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Module 32
df

DESCRIPTION

The external df command displays the disk free space. It is used to find out how much disk space is available in each mounted file system. The df command is used to:

*  Display available disk blocks and inodes(files).
*  Display total disk blocks and inodes.
*  Display available disk blocks without inode count.
*  Display the device on which the filesystem is mounted.
*  Display total kilobytes in a filesystem.
*  Display used kilobytes in a filesystem.
*  Display available (free) kilobytes in a filesystem.
*  Display percent used of kilobytes and inodes.

BSD (Berkeley)
The BSD version of df supports the same features as System V except for block counts.

COMMAND FORMAT

Following is the general format of the df command.

  df [ -F FStype ] [ -begklntV ] [ SVoptions ] [ -o FSoptions ] filesystem
  df [ -F FStype ] [ -begklntV ] [ SVoptions ] [ -o FSoptions ] mount_point
  df [ -F FStype ] [ -begklntV ] [ SVoptions ] [ -o FSoptions ] resource

BSD (Berkeley)
df [ -ai ] [ -t type ] [ filesystem ]
df [ -ai ] [ -t type ] [ file ]

Options

The following options may be used to control how df functions.

-F FStype Specifies the type of file system. Only used for unmounted file systems. The FStype should be specified with the -F option or be found in the /etc/vfstab by matching mount_point, special, or resource. Supported types are s5, ufs, nfs, efs, ffs, and rfs. Not all of these types may be supported on all systems.
-b Display only the number of free kilobytes.
-e Display only the number of free files.
-g Display the entire statvfs structure. Used only for mounted file systems. Cannot use with -beknt options, -o or the SV options.
-k Display allocation information in kilobytes. Should be used by itself since it uses a different format.
-l Display information for local file systems only. Used only for mounted file systems. Cannot use with -o or SVoptions.
-n Display on the FStype name. If no arguments, a list of all mounted file system types is displayed. Used only for mounted file systems. Cannot use with -o or SVoptions.
-t Displays a total listing. Displays the total number of blocks and inodes and the free or available blocks and inodes. Overrides the -ben options.
-V Verify the command line. The command line is echoed back to the screen after df has added information from the /etc/mnttab and /etc/vfstab.
-o FSoptions Used to specify FStype specific options. The FSoptions are a comma-separated list of file system specific options. See your system's User's Reference Manual df command man pages.
-i Displays the number of free and used inodes.
SVoptions These are System V specific options. Refer to your systems df (s5) man page.

BSD (Berkeley)
-i Displays the number of free and used inodes.
-t type Displays only filesystems of a given type. The types are nfs and 4.2. Type nfs is for a Network File System and 4.2 is for a local BSD File System.

Arguments

The following list describes the arguments that may be passed to the df command.

filesystem The filesystem device name. The name of the device where the filesystem resides physically. Such as /dev/da0a or /dev/dsk/c0d0s0.
mount_point The name of the directory where the filesystem is mounted. Referred to as the filesystem mount point.
resource An NFS or RFS resource name.
If no arguments are given then all filesystems currently mounted are reported.

BSD (Berkeley)
file The name of a file within a filesystem. The disk space for the filesystem containing file is displayed. May be a directory, such as the filesystem mount_point.

FURTHER DISCUSSION

A file system is a set of files and directories stored on one physical part of a disk. A device name (/dev/dsk/0s0) or a logical directory name may be used by df to access a file system. For a file system to be checked via its logical name it must be mounted. Mounting a file system makes it available for use. The system becomes aware of the physical media and relates a logical name to it.

In general, the rule of thumb for available space on a file system is 10 percent of the maximum size. If you have a file system that is more than 90 percent full, you should remove all files no longer needed. The system administrator is responsible for keeping file systems within the set guidelines.


BSD (Berkeley)
The BSD system reserves a portion of each file system for allocation routines to work properly. The reserved part is usually 10 percent but may be adjusted by using the super-user command tunefs.
Once a file system reaches 100 percent full, only the super-user can allocate more space.

Alleviating Full Disks

To alleviate the problem, the administrator may use the find and cpio commands to move an entire directory structure to a new file system. Another alternative is to have users mv files to a directory in their home directory named ARC. Then run a job that saves all user files stored in ARC directories to tape. Of course, a satisfactory solution is to just have the users remove all unnecessary files.

RELATED COMMANDS

Refer to the du command described in Module 37.

RELATED FILES

The following files are read and used by the df command.

/etc/checklist A list of all normally mounted filesystems (SV only)
/dev/dsk/* The disk partitions where filesystems reside (SV only)
/dev/d* The disk partitions where filesystems reside (BSD only)
/etc/mnttab A list of all currently mounted filesystems (SV only)
/etc/mtab A list of all currently mounted filesystems (BSD only)
/etc/fstab A list of all normally mounted filesystems (BSD only)
/etc/vfstab A list of default parameters for each file system (SV only)

APPLICATIONS

You can use the df command to check available disk space. The numbers returned by the System V df command are blocks, not bytes. Therefore, don't forget to multiply by 512, 1024, or 2048, depending on your system's block size.

If you're low on free space, you may want to remove all unnecessary files and send a mail note to the system administrator stating your observance. The amount of available space kept for a buffer is dependent upon each site's requirements. Some system administrators require 10000 blocks while others set a minimum of 500. The size is heavily dependent on the type of work being done on each filesystem and the size of the filesystem.

TYPICAL OPERATION

In this activity you use the df command to list the available disk space on you system. Begin at the shell prompt.

System V Only

1.  Type df -t and press Return to display the total space on the system and the total available space. You screen will look something like this:
   cj> df -t
   /       (/dev/dsk/c1d0s0):     1743   blocks    1398   inodes
                       total:    18144   blocks    2256   inodes
   /usr    (/dev/dsk/c1d0s2):    11364   blocks    8752   inodes
                       total:   121176   blocks   15136   inodes
   /u1     (/dev/dsk/c1d0s5):    33023   blocks    2103   inodes
                       total:   181934   blocks   18321   inodes

The 1743 refers to free blocks; the 1398 is free inodes. The 18144 refers to total blocks and the 2256 is total inodes. The output of some vendors' df command varies from the standard.

BSD (Berkeley) Only

1.  Type df and press Return. The output resembles the following.
   cj> df
   Filesystem    kbytes   used    avail  capacity  Mounted on
   /dev/da0a     20143    17608   520       97%       /
   /dev/da0e     122559   76660   33643     69%       /usr
   /dev/da1g     183887   105277  60221     64%       /u1
2.  Turn to Module 37 to continue the learning sequence.


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