code cat

sysroot 는 컴파일 시에 필요한 header/lib 들을 찾는 경로에 대한 베이스 경로를 지정해 줄 수 있다.

여러가지 용도로 사용할 수 있겠으나, 다음과 같은 경우에 우선 쓸 수 있다.

1. gdb 로 디버깅 시, 타깃머신(gdbserver가 동작중)의 라이브러리들이 소스머신(gdb 동작중)의 라이브러리들과 매칭이 되지 않을 때.

2. toolchain이 소스와 제공(android경우)되어 그 toolchain을 써야 하나, bionic libc에서 지원하지 않는 라이브러리 함수를 어플리케이션이 사용해야 할 때.

위의 노란 부분은 gcc에서 sysroot 사용법에 대한 설명이다.  --sysroot=dir을 설정하면, 컴파일러께서는 dir/usr/include, dir/usr/lib 등으로 찾으신다.

라고 나오는 에러는 흔히 switch-case문에서 case안에서 변수 선언 & 초기화를 할 때 나올 수 있는 문제이다.  이는 언어에서 정한 standard를 벗어난 경우이며, -fpermissive를 써서 호환가능하게 해 줄 수는 있지만, 쓰지 말고, 코드를 fix하는 방향으로 가도록 하자.

출처:http://chaoxifer-univ.blogspot.kr/2010/10/devtty-devconsole.html

/dev/tty 와 /dev/console의 차이점

There is a subtle difference between the console and the terminal. In a windowed environment, a tty terminal is associated with each shell session; in other words, each command line window such as an xterm is a separate terminal. Redirection to /dev/tty sends output to the active window. The console, on the other hand, is the screen. It is the monitor in general. Most windowing programs provide a special switch to the shell windows that will link /dev/console to the window instead of writing output directly on the screen. In any event, output can be redirected to these devices quite easily.

출처:http://unix.stackexchange.com/questions/60641/linux-difference-between-dev-console-dev-tty-and-dev-tty0

From the documentation:

/dev/tty        Current TTY device
/dev/console    System console
/dev/tty0       Current virtual console

In the good old days /dev/console was System Administrator console. And TTYs were users' serial devices attached to a server. Now /dev/console and /dev/tty0 represent current display and usually are the same. You can override it for example by adding console=ttyS0 to grub.conf. After that your /dev/tty0 is a monitor and /dev/console is /dev/ttyS0.

An exercise to show the difference between /dev/tty and /dev/tty0:

Switch to the 2nd console by pressing Ctrl+Alt+F2. Login as root. Type sleep 5; echo tty0 > /dev/tty0. Press Enter and switch to the 3rd console by pressing Alt+F3. Now switch back to the 2nd console by pressing Alt+F2. Type sleep 5; echo tty > /dev/tty, press Enter and switch to the 3rd console.

You can see that tty is the console where process starts, and tty0 is a always current console.

• /dev/console is a virtual set of devices which can be set as a parameter at boot time. It might be redirected to a serial device or a virtual console and by default points to /dev/tty0. When multiple console= options are passed to the kernel, the console output will go to more than one device.

• /dev/tty0 is the current virtual console

• /dev/tty[1-x] is one of the virtual consoles you switch to with control-alt-F1 and so on.

• /dev/tty is the console used by the process querying it. Unlike the other devices, you do not need root privileges to write to it. Note also that processes like the ones launched by cron and similar batch processes have no usable /dev/tty, as they aren't associated with any. These processes have a ? in the TTY column of ps -ef output.