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Re: screen in single user mode - "cannot open /dev/console"

From: John Davidorff Pell
Subject: Re: screen in single user mode - "cannot open /dev/console"
Date: Wed, 21 May 2008 22:01:11 -0700

Generally speaking, most of the system does not function while in single user mode. Single user mode is not meant to be used. It exists simply to assist developers who may hose their systems while developing something and who need to delete some kext or something which is preventing a full boot.

Single user mode is NOT the same as a console login. If you want a textual login then start up normally, and choose "Other..." at the login window prompt and enter ">console" (without quotes). If you do not see "Other..." then hold option and press down, then while still holding option press return. This will take you to the "Other..." pane where you can enter ">console".

The /dev/console pseudo-device exists as a compatibility kludge for two reasons: (1) for applications which assume that the implementation detail of /dev/console being the currently-active-on-screen-tty-like- device will be true forever, and (2) to provide a very small bit of information about who the current sitting-at-the-computer user is. Obviously, neither of these cases have any meaning in single-user mode. (Technically, /dev/console is a link to an invisible device which is the real currently-active-on-screen-tty-like-device, but its hidden so that people don't start making assumptions about that one too!)

You can think of "single user mode" as really meaning "pre-boot mode". Nothing is running, no services are active, and you can't do jack-shit.

The previous reply sent to the list does not apply at all in single- user mode since there are no users in single-user mode. There is no user database, there is no directory services available, there ain't nothing.

I hope that my above rant at least makes sense so you can understand why it isn't working for you.


P.S. You should generally explain what sort of system you are on. Mac OS X is the only system that I know of that calls something "single user mode". On linux, the closest thing is "run level 0". However, its not a very good description of Mac OS X's single-user mode because Mac OS X is *much* more dependent on system services which have to be started (or, rather, registered) first.

On 21 May 2008, at 05:48, soumen wrote:


When I try to run screen in single user mode, I get the error "cannot open /dev/console". I can use screen without any problems in multiuser mode.

Any idea/explanations for this?

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