linux命令df学习笔记

df命令简介
df命令用来检查文件系统的磁盘空间占用情况。可以利用该命令来获取硬盘被占用了多少空间,目前还剩下多少空间等信息。

df命令语法
df [ [ -P ] | [ -I | -M | -i | -t | -v ] ] [ -k ] [ -m ] [ -g ] [ -s ] [FileSystem … | File… ]

说明
该语法格式为AIX的语法格式,不同版本的unix或者linux该命令的参数不尽相同,仅供参考。

常用参数说明
k:
以1024-byte为单位展示结果信息。
m:
以MB为单位展示结果信息。
g:
以GB为单位展示结果信息。

i:
显示inodes的使用量及使用百分比,当指定了文件系统参数后盖参数无须显示指定这些信息也会默认输出。

i参数的英文说明如下:
Displays the number of used inodes and the percentage of inodes in use for the file system. This output is the default when the specified file system is mounted.

所谓的 inode 是用来存放档案及目录的基本信息 (metadata),包含时间、档名、使用者及群组等。在分割扇区时,系统会先做出一堆 inode 以供以后使用,inode 的数量关系着系统中可以建立的档案及目录总数。如果要存的档案大部分都很小,则同样大小的硬盘中会有较多的档案,也就是说需要较多的 inode 来挂档案及目录。

t:
显示某一个档案系统的所有分割区磁盘使用量。

示例:
df
输出:
df命令输出

说明:
第一列Filesystem:文件系统
第二列512-blocks:以512-byte为单位该磁盘分区使用情况
第三列Free :以512-byte为单位显示该磁盘分区的空闲情况
第四列 %Used :磁盘使用百分比
第五列Iused :Inode使用量
第六列%Iused :Inode使用百分比
第七列Mounted on:挂载点


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Purpose

Reports information about space on file systems. This document describes the AIX df command as well as the System V version
of df.

Syntax

df [ [ -P ] | [ -I | -M | -i | -t | -v ] ] [ -k ] [ -m ] [ -g ] [ -s ] [FileSystem … | File… ]

Description

The df command displays information about total space and available space on a file system. The FileSystem parameter
specifies the name of the device on which the file system resides, the directory on which the file system is mounted, or
the relative path name of a file system. The File parameter specifies a file or a directory that is not a mount point. If
the File parameter is specified, the df command displays information for the file system on which the file or directory
resides. If you do not specify the FileSystem or File parameter, the df command displays information for all currently
mounted file systems. File system statistics are displayed in units of 512-byte blocks by default.

The df command gets file system space statistics from the statfs system call. However, specifying the -s flag gets the
statistics from the virtual file system (VFS) specific file system helper. If you do not specify arguments with the -s flag
and the helper fails to get the statistics, the statfs system call statistics are used. Under certain exceptional
conditions, such as when a file system is being modified while the df command is running, the statistics displayed by the
df command might not be accurate. Note: Some remote file systems, such as the Network File System (NFS), do not provide all
the information that the df command needs. The df command prints blanks for statistics that the server does not provide.

The df command does not fully support NFSv4 filesystems. Use the nfs4cl command to extract block and space information.

Flags

-g
Displays statistics in units of GB blocks. The output values for the file system statistics would be in floating point
numbers as value of each unit in bytes is significantly high.
-i
Displays the number of used inodes and the percentage of inodes in use for the file system. This output is the default
when the specified file system is mounted.
-I
Displays information on the total number of blocks, the used space, the free space, the percentage of used space, and
the mount point for the file system.
-k
Displays statistics in units of 1024-byte blocks.
-m
Displays statistics in units of MB blocks. The output values for the file system statistics would be in floating point
numbers as value of each unit in bytes is significantly high.
-M
Displays the mount point information for the file system in the second column.
-P
Displays information on the file system in POSIX portable format.

When the -P flag is specified, the header line appears similar to:

Filesystem 512-blocks Used Available Capacity Mounted on\n

If the -k, -m or -g flag is specified in addition to the -P flag, the column heading 512-blocks is replaced by the
respective units, depending on which of these flags is used with the -P flag.

File system statistics are displayed on one line in the following order:

FileSystem, TotalSpace, UsedSpace, FreeSpace, UsedPercentage, MountPoint
-s
Displays statistics on unmounted JFS or Enhanced JFS file systems by the command line arguments. If there are no
arguments specified, the -s flag has no effect. If the file systems specified by the argument are currently mounted or
an argument is a file, the -s flag has no effect for that particular argument. To collect statistics on unmounted file
systems, an argument must be a JFS or Enhanced JFS file system mount point or device, the file system must be listed
in /etc/filesystems, and the user must have read access to the device.
-t
Includes figures for total allocated space in the output.
-v
Displays all information for the specified file system.

The values of the output parameters with the flags -m and -g would be rounded off to nearest second decimal digit. If all
or any two of the -k, -m and -g flags are specified, the last one specified takes effect.

Exit Status

This command returns the following exit values:
0
Successful completion.
>0
An error occurred.

