df -hl 查看磁盘剩余空间

du -sm 文件夹
返回该文件夹总M数

更多功能查看：
df --help
du --help

du --help
用法：du [选项]... [文件]...
总结每个<文件>的磁盘用量，目录则取总用量。

长选项必须用的参数在使用短选项时也是必须的。
-a, --all             write counts for all files, not just directories
      --apparent-size   print apparent sizes, rather than disk usage; although
                          the apparent size is usually smaller, it may be
                          larger due to holes in (`sparse') files, internal
                          fragmentation, indirect blocks, and the like
-B, --block-size=SIZE use SIZE-byte blocks
-b, --bytes           equivalent to `--apparent-size --block-size=1'
-c, --total           produce a grand total
-D, --dereference-args dereference FILEs that are symbolic links
-H                    like --si, but also evokes a warning; will soon
                        change to be equivalent to --dereference-args (-D)
-h, --human-readable print sizes in human readable format (e.g., 1K 234M 2G)
      --si              like -h, but use powers of 1000 not 1024
-k                    like --block-size=1K
-l, --count-links     count sizes many times if hard linked
-L, --dereference     dereference all symbolic links
-P, --no-dereference don't follow any symbolic links (this is the default)
-0, --null            end each output line with 0 byte rather than newline
-S, --separate-dirs   do not include size of subdirectories
-s, --summarize       display only a total for each argument
-x, --one-file-system skip directories on different filesystems
-X FILE, --exclude-from=FILE Exclude files that match any pattern in FILE.
      --exclude=PATTERN Exclude files that match PATTERN.
      --max-depth=N     print the total for a directory (or file, with --all)
                          only if it is N or fewer levels below the command
                          line argument; --max-depth=0 is the same as
                          --summarize
      --help     显示此帮助信息并离开
      --version 显示版本信息并离开