Thursday, 13 February 2014

Practical Guide to AIX "Filesystems"

Practical Guide to AIX Filesystems

Contents

1) Creation of Filesystem:

The crfs command creates a file system on a logical volume within a previously created volume group.

A new logical volume is created for the file system unless the name of an existing logical volume is specified using the -d. An entry for the file system is put into the /etc/filesystems file.
Commands
##With an existing logical volume:
 
   # crfs -v jfs2 -d <lv> -m <mountpoint> -A yes
 
  -v vfs type (Specifies the virtual file system type)
  -d Specifies the device name of a device or logical volume on which to make the file system.
  -m Specifies the mount point, which is the directory where the file system will be made available
  -A Specifies whether the file system is mounted at each system restart:
        yes:File system is automatically mounted at system restart.
        no:File system is not mounted at system restart (default value).

Note: start of changeThe crfs command accesses the first letter for the auto mount -A option.end of change

## Create logical volume, filesystem, mountpoint, add entry to /etc/filesystems at the specified size

 # crfs -v jfs2 -g <vg> -m <mountpoint> -a size=<size in 512k blocks|M|G) -A yes

Note: there are two types of filesystems jfs and jfs2, jfs2 allows you to decrease the filesystem size , you cannot reduce a jfs filesystem.

2) mount/unmount Filesystems:

mount is the command used to mount filesystems
mount [<fs>|<lv>] 
mount -a 
mount all
To unmount filesystem use "umount"
umount <fs>

Note: You can't write into or read any content from  filesystem when its in unmounted state

-f unmount filesystem forcibly
umount -f <fs>

for v7.1 onwards you can use name for "unmount" command as well.

umountall: Unmounts groups of dismountable devices or filesystems ( applicable to v7.1)

3) List Filesystems:

To list filesysem use "lsfs" or "mount"
lsfs Lists all filesystems in the /etc/filesystems entry

lsfs -a To list all filesystems (default)

lsfs -q <fs> (detailed) 

lsfs -q List all filesystems with detailed info (shows size of FS and LV in it. so we can check whether size of LV=size os FS)

lsfs -l Specify the output in list format

lsfs -c Specify the output in column format

lsfs -v jfs Lists all jfs filesystems 

mount       (to list all mounted filesystems)

mount <fs> ( to list the mounted filesysem)

Note: use the '-q' to see if the logical volume size is bigger than the filesystem size

4) Display Filesystem usage:

To display information about all mounted file systems, enter: df
Command Examples
1) If your system has the /, /usr, /site, and /usr/venus file systems mounted, the output from the df command resembles the following:

df

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) Resize Filesystems:

chfs -a size=<new size> <fs>

Command Examples
chfs -a size=1G /var (specific size, can be used to increase and decrease)
chfs -a size=+1G /var (increase by 1GB)
chfs -a size=-1GB /var (reduce by 1GB)

Note1:This will automatically increase or decrease the underlying logical volume as well.
Note2:You can't reduce jfs filesystem

6) Modify/Change Filesystems:

Command Examples
## Change the mountpoint

chfs -m <new mountpoint>
chfs -m /test /new ==>Change the mount point from /test to /new

## Do not mount after a restart

chfs -A no <fs>
## Mount read-only

chfs -p ro <fs>
## Remvoe attribute of a filesystem

Remove account attribute of /test.(from /etc/filesystems file)

chfs -d account /test
chfs -a options='rw' /shadow ==> shows with lsfs rw (I think rw is the deafault anyway)

7) Remove Filesystems:

Command Examples
rmfs <fs>
rmfs -r /test ==>Deletes FS /test its mount point and associated LV

Note1: You need to unmount the filesyem before removing.
Note2: if all filesystems have been removed from a logical volume then the logical volume is removed as well.

8) Freeze File System:

If you don't want your file system to perform any writes for a period of time, maybe due to an admin task like a split copy or a backup, you can freeze the file system. After the admin tasks are completed, you can thaw the file system.
chfs -a freeze=<time in seconds> <fs>
chfs -a freeze=off <fs>

9) Split mirrored copy of filesystem:

chfs -a splitcopy=<split copy mountpoint> -a copy=2 <fs>
chfs -a splitcopy=/backup -a copy=2 /testfs

This will mount the 2nd copy of mirrored filesystem testfs to /backup in read-only mode for backup purpose

10) defrag fielsystem:

The defragfs command can be used to improve or report the status of contiguous space within a file system.
Command Examples
defragfs /test ==>To defragment the file system /test
defragfs -q /test ==>Display the current defrag status of the file system

For example, to defragment the file system /home, use the following command:

defragfs /home

Here is an example output:

# defragfs /home
Defragmenting device /dev/hd1. Please wait.

Total allocation groups : 32
Allocation groups skipped - entirely free : 26
Allocation groups defragmented : 6
defragfs completed successfully.

Total allocation groups : 32
Allocation groups skipped - entirely free : 26
Allocation groups that are candidates for defragmenting : 6
Average number of free runs in candidate allocation groups : 1
#

11) fuser & filesystem:

Command Examples
fuser /etc/passwd lists the process numbers of local processes using the /etc/passwd file

fuser -cux /var shows which processes are using the given filesystem

fuser -cuxk /var it will kill the above processes

fuser -dV /tmp shows deleted files (inode) with process ids which were open by a process (so its space could not be freed up)

(-V: verbose will show the size of the files as well)
if we rm a file, while it is opened by a process its space will not free up.
solution: kill the process, wait for the process to finish or reboot the system

12) Checking and Repairing:

Command Examples
fsck [-y|-n] <fs> (check a filesystem)

fsck -p lt;fs> (restores primary superblock from backup copy if corrupt)

fsck -y n /dev/lv00 ==>To check the filesystem associated to /dev/lv00 assuming response "yes"

13) Miscellaneous Filesystem Commands:

Command Examples
skulker ==> cleans up file systems by removing unwanted or obsolete files

fileplace <filename> ==> displays the placement of file blocks within logical or physical volumes, it will show if a file fragmented

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