fedora21启动时屏幕变暗backlight

原因：systemd-backlight服务自启动控制了亮度的加载恢复亮度！

SYSTEMD-BACKLIGHT@.SERVICEsystemd-backlight@.servSYSTEMD-BACKLIGHT@.SERVICE(8)

NAME
       systemd-backlight@.service, systemd-backlight - Load and save the
       display backlight brightness at boot and shutdown

SYNOPSIS
       systemd-backlight@.service

       /usr/lib/systemd/systemd-backlight

DESCRIPTION
       systemd-backlight@.service is a service that restores the display
       backlight brightness at early boot and saves it at shutdown. On disk,
       the backlight brightness is stored in /var/lib/systemd/backlight/.

KERNEL COMMAND LINE
       systemd-backlight understands the following kernel command line
       parameter:

       systemd.restore_state=
           Takes a boolean argument. Defaults to "1". If "0", does not restore
           the backlight settings on boot. However, settings will still be
           stored on shutdown.

SEE ALSO
       systemd(1)

systemd 216                                      SYSTEMD-BACKLIGHT@.SERVICE(8)

解决：查看亮度:cat /sys/class/backlight/intel_backlight/brightness

1、停止systemd-backlight服务：systemctl stop systemd-backlight

2、然后获取最大亮度:cat /sys/class/backlight/intel_backlight/max_brightness

3、设置亮度:echo 4882>/var/lib/systemd/backlight/pci-0000:00:02.0:backlight:intel_backlight