Examples
1 To display information about all mounted file systems, enter:

df

If your system has the /, /usr, /site, and /usr/venus file systems mounted, the output from the df command resembles
the following:

Filesystem 512-blocks Free %Used Iused %Iused Mounted on
/dev/hd0 19368 9976 48% 4714 5% /
/dev/hd1 24212 4808 80% 5031 19% /usr
/dev/hd2 9744 9352 4% 1900 4% /site
/dev/hd3 3868 3856 0% 986 0% /usr/venus
2 To display information about /test file system in 1024-byte blocks, enter:

df -k /test

Filesystem 1024 blocks Free %Used Iused %Iused Mounted on
/dev/lv11 16384 15824 4% 18 1% /tmp/ravi1
This displays the file system statistics in 1024-byte disk blocks.
3 To display information about /test file system in MB blocks, enter:

df -m /test

Filesystem MB blocks Free %Used Iused %Iused Mounted on
/dev/lv11 16.00 15.46 4% 18 1% /tmp/ravi1
This displays file system statistics in MB disk blocks rounded off to nearest 2nd decimal digit.
4 To display information about the /test file system in GB blocks, enter:

df -g /test

Filesystem GB blocks Free %Used Iused %Iused Mounted on
/dev/lv11 0.02 0.02 0% 18 1% /tmp/ravi1
This displays file system statistics in GB disk blocks rounded off to nearest 2nd decimal digit.

5 To display available space on the file system in which your current directory resides, enter:

cd/
df .

The output from this command resembles the following:

Device 512-blocks free %used iused %iused Mounted on
/dev/hd4 19368 9976 48% 4714 5% /

Files

/etc/filesystems
Lists the known file systems and defines their characteristics.
/etc/vfs
Contains descriptions of virtual file system types.

Related Information

The fsck command.

The filesystems file.

The File systems in Operating system and device management explains file system types, management, structure, and
maintenance.

The Mounting in Operating system and device management explains mounting files and directories, mount points, and automatic
mounts.

System V df Command

Purpose

Reports number of free disk blocks and files.

Syntax

/usr/sysv/bin/df [ -a ] [ -l ] [ [ [ -e ] [-g ] [ -n ] ] | [ [ -i ] [ -v ] ] | -t ] ] [FileSystem …] [File …]

Description

The df command displays information about total space and available space on a file system. File system statistics are
displayed in units of 512-byte blocks

Flags
-a
Performs the default operation and prints the mount point, the device name, number of free blocks and number of used
inodes (files).
-e
Print only the number of free files.
-g
Print the entire statvfs structure. This option overrides the -a , -e, -i, -n, -t and -v options. The numbers for
available, total, and free blocks are reported in 512 byte blocks.
-i
Displays the total number of inodes, the number of free inodes, the number of used inodes, and the percentage of
inodes in use.
-l
Reports on local file systems only.

-n
Prints the type of filesystem.
-t
Causes total allocated block figures to be reported.
-v
Reports percent of blocks used as well as the number of blocks used and free.

Parameters
File
The File parameter specifies a file or a directory that is not a mount point. If the File parameter is specified, the
df command displays information for the file system on which the file or directory resides.
FileSystem
The FileSystem parameter specifies the name of the device on which the file system resides, the directory on which the
file system is mounted, or the relative path name of a file system. Note: If the FileSystem or File parameter is not
specified, the df command displays information for all currently mounted file systems.

Exit Status
0
The command completed successfully
>0
An error occurred.

Examples
1 To display information about all mounted file systems, enter:

/usr/sysv/bin/df
The output looks similar to the following:

/ (/dev/hd4 ): 19656 blocks 1504 files
/usr (/dev/hd2 ): 1139904 blocks 20254 files
/var (/dev/hd9var ): 23096 blocks 512 files
/tmp (/dev/hd3 ): 2464 blocks 204 files
/home (/dev/hd1 ): 44208 blocks 146 files
/proc (/proc ): 0 blocks 0 files
/opt (/dev/hd10opt ): 13880 blocks 310 files
2 To display information about the file system in which your current directory resides, enter:

/usr/sysv/bin/df .
3 To display the total number of inode, the number of free inodes and the number of available inodes in all mounted file
systems, enter:

/usr/sysv/bin/df -i
The output looks similar to the following:

Mount Dir Filesystem iused avail itotal %iused
/ /dev/hd4 1504 6688 8192 19%
/usr /dev/hd2 20254 127202 147456 14%
/var /dev/hd9var 512 3584 4096 13%
/tmp /dev/hd3 204 5940 6144 4%
/home /dev/hd1 146 14190 14336 2%
/proc /proc 0 0 0 0
/opt /dev/hd10opt 310 5834 6144 6%
4 To display the total number of blocks , the number of used blocks and the number of free blocks on a the /tmp file
system, enter:

/usr/sysv/bin/df -v /tmp
5 To display the type of filesystem, enter:

/usr/sysv/bin/df -n

6 To display inode information on all local filesystems, enter:

/usr/sysv/bin/df -i -l
7 To display the statvfs structure information on all the filesystems, enter:

/usr/sysv/bin/df -g
8 To display the number of free files on filesystems, enter:

/usr/sysv/bin/df -e

Files
/usr/sysv/bin/df
Contains the System V df command.
/etc/filesystems
Contains filesystem information.

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