关于du命令：

du命令显示Linux文件系统上的文件或者目录使用的磁盘空间估计。
如果我们想知道Ubuntu中的特定目录或者文件使用的空间，请使用du命令。

语法：

以下是如何使用du命令的示例语法。

du [OPTION. ] [FILE].

选项：

例子：

以下是如何在Ubuntu Linux上运行和使用du的一些示例。

查看/var目录大小或者/var目录在磁盘上使用多少空间：

du /var

以人类可读格式显示

du -sh /var

如果我们未以root身份登录，则需要运行sudo来使用du命令。

sudo du -sh /var

查看/var目录中的子目录使用的大小：

sudo du -sh /var/*

或者使用-max-depth = 1命令选项。

sudo du -h --max-depth=1 /var

输出：

Output:
4.0K    /var/mail
4.0K    /var/local
59M /var/log
127M    /var/cache
44K /var/tmp
1.5G    /var/lib
4.0K    /var/opt
4.0K    /var/metrics
168K    /var/snap
40K /var/spool
4.0K    /var/crash
3.3M    /var/backups
1.7G    /var

我们还可以将DU命令与其他命令和管道组合起来，并显示更准确的信息。

在/var目录中打印出前3大的目录：

sudo du -h /var | sort -rh | head -3

它应该输出类似于以下行的内容：

Output:
1.7G    /var
1.5G    /var/lib
1.2G    /var/lib/snapd

du 命令帮助文档：

Usage: du [OPTION].  [FILE]. 
  or:  du [OPTION].  --files0-from=F
Summarize disk usage of the set of FILEs, recursively for directories.
Mandatory arguments to long options are mandatory for short options too.
  -0, --null            end each output line with NUL, not newline
  -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  scale sizes by SIZE before printing them; e.g.,
                           '-BM' prints sizes in units of 1,048,576 bytes;
                           see SIZE format below
  -b, --bytes           equivalent to '--apparent-size --block-size=1'
  -c, --total           produce a grand total
  -D, --dereference-args  dereference only symlinks that are listed on the
                          command line
  -d, --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
      --files0-from=F   summarize disk usage of the
                          NUL-terminated file names specified in file F;
                          if F is -, then read names from standard input
  -H                    equivalent to --dereference-args (-D)
  -h, --human-readable  print sizes in human readable format (e.g., 1K 234M 2G)
      --inodes          list inode usage information instead of block usage
  -k                    like --block-size=1K
  -L, --dereference     dereference all symbolic links
  -l, --count-links     count sizes many times if hard linked
  -m                    like --block-size=1M
  -P, --no-dereference  don't follow any symbolic links (this is the default)
  -S, --separate-dirs   for directories do not include size of subdirectories
      --si              like -h, but use powers of 1000 not 1024
  -s, --summarize       display only a total for each argument
  -t, --threshold=SIZE  exclude entries smaller than SIZE if positive,
                          or entries greater than SIZE if negative
      --time            show time of the last modification of any file in the
                          directory, or any of its subdirectories
      --time=WORD       show time as WORD instead of modification time:
                          atime, access, use, ctime or status
      --time-style=STYLE  show times using STYLE, which can be:
                            full-iso, long-iso, iso, or +FORMAT;
                            FORMAT is interpreted like in 'date'
  -X, --exclude-from=FILE  exclude files that match any pattern in FILE
      --exclude=PATTERN    exclude files that match PATTERN
  -x, --one-file-system    skip directories on different file systems
      --help     display this help and exit
      --version  output version information and exit