• When installing Red Hat Linux Fedora Core 2, I install ALL components. (Everything). This makes it easier than trying to troubleshoot missing software components.

• As of March 26, 2004, Oracle includes the Oracle9i database software with the 9.2.0.4.0 patchset already included. This will save considerable time since the patchset does not have to be downloaded and installed. We will, however, be applying the 9.2.0.5.0 patchset.

• Although it is not required, it is recommend to apply the 9.2.0.5.0 patchset.

• The post installation section includes steps for configuring the Oracle Networking files, configuring the database to start and stop when the machine is cycled, and other miscellaneous tasks.

• Finally, at the end of this article, we will be creating an Oracle 9.2.0.5.0 database named ORA920 using supplied scripts.

• Installing Oracle9i requires a minimum of 512MB of memory.
  (An inadequate amount of swap during the installation will cause the Oracle Universal Installer to either "hang" or "die")

• To check the amount of memory / swap you have allocated, type either:

  # free

  - OR -

  # cat /proc/swaps

  - OR -

  # cat /proc/meminfo | grep MemTotal

• If you have less than 512MB of memory (between your RAM and SWAP), you can add temporary swap space by creating a temporary swap file. This way you do not have to use a raw device or even more drastic, rebuild your system.

  As root, make a file that will act as additional swap space, let's say about 300MB:
  # dd if=/dev/zero of=tempswap bs=1k count=300000

  Now we should change the file permissions:
  # chmod 600 tempswap

  Finally we format the "partition" as swap and add it to the swap space:
  # mke2fs tempswap
  # mkswap tempswap
  # swapon tempswap
  

Oracle uses shared memory in UNIX to hold its Shared Global Area (SGA). This is an area of memory within the Oracle instance that is shared by all Oracle backup and foreground processes. It is important to size the SGA to efficiently hold the database buffer cache, shared pool, redo log buffer as well as other shared Oracle memory structures. Inadequate sizing of the SGA can have a dramatic decrease in performance of the database.

To determine all shared memory limits you can use the ipcs command. The following example shows the values of my shared memory limits on a fresh RedHat Linux install using the defaults:

# ipcs -lm

------ Shared Memory Limits --------
max number of segments = 4096
max seg size (kbytes) = 32768
max total shared memory (kbytes) = 8388608
min seg size (bytes) = 1

SHMMAX

The SHMMAX parameter is used to define the maximum size (in bytes) for a shared memory segment and should be set large enough for the largest SGA size. If the SHMMAX is set incorrectly (too low), it is possible that the Oracle SGA (which is held in shared segments) may be limited in size. An inadequate SHMMAX setting would result in the following:

ORA-27123: unable to attach to shared memory segment

You can determine the value of SHMMAX by performing the following:

# cat /proc/sys/kernel/shmmax
33554432

As you can see from the output above, the default value for SHMMAX is 32MB. This is often too small to configure the Oracle SGA. I generally set the SHMMAX parameter to 2GB.

NOTE: With a 32-bit Linux operating system, the default maximum size of the SGA is 1.7GB. This is the reason I will often set the SHMMAX parameter to 2GB since it requires a larger value for SHMMAX. On a 32-bit Linux operating system, without Physical Address Extension (PAE), the physical memory is divided into a 3GB user space and a 1GB kernel space. It is therefore possible to create a 2.7GB SGA, but you will need make several changes at the Linux operating system level by changing the mapped base. In the case of a 2.7GB SGA, you would want to set the SHMMAX parameter to 3GB. Keep in mind that the maximum value of the SHMMAX parameter is 4GB.

To change the value SHMMAX, you can use either of the following three methods:

• This is method I use most often. This method sets the SHMMAX on startup by inserting the following kernel parameter in the /etc/sysctl.conf startup file:

  # echo "kernel.shmmax=2147483648" >> /etc/sysctl.conf

• If you wanted to dynamically alter the value of SHMMAX without rebooting the machine, you can make this change directly to the /proc file system. This command can be made permanent by putting it into the /etc/rc.local startup file:

  # echo "2147483648" > /proc/sys/kernel/shmmax

• You can also use the sysctl command to change the value of SHMMAX:

  # sysctl -w kernel.shmmax=2147483648

SHMMNI

We now look at the SHMMNI parameters. This kernel parameter is used to set the maximum number of shared memory segments system wide. The default value for this parameter is 4096. This value is sufficient and typically does not need to be changed.

