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File System
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Disk Status
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Directories & Files
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Understanding the AIX File System
The AIX file system contains 3 major elements:
- Physical Volumes (PV)
- Volume Groups (VG)
- Logical Volumes (LV) IBM likes to use abbreviations, so get used to calling Physical Volumes PV’s, etc.
| Definition | What is it | Examples |
| Physical Volumes | A Physical Volume is an actual physical device, i.e. disk drive. Each disk drive contains a Physical Volume. Physical Volume’s are broken into Physical Partitions (PP’s) where each Physical Partition is 4MB in size. | A system with 2 drives, could contain Physical Volume’s hdisk0 and hdisk1. |
| Volume Groups | Volume Group’s are a set of one or more Physical Volume’s. Each Volume Group can contain one or more Logical Volumes | Physical Volume hdisk0 could contain Volume Group rootvg and Physical Volume hdisk1 could contain Volume Group datavg. |
| Logical Volumes | Logical Volume’s are used to define groups of files, i.e. File Systems. Each Logical Volume contains Logical Partitions (LP’s) | Volume Group rootvg could contain Logical Volume’s hd1, hd2, hd3. Where the mounting points for hd1 = ‘/’ (root), hd2 = /usr, hd3 = /tmp |
Here’s a table to help make this clearer, I hope.
| Physical Volume | Volume Group | Logical Volume |
| drive 1 = hdisk0 | rootvg | hd1 mounted as / |
| drive 2 = hdisk1 | datavg | hd2 mounted as /var, hd3 mounted as /tmp |
You can use smit to display or configure your file systems. Here are some commands that smit uses that you can use at the command line to provide the necessary information. The following commands only display information.
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Physical Volume Information
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| Examples | What it does |
| lspv | Displays a list of all Physical Volume’s with the drive name and associated Volume Group’s |
| lspv <physicalvolume> | Displays a specific Physical Volume. Stale partitions refers to mirroring. If the Physical Volume has no mirrored Logical Partitions, then the value for this field is zero |
| lspv -l <physicalvolume> | Displays what Logical Volumes reside on the named Physical Volume along with Logical Partition’s Physical Partition’s and Mounting Point. |
| lspv -p <physicalvolume> | Displays distribution of Physical Partitions for each Logical Volume that reside on the named Physical Volume along with State, Region, Type and Mounting Point. |
| lspv -s <physicalvolume> | Displays Physical Volume, total, free and used Physical Partitions. |
| lsvg -n <physicalvolume> | Displays total, free and used Physical Partitions and other information. |
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Volume Group Information
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| Examples | What it does |
| lsvg | Displays all Volume Groups |
| lsvg <volumegroup> | Displays all Volume Groups, total, free and used Physical Partitions |
| lsvg -p <volumegroup> | Displays Physical Volume, State and Physical Partition information |
| lsvg -l <volumegroup> | Displays Logical Volume name, Type, Logical Partitions, Physical Partitions, Physical Volumes, Logical Volume State and Mounting Point |
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Logical Volume Information
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| Examples | What it does |
| lslv <logicalvolume> | Displays Volume Group, Mirror State, Mount Point and more… |
| lslv -l <logicalvolume> | Displays Physical Volume, Copies, Distribution info |
Maximums
The smallest file extension is 4Kb. If a user creates or extends a file anywhere from 0-4096 bytes, a 4K block will be allocated from the free list to accommodate that request. When a file system is extended by 1 Physical Partition (4 MB), 1024 inodes are allocated to that file system.
length of a filename : 255 characters
number of open files per process : 2,000
number of open files system-wide : 200,000
number of record locks per process: 200,000
number of record locks system-wide: 200,000
bytes per pipe : 32,768
number of pipes per process : 2,000
number of semaphore IDs : 4,096
number of semaphores per ID : 100 K
number of operations per semop call : 1,024
semaphore value : 32,767
adjust on exit : 16,384
number of message queue IDs : 4,096
bytes per message : 8,192
bytes per message queue : 65,536
messages per message queue : 8,192
number of segments system-wide : 16 MB
number of shared memory segments : 4,096
number of segments per process : 10
bytes per segment 256 MB
Path Definitions
| Directory | What’s in it |
| /bin | utilities |
| /sbin | files needed to boot the machine and mount the /usr file system |
| /dev | special files (I/O devices) |
| /etc | miscellaneous administrative utilities |
| /home | user directories and files |
| /lib | libraries |
| /tmp | temporary files. Needs to be at least 12 MB |
| /usr | common executables that are shared across the same architecture |
| /usr/adm | administrative commands and files |
| /usr/bin | utilities (overflow for /bin) |
| /usr/lib | archive libraries, text processing macros |
| /usr/spool/mail | Email files |
| /usr/sbin | utilities used in system administration, including smit |
| /usr/share | architecture-independent, shareable text files |
| /usr/share/man | manual pages |
| /usr/share/dict | spelling dictionary and its indexes |
| /usr/share/info | InfoExplorer database files |
| /usr/share/lib | architecture-independent data files, including terminfo |
| /usr/share/lpp | data about optional program products (OPP) |
| /var/adm | system logging and accounting files |
| /var/preserve | preserved data from interrupted edit sessions |
| /var/spool | spool files for printing |
| /var/tmp | temporary files |
cat – Concatenates or displays one or more files
| Examples | What it does |
| cat -v textfile | The -v option will display non-printing characters. |
| tput clear | cat -v | Displays the control codes generated to clear the screen. |
chlv – Used to expand beyond the maximum Logical Volume limit
chlv -x 256 <lv_name> (Where logical volume name is entered without the /dev)
chfs – Changes attributes of a file system
Block size for this command is 512 byte blocks, where the command df, returns disk info in 1024 byte blocks. The simplest method of extending a file system is to
- Take the target size of the file system in MB’s and multiple by 2000.
