Renaming a host is not, in general, a pleasant experience. The general requirement is that you must find everywhere that your hostname is specified and change it.
In OpenVMS, this can be an extensive process, and even require relicensing if you have licenses that depend on your hostname. It can also require rebooting of an entire VMS cluster if you miss changing a parameter. The full details are in the VMS FAQ such as this one (dated from 2001) from faqs.org or this one from HP (undated). Hoffman Labs has a copy from September 2006; there is information on changing a node name in section 5.7.
Not that in changing the OpenVMS hostname in a cluster, you must change the SCSNODE parameter (which changes the cluster node’s nodename). If you change the SCSNODE parameter, you must change the SCSSYSTEMID as well or the entire cluster will refuse to function until it is reconfigured. The cluster tracks the pairing between these two parameters, and if the pair changes, then the cluster stops working normally.
For UNIX in general, one way to do it is to go to the /etc directory as root and run a search:
$ su -
# cd /etc
# find . -type f -print | xargs grep -i myhost
After running this, change all of the instances of myhost that is found.
This is the way to change hostnames in Solaris, including Solaris 9 and Solaris 10. Debian and derivatives (including Ubuntu and Linux Mint) and HP-UX make it simpler.
In Debian, there is a file called /etc/hostname. This will contain the current setting of the hostname. Change this to your desired new hostname, then run the shell script /etc/init.d/hostname.sh.
In HP-UX, change to root and run the program set_parms with the hostname option:
# set_parms hostname
For all of these possibilities, the best thing to do is to reboot afterwards: this will test the new setup as well as change any in-memory hostname settings.
Changing a hostname is a drastic measure, and will include much in the way of system modification and updates. Changing the actual hostname is very likely only the beginning; there may be clients that are set up to contact the host, and any services that the server provided (e.g., NTP server, FTP server, web server, NIS server, etc.) will require reconfiguration on the clients to use the new hostname.
In summary, the very best thing to do is to get the name right in the first place.
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