deleting files requires password

Go to the Finder - click anywhere on your Mac's desktop, and choose File > New Folder.

If a folder appears on your Desktop then continue reading. If not, stop reading.

Open Terminal - it is in your Utilities folder and looks like this

You can find Terminal by using the Finder's Go menu and choosing Utilities, then double-click the Terminal icon.

Copy (drag or triple-click to select the line) and Paste the following commands into the Terminal window, each one followed by the Return key:

mkdir ~/.Trash

If you get the message "File exists" you can ignore it.

Next Copy and Paste the following line, followed by the Return key:

sudo chown $UID ~/.Trash

This time Terminal will ask for your Admin password - the same one you use when you log in to your Mac. Type it and then press the Return key. What you type will not appear, not even with •••• characters.

Next Copy and Paste the following:

chmod u+rwx ~/.Trash

To summarize the above you will be doing this:

Last login: Wed Feb 12 03:21:53 on ttys000

Johns-iMac:~ john$ mkdir ~/.Trash

mkdir: /Users/john/.Trash: File exists

Johns-iMac:~ john$ sudo chown $UID ~/.Trash

Password: (type your password then press Return)

Johns-iMac:~ john$ chmod u+rwx ~/.Trash

Johns-iMac:~ john$

You will be typing the entries in red exactly as shown.

Quit Terminal.

Drag the empty folder you just created to the Trash, confirm that it appears in the Trash, and that you can empty the Trash without requiring your password.

Yes. To fix that, go to System Preferences > Sharing. Click the Edit... button and verify what you enter there is what you want.

You're welcome. Try logging out and logging in again.

The Mac's LocalHostName and ComputerName are derived from the contents of /Library/Preferences/SystemConfiguration/preferences.plist.

You could try deleting that file, but I'd be reluctant to do that without knowing what caused it to be changed to begin with. Needless to say have a backup strategy before contemplating any modifications to your system.

Read what BobHarris had to say about hostname and its relationship to your DNS server in this post: Unknown hostname in Terminal

It's easy enough to fix, but I'd still be concerned about what caused it to change to begin with. Perhaps concern is too strong a word. The OP in that thread said it fixed itself after some number of hours, in which case we'll never know the reason.

I would say my advice in that other post is still valid. Most likely your home router is returning the unknown############ name. Where ############ is your computer's MAC address (Media Access Control address), often displayed as 12:34:56:78:9a:bc.

You can follow the suggestion to change our PS1 prompt, or try thing like power cycling your home router, assuming the home router is your DNS server.

I've just started a new thread, somewhat related perhaps, "strange hostname being assigned." Details are there: Re: strange hostname being assigned . About every two weeks, my Pro (latest Yosemite) will show in console that the hostname is set as .... mac book (correctly), and then seconds later will say hostname is set to internalcheck.apple.com. Each time the lid is opened and the computer used, it does the same, sets correctly then sets to internalcheck.apple.com (always that URL). Turning off the airport, unplugging the Actiontec modem/router for a few seconds, always fixes it as well as assigning a new wan IP. No issues with computer performance or connectivity. I just wonder if it's the Pro doing this, or the modem/router, or the ISP, or Apple, or the boogieman. All sharing off, including bluetooth & Time Machine, modem/router with wpa/wpa2 on, MAC Auth on... Can't find anything else about it anywhere being reported. I even see internalcheck.apple.com in the mail headers that come from the Apple Mail program on the Pro. I don't see this happening with the Mini. Sorry to intervene here, carry on, I just wanted to get Bob's attention and thoughts when you're done here.