此文档用于记录自己遇到的问题和解决办法！ 

1、CentOS执行ftp命令提示ftp:command not found解决方法

centos7.3.1611 安装ftp 客户端工具

[root@xxxx ~]# cat /etc/redhat-release
CentOS Linux release 7.3.1611 (Core)
cat /etc/redhat-release
http://mirror.centos.org/centos/7/os/x86_64/Packages/ftp-0.17-67.el7.x86_64.rpm
rpm -Uvh http://mirror.centos.org/centos/7/os/x86_64/Packages/ftp-0.17-67.el7.x86_64.rpm

2、df -h  du -h ls -h 命令

xxxx@ubuntu:/tmp$ ls -l
total 12200788
-rw-r--r-- 1 xxxx xxxx 12493601071 Mar 14 18:18 Windows.zip

xxxx@ubuntu:/tmp$ ls -lh
total 12G
-rw-r--r-- 1 xxxx xxxx 12G Mar 14 18:18 Windows.zip

Linux du命令用于显示目录或文件的大小。du会显示指定的目录或文件所占用的磁盘空间。

xxxx@ubuntu:/tmp$ du -h
4.0K    ./.X11-unix
4.0K    ./.ICE-unix
12G     .

查看系统磁盘设备，默认是KB为单位：
xxxx@ubuntu:/tmp$ df
Filesystem                  1K-blocks     Used Available Use% Mounted on
/dev/mapper/ubuntu--vg-root  87845160 24205024  59154812  30% /
none                                4        0         4   0% /sys/fs/cgroup
udev                          4019860        4   4019856   1% /dev
tmpfs                          806220      592    805628   1% /run
none                             5120        0      5120   0% /run/lock
none                          4031088        0   4031088   0% /run/shm
none                           102400        0    102400   0% /run/user
/dev/sda1                      240972    37043    191488  17% /boot
使用-h选项以KB以上的单位来显示，可读性高：
xxxx@ubuntu:/tmp$ df -h
Filesystem                   Size  Used Avail Use% Mounted on
/dev/mapper/ubuntu--vg-root   84G   24G   57G  30% /
none                         4.0K     0  4.0K   0% /sys/fs/cgroup
udev                         3.9G  4.0K  3.9G   1% /dev
tmpfs                        788M  592K  787M   1% /run
none                         5.0M     0  5.0M   0% /run/lock
none                         3.9G     0  3.9G   0% /run/shm
none                         100M     0  100M   0% /run/user
/dev/sda1                    236M   37M  187M  17% /boot
查看全部文件系统：
xxxx@ubuntu:/tmp$ df -a
Filesystem                  1K-blocks     Used Available Use% Mounted on
/dev/mapper/ubuntu--vg-root  87845160 24205024  59154812  30% /
proc                                0        0         0    - /proc
sysfs                               0        0         0    - /sys
none                                4        0         4   0% /sys/fs/cgroup
none                                0        0         0    - /sys/fs/fuse/connections
none                                0        0         0    - /sys/kernel/debug
none                                0        0         0    - /sys/kernel/security
udev                          4019860        4   4019856   1% /dev
devpts                              0        0         0    - /dev/pts
tmpfs                          806220      592    805628   1% /run
none                             5120        0      5120   0% /run/lock
none                          4031088        0   4031088   0% /run/shm
none                           102400        0    102400   0% /run/user
none                                0        0         0    - /sys/fs/pstore
cgroup                              0        0         0    - /sys/fs/cgroup/cpuset
cgroup                              0        0         0    - /sys/fs/cgroup/cpu
cgroup                              0        0         0    - /sys/fs/cgroup/cpuacct
cgroup                              0        0         0    - /sys/fs/cgroup/memory
cgroup                              0        0         0    - /sys/fs/cgroup/devices
cgroup                              0        0         0    - /sys/fs/cgroup/freezer
cgroup                              0        0         0    - /sys/fs/cgroup/blkio
cgroup                              0        0         0    - /sys/fs/cgroup/perf_event
cgroup                              0        0         0    - /sys/fs/cgroup/hugetlb
/dev/sda1                      240972    37043    191488  17% /boot
binfmt_misc                         0        0         0    - /proc/sys/fs/binfmt_misc
systemd