You can determine the value of SHMMNI by performing the following:

# cat /proc/sys/kernel/shmmni
4096

SHMALL

Finally, we look at the SHMALL shared memory kernel parameter. This parameter controls the total amount of shared memory (in pages) that can be used at one time on the system. In short, the value of this parameter should always be at least:

ceil(SHMMAX/PAGE_SIZE)

The default size of SHMALL is 2097152 and can be queried using the following command:

# cat /proc/sys/kernel/shmall

2097152

From the above output, the total amount of shared memory (in bytes) that can be used at one time on the system is:

SM = (SHMALL * PAGE_SIZE)
   = 2097152 * 4096
   = 8,589,934,592 bytes

The default setting for SHMALL should be adequate for our Oracle installation.

NOTE: The page size in Red Hat Linux on the i386 platform is 4096 bytes. You can, however, use bigpages which supports the configuration of larger memory page sizes.

To determine all semaphore limits, use the following:

# ipcs -ls

------ Semaphore Limits --------
max number of arrays = 128
max semaphores per array = 250
max semaphores system wide = 32000
max ops per semop call = 32
semaphore max value = 32767

# cat /proc/sys/kernel/sem
250     32000   32      128

SEMMSL

The SEMMSL kernel parameter is used to control the maximum number of semaphores per semaphore set.

Oracle recommends setting SEMMSL to the largest PROCESS instance parameter setting in the init.ora file for all databases hosted on the Linux system plus 10. Also, Oracle recommends setting the SEMMSL to a value of no less than 100.

SEMMNI

The SEMMNI kernel parameter is used to control the maximum number of semaphore sets on the entire Linux system.

Oracle recommends setting the SEMMNI to a value of no less than 100.

SEMMNS

The SEMMNS kernel parameter is used to control the maximum number of semaphores (not semaphore sets) on the entire Linux system.

Oracle recommends setting the SEMMNS to the sum of the PROCESSES instance parameter setting for each database on the system, adding the largest PROCESSES twice, and then finally adding 10 for each Oracle database on the system. To summarize:

SEMMNS =   sum of PROCESSES setting for each database on the system
         + ( 2 * [largest PROCESSES setting])
         + (10 * [number of databases on system]

To determine the maximum number of semaphores that can be allocated on a Linux system, use the following calculation. It will be the lesser of:

SEMMNS  -or-  (SEMMSL * SEMMNI)

SEMOPM

The SEMOPM kernel parameter is used to control the number of semaphore operations that can be performed per semop system call.

The semop system call (function) provides the ability to do operations for multiple semaphores with one semop system call. A semaphore set can have the maximum number of SEMMSL semaphores per semaphore set and is therefore recommended to set SEMOPM equal to SEMMSL.

Oracle recommends setting the SEMOPM to a value of no less than 100.

Setting Semaphore Kernel Parameters

Finally, we see how to set all semaphore parameters using several methods. In the following, the only parameter I care about changing (raising) is SEMOPM. All other default settings should be sufficient for our example installation.

• This is method I use most often. This method sets all semaphore kernel parameters on startup by inserting the following kernel parameter in the /etc/sysctl.conf startup file:

  # echo "kernel.sem=250 32000 100 128" >> /etc/sysctl.conf

• If you wanted to dynamically alter the value of all semaphore kernel parameters without rebooting the machine, you can make this change directly to the /proc file system. This command can be made permanent by putting it into the /etc/rc.local startup file:

  # echo "250 32000 100 128" > /proc/sys/kernel/sem

• You can also use the sysctl command to change the value of all semaphore settings:

  # sysctl -w kernel.sem="250 32000 100 128"