14.1 df: 报告文件系统磁盘空间的使用情况

 

 

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14.1 df: 报告文件系统磁盘空间的使用情况

df 报告文件系统中已用和可用的磁盘空间。语法：

df [option]… [file]…

如果没有给定参数， df 会列出所有当前已挂载文件的已用和可用空间。 否则， df 只会列出给定的 file 的报告。

默认情况，磁盘空间以 1024 个字节为单位进行打印。这个设置可以被修改 (参考 Block size). 如果计算结果不是整数则按四舍五入的原则显示一个整数。

For bind mounts and without arguments, df only outputs the statistics for that device with the shortest mount point name in the list of file systems (mtab), i.e., it hides duplicate entries, unless the -a option is specified.

With the same logic, df elides a mount entry of a dummy pseudo device if there is another mount entry of a real block device for that mount point with the same device number, e.g. the early-boot pseudo file system ‘rootfs’ is not shown per default when already the real root device has been mounted.

If an argument file resolves to a special file containing a mounted file system, df shows the space available on that file system rather than on the file system containing the device node. GNU df does not attempt to determine the disk usage on unmounted file systems, because on most kinds of systems doing so requires extremely nonportable intimate knowledge of file system structures.

The program accepts the following options. Also see Common options.

‘-a’

‘--all’

Include in the listing dummy, duplicate, or inaccessible file systems, which are omitted by default. Dummy file systems are typically special purpose pseudo file systems such as ‘/proc’, with no associated storage. Duplicate file systems are local or remote file systems that are mounted at separate locations in the local file hierarchy, or bind mounted locations. Inaccessible file systems are those which are mounted but subsequently over-mounted by another file system at that point, or otherwise inaccessible due to permissions of the mount point etc.

‘-B size’

‘--block-size=size’

以指定的块 大小 进行显示 (参见 Block size). 例如 -BG 以 1,073,741,824 字节为单位进行显示。

‘-h’

‘--human-readable’

在显示的数字后面加上单位，例如 ‘M’ 代表兆。使用的 以 1024 为倍数，而不是 1000； ‘M’ 代表了 1,048,576 个 字节。这个选项等同 --block-size=human-readable。如果你习惯以 1000 为倍数请使用 --si 选项。

‘-H’

相当于 --si.

‘-i’

‘--inodes’

用索引节点代替块表示使用情况，一个索引节点包含了一个文件的信息，如文件的所 有者、权限、时间戳和在磁盘中的位置。

‘-k’

使用指定的块大小 1024-byte 来显示，覆盖默认的块大小。 (参见 Block size). 该选项相当于 --block-size=1K.

‘-l’

‘--local’

只显示本地文件系统的使用状况。默认远程文件系统也会被列出。

‘--no-sync’

在获得数据之前，不要调用 sync。这个设置在许多磁盘系统上会使 df 更快地执行，但在某些系统上（特别是 SunOS）结果可能会稍微过时。 这个选项是默认选选。

‘--output’

‘--output[=field_list]’

Use the output format defined by field_list, or print all fields if field_list is omitted. In the latter case, the order of the columns conforms to the order of the field descriptions below.

The use of the --output together with each of the options -i, -P, and -T is mutually exclusive.

FIELD_LIST is a comma-separated list of columns to be included in df’s output and therefore effectively controls the order of output columns. Each field can thus be used at the place of choice, but yet must only be used once.

Valid field names in the field_list are:

‘source’

The source of the mount point, usually a device.

‘fstype’

File system type.

‘itotal’

Total number of inodes.

‘iused’

Number of used inodes.

‘iavail’

Number of available inodes.

‘ipcent’

Percentage of iused divided by itotal.

‘size’

Total number of blocks.

‘used’

Number of used blocks.

‘avail’

Number of available blocks.

‘pcent’

Percentage of used divided by size.

‘file’

The file name if specified on the command line.

‘target’

The mount point.

The fields for block and inodes statistics are affected by the scaling options like -h as usual.

The definition of the field_list can even be split among several --output uses.

#!/bin/sh
# Print the TARGET (i.e., the mount point) along with their percentage
# statistic regarding the blocks and the inodes.
df --out=target --output=pcent,ipcent

# Print all available fields.
df --o

‘-P’

‘--portability’

Use the POSIX output format. This is like the default format except for the following:

1. The information about each file system is always printed on exactly one line; a mount device is never put on a line by itself. This means that if the mount device name is more than 20 characters long (e.g., for some network mounts), the columns are misaligned.
2. The labels in the header output line are changed to conform to POSIX.
3. The default block size and output format are unaffected by the DF_BLOCK_SIZE, BLOCK_SIZE and BLOCKSIZE environment variables. However, the default block size is still affected by POSIXLY_CORRECT: it is 512 if POSIXLY_CORRECT is set, 1024 otherwise. See Block size.

‘--si’

Append an SI-style abbreviation to each size, such as ‘M’ for megabytes. Powers of 1000 are used, not 1024; ‘M’ stands for 1,000,000 bytes. This option is equivalent to --block-size=si. Use the -h or --human-readable option if you prefer powers of 1024.

‘--sync’

Invoke the sync system call before getting any usage data. On some systems (notably SunOS), doing this yields more up to date results, but in general this option makes df much slower, especially when there are many or very busy file systems.

‘--total’

Print a grand total of all arguments after all arguments have been processed. This can be used to find out the total disk size, usage and available space of all listed devices. If no arguments are specified df will try harder to elide file systems insignificant to the total available space, by suppressing duplicate remote file systems.

For the grand total line, df prints ‘"total"’ into the source column, and ‘"-"’ into the target column. If there is no source column (see --output), then df prints ‘"total"’ into the target column, if present.

‘-t fstype’

‘--type=fstype’

Limit the listing to file systems of type fstype. Multiple file system types can be specified by giving multiple -t options. By default, nothing is omitted.

‘-T’

‘--print-type’

Print each file system’s type. The types printed here are the same ones you can include or exclude with -t and -x. The particular types printed are whatever is supported by the system. Here are some of the common names (this list is certainly not exhaustive):

‘nfs’

An NFS file system, i.e., one mounted over a network from another machine. This is the one type name which seems to be used uniformly by all systems.

‘ext2, ext3, ext4, xfs, btrfs…’

A file system on a locally-mounted hard disk. (The system might even support more than one type here; Linux does.)

‘iso9660, cdfs’

A file system on a CD or DVD drive. HP-UX uses ‘cdfs’, most other systems use ‘iso9660’.

‘ntfs,fat’

File systems used by MS-Windows / MS-DOS.

‘-x fstype’

‘--exclude-type=fstype’

Limit the listing to file systems not of type fstype. Multiple file system types can be eliminated by giving multiple -x options. By default, no file system types are omitted.

‘-v’

Ignored; for compatibility with System V versions of df.

df is installed only on systems that have usable mount tables, so portable scripts should not rely on its existence.

An exit status of zero indicates success, and a nonzero value indicates failure. Failure includes the case where no output is generated, so you can inspect the exit status of a command like ‘df -t ext3 -t reiserfs dir’ to test whether dir is on a file system of type ‘ext3’ or ‘reiserfs’.

Since the list of file systems (mtab) is needed to determine the file system type, failure includes the cases when that list cannot be read and one or more of the options -a, -l, -t or -x is used together with a file name argument.

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