eXtensions: AMITIAE

AMITIAE - Wednesday 21 December 2011

Key Commands on a Mac (3): More Startup keys and Suggestions for Use

Keys

I split the startup section into two parts because of the complex nature of some commands here. A long text is also harder to read and users may miss something important. In this part I outline keys that may be used at startup for some deeper maintenance, including work at the Unix command line. Back up essential data before considering using them. If in doubt, don't. A pause, or asking someone who does know may be better approaches. Links to other sections are at the end of this article.

Unix at Startup

Not all users realise how important the grey disks are; while some users may buy used Macs and the previous owner may forget to send the disks along. It may be possible to ask for a replacement set from Apple, but users always want these yesterday and not in a few days time when they arrive by DHL. There is a way to make a repair but some users may balk as it requires using the Unix interface. I suggest that before users do this for real, they have a look at what the startup looks like underneath that graphic interface we are used to.

Pressing the start button then the combination of Command + V keys. This enters "Verbose" mode and the screen appears black with lots of white text scrolling past. It may be possible to spot a problem just by using this startup method, but if not, at least a user could have an idea of what to expect when it is time to do it for real.

Running a file and system check in Unix is like using the Disk Utility. If the disks are lost, it may fix the problem. it is not guaranteed as, like with Disk Utility, there are some problems that may need stronger software like Disk Warrior or TechTool Pro. We start the computer in a similar way as for Verbose mode, but for Single User mode we use the Command + S keys. When the Unix text has stopped scrolling, we see a prompt: usually indicated by a # (or a $) sign. It is here that commands are typed in. At this stage, it may be just worthwhile to press the return (enter) key a couple of times: get the feel of it. The check and repair is made by entering the characters fsck followed by a space, then a dash - and then fy (or yf). It should look on the screen like

fsck -fy

The command is for a file-system check (fsck) with some additional parameters indicated by the dash: f for "force" and y for "Yes". This will make sure the check is completed and all repairs are done without asking each time.

We press the Enter (return) key and several lines of text will appear one by one as the disk is checked. If all is well, at the end it should report the disk (name) appears to be OK. If there is a fault, it will run again. Sometimes several faults are found and it may take a while to effect repairs. At the end, I type in the command, reboot and after a few end tasks the computer will start again with the familiar OS X interface.

Target Mode - T-key

If it is necessary to make more repairs, or to connect one machine to another, a computer started in Target mode acts as slave to the other computer's Master. Both computers should be shut down then linked using a Firewire cable. The slave (the one needing repair) is started with the T key pressed. This will not work if there is a Firmware Password used (see below). The monitor will display a large Firewire icon that floats round the screen area. When the other computer is started normally, the slave computer appears as a disk on the desktop. In this situation, files can be added, copied or removed from the slave (data transfer is fast in this way) or the disk can be repaired using utilities (like Disk Warrior) from the Master computer. When finished, the slave computer is powered down and the cable is removed.

Finding OS X

If there are startup problems, as may happen if the installation is not clean, using X at startup will force the computer to seek an OS X startup disk. It may be that the hard disk will not be accessible for a number of reasons, so this would look for a system on an external disk (USB, Firewire). The Option key is especially useful, particularly if the computer is protected with a Firmware Password: it cannot be started using any external disk until unlocked.

When the Option key is used, a bare interface is shown with icons for any disks that are connected to the computer. If a padlock icon is displayed, nothing can be done until the Firmare password is entered. If there is no lock, or the protection is unlocked, the startup disk can be selected using the arrow keys. When the right disk is highlighted, the enter key should start the computer (presuming all is well with the disk).

Using Option + N is a Network boot (from a disk image). It has always been in OS X, but I have never seen it used.

NVRAM reset

At times it may be necessary to reset NVRAM (non-volatile random access memory): a type of memory that holds its information when there is no power. It contains information necessary for the Mac to run properly, but sometimes it needs resetting. Try to place the fingers over the keys before doing it for real. The keys are spaced in such a way that, pressing the power key as well, 3 hands may be better. It can be done with 2. The keys for resetting NVRAM are Option + Command + P + R and when the computer starts, keep holding the keys until it cycles through a couple of times: there are beeps each time.

Ejecting a Disk

Related to the startup is the way to eject a disk that did not come out of the optical drive when it should have done. Instead of a key, however, a user would hold down the mouse (or trackpad) button during the normal start. This ejects disks if they are not physically stuck.

Not Recommended

The key commands outlined in Part 1 that we have at our disposal when using the Mac and its applications are useful and I urge users to learn these for more efficient working practices. The key commands I have outlined above are not recommended at all for the new user (with the exception of Safe Boot). Access to certain parts of the system using some of these key commands may leave you open to causing damage, resulting in a loss of data (particularly if not backed up) or needing a reinstall of OS X. That is not to say they should not be used: they are included precisely because we may need access to some functions outside the normal operating system. Do not try these unless absolutely necessary and read before you try: knowing what to expect will reduce risk. As ever, I also urge that any user backup data before trying any such maintenance processes.