Single User Mode:

dstranathandstranathan
Posted:
in macOS edited January 2014
I have questions about single-user mode in OS X. Please answer if you can. (FYI: single-user mode is achieved by holding the "S" and "Apple"(command) keys at boot time)



1) Do all *NIX's have a single-user mode? If so, are they all as easy to activate as OS X (i.e.; a key combo at startup)?



2) Does root account have to be enabled to use single-user mode? No, right?



3) Logging in using single-user mode gives the user root powers, right?



3) Isn't single-user mode a HUGE security issue? What's the point of password-protecting my root account if somebody can walk right up to my OS X box and reboot in single-user mode and get the results of root,right?



4) What is the primary usuage of single-user mode, besides running fsck utilities?



5) What are the limitations of single-user mode?



6) I heard that single-user mode is "read-only". What does that mean, exactly? If single-user mode is similar to root, then how can it be "read-only"?



7) Can single-user mode be password protected?



8) Is OS X's single-user mode similar to a Windows "safe mode" session?





Thanks!

Comments

  • Reply 1 of 2
    kickahakickaha Posts: 8,760member
    [quote]Originally posted by dstranathan:

    <strong>I have questions about single-user mode in OS X. Please answer if you can. (FYI: single-user mode is achieved by holding the "S" and "Apple"(command) keys at boot time)



    1) Do all *NIX's have a single-user mode? If so, are they all as easy to activate as OS X (i.e.; a key combo at startup)?</strong><hr></blockquote>



    Most all, and usually something similar.



    [quote]<strong>

    2) Does root account have to be enabled to use single-user mode? No, right?</strong><hr></blockquote>



    Correct.



    [quote]<strong>

    3) Logging in using single-user mode gives the user root powers, right?</strong><hr></blockquote>



    Correct, in that permissions are effectively ignored.



    [quote]<strong>

    3) Isn't single-user mode a HUGE security issue? What's the point of password-protecting my root account if somebody can walk right up to my OS X box and reboot in single-user mode and get the results of root,right?



    7) Can single-user mode be password protected?</strong><hr></blockquote>



    You can password protect the *hardware* at the OpenFirmware level.



    And you're right, anyone can walk up and violate your security... that's just a given. Heck, they don't even have to know their way around the command line: pop a boot CD in the CD-ROM, hold down 'C' on boot. Hook up an iPod with a bootable copy of the OS, and hold down 'option' on boot. Plenty of ways. Single-user is just one of many approaches... hence the OpenFirmware lockdown. You can get more info at Apple.



    [quote]<strong>4) What is the primary usuage of single-user mode, besides running fsck utilities?



    5) What are the limitations of single-user mode?</strong><hr></blockquote>



    General troubleshooting, and not many. You're root. You can do anything you like... but you have to do everything yourself. Want that external FireWire drive mounted? You have to do it. It's the ultimate in being able to do anything... and needing to know a lot to do anything useful.



    [quote]<strong>6) I heard that single-user mode is "read-only". What does that mean, exactly? If single-user mode is similar to root, then how can it be "read-only"?</strong><hr></blockquote>



    The drives initially come up read only - you have to manually check them and mount them to be read/write.



    [quote]<strong>8) Is OS X's single-user mode similar to a Windows "safe mode" session?</strong><hr></blockquote>



    Only in that the minimal OS has been brought up. I believe what you're looking for is something like the old MacOS behaviour when booting while holding down shift to disable extensions. I *believe* this is back in 10.2... anyone care to confirm?
  • Reply 2 of 2
    ghost_user_nameghost_user_name Posts: 22,667member
    [quote]Originally posted by Kickaha:

    <strong>Only in that the minimal OS has been brought up. I believe what you're looking for is something like the old MacOS behaviour when booting while holding down shift to disable extensions. I *believe* this is back in 10.2... anyone care to confirm?</strong><hr></blockquote>Correct. This works in both 10.1 and 10.2 when holding the shift key. I believe it allows only a specific, minimal set of kexts to load. In 10.2, the message Safe Mode is displayed at the bottom of the startup progress window.
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