check fs type:

file -sL /dev/vda1

/dev/vda1: Linux rev 1.0 ext4 filesystem data (needs journal recovery) (extents) (huge files)

-s, --special-files

Normally, file only attempts to read and determine the type of argument files which stat(2) reports are ordinary files. 

This prevents problems, because reading special files may have pecualiar consequences. 

Specifying the -s option causes file to also read argument files which are block or character special files.

This is useful for determining the filesystem types of the data in raw disk partitions, which are block special files.

This option also causes file to disregard the file size as reported by stat(2) since on some systems it reports a zero size for raw disk partitions.

沒有 -s  會

/dev/vda1: block special

-L, --dereference

option causes symlinks to be followed, as the like-named option in ls(1) (on systems that support symbolic links). 

This is the default if the environment variable POSIXLY_CORRECT is defined.

沒有 -L 會

vda1: symbolic link to `/dev/vda1'