Install 3 Package(s)
Update 3 Package(s)
Remove 0 Package(s)
Total download size: 4.0 M
Is this ok [y/N]: y
Downloading Packages:
warning: rpmts_HdrFromFdno: V3 DSA signature: NOKEY, key ID 1aa78495


Public key for cacti-0.8.7b-2.el4.rf.noarch.rpm is not installed

I don't know how such things work in RedHat or Fedora or whatever you're using, but you are getting a warning and not an error. There should be keyrings to hold the keys for the repos you are accessing. In debian systems they're called debian-multimedia-keyring, debian-archive-keyring, and so forth. You might try downloading the equivalent from your own repos.
Cheers,
jdk