主要涉及df、du、ls等命令
df 统计文件系统的使用情况。
英文说明：
This manual page documents the GNU version of df. df displays the amount of disk space available on the filesystem containing each file name argument. If no file name is given, the space available on all currently mounted filesystems is shown. Disk space is shown in 1K blocks by default, unless the environment variable POSIXLY_CORRECT
is set, in which case 512-byte blocks are used.
If an argument is the absolute file name of a disk device node containing a mounted filesystem, df shows the space available on that filesystem rather than on the filesystem containing the device node (which is always the root filesystem). This version of df cannot show the space available on unmounted filesystems, because on most kinds of systems doing so requires very nonportable intimate knowledge of filesystem structures.
要点如下：
如果不加参数，显示现在加载的文件系统。默认单位1K-blocks。如果设置了POSIXLY_CORRECT，则以512-byte blocks为单位。该命令针对文件系统，而不是目录，尽管的给的参数可以是目录。
主要参数：
空 显示现在加载的文件系统，不包含0块空间
-a 包含0块空间
－h 易读方式
－k kB为单位
－l 本地
－T 显示文件系统类型
－－sync 返回结果前调用sync命令（有什么用呢？）
实例：
[root@Mother_FLASH ~]# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/md0 28826556 1507948 25854292 6% /usr
/dev/md1 19220436 9153312 9090780 51% /var
/dev/ram1 158667 85032 73635 54% /
/dev/shm 1037388 0 1037388 0% /dev/shm
[root@Mother_FLASH ~]# df -ah
Filesystem Size Used Avail Use% Mounted on
/dev/md0 28G 1.5G 25G 6% /usr
/dev/md1 19G 8.8G 8.7G 51% /var
/dev/ram1 155M 84M 72M 54% /
/dev/proc 0 0 0 - /proc
/dev/sys 0 0 0 - /sys
/dev/devpts 0 0 0 - /dev/pts
/dev/shm 1014M 0 1014M 0% /dev/shm
none 0 0 0 - /proc/sys/fs/binfmt_misc
详细的参考：
-a, --all
include filesystems having 0 blocks
-B, --block-size=SIZE use SIZE-byte blocks
-h, --human-readable
print sizes in human readable format (e.g., 1K 234M 2G)
-H, --si
likewise, but use powers of 1000 not 1024
-i, --inodes
list inode information instead of block usage
-k like --block-size=1K
-l, --local
limit listing to local filesystems
--no-sync
do not invoke sync before getting usage info (default)
-P, --portability
use the POSIX output format
--sync invoke sync before getting usage info
-t, --type=TYPE
limit listing to filesystems of type TYPE
-T, --print-type
print filesystem type
-x, --exclude-type=TYPE
limit listing to filesystems not of type TYPE
-v (ignored)
--help display this help and exit
--version
output version information and exit
SIZE may be (or may be an integer optionally followed by) one of following: kB 1000, K 1024, MB 1000*1000, M
1024*1024, and so on for G, T, P, E, Z, Y.