man: Manual
pwd：Print working directory
su：Swith user
cd：Change directory
ls：List Files
ps：Process Status
mkdir：Make directory
rmdir：Remove directory
mkfs: Make file system
fsck：File system check
cat: Concatenate
uname: Unix name
df: Disk free
du: Disk usage
lsmod: List modules
mv: Move file
rm: Remove file
cp: Copy file
ln: Link files
fg: Foreground
bg: Background
chown: Change owner
chgrp: Change group
chmod: Change mode
umount: Unmount
dd: 本来应根据其功能描述“Convert an copy”命名为“cc”，但“cc”已经被用以代表“C Complier”，所以命名为“dd”
tar：Tape archive
ldd：List dynamic dependencies
insmod：Install module
rmmod：Remove module
lsmod：List module
