Hi all,

I am going to retire a RHEL5 server.
What are the important configuration files (in general) to backup.
Thanks in advance!

It depends on which service the server was running.

Not to sound flip about it but disk space is cheap. If I were you I'd back it all up. Once the new server install is up and running fore some time... then you can get rid of the backup.

I have to agree with both of the above.
Without a detailed(!) knowledge of the system in qn, there's no way to tell...

The very basic configuration is in common *.config files that are in /etc and in rc/init scripts and in /etc/sysconfig/ but I'd backup everything to be sure I didn't forget a thing

System files:
Most of the configuration files are inside /etc area.
/etc area:
*.conf, *.ini, auto.master, auto.misc, export, fstab, group, passwd, shadow
{Some important .conf files are dhcpd.conf, namd.conf, resolv.conf, nsswitch.conf, modules.conf etc.}
One important .ini file is php.ini.
/etc/httpd/conf/ area: httpd.conf {Only for web servers}
/etc/samba/ area: smb.conf, smbpasswd {Only for Samba servers}
/etc/ssh area: sshd_config {Only for restricted servers like NIS, DNS, DHCP, mailhost}
/etc/sysconfig: desktop, network, yppasswd
/etc/sysconfig/network-scripts: ifcfg-eth0

Sytem Data:
Most of the data is inside /var area
/var/named {DNS server data files}
/var/lib/mysql {MySQL database files}
/var/yp {NIS data}

Home Directories:
Any native directory (Not NFS mounted area)
/root area

Data area:
Any area which is being used for keeping data
Currently Started/Killed Daemons list à ls /etc/rc5.d > daemon5list
{If machine is running at level 5, similarly for level 3 etc}

The important directories are /etc, /home, /var, and /srv. You may want to add /root, and remove unneeded bits from /var.

rsync is good if you want the files to be directly accessible, tar is fine if you don't.