Commands Reference, Volume 1

chfs Command

Purpose

Changes attributes of a file system.

Syntax

chfs [ -n NodeName ] [ -m NewMountPoint ] [ -u MountGroup ] [ -A { yes | no } ] [ -p { ro | rw } ] [ -t { yes | no } ] [ -a Attribute=Value ] [ -d Attribute ] FileSystem

Description

The chfs command changes the attributes of a file system. The new mount point, automatic mounts, permissions, and file system size can be set or changed. The FileSystem parameter specifies the name of the file system, expressed as a mount point.

Some file system attributes are set at the time the file system is created and cannot be changed. For the Journaled File System (JFS), such attributes include the fragment size, block size, number of bytes per i-node, compression, and the minimum file system size. For the Enhanced Journaled File System (JFS2), the block size cannot be changed.

You can use the File Systems application in Web-based System Manager to change file system characteristics. You could also use the System Management Interface Tool (SMIT) smit chfs fast path to run this command.

Flags

-a Attribute=Value

Specifies the Attribute=Value pairs; dependent on virtual file system type. To specify more than one Attribute=Value pair, provide multiple -a Attribute=Value parameters.

The following attribute/value pairs are specific to the Journaled File System (JFS):

-a Size=NewSize

Specifies the size of the Journaled File System. Size can be specified in units of 512-byte blocks, Megabytes or Gigabytes. If Value has the M suffix, it is interpreted to be in Megabytes. If Value has a G suffix, it is interpreted to be in Gigabytes. If Value begins with a +, it is interpreted as a request to increase the file system size by the specified amount. If the specified size is not evenly divisible by the physical partition size, it is rounded up to the closest number that is evenly divisible.

The maximum size of a JFS file system is a function of its fragment size and the nbpi value. These values yield the following size restrictions:

nbpi	Fragment size in bytes	Maximum size in 512-byte blocks	Maximum size in Megabytes	Maximum size in Gigabytes
512	512, 1024, 2048, 4096	16777216	8192	8
1024	512, 1024, 2048, 4096	33554432	16384	16
2048	512, 1024, 2048, 4096	67108864	32768	32
4096	512, 1024, 2048, 4096	134217728	65536	64
8192	512, 1024, 2048, 4096	268435456	131072	128
16384	512	268435456	262144	256
16384	1024, 2048, 4096	536870912	524288	512
32768	512	268435456	1048576	1024
32768	1024	536870912	2097152	2048
32768	2048, 4096	1073741824	4194304	4096
65536, 131072	512	268435456	8388608	8192
65536, 131072	1024	536870912	16777216	16384
65536, 131072	2048	1073741824	33554432	32768
65536, 131072	4096	2147483648	67108804	65536
In AIX 4.3, you can have NBPI values from 512 to 128K, with corresponding maximum file system sizes.

The volume group in which the file system resides defines a maximum logical volume size and also limits the file system size.

-a Log=LVName

Specifies the full path name of the filesystem logging logical volume name of the existing log to be used. The log device for this filesystem must reside on the same volume group as the filesystem

-a splitcopy=NewMountPointName

Splits off a mirrored copy of the file system and mounts it read-only at the new mount point. This provides a copy of the file system with consistent JFS meta-data that can be used for backup purposes. User data integrity is not guaranteed, so it is recommended that file system activity be minimal while this action is taking place. Only one copy may be designated as an online split mirror copy.

-a copy=Copy#

Specifies which mirror copy to split off when used in conjunction with the splitcopy attribute. The default copy is the second copy. Valid values are 1, 2, or 3.

The following attribute/value pairs are specific to the Enhanced Journaled File System (JFS2):

-a size=NewSize

Specifies the size of the Enhanced Journaled File System in 512-byte blocks, Megabytes or Gigabytes. If Value has the M suffix, it is interpreted to be in Megabytes. If Value has a G suffix, it is interpreted to be in Gigabytes. If Value begins with a +, it is interpreted as a request to increase the file system size by the specified amount. If the specified size is not evenly divisible by the physical partition size, it is rounded up to the closest number that is evenly divisible. The volume group in which the file system resides defines a maximum logical volume size and limits the file system size.

Note

JFS2 does not have nbpi or fragment size values to affect the resulting size of the file system.

-a logname=LVName

Specifies the full path name of the filesystem logging logical volume name of the existing log to be used. The log device for this filesystem must reside on the same volume group as the filesystem. Keyword INLINE can be used to specify that the log is in the logical volume with the JFS2 file system. The file system must have been created with an INLINE log to use this option. This option updates the /etc/filesystems file so that if the name of the logical volume containing the file system changes the log will be recognized.

-a logsize=Value

Specifies the size for an INLINE log in MBytes. Ignored if INLINE log not being used. Cannot be greater than 10% of the size of the filesystem.

-A

Specifies the attributes for auto-mount.

yes

File system is automatically mounted at system restart.

no

File system is not mounted at system restart.

-d Attribute

Deletes the specified attribute from the /etc/filesystems file for the specified file system.

-m NewMountPoint

Specifies the new mount point.

-n NodeName

Specifies a node name for the specified file system. The node name attribute in the /etc/filesystems file is updated with the new name. The node name attribute is specific to certain remote virtual file system types, such as the NFS (Network File System) virtual file system type.

-p

Sets the permissions for the file system.

ro

Specifies read-only permissions.

rw

Specifies read-write permissions.

-t

Sets the accounting attribute for the specified file system:

yes

File system accounting is to be processed by the accounting subsystem.

no

File system accounting is not to be processed by the accounting subsystem; this is the default.

-u MountGroup

Specifies the mount group. Mount groups are used to group related mounts, so that they can be mounted as one instead of mounting each individually. For example, if several scratch file systems always need to be mounted together when performing certain tests, they can each be placed in the test mount group. They can then all be mounted with a single command, such as the mount -t test command.

Security

Access Control: Only the root user can run this command.

Examples

1. To change the file system size of the /test Journaled File System, enter:

   chfs  -a size=24576 /test

   This command changes the size of the /test Journaled File System to 24576 512-byte blocks, or 12MB (provided it was previously no larger than this).
2. To increase the size of the /test Journaled File System, enter:

   chfs  -a size=+8192 /test

   This command increases the size of the /test Journaled File System by 8192 512-byte blocks, or 4MB.
3. To change the mount point of a file system, enter:

   chfs  -m /test2 /test

   This command changes the mount point of a file system from /test to /test2.
4. To delete the accounting attribute from a file system, enter:

   chfs -d account /home

   This command removes the accounting attribute from the /home file system. The accounting attribute is deleted from the /home: stanza of the /etc/filesystems file.

5. To split off a copy of a mirrored file system and mount it read-only for use as an online backup, enter:

   chfs -a splitcopy=/backup -a copy=2 /testfs

   This mount a read-only copy of /testfs at /backup.

6. To change the file system size of the /test Journaled File System, enter:

   chfs -a size=12M /test

   This command changes the size of the /test Journaled File System to 12MB (provided it was previously no larger than this).

File

Related Information

The crfs command, mkfs command, mklv command.

The Accounting Overview in AIX 5L Version 5.2 System Management Concepts: Operating System and Devices explains the file system accounting subsystem.

The File Systems in AIX 5L Version 5.2 System Management Concepts: Operating System and Devices explains file system types, management, structure, and maintenance.

For information on installing the Web-based System Manager, see Chapter 2: Installation and System Requirements in AIX 5L Version 5.2 Web-based System Manager Administration Guide.

The System Management Interface Tool in AIX 5L Version 5.2 System Management Concepts: Operating System and Devices explains SMIT structure, main menus, and tasks.