asmcmd tips Oracle Tips by Burleson Consulting

When making the decision to bypass the JFS buffers with raw devices, the problem has always been the management of the "raw" disk files, which are read directly by Oracle, into Oracle data buffers, bypassing the OS overhead.  For details on using ASM, I recommend the book "Oracle RAC and Grid" by Madhu Tumma and Mile Ault.

Oracle introduced Automatic Storage Management (ASM) to simplify Oracle data management, enforce the SAME (Stripe And Mirror Everywhere, RAID10), and provide a platform for file sharing in RAC and Grid computing.

Managing raw datafiles with asmcmd

The 10g release 2 has introduced an ASM command line utility dibbed "asmcmd" to act as a DMCL (device media control language), to manage the interface between the ASM logical data view and the physical disk files.

The asmcmd interface is launched by first setting the environment for +ASM, then calling it with the asmcmd command. The idea of this tool is to make administering the ASM files similar to administering standard operating system files.

Invoking asmcmd

The asmcmd utility is located in $ORACLE_HOME/bin/asmcmd and it should already be pathed into your UNIX/Linux environment.  We start asmcmd by setting $ORACLE_SID to the ASM instance with +ASM, and we can them execute asmcmd.  You can use the "?" or "help" command to display all asmcmd commands:

root> export ORACLE_SID=+ASM
root> asmcmd
ASMCMD> help

You can run the list data groups (lsdg) ASM command from a bash shell script to quickly see the disk space usage:

#!/bin/bash
. /home/oracle/set_oraenv
sid="+ASM1"
echo "Check Space on "$sid
export ORACLE_SID=$sid
asmcmd << EOF
lsdg
EOF  

This is an example of an asmcmd session:

asmcmd command examples

The asmcmd command line interface is very similar to standard UNIX/Linux commands, but it only manages files at the OS level. 

The asmcmd utility supports all common Linux commands:

ASMCMD> ls -alt -- list directory contents

ASMCMD> cd -- change directory

ASMCMD> mkdir -- create (make)directory

ASMCMD> du -- display directory space

ASMCMD> find -- standard UNIX find command

ASMCMD> rm -- remove file/directory

ASMCMD> lsdg -- list diskgroups

ASMCMD> pwd -- display current directory

Plus, we see some Oracle-only asmcmd commands:

ASMCMD> lsct -- list all connected Oracle instances

For a list of common Linux commands for Oracle, see the Oracle Linux command poster or Jon Emmon's book "Oracle Shell Scripting".

Using asmcmd with ASM commands

For internal operations against the ASM database you need other commands such as "alter diskgroup".

You can also use asmcmd to delete files using the standard rm command:

 

Set asmcmd prompt display

You can invoke asmcmd with the -p option to display the current path, very similar to the UNIX/Linux.

PS1="
`hostname`*\${ORACLE_SID}-\${PWD}
>"
export PS1

fred:/u01/app/oracle/admin>

asmcmd command line history

The asmcmd utility does not provide a command history with the up-arrow key. With rlwrapinstalled, this can be fixed by adding the following entry to the ~oracle/.bashrc file:

    alias asmcmd='rlwrap asmcmd'

 

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