I am trying to understand the output of the who command. When I add the -H flag to print the headers, the second column ( the one signifying the users logged in) is titled LINE. I am trying to understand what LINE is. I am logged into my computer twice, according to the who command, but one of the lines is bad. To understand what that means, I would like to know what LINE is.


1 Answer 1


LINE indicates the TTY the process is running on. It is correct about you being logged into your computer twice, as you are logged in once to Cocoa (the OS X desktop), console, full path: /dev/console, and again in the terminal, ttysXXX, full path: /dev/ttysXXX (where "XXX" is a three-digit number, starting from 001).

console is Darwin's (OS X kernel) only 'real' TTY, the only one that isn't running in a terminal emulator. console, being the only non-emulated TTY is therefore the only one GUIs can run on.

The Apple logo that appears when Cocoa is not running (booting and shut-down) is generated by the kernel except when in verbose mode (start the Mac with the boot argument -V either by holding ctrl-V while booting or running nvram boot-args="-v" as root, however that will make your Mac always boot in verbose mode until you run nvram boot-args="" or clear nvram).

When boot in verbose mode instead of an Apple logo the kernel will log any boot messages and related to /dev/console and anything written to /dev/console will show up on the console and therefore on-screen (since nothing is generating a GUI on it, whether that be Cocoa or the Kernel). The main part of this is how other Unix-like/POSIX systems work.

I know this answer is kind of crappy but I hope it helps.

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