字符设备
ls –l /dev/ “c” 指明该设备节点是字符设备
crw-rw---- 1 root uucp 4, 64 Feb 23 2004 /dev/ttyS0
crw--w---- 1 jdoe tty 136, 1 Feb 23 2004 /dev/pts/1
crw-------- 1 root root 13, 32 Feb 23 2004 /dev/input/mouse0
crw-rw-rw 1 root root 1, 3 Feb 23 2004 /dev/null