Unknown hostname in Terminal

Question

I suddenly saw that my hostname in the Terminal has changed to "unknown406c8f255bd7". I checked the Computer name under System Pref>>Sharing and its the correct one("ABC_Macbook_Pro"). I further checked the environment variable or used hostname command and i could see the unknown hostname "unknown406c8f255bd7" there.
When i try to change the hostname thru terminal, it gives me this error "hostname: sethostname: Operation not permitted".
I tried opening a new terminal window but it did not help.
I searched thru the existing forum discussions but could not find anything relevant.
Can someone tell me why the hostname under Sharing and environment variable have different values?
Thanks

Answer 1

'bash' the default shell has a default prompt that gets your hostname by taking your IP address and doing a reverse DNS lookup and if the DNS server returns a value, it uses that value. If AND ONLY IF the DNS server does not return anything will your System Preferences -> Sharing -> Computer name.
So your DNS server has returned unknown406c8f255bd7 and bash is using it.
You have a few choices.
Get your DNS server to stop returning unknown406c8f255bd7
Change your bash prompt to use something else for your command prompt.  Add the following to your .bash_profile or .bash_login or .profile (whichever one you happen to already have; if you do not have one of the above, then create your own .bash_profile using - nano .bash_profile)
            PS1='$(networksetup -getcomputername):\W \u\$ '
Other?