不是后缀，记住linux不使用后缀来识别文件类型
你使用 ls -al
drwxr-xr-x. 4 root root 100 Apr 26 15:05 cpu
lrwxrwxrwx. 1 root root 13 Apr 26 15:05 fd -> /proc/self/fd
brw-rw----. 1 root disk 7, 0 Apr 26 15:05 loop0
crw-rw----. 1 root lp 6, 2 Apr 26 15:05 lp2
你仔细看第一位 d代表文件目录文件，l代表链接文件，b代表块设备文件，c代表字符设备文件
`-'
regular file
`b'
block special file
`c'
character special file
`C'
high performance ("contiguous data") file
`d'
directory
`D'
door (Solaris 2.5 and up)
`l'
symbolic link
`M'
off-line ("migrated") file (Cray DMF)
`n'
network special file (HP-UX)
`p'
FIFO (named pipe)
`P'
port (Solaris 10 and up)
`s'
socket
`?'
some other file type