常用ubantu的同学们可能经常会遇到设置开机进入文本模式的选择问题，今天就写一下这方面的一点小技巧，相信会对每个人都有一定的帮助。

具体步骤如下：

（1）、修改启动菜单配置文件
# vi /etc/default/grub
修改
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
为：
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash text vga=0x311" 
 
注释：
这里text表示进入文本模式，vga=0x311表示使用Framebuffer显示驱动，
0x311是指示色深和分辨率的参数
      | 640x480 800x600 1024x768 1280x1024
------+-----------------------------------------------------
256   | 0x301     0x303     0x305       0x307
32k   | 0x310     0x313     0x316       0x319
16bpp | 0x311     0x314     0x317       0x31A
16M   | 0x312     0x315     0x318       0x31B
（2）、更新启动菜单
$ sudo update-grub
写入到/boot/grub/grub.cfg
（3）、修改initramfs
$ sudo gedit /etc/initramfs-tools/modules
添加：
vesafb
（4）、
$ sudo gedit /etc/modprobe.d/blacklist-framebuffer.conf
用#注释以下行
# blacklist vesafb
（5）、更新initramfs
$ sudo update-initramfs -u
（生成新的initrd）
（6）、
然后重启机器，即可进入Framebuffer
如果要切换回X11，可以输入：
$ startx
（7）、图形界面切换到字符界面
A、atl+ctrl+shift+F1
B、ctrl+c

写了一个对LCD的测试代码：

#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>
int main()
{
    int fbfd = 0;
    struct fb_var_screeninfo vinfo;
    struct fb_fix_screeninfo finfo;
    long int screensize = 0;
    char *fbp = 0;
    int x = 0, y = 0;
    long int location = 0;

    // Open the file for reading and writing
    fbfd = open("/dev/fb0", O_RDWR);
    if (0 > fbfd) {
        printf("Error: cannot open framebuffer device.\n");
        exit(1);
    }
    printf("The framebuffer device was opened successfully.\n");

    // Get variable screen information
    if (0 > ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {
        printf("Error reading variable information.\n");
        exit(3);
    }

    printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel);

    // Figure out the size of the screen in bytes
    screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;

    // Map the device to memory
    fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,
                       fbfd, 0);
    if ( fbp == MAP_FAILED) {
        printf("Error: failed to map framebuffer device to memory.\n");
        exit(4);
    }
    printf("The framebuffer device was mapped to memory successfully.\n");

unsigned short *lcd = (unsigned short *)fbp;
// Figure out where in memory to put the pixel
    for (int x = 0; x < vinfo.xres; x++)
{
for (int y = 0; y < vinfo.yres; y++) 
        {
*lcd++ = (0x1F << 11);
//*lcd++ = (0x3F << 5);
//*lcd++ = (0x1F);
        }
}

munmap(fbp, screensize);
    printf("The framebuffer device was munmapped to memory successfully.\n");
    close(fbfd);
    printf("The framebuffer device was closed successfully.\n");
    return 0;
}