Single-User Mode


Single-user mode is a Unix system mode from bootup created for administrative and maintenance activities, a mode where the machine has no network resources and can only support a single user logged in. Single-user mode will absolutely demand complete control of the system. When the system is in this single-user mode, whoever is logged in becomes root. This is, however, a minimal system startup state so don't fear, it is merely for diagnostics. If you do become interested in repairing a non-booting Unix system, or want to try to repair problems in your system, you may want to learn about this mode. Only the root partition is mounted, so only commands that reside in the root file system are available. As well, every Unix machine can be configured to boot into single-user mode.

Single-user mode can also be viewed as a maintenance mode that enables the root user to repair problems with the system without having to worry about other users changing things that they are working on. This is essentially what it is used for. If you have bootup problems, then ask your system administrator, and look yourself to see what is done.

With some versions of Unix, if a machine experiences a particularly hard crash, it might reboot itself into single-user mode automatically. This is why you may see it as a Unix end user; if you notice something different, then ask for help. The system may have suffered a hard crash and is now waiting for your help!

Some versions of Unix and Linux will require you to give up a root password before any commands can be entered, and others come up directly into a root shell; this varies by distribution and configuration. If you happen to crash a Unix machine and it comes up in single-user mode, it is better you do absolutely nothing and ask for help because the system is prepped for the experienced administrator, not the inexperienced end user. If the wrong things are entered, the system could become worse, or logging and troubleshooting data can be lost. Anything you do has the potential to make diagnosing the crash impossible; worse, it can have devastating effects on the system. At the same time, if you are at home in your lab, go to town. Look online or get more books on how to figure out how to operate this mode and try to simulate issues to get yourself comfortable with troubleshooting and entering the mode manually.



    SAMS Teach Yourself Unix in 10 Minutes
    Sams Teach Yourself Unix in 10 Minutes (2nd Edition)
    ISBN: 0672327643
    EAN: 2147483647
    Year: 2005
    Pages: 170

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