- If the file system size is to be extended to 12MB in size, then 12 * 2000 = 24000.
Remember, when you extend a file system, you extend the logical volume that resides under it. Most systems have a default Physical Partition size of 4MB (review output of lsvg rootvg command) and therefore when the file system increases in size, it will increase by a multiple of 4MBs.
chfs -a size=24000 /usr (Increase the /usr file system to 12MBs.)
cp – Copies one or more files
| Examples | What it does |
| cp /u/roger/test /tmp | Copies the file test in the directory /u/roger to the /tmp directory |
| cp -ipr . /tmp/temp | Copies all the files and subdirectories from the current directory to the directory named /tmp/temp.
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| cp -r /usr/data /home/data | Copies all files and directories from /usr to /home |
crfs – Adds a new file system
Block size for this command is 512 byte blocks, where the command df, returns disk info in 1024 byte blocks.
crfs -v jfs -g rootvg -m /mydata -p rw -a size=100000
- -v file systems type, jfs=journalized file system
- -g volume group name where filesystem will reside, rootvg
- -m mount point for new filesystem, /mydata
- -p access permissions, rw=read/write
- -a file system attribute, size=100000
The above command creates a 50MB journeled file system named /mydata with read/write permissions, created under the volume group rootvg
del – Delete files where system will prompt you to delete the files
del /u/roger/*
If ‘y’ is entered for yes, all files will be removed.
df – Displays summary of disk usage for mounted file systems
df -v
dircmp – Compares two directories and contents of files found in both directories
dircmp /tmp/COMPANY /u/COMPANY | grep different
Displays only those files that are found in both directories but have differences
du – Display a summary of disk usage for directories
Output in is 512 byte blocks. Without an argument, du lists the current directory.
| Examples | What it does |
| du /tmp | Displays total number of 512 byte blocks used by /tmp filesystem and all directories underneath it |
| du -s /tmp | Summarizes disk allocation for /tmp filesystem (including ALL files and subdirectories) in 512 byte blocks |
| du -a /u/roger/doc.txt | Summarizes disk allocation for a particular file |
fsck – Checks and interactively repairs inconsistent file systems
File systems are normally checked everytime the system is rebooted. If a file system is cleanly unmounted via the umount command, it’s unlikely to encounter any problems when the fsck command is run on the file system again. Fsck can only be run on a file system that is unmounted (fsck will not make changes to a mounted file-system). If fsck passes without errors, its safe to mount the file system in question.
- If there’s a discrepancy between the number of directory references to a file and the link count in the file and the file contains data (UNCLAIMED BLOCKS), the file is linked into the subdirectory named lost+found directory.
- fsck does not flag a bad block on your Physical Volume.
- Bad blocks are only relocated on a write operation.
- Fsck performs read operations and therefore is useful for soft errors – not hard errors.
- Also updates the JFS log – /dev hd8
| Examples | What it does |
| 1) fsck -fp /dev/hd1 mount /u | To make sure the /dev/hd1 (/u file system) is not damaged, followed by mounting that file system for user access.
