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Windows guy need details for changing MTU Settings
Authored by: JohnMFischer on Aug 07, '02 06:57:23PM

I'm a Windows guy, helping our college-bound son get his new iMac setup for use at college this fall. I hope you don't mind a Windows-user asking for help here -- at least I allowed our son to buy an iMAC!

I was relieved to find the help here on changing MTU settings in the Mac OSX environment. I had to do the same thing on our Windows client machines on our home LAN, when I switched from a dial-up to DSL account this summer.

Anyway, I've read FriedDylan's note with the info about changing the root setting, so that the MTU change will "hold" after a reboot. I understand the concept (much like changing the settings in the Windows registry, which I've already done) -- but I'd be bit more comfortable doing it, if I could bother you folks for a bit more detail.

I called Apple to ask for this help, but was told they don't touch the root in Tech Support! I understand their caution, but it sure leaves me out in the cold. So, I'm here hoping you folks will walk me through it. To save some time, let me confirm what I know already, so that your replies can be as specific as possible.

FriedDylan posted this:

"Log in as root and launch the terminal. I used pico but vi and emacs will work, too. Open the network file located at /System -> Library -> StartupItems -> Network -> Network and find the references to setting up your network interface. Add a line and enter ifconfig en1 mtu 1492 for airport or ifconfig en0 mtu 1492 for ethernet."

OK, I followed that, but when I got to the Network folder, I couldn't find anything that referred to "setting up your network interface." I did open a few files/settings, but nothing seemed to be specific to that issue. So, I had nowhere to enter his recommended command of: "ifconfig en1 mtu 1492".

Also, I got the Apple Tech guy to at least tell me how to find the Terminal, and I tried the temporary MTU settings change, which FriedDylan posted uptopic as: "% sudo ifconfig en1 mtu 1492" -- got an error message that there were too many entries or something (didn't record the exact error msg., sorry!) I tried a few variations of that line, but all of them gave an error msg. of one sort or another.

So, I'm back to square one -- I need help! And hopeful this is a good environment in which to find it.

Sincerely,

John M. Fischer,
Portland, Oregon



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Windows guy need details for changing MTU Settings
Authored by: FriedDylan on Aug 07, '02 09:39:51PM

Sorry for the long delay here.. I now realize I didn't offer much for folks not already familiar with OS X's Terminal.

First I'll go through enabling ROOT.

Click your Macintosh HD icon (double) and navigate to Applications->Utilities->NetInfo Manager. Now you will see a window which we'll ignore right now. At the top of the screen roll through the menus for DOMAIN->SECURITY->AUTHENTICATE...

You will be prompted for your admin password. Enter it and repeat the roll through the menus for DOMAIN->SECURITY->Enable Root User.

You're done when you create a password for ROOT.

Log out.

Log in as username: root and enter the password you gave it.

Now you can launch the Terminal Application found at: Macintosh HD->Applications->Utilities->Terminal (drag it to your dock for quick access)

When you see the message: welcome to darwin you can begin to edit the file.

(note: I don't like using sudo.. but you can if you don't want to log out and back in as root. heck, you have to reboot anyway)

At the Terminal prompt type: pico

A text editor will open. Type CTRL+R to read a file and then follow my instructions in my original post to make the changes.

When you are ready to save the changes you need to save the new file. Type CTRL+O to write out the file. And answer the prompts to let it know where to write this file. If you repeat the path you got it from (System/Library/StartupItems/Network/Network) you should be asked if you are sure your want to overrite the file. Answer YES and you're done. Now reboot and you should now have the settings you want everytime!



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Windows guy need details for changing MTU Settings
Authored by: JohnMFischer on Aug 09, '02 12:01:16AM

Thanks so much for the details. I think I can follow that sequence alright. Now, just one more "picky-little-detail" question before I have a go at it:

From talking to the Apple Tech Support guy (who's not allowed to help with root commands!), I got the impression that they won't give that kind of Tech Support because making changes in the Mac OSX root is similar to messing with the Windows Registry. Mickey$oft states strong cautions about fiddling with the registry, but they do give all kinds of info about making such changes. I'm comfortable making changes in my Windows Registry, so I'm not averse to making them in my son's iMac root.

However, Micro$soft strongly encourages that before making any changes to the registry, that we back it up, first. I would assume a similar caution pertains to the Mac OSX root? I'll sniff around here at the Mac OS X Hints website to see if I can find reference to such... but if you happen to check-in here again, perhaps you could drop me a note about this?

Thanks again!

Sincerely,

John M. Fischer,
Portland, Oregon



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Windows guy need details for changing MTU Settings
Authored by: osx4me on Aug 19, '02 08:49:01PM
A few clarifications:

"Working 'in my son's iMac root' " is not what's going on. Think of the Root user (this is a Unix concept) as the "master" user on the computer, that supercedes even the "Administrator." The main account you set up in OS X is in fact the Admin by default.

There are (for example) system config (configuration) files that the computer reads when booting in OS X, that you can only edit as Root (meaning, as the Root user).

Editing these files might seem similar to editing the Registry in Windows. It might seem similar, but there's a better analogy: Have you ever edited Windows (system) config files ? Like editing the msdos.sys file in Windows 98 ? That's a closer parallel to what you're doing in this case, in terms of editing the "Network" config file, in OS X.

The problem with working as Root, is that you can do WHATEVER you want, including deleting key system files. The System will not come back and ask you, "are you sure ?" because it's assumed that as Root, you already know what you're doing. Unix is not chatty, in terms of ever (almost never) asking for confirmation of a given command. When you work in the OS X Terminal, you're getting under the hood of OS X - there's Unix in there. Not what some would call "pure" Unix, but a flavor of Unix nonetheless.

Once you've enable the Root user, you should normally use the command "sudo" in the terminal, instead of actually logging in as the Root. This allows you to do something with Root priveleges without being Root.

The easiest way to enable "Root" is to launch the terminal and type: sudo passwd root

it will ask you for your admin (normal) password. Enter it. Then it will ask for a password for Root, and then again to confirm. Don't lose your password for the Root user.

Next, in the terminal, you'd type: cd /system/library/startupitems/network

and then: sudo pico network

In which you're giving the commands: I want to temporarily work as the Root user ("sudo"), and using the file-editor named "Pico", I want to edit the file named "network."

Then, use the down arrow key to scroll through and look for a header/comment filed that reads:

## # Configure interfaces ##

I don't have DSL or use PPoE at home, but I'm pretty sure that the spot I describe above, is what you're looking for.

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