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| fsck -y /dev/hd1 | The -y option gives fsck permission to automatically repair file systems when necessary. |
| dd count=1 bs=4k skip=31 seek=1 if=/dev/hd4 of=/dev/hd4fsck /dev/hd4 2>&1 | tee /tmp/fsck.errors | Use this command in case the superblock is corrupted. This will restore the BACKUP COPY of the superblock to the CURRENT copy. |
fuser – Identifies processes using a file or file system
fuser -u /dev/hd3
Sample output: /dev/hd3: 2964(root) 6615c(root) 8465(casado) 11290(bonner)
istat – Displays dates of access for a file
istat myfile (Displays attributes about the file named myfile)
ln – Gives a file more than one name (alias)
The symbolic link (-s) allows a user to point to a file and/or a directory. Symbolic links can link either a file or directory across a file system. Use
unlink to remove a link.
| Examples | What it does |
| ln test1 test2 | Creates a link from the original file named test1 to a new file named test2 |
| ln -s /tmp ./junk | Links subdirectory junk under the current directory to directory /tmp. |
| 1) cd /u/COMPANY2) ln -s /u/roger/* | All the files under /u/roger will now have links to /u/COMPANY. |
ls – Displays the contents of a directory
| Options | What it does |
| -a | Lists all entries including hidden files that start with a “.” |
| -d | List directories only |
| -e | Indicates if a file has extended security information – 11th character: + means yes, means no |
| -l | Long listing – more detail |
| -t | Sorts by time of last modification (latest listed first) |
| -F | Puts a / (slash) after each filename if the file is a directory. An * (asterisk) after each filename if the file can be executed. An @ for a symbolic link |
| -R | Lists all subdirectories recursively |
| -b | Lists garbage or hidden characters in octal |
| Examples | What it does |
| ls -ld . | List directory attributes for CURRENT directory |
| ls -ld .. | List directory attributes for PARENT directory (one level up) |
| ls -aeltFR | Lists all files and subdirectories under current directory |
| ls -l | Displays the last time the data in a file has been changed. |
| ls -lc | Displays the last time the attributes of a file have been changed. |
| ls -lu | Displays the last time the data in a file has been accessed. |
mkfs – Makes a file system
Example:
cd /u
find . -print|backup -ivqf/dev/rmt0
cd /
umount /u
mkfs dev/hd1
fsck -p /dev/hd1
mount /u
cd /u
restore -xvf/dev/rmt0
The above procedure is one way of making a file system contiguous again. Over the course of time, thousands of additions, deletions, creation, and extensions of files and/or records will create a file system that looks like Swiss cheese. This results in multiple disk accesses that formally may have taken only one. As a result, the system appears sluggish.
mount – Displays file system attributes or makes file system available for use
| Examples | What it does |
| mount | Displays attributes about all file systems that are on-line |
| mount /u/data | Mounts the file system named /u/data for accessibility. |
| mount /usr/tmp /tmp | If you don’t have enough room in the /tmp filesystem for a specific utility to work properly, and you do have enough room in the /usr filesystem, then you can mount the space from the /usr filesystem onto /tmp |
| mount -o wsize-8192, rsize=8192 | Set the read/write buffers to 8K to increase performance for NFS file systems. Since NFS verifies each packet that gets written to the server before it requests the next packet from the client, writes will take longer to execute than a read. By increasing the buffer size, less I/O operations will be needed, thereby increasing performance. |
| mount -n cad -v nfs /transfer | Mount a remote file system (type=nfs) on the mount point named /transfer, that resides on node cad |
mv – Renames one or more files
mv report1 report2 (Renames the file named report1 to report2)
mvdir – Renames a directory
mv /u/roger /u/scott (Renames the directory roger to scott)
rm – Removes a file or directory
| Examples | What it does |
| rm -i * | Will prompt the user to remove each of the files in the current directory beforeremoving them EXCEPT for hidden files. |
| rm -r /u/roger/docs | Will recursively remove all files and any subdirectories found under /u/roger/docs. |
| rm -i S\&e38912 | Removes the file named S&38912. Since this file has a special character (‘&’) that the shell treats differently than most. -i system prompt if you wish to remove. |
| rm `find . -print` | Removes all files from current directory including hidden files (file names such as {}, -exec, ;, etc) |
| rm ./-junkfile | By preceding the filename (-junkfile) with the pathname (./), you are able to hide the ‘-‘ character that starts the filename. If this was not done, the following error message would be generated: usage: rm [-fir] file ... |
| rm /home/*/mbox | Removes all files named mbox found under any of the subdirectories located in /home. |
rmfs – Removes a file system
mfs /u
Removes a file system and the logical volume under it. The file system must be unmounted prior to the ‘rmfs’ command being executed else you will get a ‘BUSY’ error message. The ‘/u’ entry in /etc/filesystems will also be removed.
sync – Flushes system buffers to disk
There’s a sync daemon (/etc/syncd) that flushes buffers automatically every 60 seconds (default).
umount – Unmounts a file system from system usage
umount /u
Unmounts a file system so that files found under that file system will not be able to be accessed. The ‘umount’ will fail if one or more users are either currently on that file system or somebody has a file opened on that file system.
unlink – Used to remove a link or symbolic link
unlink MyDoc (Removes the link MyDoc from the system)